Effect of constant-release implants of melatonin on seasonal cycles in reproduction, prolactin secretion and moulting in rams

Transcription

1 Effect f cnstant-release implants f melatnin n seasnal cycles in reprductin, prlactin secretin and multing in rams G. A. Lincln and F. J. P. Ebling MRC Reprductive Bilgy Unit, Centre fr Reprductive Bilgy, 7 Chalmers Street, Edinburgh EH 9EW, U.K. Summary. Seasnal cycles in the size f the testes, bld plasma cncentratin f teststerne, FSH and prlactin, intensity f the sexual skin flush, timing f rutting behaviur and multing f the bdy cat were recrded in Say rams after s.c. implantatin f melatnin cntained in a Silastic envelpe which increased the circulating bld levels f melatnin t 200\p=n-\600pg/ml fr many mnths. Tw grups f 8 adult rams were held under alternating perids f shrt days (8L:16D) and lng days (16L : 8D) t drive the seasnal cycles and the treatments with melatnin were initiated during the lng r shrt days, and ne grup f 8 ram lambs was kept ut f drs and given implants during the lng days f summer (4 melatnin-implanted and 4 cntrl (empty implants) rams per grup). The treatments demnstrated that (1) melatnin implants during expsure t lng days resulted in a rapid 'switch n' f reprductive redevelpment similar t that prduced by expsure t shrt days; (2) melatnin implants prevented the rams frm shwing the nrmal respnses t changes in the prevailing phtperid rendering them nn\x=req-\ phtperidic ; and () lng-term cyclic changes in testicular activity, prlactin secretin and ther characteristics ccurred in the melatnin-implanted rams; the pattern was similar t that previusly bserved in rams expsed t prlnged perids f shrt days. The verall results are cnsistent with the view that melatnin is the physilgil hrmne that relays the effects f changing phtperid n reprductin and ther seasnal features, and that cntinuus exgenus melatnin frm an implant interferes with the nrmal 'signal' and prduces an ver-riding shrt-day respnse. Intrductin Recent studies with sheep have shwn that the secretin f melatnin frm the pineal gland plays key a rle in mediating the effects f changing phtperid n reprductin and ther seasnal re spnses. In ewes and rams, the secretin f melatnin is clsely linked t the daily light-dark cycle with a marked increase in the peripheral bld levels f melatnin at night (Rllag, O'Callaghan & Niswender, 1978; Lincln, Almeida, Klandrf & Cunningham, 1982; Almeida & Lincln, 1982, 1984; Bittman, Dempsey & Karsch, 198). The changes in the daily pattern f secretin f mela tnin are related t changes in daylength and there is cnvincing evidence fr ewes that it is the duratin f daily expsure t melatnin which prvides the index f night length and therefre daylength; a lng duratin f melatnin secretin signals a shrt day and vice versa (Bittman et al, 198; Karsch et al., 1984). Cnsistent with this view are bservatins that daily treatment f ewes with melatnin during anestrus will induce shrt-day respnses, including suppressin f prlactin secretin and early nset f estrus cyclicity (Nett & Niswender, 1982; Kennaway, Gil mre & Seamark, 1982a; Arendt, Symns, Laud & Pryde, 198). Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

2 The aim f the present study was t extend these bservatins n the rle f melatnin as a timecue by recrding the effect f cnstant-release implants f melatnin n the phtperidic respnses in rams. The predictin based n the duratin hypthesis is that a melatnin implant wuld act like a shrt day. Three experiments were perfrmed t test the fllwing questins: (1) will a melatnin implant given t adult rams during expsure t lng days (16L : 8D) result in the inductin f testicular activity in the same way as ccurs in respnse t a switch t shrt days (8L : 16D), and will these implanted rams be able t respnd t subsequent changes in phtperid? (2) will a melatnin implant given t adult rams during expsure t shrt days (8L : 16D) prevent regressin f the testes and increase in prlactin secretin induced by lng days (16L : 8D), and hw quickly d the rams return t nrmal after remval f the implant? and () n a melatnin implant hasten the nset f puberty