Evidence that a decrease in testosterone negative feedback mediates the pubertal increase in luteinizing hormone pulse frequency in male ferrets

Neuroendocrine mechanisms regulating luteinizing hormone (LH) secretion during puberty were investigated in intact male ferrets and ferrets castrated at 8 wk of age that received s.c. implants of either empty or testosterone-filled Silastic capsules. To synchronize puberty onset among individuals, ferrets were exposed to short days between 8 and 16 wk of age, and then transferred to long days. Testis growth began in intact ferrets soon after photoperiod transition. Blood samples were obtained at 11, 15, 19, and 23 wk of age. LH pulse frequency was low in intact ferrets at 11 and 15 wk of age (less than or equal to 0.27 pulses/h), but rose to 0.94 pulses/h by 23 wk of age. No age-related increase in LH pulse frequency was observed in untreated castrated ferrets. LH pulses were rare in testosterone-treated castrated ferrets at 11 and 15 wk of age; but by 23 wk of age, frequency rose to 0.33 pulses/h. Thus, testis maturation in ferrets is accompanied by a dramatic increase in LH pulse frequency. No steroid-independent developmental increase in LH pulse frequency occurs in castrated ferrets. Furthermore, doses of testosterone that prevent LH secretion in young castrated ferrets do not as effectively suppress LH pulses in older ferrets. These data suggest that a decrease in the efficacy of testosterone negative feedback mediates the pubertal rise in LH pulse frequency in male ferrets.     

Photoperiodic modulation of testicular LH receptors in the bank vole (Clethrionomys glareolus)

The temporal changes in testicular binding of 125I-labelled hCG in juvenile bank voles (18 days of age, born and reared in a 18L:6D photoperiod) exposed to a long (18L:6D, Group L) or short (6L:18D, Group S) photoperiod for 0, 3, 7, 14 and 42-56 days were investigated. During testicular maturation, in Group L, there was a slight initial decrease in LH receptor numbers per testis followed by a marked prepubertal rise during the initial phase of rapid testicular growth after which a decrease took place. In Group S, during testicular regression, the temporal changes in LH receptor numbers per testis resembled those of Group L except that the corresponding increase in hCG binding during the initial week was considerably less marked and the receptor numbers remained thereafter at a significantly lower level than in Group L. Leydig cell count indicated that the observed changes in LH receptors per testis were due to changes in the number of Leydig cells as well as in LH receptors per Leydig cell. The present results indicate, that (1) photoperiod is an important modulator of testicular LH receptor numbers in this species, (2) photoperiod or age has no significant effect on the binding affinity of LH receptors, (3) short photoperiods arrest the induction of LH receptors as well as the increase in Leydig cell numbers associated with normal testicular maturation, and (4) changes in LH receptor numbers per testis correlate well with the photoperiod-induced changes in androgen biosynthesis, spermatogenesis and Leydig cell morphology observed in our previous studies.     

Photomanipulation of sexual maturation and breeding cycle of the steppe polecat (Mustela eversmanni) and other techniques for more rapid propagation of the species

Twenty steppe polecats were divided into 2 groups, each consisting of 4 males and 6 females, and subjected to either a natural photoperiod (controls) or alternating periods of short (8 h light/16 hr dark for 8-9 weeks) and long days (16 h light/8 h dark for 16-20 weeks). The experimental photoperiod significantly accelerated sexual maturation in both sexes, with males developing maximal testis size within 57 days and females breeding after an average of 52 days exposure to 16L/8D. Males in the experimental group completed 2 1/2 testicular cycles and participated in mating during 3 successive breeding seasons during the 18 month period whereas males in the control group completed a single testicular cycle and only had an opportunity to mate during a single breeding season. Females in the experimental group produced 3 litters whereas females in the control group only gave birth to a single litter. Litter size averaged 6.9 +/- 2.0 (n = 23) and did not significantly differ with age, parity, or treatment. Pseudopregnant females returned to estrus within 12 days after the expected date of parturition, were bred, and gave birth to kits. Polecats which were subjected to the experimental photoperiods completed more molting cycles and underwent more photoperiod-induced changes in body weight than those in the control group. Death or removal of kits within 8 days after birth resulted in 12/12 females returning to estrus within 6-26 days. Eleven of these females were remated and gave birth to kits. Eight domestic ferrets readily accepted neonatal polecat kits and 5 successfully reared kits, although kit survival was quite poor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of hemicastration at various ages and of oestradiol-17 beta on plasma concentrations of gonadotrophins and androgens, testicular growth and interstitial cell responses in prepubertal lambs

