Photoperiod entrainment of testosterone, luteinizing hormone, follicle-stimulating hormone, and prolactin cycles in rams in relation to testis size and semen quality

Adult rams were exposed to photoperiod treatments over 2 years to study the influence of light regimes on pituitary-testicular activity and semen quality. Initially, all rams (12 per group) were exposed to 3 months of long days (16L:8D). Group 1 was then exposed to a regime of continuous short days (8L:16D) and Groups 2, 3, and 4 were exposed to 4 months of short days alternated with 1, 2, or 4 months, respectively, of long days. Every 2 weeks, serum hormone levels and scrotal circumference were determined and semen quality was evaluated. Regular cycles in pituitary and testicular activities corresponding to the period of the lighting regime resulted in Groups 2, 3, and 4, but not in Group 1. In general, the change from long days to short days induced increases in follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone levels, scrotal size and sperm numbers and a decrease in prolactin. The reverse occurred after subsequent exposure to long days. After 4 months of long days, testicular regression was complete, but when long-day exposure was reduced, less regression occurred. With continuous exposure to short days, FSH and testosterone remained above basal levels, prolactin levels were depressed, scrotal size remained near the maximum, and elevated numbers of motile sperm were sustained.     

24-hour changes in circulating prolactin, follicle-stimulating hormone, luteinizing hormone, and testosterone in young male rats subjected to calorie restriction

This work analyzes the effect of calorie restriction on the 24 h variation of pituitary-testicular function in young male Wistar rats by measuring the circulating levels of prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone. Control animals were provided an equilibrium calorie diet and the experimental animals a calorie-restriction diet equivalent to 66% of food restriction for four weeks starting on day 35 of life. Different groups of control and experimental rats were killed at 6 h intervals around the clock, beginning 1 h after light on (HALO). Compared to the control animals, the mean secretion of prolactin was augmented and that of LH and testosterone decreased in calorie-restricted rats, whereas FSH release remained unchanged. Significant changes in the 24 h secretory pattern of circulating prolactin, LH, and testosterone occurred in the calorie-restricted rats. These include the appearance of a second maximum of plasma prolactin at 21 HALO, blunting of the LH peak seen at 13 HALO, and phase-shift of the testosterone peak from 13 HALO in controls to 17 HALO in calorie-restricted rats. The significant positive correlation between individual LH and testosterone levels found in controls was no longer observed in calorie-restricted rats. Availability of nutrients presumably affects the mechanisms that modulate the circadian variation of the pituitary-gonadal axis in growing male rats.     

Puberty in the male chimpanzee: time-related variations in luteinizing hormone, follicle-stimulating hormone, and testosterone

The onset of pubertal testicular growth (Po) occurred in 12 out of 20 male chimpanzees surveyed monthly for at least 3.7 yr. When animals were synchronized according to Po, the mean weight gain was found to be higher before than after Po, and testicular volume started to rise immediately after Po. The earlier significant hormonal events were a rapid rise in LH and a slight testosterone increase occurring 6 mo before Po. Thereafter, the levels of LH remained elevated while testosterone continued to rise in parallel with the testicular volume. FSH levels increased suddenly at Po, 6 mo after the LH increase. FSH remained elevated for only 9 mo, then dropped to prepubertal levels. The dissociation between onsets of pubertal increases in LH and FSH secretions suggests that the complete reawakening of the hypothalamic-pituitary unit lasts several months. The secondary drop of FSH, occurring at the time of spermarche, may be induced by factor(s) secreted by the testis.     

Expression of luteinizing hormone and follicle-stimulating hormone receptor in the dog prostate

A possible role for gonadotrophins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the prostate physiology has been suggested in humans and rats. This study aimed at investigating the presence of receptors for LH and FSH (LHR and FSHR) in the canine prostate. Prostates were collected at post mortem from 6 clinically healthy, sexually intact beagles free from any prostatic disorder. Tissue was sampled from dorsal, middle and ventral regions of each prostate. Immunohistochemical localization was performed on wax-embedded sections using polyclonal antibodies for LHR or FSHR. The pattern and intensity of staining in the parenchyma (glandular epithelium) and stroma were determined using a semiquantitative histologic assessment. Receptors for LH and FSH were consistently present in both the glandular epithelium and the stroma in all tissue samples examined. Expression for both receptors was higher in the glandular epithelium than the stroma of all prostatic regions (P < 0.001). In the glandular epithelium, LHR (P < 0.01) and FSHR (P < 0.05) expression was lower in the lateral than the other regions, and there was no difference between dorsal and ventral regions. However, variations in the expression for LHR and FSHR among prostatic regions were not found in the stroma. These findings have demonstrated that LHR and FSHR are expressed in the dog prostate, and the variation observed in their levels of expression among its regions and tissue layers suggests a potential role of gonadotrophins LH and FSH in the regulation of the prostate physiology, particularly the glandular epithelium.     