in ram lambs living under summer daylengths ut-f-drs? Materials and Methds Rams f the Say breed were used beuse they have prnunced seasnal cycles in testicular activ ity, prlactin secretin and multing f the bdy wl, and these cycles are respnsive t artificial changes in phtperid (Lincln & Shrt, 1980). The animals were kept at the Dryden Field Statin f the Animal Breeding Research Organisatin near Edinburgh (56 N). The melatnin implants were made frm Silastic sheeting (500-1 Dw Crning, Midland, MI, U.S.A.) sealed int an enve lpe with a ttal surface area f 2-42 cm2, cntaining 1-4 g melatnin (Sigma Chemils, Ple, Drset, U.K.). The implants were placed beneath the skin abve the rib ge while the animals were briefly anaesthetized with fluthane. Experiment 1 Eight adult Say rams were hused in a light-prf shed and expsed t an artificial lighting schedule cnsisting f alternating 10-0-week perids f lng days (16 h light:8 h darkness, 16L : 8D) and shrt days (8 h light : 16 h darkness, 8L : 16D) fr 68 weeks (see Text-fig. 1 ). At Week 14 during lng days, 4 f the rams received a melatnin implant (surface area 42 cm2 cntaining 4 g melatnin) and the ther 4 rams received empty implants t act as sham-perated cntrls. The im plants remained in place thrughut the remainder f the experiment during which the pht perid was alternated between lng days and shrt days. Experiment 2 Eight adult Say rams were hused in a light-prf shed and expsed t alternating week perids f lng days (16L:8D) and shrt days (8L:16D) fr 72 weeks (Text-fig. ). At Week 12 during a perid f shrt days, 4 f the animals were given a melatnin implant (surface area 42 cm2 cntaining 4 g melatnin), and the ther 4 rams were given empty implants t act as cntrls. The implants were remved at Week 40. Experiment Eight Say ram lambs brn April were kept with their mthers in a grass paddck ut-fdrs until 6 mnths ld. Fur f the lambs received melatnin implants (surface area 2 cm2 cn taining 1 g melatnin) in mid-may when abut 1 mnth ld, and the ther 4 were given empty implants. The implants were remved in mid-octber after 22 weeks beuse the experimental lambs were stunted and in pr cnditin at this stage; all the animals were mved indrs and expsed t lng days (16L : 8D). One cntrl lamb was killed by a dg in September while ut-fdrs, and ne experimental lamb died f pneumnia in Octber (Text-fig. 5). Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

3 In the experiments, the changes in the diameter f the testes, the intensity f the sexual skin flush in the inguinal regin, and multing f the wl frm the scrtum were recrded every 2 weeks (Lincln & Davidsn, 1977). The perid f rutting behaviur was indited by the vert aggressive behaviur f the rams including threats, hrn banging, vlizatins, pawing the bedding int a mund and the increased incidence f Flehmen. The rams were weighed every 1-2 mnths (Exp. 1) r every 2 weeks (Exp. ). A bld sample was cllected frm all animals frm the jugular vein every week, and n csins (nce during Exp. 1 and twice during Exp. 2) bld samples were cllected hurly fr 24 h using a jugular nnula inserted the day befre. All bld samples were heparinized, and the plasma separated within 0 min f cllectin and frzen at 20 C until re quired fr the hrmne assays. Radiimmunassays The cncentratins f fllicle-stimulating hrmne (FSH), prlactin, teststerne and melatnin in the bld plasma were measured by radiimmunassay using the methds described by McNeilly, McNeilly, Waltn & Cunningham (1976) fr FSH, McNeilly & Andrews (1974) fr prlactin, Crker & Davidsn (1978) fr teststerne, and Rllag & Niswender (1976) fr melatnin. The limit f detectin was 10 ng/ml fr FSH using NIH-FSH-S18 as standard, 2-0 ng/ml fr prlactin using NIH-P-S9 as standard, 01 ng/ml fr teststerne and 10 pg/ml fr melatnin. The intra- and inter-assay cefficients f variatin fr all assays were < 12-0%. Statistil analysis The changes in the size f the testes and the cncentratin f the varius hrmnes thrughut each experiment were tested fr a signifint time effect and time/grup interactin using analysis f variance and c-variance with repeated measures (ANOVAR). The nature f the