The effect of the removal of one testis from cross-bred lambs at 1, 4, 8 or 12 weeks of age on plasma FSH, LH and testosterone was studied until 16 weeks of age. Hemicastration at all ages elicited a significant increase in plasma FSH compared to controls without a corresponding change in plasma LH or testosterone. The raised FSH after hemicastration at 1 or 4 weeks of age was suppressed to control levels between weeks 7 and 8; such a suppression was not observed in the 4 weeks following hemicastration at 8 or 12 weeks of age. The weight of the remaining testis had increased compared with the control by 12 weeks of age after hemicastration at 1 week (+ 69%), 4 weeks (+ 13%) and 8 weeks (+ 40%); hemicastration at 12 weeks of age also resulted in growth of the remaining testis at 16 weeks (+ 82%). The total androgen production of interstitial cells in response to ovine LH stimulation in vitro did not differ significantly between lambs of 1 and 12 weeks of age, or in animals of 4, 8 and 12 weeks of age after hemicastration at 1 week of age. Subdermal implantation of oestradiol-17 beta into 1-week hemicastrated lambs at the time of operation or at 6 weeks of age increased plasma oestradiol concentrations by approximately 2-4-fold, prevented the FSH and testicular growth responses to hemicastration and suppressed plasma LH and testosterone to levels lower than those in control lambs. The total androgen response of interstitial cells from the remaining testis of oestradiol-implanted lambs at 12 weeks of age was significantly reduced. We suggest that the pituitary-testis axis varies in sensitivity during the prepubertal period although the interstitial cellular response of the testis to LH stimulation remains constant.     

Testicular compensatory hypertrophy in the hemicastrated calf: effects of exogenous estradiol

Unilaterally orchidectomized (hemicastrated) bull calves were studied to monitor possible changes in serum concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) during the phase of testicular compensatory growth, to examine the characteristics of LH and FSH binding to the testis of the post-pubertal animal, and to determine whether any of these responses were altered by exogenous estradiol. Twenty-four calves were assigned randomly at one week of age to a 2 X 2 factorial experiment involving intact control (I) and hemicastrated animals (H), as well as estradiol-implanted intact (I+E2) and hemicastrated animals (H+E2). Relative to I, testis growth was accelerated in H and suppressed in I+E2 and H+E2. Mean testis weights at 27 weeks of age were 42 +/- 4, 72 +/- 6, 12 +/- 1 and 14 +/- 1 g for the four respective treatment groups. Serum FSH, but not serum LH, was positively associated with the accelerated testis growth of H. LH and FSH binding per testis were both enhanced approximately twofold in the testis from hemicastrated animals relative to those from intact calves. In contrast, estradiol markedly suppressed the number of LH-binding sites per testis in both I and H calves, but only suppressed the number of FSH-binding sites per testis in H calves. LH-affinity constants were not affected by treatment, whereas those for FSH were significantly decreased by estradiol. In conclusion, neonatal hemicastration results in elevated serum FSH, testicular compensatory hypertrophy, and an increased number of gonadotropin receptors in the bovine testis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of naloxone on gonadotrophin secretion at various stages of development in the ewe lamb

Spring-born crossbred ewe lambs were raised in a natural photoperiod and saline (N = 6) or naloxone (1 mg/kg) in saline (N = 6) was injected (i.m.) every 2 h for 6 h at 5, 10 and 15 weeks of age and for 8 h at 20, 25 and 30 weeks of age. Blood samples were taken every 12 min during treatment periods. Naloxone had no effect on time to first oestrus (controls 235 +/- 6 days, naloxone 242 +/- 7 days). Mean serum LH concentrations and LH pulse frequency were elevated by naloxone in ewe lambs at 20, 25, and 30 weeks of age (P less than 0.05). The only FSH response to naloxone was a depression of mean serum concentrations at 30 weeks of age (P less than 0.05). LH pulse amplitude was elevated at 5 weeks of age in all ewe lambs and declined thereafter to a nadir at 30 weeks of age in control, but not in naloxone-treated animals (P less than 0.05). LH pulse frequency was elevated at 10 weeks of age in control ewe lambs and in all animals at 30 weeks of age (P less than 0.05). FSH pulse frequency declined from 5 weeks of age in control ewe lambs (P less than 0.05), with very few pulses noted in 25- and 30-week-old animals. We conclude that (1) opioidergic suppression of LH, but not FSH, secretion developed at 20 weeks of age in the growing ewe lambs used in the present study, with no obvious change in suppression before the onset of first oestrus: (2) pulsatile FSH secretion occurred in the young ewe lamb but was lost as the lamb matured: (3) attainment of sexual maturity was preceded by an elevation in LH pulse frequency.     