Evaluation of sturgeon follicle-stimulating hormone, luteinizing hormone, estradiol, progesterone and testosterone in Acipenser persicus serum to identify fertile broodstock

Various methods have been proposed for the selection of suitable sturgeon broodstock for artificial reproduction. In this study, serum levels of reproductive hormones, namely sturgeon homologues of follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), estradiol (E2) and progestrone (P), were measured by radioimmunoassay (RIA) in 36 mature broodstock before and after injection of pituitary extract, and the results correlated with sex, age and oocyte polarization index (p). Mature males were significantly younger than females, and showed significant differences in serum P and T levels following pituitary extract injection, although not before that. A significant difference was found between LH, E2 and T before and after injection in the female group. There was also a significant difference between serum levels of T and P in the fertile and infertile groups. Stepwise discriminant function analysis was used to discriminate between fertile and infertile groups. The function had 93,8% overall correct classification, i.e. amongst 100 female broodstock fish, almost 94% of them would be correctly allocated to the relevant group. So the proposed model provides a reliable method for selecting suitable broodstock fish.     

Seasonal variation in plasma testosterone, luteinizing hormone concentrations and LH-RH responsiveness in mature, male rusa deer (Cervus rusa timorensis)

Plasma testosterone and luteinizing hormone (LH) concentrations in immobilized or yarded rusa stags (Cervus rusa timorensis) were investigated over a two-year period. Testosterone concentrations showed a minor elevation in autumn (May) and reached maximal levels in late winter-early spring (August) coinciding with the rut. Luteinizing hormone in plasma was only detectable from January to May. Maximal responsiveness of the pituitary-gonadal axis to LH-RH stimulation was recorded in August. The combination of Fentaz (fentanylcitrate and azaperone) and Rompun (xylazine hydrochloride) for immobilizing deer influences hypothalamic function.     

Effects of gonadotropin-releasing hormone pulse-frequency modulation on luteinizing hormone, follicle-stimulating hormone and testosterone secretion in hypothalamo/pituitary-disconnected rams

The effects of changes in pulse frequency of exogenously infused gonadotropin-releasing hormone (GnRH) were investigated in 6 adult surgically hypothalamo/pituitary-disconnected (HPD) gonadal-intact rams. Ten-minute sampling in 16 normal animals prior to HPD showed endogenous luteinizing hormone (LH) pulses occurring every 2.3 h with a mean pulse amplitude of 1.11 +/- 0.06 (SEM) ng/ml. Mean testosterone and follicle-stimulating hormone (FSH) concentrations were 3.0 +/- 0.14 ng/ml and 0.85 +/- 0.10 ng/ml, respectively. Before HPD, increasing single doses of GnRH (50-500 ng) elicited a dose-dependent rise of LH, 50 ng producing a response of similar amplitude to those of spontaneous LH pulses. The effects of varying the pulse frequency of a 100-ng GnRH dose weekly was investigated in 6 HPD animals; the pulse intervals explored were those at 1, 2, and 4 h. The pulsatile GnRH treatment was commenced 2-6 days after HPD when plasma testosterone concentrations were in the castrate range (less than 0.5 ng/ml) in all animals. Pulsatile LH and testosterone secretion was reestablished in all animals in the first 7 days by 2-h GnRH pulses, but the maximal pulse amplitudes of both hormones were only 50 and 62%, respectively, of endogenous pulses in the pre-HPD state. The plasma FSH pattern was nonpulsatile and FSH concentrations gradually increased in the first 7 days, although not to the pre-HPD range. Increasing GnRH pulse frequency from 2- to 1-hour immediately increased the LH baseline and pulse amplitude. As testosterone concentrations increased, the LH responses declined in a reciprocal fashion between Days 2 and 7. FSH concentration decreased gradually over the 7 days at the 1-h pulse frequency. Slowing the GnRH pulse to a 4-h frequency produced a progressive fall in testosterone concentrations, even though LH baselines were unchanged and LH pulse amplitudes increased transiently. FSH concentrations were unaltered during the 4-h regime. These results show that 1) the pulsatile pattern of LH and testosterone secretion in HPD rams can be reestablished by exogenous GnRH, 2) the magnitude of LH, FSH, and testosterone secretion were not fully restored to pre-HPD levels by the GnRH dose of 100 ng per pulse, and 3) changes in GnRH pulse frequency alone can influence both gonadotropin and testosterone secretion in the HPD model.     