shrt-term re spnses t a change in phtperid r the implantatin f melatnin were cmpared fr the cntrl and treated rams by lculating the incremental change frm Week 0 t the time f the maximum respnse based n previus studies fllwing an abrupt switch between lng days and shrt days (Lincln & Davidsn, 1977; Lincln, McNeilly & Camern, 1978). The times f maximum incre ment were taken as Weeks fr testicular diameter and plasma levels f teststerne, Weeks 8-11 fr plasma levels f FSH, Weeks 6-9 fr the sexual skin flush and Weeks 2-5 fr plasma levels f prlactin. The incremental change fr each animal was lculated (mean fr 4-week perid f expected maximum minus mean fr 4-week perid befre experimental test) and the grup means were cmpared by Student's t test (Tables 1-). In additin, the mean ± s.e.m. plasma cncentratins f melatnin in the cntrl and melatnin-treated rams based n the mean f a se ries f daily bld samples r hurly samples cllected fr 24 h were cmpared by Student's / test. Results Experiment 1 : adult rams given melatnin implants during lng days The rams were implanted with melatnin at Week 14 during expsure t lng days, and the results are summarized in Text-fig. 1. Plasma cncentratins f melatnin were signifintly (P < 001) increased in the melatnin-implanted rams in daytime samples cllected at 6-week intervals (verall daytime mean ± s.e.m. values 2 ± 0 and 4 ± 14 pg melatnin/ml) and in hurly samples cllected fr 24 h at Week 52 (24 h mean + s.e.m. 461 ± 94 and 128 ± 2 pg melatnin/ ml). There was a diurnal change in the plasma cncentratins f melatnin at Week 52 in bth grups f rams, with the highest levels at night ; melatnin cncentratins in the experimental rams were higher thrughut the 24 h than the ncturnal maximum fr the cntrl rams (Text-fig. 2). Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

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5 H 400 H :00 16:00 24:00 08:00 Hurs Text-fig. 2. Changes in the cncentratin (mean + s.e.m.) f melatnin and prlactin in the bld plasma in 4 melatnin-implanted and 4 cntrl adult Say rams in Exp. 1, based n sam ples cllected hurly fr 25 h under lng days at Week 52. The times f daylight (pen bar) and darkness (clsed bar) are shwn. The size f the testes and the bld plasma levels f teststerne, FSH and prlactin fr the experimental and cntrl rams changed signifintly (P < 0-001) with time and there was a signifi nt (P < 0-001) time/grup effect, inditing that the lng-term changes in all the values differed in the tw grups (see Text-fig. 1). The differences between the experimental and cntrl rams were evident within 14 weeks f the implantatin since there was a signifintly (P < 0-01) mre rapid increase in the size f the testes and the plasma cncentratins f teststerne and FSH, and a decrease in the plasma levels f prlactin in the melatnin-implanted animals (Table 1). In additin these treated animals were preccius in develping their sexual skin flush and rutting behaviur (Table 1 ; Text-fig. 1). After the phase f full reprductive activity induced by the implantatin f melatnin, there was a rapid decline in the size f the testes and the plasma cncentratins f FSH and teststerne. These regressive changes in the treated rams ccurred ver the change frm lng days t shrt days which appeared t stimulate testicular activity in the cntrls (Text-fig. 1). Fr the melatnin-im planted rams a sexual nadir ccurred at abut 0 weeks after implantatin fllwed by a slw recv ery. The lng-term reprductive changes were nt crrelated with the alteratins in phtperid as was bvius in the cntrl rams, and the reciprl relatinship between the changes in the plasma levels f FSH and prlactin was n lnger apparent (Text-fig. 1). During this perid the plasma levels f prlactin gradually increased assciated with an earlier and gradual nset f the multing f the bdy wl (Text-fig. 1). The difference in prlactin secretin between the experimental and cntrl rams was apparent at Week 52 when bld samples were cllected hurly fr 24 h; the cntrl rams were clearly hyperprlactinaemic as expected during expsure t lng days, but the verall levels in the experimental rams were lwer and there was n bvius diurnal variatin (Text-fig. 2). The difference between the tw grups in the respnses t phtperid was als evi dent at Week 56 when the lighting was switched frm lng days t shrt days; reprductive devel- Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