Reproductive photorefractoriness in rams and accompanying changes in the patterns of melatonin and prolactin secretion

Exposure of rams to alternating 16-week cycles of long and short days (16L:8D and 8L:16D) results in periods of testicular regression followed by testicular redevelopment, and there is an inverse relationship between the blood levels of prolactin and testis activity. In this study, two groups of rams were held under long or short day lengths for a period of 94 weeks. When held under either long or short days for more than 16 weeks, the animals showed spontaneous changes in gonadal activity and in the secretion of prolactin, both of which were no longer correlated with the prevailing photoperiod, i.e., they became photorefractory. The photorefractoriness was characterized by cyclical changes in testis function which were independent of day length. The period of these spontaneous cycles was similar during both treatment regimens (long days: 40.9 +/- 1.5 weeks; short days: 38.1 +/- 0.33 weeks), suggesting the presence of an endogenous pacemaker for the reproductive system. The changes in blood prolactin levels during photorefractoriness were no longer correlated with testis activity, and though cyclical, the period lengths differed under the two regimens (long days: 31.8 +/- 1.4 weeks; short days: 48.6 +/- 0.3 weeks). The rates of change in testis function and prolactin secretion were slower during the refractory state than during the photosensitive state. Upon switching the rams to a different photoperiod after the 94 weeks of exposure to fixed day lengths, the rams showed relatively rapid testicular and prolactin responses. Photoperiodic information appears to be relayed to the endocrine system through the daily pattern of melatonin secretion by the pineal. We measured the daily blood levels of melatonin on several occasions during phases of photosensitivity and photorefractoriness in the same group of rams. During the first 21 weeks under both lighting treatments, the rams showed synchronized daily patterns in their blood levels of melatonin, with elevated levels occurring mainly during the daily period of darkness. Similar synchronized daily rhythms were also seen when the rams were switched to a different photoperiod following 94 weeks of exposure to either long or short days. Between Weeks 21 and 94, the daily rhythms of melatonin did not occur consistently in all rams; often, the patterns differed markedly between individual rams held under the same day length and peak levels of melatonin were not always confined to periods of darkness.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pituitary and Leydig cell function in boars actively immunized against gonadotrophin-releasing hormone

Crossbred boars were (a) immunized against GnRH conjugated to human serum globulin (200 micrograms GnRH-hSG) in Freund's adjuvant at 12 weeks of age and boosted at weeks 18 and 20 (N = 10), (b) served as controls and received hSG only in adjuvant (N = 10), or castrated at weaning (N = 10). At 24 weeks of age (immediately before slaughter), the boars were challenged with saline or pig LH (1 microgram/10 kg body weight). After slaughter, fresh testicular fragments were incubated with pig LH (0.05 and 0.2 ng/2 ml medium) to assess the effects of immunization on Leydig cell function. Pituitary contents of LH and FSH, and testicular LH receptor content were also measured. The results indicated that plasma LH and testosterone concentrations, pituitary LH content, testicular LH receptor content, testis and sex accessory organ weights were significantly reduced in GnRH-immunized boars compared to hSG-adjuvant controls. However, plasma and pituitary FSH content were not affected by high antibody titres generated against GnRH. The testicular testosterone response to exogenous LH in vivo and in vitro was significantly reduced (P less than 0.05) in GnRH-immunized boars. These results indicate that active immunization against GnRH impairs pituitary and Leydig cell functions in boars.     