Maturational changes in opioidergic control of luteinizing hormone and follicle-stimulating hormone in ram lambs

Stimulation by naloxone, an opioid antagonist, of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion was examined in spring-born crossbred ram lambs raised under natural photoperiod. Vehicle (n = 6) or 1 mg naloxone/kg vehicle (n = 6) was injected (i.m.) 3 times at 2-h intervals at 5, 10 and 15 weeks of age and 4 times at 2-h intervals at 20, 25, 30 and 35 weeks of age. Blood samples were taken every 12 min for 6 h at 5, 10 and 15 weeks of age and for 8 h at 20, 25, 30 and 35 weeks of age. Naloxone had no effect on age at sexual maturity (controls 239 +/- 23 days; naloxone 232 +/- 33 days). The only significant (P less than 0.05) effect of naloxone on FSH was a greater pulse amplitude in 10-week-old treated lambs than in control lambs. Naloxone treatment resulted in greater LH pulse amplitude at 5 and 10 weeks of age (P less than 0.05), lower basal serum concentration of LH at 10 weeks of age (P less than 0.05), greater LH pulse frequency at 25 weeks of age (P less than 0.05), and greater mean serum concentrations of LH, basal LH and LH pulse amplitude at 35 weeks of age (P less than 0.01) than in the controls. In both groups of lambs, mean and basal FSH, and LH and FSH pulse amplitude were highest at 5 weeks of age and fell with age. LH pulse amplitude was lowest at 35 weeks of age (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal dynamics of digestion in relation to diet quality and intake in European roe deer (Capreolus capreolus)

Three tame, hand-reared adult roe deer (Capreolus capreolus) were fed a low-quality diet (blueberry stems) or high-quality concentrate either restricted or ad libitum in summer and winter. Total mean retention time (TMRT) and rumen retention time (RRT) were significantly longer, indigestible fill was significantly higher and apparent digestibility and intake were significantly lower when fed blueberry stems compared to concentrate. The feeding regimes of concentrate did not affect the digesta kinetic estimates, except that total fill and apprent digestibility were significantly higher when deer were fed ad libitum than when they were fed a restricted ration. TMRT was significantly longer when they were fed a restricted ration of blueberry stems than for ad libitum intake, whereas all other estimates were equal. Intake was significantly higher and TMRT and RRT were significantly shorter in summer compared to winter when they were fed concentrate. These findings support the theory that roe deer, as small-bodied concentrate selectors, are adapted to high intake, rapid turnover, and rapid digestion when fed high-quality concentrate. When fed a low-quality diet the roe deer may be limited by rumen bulk. A strategy based on increased rumen retention accompanied by increased cell-wall digestion has therefore severe limitations in roe deer. This indicates that roe deer are dependent on a selective feeding strategy to enhance winter survival.     

Influence of photoperiod on the seasonal pattern of secretion of luteinizing hormone and testosterone and on the antler cycle in roe deer (Capreolus capreolus).

Annual variations in concentrations of luteinizing hormone (LH) and testosterone in plasma were analysed in relation to the antler cycle in six adult male roe deer exposed to a natural photoperiod (latitude 46 degrees 10'N) and in four adult males maintained in a constant short-day photoperiod (8 h light: 16 h dark) for a year, from the winter solstice at which time both groups of animals had antlers in velvet. The animals were sampled, every 15 min for 2 or 4 h at intervals of one month for a year. Under both natural and experimental conditions, LH concentrations were high from January to March, but in the experimental conditions they decreased between April and May-June, whereas in the natural conditions they increased. Plasma LH concentration was lowest between July and November in animals under natural photoperiod, whereas under 8 h light:16 h dark photoperiod a second increase in plasma LH occurred between August and September. Between March and August, concentrations of plasma testosterone increased under natural photoperiod, whereas under experimental photoperiod there was a biphasic pattern of plasma testosterone with peaks between February and May and between September and November. Under natural photoperiod, antlers were cast in November, 369 +/- 6 days after the previous antlers were cast. Under experimental photoperiod, antlers were cast after 193 +/- 10 days, and a new set developed. The sexual cycle of the male appears to be initiated by an endogenous rhythm in winter and is then maintained by hormonal changes resulting from increasing photoperiod in spring.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activin A and gonadotropin regulation of follicle-stimulating hormone and luteinizing hormone receptor messenger RNA in avian granulosa cells.