6 Table 1. Experiment 1 : summary f the reprductive changes in cntrl (N = 4) and melatnin-implant ed (N = 4) adult Say rams in respnse t the initial implantatin f melatnin r sham-peratin during lng days (16L:8D) at Week 14 r a switch in phtperid frm lng days (16L-.8D) t shrt days (8L:16D) at Week 56 Testis diameter (mm) Plasma teststerne (ng/ml) Sexual skin flush (sle 0-5) Plasma FSH (ng/ml) Plasma prlactin (ng/ml) Reprductive changes after: Implantatin at Week 14 Shrt days at Week 56 Cntrl Melatnin-implanted Cntrl Melatnin-implanted -9 ± ± ± ± ± ± 1-2 *4-5 ± 0-4 *685 6 ± *-65-9 ± ± ± ± ± ±2-1 *2-5± ±0-7 *4-4± ± 12-4 Values represent the mean ± s.e.m. incremental change (see text fr time perid fr each measurement). * Signifintly different frm crrespnding cntrl value, < 005 (Student's t test). pment was stimulated in the cntrl rams but nt in the melatnin-implanted rams (Table 1). The changes in the cntrl rams in respnse t shrt days at Week 56 were similar in timing and extent t thse in the melatnin-implanted rams in respnse t the initial implantatin f melatnin at Week 14, cnfirming that melatnin given during lng days induces 'shrt day' respnses. Experiment 2 : adult rams given melatnin during shrt days Melatnin implants were inserted at Week 12 during expsure t shrt days, and the results are summarized in Text-fig.. There was a signifint (P < 0-01) increase in the bld plasma cncen tratin f melatnin in the experimental rams based n daytime bld samples cllected every 6 weeks (verall daytime mean ± s.e.m. values and 10 ± 1 pg melatnin/ml) and hurly samples cllected fr 24 h n ne day during lng days and ne day during shrt days (24 h mean ± s.e.m. melatnin values 85 ± 7 and 9 ± 40 pg/ml in experimental rams and 55 ±11 and 68 ± 21 pg/ml in cntrl rams at Weeks 28 and 7, respectively). The highest cncentratins f melatnin ccurred at night in bth grups in lng and shrt days, but the values in the experi mental rams were always higher than the ncturnal maximum fr the cntrls (Text-fig. 4). All the reprductive characteristics changed signifintly (P < 0-001) in relatin t time in the experimental and cntrl rams, and there was a signifint (P < 0-001) time versus grup effect, inditing that the lng-term changes were different in the tw grups. These differences were nt apparent, hwever, during the initial perid f shrt days (up t Week 16) r during the subsequent perid f lng days (Week 16-28) as judged by the size f the testes and the plasma cncentratins f FSH and teststerne; a decline ccurred in bth grups after full testicular activity (Table 2; Text-fig. ). Hwever, the expsure t lng days resulted in a signifintly (P < 0-05) reduced pr lactin respnse (Table 2) in the experimental rams, and there was n clear reprductive respnse t the switch frm lng days t shrt days at Week 28 unlike the marked changes in the cntrl grup (Table 2). The difference in prlactin secretin in the tw grups ver this perid was als apparent at Weeks 28 (lng days) and 7 (shrt days), when bld samples were cllected hurly fr 24 h (Text-fig. 4). On bth csins the plasma levels f prlactin were in the intermediate range in the experimental rams cmpared t the high (lng days) and lw (shrt days) values fr the cntrls. Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