Maternal photoperiodic history affects offspring development in Syrian hamsters

During the first 7 weeks of postnatal life, short day lengths inhibit the onset of puberty in many photoperiodic rodents, but not in Syrian hamsters. In this species, timing of puberty and fecundity are independent of the early postnatal photoperiod. Gestational day length affects postnatal reproductive development in several rodents; its role in Syrian hamsters has not been assessed. We tested the hypothesis that cumulative effects of pre- and postnatal short day lengths would restrain gonadal development in male Syrian hamsters. Males with prenatal short day exposure were generated by dams transferred to short day lengths 6 weeks, 3 weeks, and 0 weeks prior to mating. Additional groups were gestated in long day lengths and transferred to short days at birth, at 4 weeks of age, or not transferred (control hamsters). In pups of dams exposed to short day treatment throughout gestation, decreased testis growth was apparent by 3 weeks and persisted through 9 weeks of age, at which time maximum testis size was attained. A subset of males (14%), whose dams had been in short days for 3 to 6 weeks prior to mating displayed pronounced delays in testicular development, similar to those of other photoperiodic rodents. This treatment also increased the percentage of male offspring that underwent little or no gonadal regression postnatally (39%). By 19 weeks of age, males housed in short days completed spontaneous gonadal development. After prolonged long day treatment to break refractoriness, hamsters that initially were classified as nonregressors underwent testicular regression in response to a 2nd sequence of short day lengths. The combined action of prenatal and early postnatal short day lengths diminishes testicular growth of prepubertal Syrian hamsters no later than the 3rd week of postnatal life, albeit to a lesser extent than in other photoperiodic rodents.     

Stereological study of postnatal testicular development in Blackbelly sheep

The objective was to characterize testicular development in Blackbelly sheep, focusing primarily on Sertoli cell number. Lambs (n=43) were allotted into eight groups, and surgically castrated at 0, 3, 6, 9, 12, 15,18 or 21 weeks of age (n=4-6 lambs per group). Testes were fixed and paraffin-embedded, cross-sections (5 microm) were stained and evaluated with quantitative morphometry techniques. Testis weight increased at a greater rate between 9 and 15 weeks of age, which was associated with remarkable changes in testicular histology, including increases in tubular tissue volume, and tubule diameter and length. Spermatogenesis started in a period between 9 and 12 weeks, lumen and elongated spermatids were observed for the first time at 12 weeks (78% of the tubules) and 15 weeks (37% of the tubules), respectively. Total number of Sertoli cells (mean+/-S.E.M.) increased steadily from birth (531+/-76 x 10(6)) to 15 weeks (12,008+/-1722 x 10(6)), with no changes afterwards. Sertoli cell number per gram of testicular tissue decreased as lambs were older, with the most remarkable change occurring between Weeks 9 and 12. An early increase in serum LH was observed at 6 weeks of age, with testosterone (T) increasing at Weeks 12 and 21. In conclusion, Sertoli cells maintained the capacity of proliferating from birth to 15 weeks of age in Blackbelly sheep; furthermore, the period of accelerated testis growth was associated with increased serum T concentration and with important changes in testicular morphology, as a consequence of the beginning and establishment of spermatogenesis and Sertoli cell maturation.     

Photoperiodic regulation of glutamatergic stimulation of secretion of luteinizing hormone in male Syrian hamsters.

It has been suggested that changes in endogenous glutamatergic stimulation of secretion of luteinizing hormone (LH) induced by photoperiod play a role in regulating seasonal cycles of reproductive activity. The aim of this study was to test the hypothesis that the glutamatergic control of the secretion of LH in the male Syrian hamster is sensitive to photoperiod, by determining whether the glutamate agonist N-methyl-D-aspartate (NMDA) could stimulate LH secretion in this species and, if so, to determine whether the response varied among animals exposed to different daylengths. In the first experiment, adult male hamsters were housed in either short day (8 h light: 16 h dark) for 6 weeks to induce testicular regression, or long days (16 h light: 8 h dark) to maintain testicular function, and the effects of systemic administration of NMDA on serum LH concentrations were determined. In the short-day hamsters, all s.c. doses of NMDA (25-75 mg kg-1 body weight) produced a robust rise in serum LH concentrations within 15 min. In the long-day hamsters, basal LH concentrations were higher than in short-day hamsters, but only the highest dose of NMDA produced a significant increase in LH concentrations, and the magnitude of this increment was less than those observed in short days. In hamsters in long days, the low doses of NMDA that did not significantly alter LH concentrations nevertheless significantly suppressed serum prolactin concentrations, demonstrating the efficacy of the drug. In hamsters in short days, serum prolactin concentrations were at the limit of detection of the assay, so no inhibitory effect of NMDA on prolactin secretion could be determined on this photoperiod. In the second experiment, the effects of a fixed dose of NMDA (50 mg kg-1 body weight) was tested at intervals in hamsters exposed to short days for a prolonged period such that their testes initially regressed, but then became scotorefractory and testicular recrudescence occurred. After 6 and 12 weeks in short days, NMDA stimulated LH secretion. However, after 24 weeks in short days when testicular recrudescence was complete, the response to NMDA was lost. A third experiment determined whether the reduced response to NMDA in hamsters on long days relative to those in short days might result from higher concentrations of circulating testosterone. Hamsters in long days were castrated to remove the influence of gonadal feedback, and the response to NMDA tested 3 weeks later when endogenous LH concentrations had risen to levels characteristic of the chronically castrated condition.(ABSTRACT TRUNCATED AT 400 WORDS)     