Activin A regulation of the expression of mRNA for the LH receptor, FSH receptor, and the inhibin alpha subunit as well as the effect of activin A on the secretion of progesterone were investigated in chicken granulosa cell cultures. Granulosa layers were isolated from the F(1) and F(3) + F(4) follicles from five hens, pooled according to size, dispersed, and cultured for 48 h. In experiment 1 (n = 3 replications), granulosa cells were cultured with or without highly purified ovine (o) FSH at 50 ng/ml and in the presence of 0, 10, or 50 ng/ml of recombinant chicken activin A. Experiment 2 (n = 4 replications) followed the same protocol as experiment 1, except that oFSH was replaced with oLH. Results from these experiments showed that addition of activin A to the granulosa cell cultures had no effect on the expression of mRNA for the inhibin alpha subunit or the FSH receptor, but it did affect the expression of mRNA for the LH receptor. Treatment of F(3) + F(4) granulosa cells with LH stimulated the expression of mRNA for the LH receptor; however, when LH was combined with either dose of activin A, this induction was prevented. The highest dose of activin A with or without LH resulted in decreased expression of the LH receptor compared to the untreated controls in the F(3) + F(4) cell cultures. Progesterone secretion by the granulosa cells from both follicle sizes was not altered by activin A. In experiment 3 (n = 3 replications), the effect of activin A on the growth of granulosa cells was examined with the following treatments: 0, 10, or 50 ng/ml of activin A; 50 ng/ml of either oLH or oFSH; and oLH or oFSH combined with 10 ng/ml of activin A. The highest dose of activin reduced the rate of granulosa cell proliferation in both follicle types. Growth of F(1) and F(3) + F(4) granulosa cells was stimulated by the addition of either gonadotropin, and the presence of 10 ng/ml of activin A with either gonadotropin did not alter this proliferation, except for the LH-treated F(3) + F(4) granulosa cells, in which the increase in proliferation was prevented. The results suggest that activin A could act as a local factor that regulates follicular maturation by preventing excessive or untimely LH receptor expression.     

Early maturity in the male striped bass, Morone saxatilis: follicle-stimulating hormone and luteinizing hormone gene expression and their regulation by gonadotropin-releasing hormone analogue and testosterone

Striped bass are seasonal breeding fish, spawning once a year during the spring. All 3-yr-old males are sexually mature; however, 60-64% of the fish mature earlier as 1- or 2-yr-old animals. The endocrine basis underlying early maturity in 2-yr-old males was studied at the molecular level by monitoring changes in pituitary beta FSH and beta LH mRNA levels by ribonuclease protection assay, and correlating these changes to stages of testicular development. In maturing males, the mRNA levels of beta FSH were elevated during early spermatogenesis, whereas beta LH mRNA levels peaked during spermiation. The appearance of spermatozoa in the testis was associated with a decrease in beta FSH mRNA and a rise in beta LH mRNA abundance. Immature males had lower levels of beta LH mRNA than maturing males, but there were no differences in beta FSH mRNA levels between immature and maturing males. The regulation of gonadotropin gene expression in 2-yr-old males was studied by the chronic administration of GnRH analogue (GnRHa) and testosterone (T), with or without pimozide (P) supplementation. In immature males, the combination of T and GnRHa stimulated a three- to fivefold increase in beta FSH and beta LH mRNA levels, but the same treatment had no effect on gonadotropin gene expression in maturing males. In addition, the coadministration of P to immature males suppressed the stimulatory effect of GnRHa and T on beta FSH and beta LH mRNA levels, suggesting that dopamine may have a novel role in regulating gonadotropin gene expression.     