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8 _ 600 E "ạ 400 Week 28, lng days Week 7, shrt days :00 16:00 24:00 08:00 08:00 16:00 24:00 08:00 Hurs Text-fig. 4. Changes in the cncentratins (mean + s.e.m.) f melatnin and prlactin in the bld plasma f 4 melatnin-implanted and 4 cntrl adult Say rams in Exp. 2 sampled at hurly intervals fr 25 h nce during lng days (16L : 8D; Week 28) and nce during shrt days (8L:16D; Week 7). The times f daylight (pen bar) and darkness (clsed bar) are shwn. Table 2. Experiment 2 : summary f the reprductive changes in cntrl (N 4) and melatnin-implant = ed (N 4) adult Say = rams in respnse t a switch frm shrt days (8L : 16D) t lng days (16L :8D) at Week 16 and a switch frm lng days (16L :8D) t shrt days (8L : 16D) at Week 28 Testis diameter (mm) Plasma teststerne (ng/ml) Sexual skin flush (sle 0-5) Plasma FSH (ng/ml) Plasma prlactin (ng/ml) Reprductive changes after: Lng days at Week 16 Shrt days at Week 28 Cntrl Melatnin-implanted Cntrl Melatnin-implanted ± ± ± ± ± ± ± ± ± ± ±5-7 *-0-4± ± 1-0 *-0-2±0- *10-8± Values represent the mean + s.e.m. incremental change (see text fr time perid fr each measurement). * Signifintly different frm crrespnding cntrl value, < 0-05 (Student's t test). The implants were remved at Week 40 during expsure t shrt days, and within a few weeks the rams that had been previusly treated with melatnin began t shw nrmal respnses t the changing phtperid. Fr example, at Week 44 (4 weeks after implant remval) there was a marked increase in the bld plasma level f prlactin in all the rams (Text-fig. ) althugh the testicular cycle tk lnger t readjust t the nrmal pattern Dwnladed (Text-fig. frm Biscientifi.cm ). at 09/07/ :17:2PM

9 Table. Experiment : summary f the reprductive changes in = cntrl (N 4) and melatnin-implanted (N 4) = yung Say ram lambs in respnse t implantatin r sham-peratin perfrmed in May while the animals were living ut-f-drs under natural lighting Reprductive changes after: Sham-peratin Testis diameter (mm) Plasma teststerne (ng/ml) 1-1 ±0-5 Sexual skin flush (sle 0-5) 0 Plasma FSH (ng/ml) Plasma prlactin (ng/ml) 10-5 ± 28-9 Implantatin with melatnin *4 8 ± 0-6 *l- ±0-5 *600± Values are the mean + s.e.m. incremental change (see text fr time perid fr each measurement). * Signifintly different frm crrespnding cntrl value, < 0-05 (Student's t test). NATURAL LIGHT Melatnin lelatonin-implanted RAMS NATURAL Melatnin LIGHT CONTROL RAMS Empty implant Weeks Text-fig. 5. Changes in the diameter f the testes (mean + s.e.m.), plasma cncentratins f teststerne, FSH and prlactin (mean + s.e.m.), intensity f the sexual skin flush (individual values) and the timing f the mult f wl frm the scrtum (range) in 4 melatnin-implanted and 4 cntrl Say ram lambs in Exp., living under natural lighting frm birth in April until Octber when they were mved indrs under lng days (16L:8D). The implants were intrduced in May (Week 0) when the lambs were abut 1 mnth ld and remved in Octber (Week 22). Experiment : yung rams given melatnin implants during lng days ut-f-drs Melatnin implants were given t 1-mnth-ld ram lambs living ut-f-drs in May, and the results are summarized in Text-fig. 5. The experimental lambs had a signifintly (P < 0-001) in creased bld plasma level f melatnin based n daytime samples Dwnladed cllected frm every Biscientifi.cm 6 weeks at (verall 09/07/ :17:2PM

10 daytime mean ± s.e.m. 447 ± 16 cmpared with pg melatnin/ml fr the cntrls). During the 0-week study, bth grups f lambs beme sexually mature as judged by the increase in the size f the testis, althugh there were signifint (P < 0-05) differences between the tw grups. Plasma FSH and teststerne cncentratins increased mre rapidly in the melatnin-implanted lambs and these animals develped the sexual skin flush prematurely (Table 1 ; Text-fig. 5). After this initial stimulatry respnse the testes f the melatnin-implanted rams began t regress earlier than in the cntrls, assciated with a decline in teststerne cncentratin and disappearance f the sexual skin flush. At this stage the melatnin-implanted lambs had stpped grwing and were thin cmpared t the cntrls (bdy weight at Week 16: kg fr experimental lambs, 16- ± 0-9 kg fr cntrls) and this effect cntinued until Week 22 ( and 16-8 ± 0-7 kg) when ne f the treated lambs died in pr cnditin and the experiment was terminated. Discussin The results presented here illustrate that cnstant administratin f melatnin frm a s.e. implant induces changes in the cycles in testicular activity in rams, and interferes with the nrmal pht peridic regulatin f reprductin. The effects n be summarized as fllws. (1) Implantatin with melatnin during expsure t lng days induces all the reprductive changes nrmally assciated with an expsure