Effects of in vivo administration of testosterone propionate on in vitro production of follicle-stimulating hormone and luteinizing hormone by pituitaries of pony mares

The in vitro incorporation of [3H]leucine into immunoprecipitable follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was assessed for pituitaries from pony mares treated with testosterone propionate (TP) or oil (controls). Mares were treated every other day with TP (n = 4) at 350 micrograms/kg of body weight or with an equivalent volume of oil (n = 4). One day following the sixth injection of TP, each mare received an intravenous injection of gonadotropin releasing hormone (GnRH) at 1.0 micrograms/kg body weight and was bled frequently for 4 h. Treatment of mares with TP reduced FSH (P less than 0.05) and LH (P less than 0.01) concentrations in daily blood samples and increased (P less than 0.01) the amount of FSH secreted in response to GnRH compared with control mares. Incorporation of [3H]leucine into immunoprecipitable FSH was also greater (P less than 0.01) in pituitaries from TP-treated mares compared with control mares on both a per mg tissue and per anterior pituitary basis. The amount of LH secreted after GnRH, the amount left in the pituitary and the incorporation of [3H]leucine into LH were not affected by treatment. These results confirm earlier conclusions drawn from indirect evidence that androgens increase the production of FSH in the mare.     

Inhibin B,follicle stimulating hormone,luteinizing hormone and testosterone during childhood and puberty in males: changes in serum concentrations in relation to age and stage of puberty

Inhibin B is a gonadal dimeric polypeptide hormone that regulates synthesis and secretion of follicle stimulating hormone (FSH) in a negative feedback loop. The aim of the present study was to determine changes in serum inhibin B, gonadotropins and testosterone concentrations during childhood and puberty in males. We studied the relationship between circulating inhibin B, gonadotropins and testosterone in serum of healthy boys during the first two years of life and then in pubertal development. Using a recently developed two-side enzyme-linked immunosorbent assay (ELISA), inhibin B levels were measured in the serum of 78 healthy boys divided into eleven age groups from birth to the end of pubertal development. In addition, serum levels of gonadotropins and testosterone were measured. Serum inhibin B, gonadotropins and testosterone increased during the first months of postnatal life. A peak in serum inhibin B and gonadotropins concentrations was observed around 3-4 months of age. There was a significant positive correlation between serum inhibin B and gonadotropins and testosterone levels during the first 2 years of life. After this early increase, serum inhibin B, gonadotropins and testosterone levels decreased significantly and remained low until puberty followed by an increase beginning with the onset of puberty. Serum levels of inhibin B reached a peak at stage G3 of puberty. Around midpuberty, inhibin B lost its positive correlation with luteinizing hormone (LH) and testosterone from early puberty, and developed a strong negative correlation with FSH, which persisted into adulthood. We conclude that inhibin B plays a key role in the regulation of the hypothalamic-pituitary-gonadal hormonal axis during male childhood and pubertal development. Inhibin B is a direct marker of the presence and function of Sertoli cells and appears to reflect testicular function in boys.     

Feeding patterns by roe deer and rabbits on pine, willow and birch in relation to spatial arrangement

The location of a plant and its association with the surrounding vegetation may be a strong determinant of herbivore foraging decisions. The attractiveness of a food plant may be reduced if associated with a less preferred one (repellent–plant hypothesis) or, conversely, it may escape herbivory via association with a more preferred species (attractant–decoy hypothesis). In this study we tested the hypothesis that selection of the same food plants by two herbivore species with different body mass, i.e. roe deer and rabbits, is affected by the spatial disposition of preferred plants in relation to less preferred ones. We planted willows, birches and pines, representing food species of higher, intermediate and lower preference, respectively, in different spatial arrangements, to manipulate patch quality and accessibility to herbivores. Contrasting patches were constructed by planting willows or pines in the midst of birches and single-species arrays of all three species, in a blocked design, replicated six times in an area occupied by both roe deer and rabbits. Preference patterns were studied by recording browsing on current years' shoots and older plant parts. Across all trees in the experiment, we confirmed that roe deer clearly preferred willow over birch, pine was not browsed at all. There was greater herbivory by roe deer on birches occurring peripherally in an array, when the associated central species was willow or pine, as compared to birches in a single-species birch patch. Therefore food choices by roe deer appear to be determined by both patch and individual level selection. The rabbits only showed preference at a species level and did not respond to spatial arrangement of trees. The results from this study indicate that the location and association of trees can strongly affect foraging patterns of roe deer, but not in a manner wholly consistent with the repellent–plant or the attractant–decoy hypotheses.     

Restoration of the periovulatory follicle-stimulating hormone surges in sera by luteinizing hormone releasing hormone in phenobarbital-blocked rats.

The periovulatory increases of follicle-stimulating hormone (FSH) in rat sera can be divided into two phases. The first phase consists of a rise and fall during proestrus and the second phase consists of a rise and fall during estrus. The second phase was not blocked by phenobarbital (100 mg/kg BW) injected i.p. between the first and second phases. In contrast, phenobarbital administered prior to the onset of the first phase blocked both phases of increased serum FSH. In phenobarbital-blocked rats, administration of luteinizing hormone releasing hormone (LHRH) during proestrus, either by s.c. injection (10 μg) or by a 3 hr constant-rate i.v. infusion (50 ng/hr), simulated both the proestrous and estrous phases of increased serum FSH. These results indicate that 1) the second phase of the serum FSH rise is itself not susceptible to phenobarbital blockade, 2) a proestrous mechanism susceptible to phenobarbital alteration is necessary for both phases of increased serum FSH to occur, and 3) administration of LHRH to phenobarbital-blocked rats during proestrus restores both phases of FSH release.     

Age-dependent effect of Freund's adjuvant on 24-hour rhythms in plasma prolactin, growth hormone, thyrotropin, insulin, follicle-stimulating hormone, luteinizing hormone and testosterone in rats

The effect of Freund's adjuvant administration on 24-hour changes of plasma prolactin, growth hormone (GH), thyrotropin (TSH), insulin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were studied in young (2 months) and aged (18 months) male Wistar rats. Rats were injected s.c. with Freund's adjuvant or adjuvant's vehicle and, 18 days later, they were killed at 6 different time intervals throughout a 24-hour cycle to measure circulating hormone levels by specific RIAs. Young rats receiving adjuvant's vehicle exhibited significant time-of-day-dependent variations in plasma TSH, LH and testosterone, with maximal levels at 1300 h, 0100 h and 1700 h, respectively. Prolactin and insulin levels, analyzed globally in a factorial ANOVA, showed significant time-of-day changes with maximal levels at 1300 - 1700 h and 2100 h, respectively. The daily rhythms in plasma LH and testosterone found in young rats were not longer observed in Freund's adjuvant-injected rats, while as far as TSH, a second peak was observed at 0100 h after Freund's adjuvant administration. Twenty-four hour rhythms in circulating TSH, LH and testosterone were blunted in old rats receiving either Freund's adjuvant or its vehicle. Aged rats exhibited significantly higher circulating levels of prolactin, and lower levels of GH, TSH, FSH and testosterone. The results indicate that secretion of prolactin, GH, TSH, FSH and testosterone are age-dependent, as are the responses of TSH, LH and testosterone to Freund's adjuvant administration.     

Seasonal pattern of luteinizing hormone and testosterone pulsatile secretion in young adult red deer stags (Cervus elaphus) and its association with the antler cycle.

Blood from stages aged 15 months (n = 6) was sampled at monthly intervals every 30 min for 24 h for 12 months, at 45 degrees S in New Zealand. Three extra samplings each for 24 h were carried out at about the anticipated time of antler casting. All samples were analysed for luteinizing hormone (LH) and testosterone and the resulting data further analysed by the Pulsar pulse detection routine. The animals were kept indoors under natural daylength and were fed ad libitum. All animals were weighed, antler status and size recorded and testes diameter was measured on each sampling day. Mean LH and testosterone pulsatily and plasma concentration varied seasonally. LH pulse frequency was low during autumn (2.5 pulses in 24 h), winter (1.0-1.5 pulses in 24 h) and early spring (1 pulse in 24 h) and lowest in late spring (0.2 pulse in 24 h) before rising in summer (1.0-4.0 pulses in 24 h). LH pulse amplitude and mean plasma concentration were low (< 1 ng ml-1) from March to November (autumn-spring); both rose to a peak in January (summer) of 3.4 and 1.6 ng ml-1, respectively. Testosterone pulse frequency was generally similar to LH except that slightly more pulses of testosterone than of LH were detected from March to November and more pulses of LH from November to February (summer). Testosterone pulse amplitude fell from March to November (5.3 ng ml-1 to undetectable) although there was a conspicuous peak in July (midwinter) of almost 5 ng ml-1.(ABSTRACT TRUNCATED AT 250 WORDS)