t shrt days. (2) Implantatin with melatnin blcks the effects f lng days (e.g. stimulatin f prlactin secretin) and in the lng term renders rams unrespnsive t changes between lng days and shrt days, i.e. the animals becme nn-phtperidic. () Implantatin with melatnin des nt lead t a stable reprductive cnditin, instead the treated rams shw lng-term cyclic changes in their physilgy. Each f these effects is cnsistent with the view that melatnin is the hrmne that functins physilgilly t relay effects f changing phtperid, and that exgenus melatnin induces its respnses by interfering with this prcess. In particular, the cnstant supply f exgenus melatnin appears t be registered as a shrt day and t ver-ride any effects f endgenus mela tnin secretin. In the shrt term, this results in stimulatin f testicular activity if the rams are already phtrespnsive due t prir expsure t lng days (e.g. Exps 1 & ). In the lng term, this results in cyclic changes in testicular activity similar t thse previusly recrded in rams expsed t prlnged perids f shrt days (8L : 16D) (Almeida & Lincln, 1984). The lng-term respnse t implantatin f melatnin (Exp. 1) is cmpared t previusly published results n the lng-term re spnse t shrt days in Text-fig. 6. It is evident that bth treatments result in an initial phase f rapid testicular grwth fllwed by invlutin and then a phase f slw testicular grwth. The inv lutin f the testes during expsure t shrt days has been referred t as shrt-day refractriness, and it is clear this cnditin als ccurs in the presence f cnstant melatnin and might equally be referred t as melatnin refractriness. The nly previus studies in which sheep have been given s.e. implants f melatnin similar t thse used here were n Merin Brder Leicester ewes and ewe lambs treated in the summer (Kennaway, Dunstan, Gilmre & Seamark, 198; Kennaway & Gilmre, 1984). These treatments led t a decline in the bld plasma levels f prlactin as in the present studies, but there were n clear effects n reprductin in the ewes and the nset f estrus cyclicity was delayed in the ewe lambs. In the experiment f Kennaway & Gilmre (1984) the lambs were treated at a very early age and may nt have been expsed t lng days fr lng enugh t render them respnsive t shrt days r the effect f cnstant melatnin. In additin, Merin crssbred sheep are likely t be less respnsive t phtperid r melatnin manipulatins cmpared t a semi-dmestited nrthern breed f sheep like the Say. Melatnin implants have been used frequently in studies n labratry species, and the effects vary accrding t the species and the size f the implant. Fr example, a melatnin implant induces regressin f the testes in the Turkish hamster, Mescricetus brandii, Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

11 Text-fig. 6. Changes in the diameter f the testes (mean ± s.e.m.) in adult Say rams (a) im planted with melatnin (Exp. 1) and (b) expsed t shrt days fr a prlnged perid (Almeida & Lincln, 1984). Rapid testicular develpment ccurred after implantatin with melatnin during lng days, r the switch frm lng days (LD) t shrt days (SD); this was fllwed by regressin f the testes and slw redevelpment. The lines inditing the rates f testicular grwth were fitted by eye. expsed t lng days; in this species this is a shrt-day respnse. Hwever, identil treatment f the Syrian hamster, Mescricetus auratus, has n effect n animals expsed t lng days and actually blcks the reprductive respnse t a switch t shrt days (Gldman, Carter, Hall, Rychudhury & Yelln, 1982). The measurement f melatnin in the bld f the rams used in the present study illustrated that the s.e. melatnin implants were pable f maintaining the plasma levels f melatnin at pg/ml fr many mnths. Hwever, the 24-h prfiles revealed that the levels f melatnin were high er at night than during the day in the experimental and in the cntrl rams, inditing that the cnstant supply f melatnin frm the implants had nt blcked the endgenus secretin f the hrmne which still ccurred largely during the daily dark phase. This lack f an inhibitry-feed back effect f exgenus melatnin has been described previusly (Kennaway et al., 1982b). While the experimental rams cntinued t secrete melatnin, this did nt apparently result in the nrmal phtperidic respnses, and the cntinual presence f > 200 pg melatnin/ml in the bld frm the implants must negate the nrmal effects f the endgenus melatnin. Whether this peridic re lease f endgenus melatnin mdified the effects f the implants is questinable. Hwever, the advantage f using rams with a functinal pineal gland was that it was pssible t treat animals which were knwn t be phtsensitive and t bserve the effects f melatnin n the nrmal phtperidilly induced changes in reprductin. It is unlikely that the endgenus secretin f me latnin greatly cmplited the results since shrt-day effects induced by implantatin f melatnin similar t thse reprted here have been bserved in superir cervil ganglinectmized rams and red deer stags which had minimal endgenus melatnin secretin at the time f treatment (G. A. Lincln, unpublished results; Lincln, Fraser & Fletcher, 1984). Althugh treatments with melatnin clearly affect reprductin they als influence ther aspects f the animals' seasnal physilgy which are respnsive t changes in daylength. In the Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

12 present study, implantatin with melatnin influenced prlactin secretin, multing f the wl and verall bdy weight. The effect f a melatnin implant n the mult cycle has been described fr many seasnal species including the weasel (Rust & Meyer, 1969), Djungarian hamster (Hff mann, 197), white-fted muse (Lynch & Epstein, 1976) and mink (Allain, Martinet & Ruget, 1981). The studies n the mink have illustrated that the effects n the cat are prbably mediated thrugh changes in prlactin secretin, beuse the decrease in prlactin secretin that ccurs after a melatnin implant r expsure t shrt days is assciated with the grwth f the winter cat, while administratin f prlactin t these animals n lead t multing and develpment f the summer cat. In the current studies, the increase in the bld levels f prlactin was assciated with mult ing and regrwth f the wl. The change in the timing f the mult after melatnin treatments was cnsistent with the effect being mediated thrugh a change in prlactin secretin (e.g. Text-figs 1 & ). Changes in bdy weight may als be dictated by the prlactin cncentratin as judged by studies n sheep and ther ungulates in which prlactin has been shwn t stimulate appetite and bdy grwth (Meier, 1977; Ryg& Jacbsen, 1982; Brinklw& Frbes, 198). The effect f the melatnin treatment was t induce suppressin f prlactin secretin and this was assciated with anrexia and weight lss which is a respnse nrmally seen in winter during shrt days. In the adult rams, weight lss began weeks after implantatin with melatnin (results nt presented) and the animals reached a nadir f cnditin at abut 0 weeks befre spntaneusly regaining weight again. In the lambs, the effect f melatnin was t reduce grwth rate; these animals were in pr cnditin by 22 weeks after treatment and had t be mved indrs since they were vulnerable t the clder weather in autumn. In cnclusin, the cnstant administratin f melatnin t rams by means f a s.e. Silastic im plant induces effects n reprductin, multing, bdy weight and the assciated endcrine changes similar t thse induced by expsure t shrt days. We thank Miss Nrah Andersn fr re f the animals and cllectin f mst f the bld samples; Rhna Cunningham and Lrna Dwney fr help with the radiimmunassays; Pam Warner fr advice n the statistil analysis; Dr G. D. Niswender fr the melatnin antiserum and NIAMDD fr the standard preparatins f FSH and prlactin. References Allain, D., Martinet, L. & Ruget, J. (1981) Effect f melatnin implants n changes in the cat, plasma prlactin and testis cycle in the mink (Mustela visn). In Phtperidism and Reprductin in Vertebrates, pp Eds R. Ortavant, J. Pelletier & J.-P. Ravault. INRA Services Publitins, Versailles. Almeida, O.F.X. & Lincln, G.A. (1982) Phtperidic regulatin f reprductive activity in the ram: evidence fr the invlvement f cirdian rhythms in melatnin and prlactin secretin. Bil. Reprd. 27, Almeida, O.F.X. & Lincln, G.A. (1984) Reprductive phtrefractriness in rams and accmpanying changes in the patterns f melatnin and prlactin secretin. Bil. Reprd. 0, Arendt, J., Symns, A.M., Laud, C.S. & Pryde, S.J. (198) Melatnin n induce early nset f the breeding seasn in ewes. J. Endcr. 97, Bittman, EX., Dempsey, R.J. & Karsch, F.J. (198) Pineal melatnin secretin drives the reprductive respnse t daylength in the ewe. Endcrinlgy 11, Brinklw, B.R. & Frbes, J.M. (198) Prlactin infusin uses increased nitrgen retentin in lambs in cntinuus darkness. Prc. Nutr. Sc. 42, 8A, Abstr. Crker, C.S. & Davidsn, D. (1978) The radiimmunas say f teststerne in varius bilgil fluids withut chrmatgraphy. J. Sterid Bichem. 9, Gldman, B.D., Carter, F.S., Hall, V.D., Rychudhury, P. & Yelln, S.M. (1982) Physilgy f pineal melatnin in three hamster species. In Melatnin Rhythm Generating System, pp Ed. D. C. Klein. Karger, Basel. Hffmann, K. (197) The influence f phtperid and melatnin n testis size, bdy weight and pelage clur in the Djungarian hamster (Phdpus sungrus). J. cmp. Physil. 85, Karsch, F.J., Bittman, E.L., Fster, D.L., Gdman, R.L., Legan, S.J. & Rbinsn, J.E. (1984) Neur endcrine basis f seasnal reprductin. Recent Prg. Hrm. Res. 40, Kennaway, D.J. & Gilmre, T.A. (1984) Effects f melatnin implants in ewe lambs. /. Reprd. Fert. 70, Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM

13 Kennaway, D.J., Gilmre, T.A. & Seamark, R.F. (1982a) Effect f melatnin feeding n serum prlactin and gnadtrpin levels and the nset f seasnal estrus cyclicity in sheep. Endcrinlgy 110, Kennaway, D.J., Gilmre, T.A. & Seamark, R.F. (1982b) Effect f melatnin implants n the cirdian rhythm f plasma melatnin and prlactin in sheep. End crinlgy 110, Kennaway, D.J., Dunstan, E.A., Gilmre, T.A. & Sea mark, R.F. (198) Effect f shrtened daylength and melatnin treatment n plasma prlactin and mela tnin levels in pinealectmised and sham-perated ewes. Anim. Reprd. Sci. 5, Lincln, G.A. & Davidsn, W. (1977) The relatinship between sexual and aggressive behaviur and pitu itary and testicular activity during the seasnal sexual cycle f rams and the influence f phtperid. J. Reprd. Fert. 49, Lincln, G.A. & Shrt, R.V. (1980) Seasnal breeding: Nature's cntraceptive. Recent Prg Hrm. Res. 6, Lincln, G.A., McNeilly, A.S. & Camern, CL. (1978) The effect f a sudden decrease r increase in daylength n prlactin secretin in the ram. J. Reprd. Fert. 52, Lincln, G.A., Almeida, O.F.X., Klandrf, H. & Cun ningham, R.A. (1982) Hurly fluctuatins in the bld levels f melatnin, prlactin, leuteinizing hrmne, fllicle-stimulating hrmne, teststerne, tri-idthyrnine, thyrxine and crtisl in rams under artificial phtperids and the effects f cranial sympathectmy. J. Endcr. 92, Lincln, G.A., Fraser, H.M. & Fletcher, T.J. (1984) Inductin f early rutting in male red deer (Cervus elaphus) by melatnin and its dependence n LHRH. J. Reprd. Fert. 72, 9-4. Lynch, G.R. & Epstein, A.L. (1976) Melatnin induced changes in gnads, pelage and thermgenic characteristics in the white-fted muse (Permyscus leucpus). Cmp. Bichem. Physil. 5C, McNeilly, A.S. & Andrews, P. (1974) Purifitin and characterisatin f prine prlactin. J. Endcr. 60, McNeilly, J.R., McNeilly, A.S., Waltn, J.S. & Cun ningham, F.J. (1976) Develpment and applitin f a heterlgus radiimmunassay fr vine flliclestimulating hrmne. J. Endcr. 70, Meier, A.H. (1977) Prlactin, the lipregulatry hr mne. Adv. exp. Med. Bil. 80, Nett, T.M. & Niswender, G.D. (1982) Influence f exgenus melatnin n seasnality f reprductin in sheep. Therigenlgy 17, Rllag, M.D. & Niswender, G.D. (1976) Radiimmun assay f serum cncentratins f melatnin in sheep expsed t different lighting regimens. Endcrinlgy 98, Rllag, M.D., O'CaUaghan, P.L. & Niswender, G.D. (1978) Serum melatnin cncentratins during differ ent stages f the annual reprductive cycle in ewes. Bil. Reprd. 18, Rust, C.C. & Meyer, R.K. (1969) Hair clr, mlt and testes size in male, shrt-tailed weasels treated with melatnin. Science, N.Y. 165, Ryg, M. & Jacbsen, E. (1982) Effect f thyrid hrmnes and prlactin n fd intake and weight change in yung male reindeer (Rangifer tarandus tarandus). Can. J. Zl. 60, Received 21 May 1984 Dwnladed frm Biscientifi.cm at 09/07/ :17:2PM