Testicular apoptosis is down-regulated during spontaneous recrudescence in white-footed mice (Peromyscus leucopus).

Among individuals of many nontropical species, seasonal breeding is timed by tracking changes in the daily photoperiod. Transfer of rodents to short (< 12 h of light/day) day lengths for 6 to 14 weeks can induce regression of the testes mediated by apoptosis. After 16 to 20 weeks of short day exposure, reproductive function is "spontaneously" initiated, and testicular recrudescence is observed. The gonadal mechanisms that underlie testicular recrudescence are not fully understood. If the onset of testicular regrowth that occurs during spontaneous recrudescence reflects a down-regulation of apoptotic signals, then a decline in apoptosis should be noted concurrent with increased testis mass. This experiment sought to assess the role of apoptosis in the restoration of reproductive capacity to photoperiod-inhibited white-footed mice. Males were assigned to long (16:8 LD) or short (8:16 LD) photoperiods for 0, 14, 18, 22, 26, or 30 weeks. At each of these time points, testis mass and testosterone concentrations were assessed. In addition, apoptotic activity was measured using both in situ terminal deoxynucleotidyl transferase dNTP end labeling (TUNEL) and DNA laddering. Short photoperiod exposure induced maximal decreases in testicular parameters after 14 weeks (p < 0.05). After 26 weeks of short days, testis mass was no longer different between males housed in long days and those housed in short days. In contrast, the high incidence of apoptotic TUNEL labeling and DNA laddering observed at 14 weeks was reduced to long day values after 22 weeks of short day exposure. Together, our results establish that a decrease in testicular apoptosis coincides with testicular recrudescence in white-footed mice. The current study demonstrates a decline in the incidence of testicular cell death concomitant with changes in testis mass or length, elucidating a timeline of changes at the cellular level related to the onset of recrudescence.     

Testosterone, luteinizing hormone, follicle stimulating hormone, and prolactin response to unilateral castration in prepubertal Holstein bulls

Hemicastration of Holstein bulls at 3 months of age resulted in increased (P<0.005) testicular weitht and testis sperm cell content at 330 days after treatment, but did not alter sperm cell concentration in the remaining hypertrophied testis. Radioimmuroassay of blood hormones at 1, 6, 12, and 24 weeks after treatment revealed that unilateral castration did not alter (P>0.1) basal levels or GnRH response profiles of either LH or testosterone compared to intact bulls. Hemicastration caused FSH to be elevated (P<0.01) compared to intact bulls at all sampling periods in both unstimulated and GnRH stimulated bulls. Prolactin varied with season and was greater (P<0.001) in hemicastrated bulls than in intact bulls at 1 and 6 weeks after treatment. Results indicate that unilateral castration at 3 months of age caused testicular hypertrophy of both steroidogenic and gametogenic function and this phenomena may be triggered by increased FSH or prolactin secretion, or both. Further, results indicate different testicular regulation mechanisms exist for pituitary LH and FSH release in bulls.     

Spermatogenesis in the turkey (Meleagris gallopavo): quantitative approach in immature and adult males subjected to various photoperiods

The objectives of this study were to identify and quantitate the germ cell populations of the testes in sexually mature male turkeys (Trial 1), determine the duration of meiosis based on BrdU labeling and stereological analyses (Trial 2), and examine the impact of various photoperiods on germinal and somatic cell populations in immature and adult males (Trial 3). In Trial 1, both testes within a male had similar stereological components (P>0.05) for all parameters analyzed. In Trial 2, the duration of Type-1 spermatocytes and round spermatids in turkeys lasted 4.5+/-0.5 and 2.0+/-0.5 days, respectively. In Trial 3, the short photoperiod (7L:17D) delayed testicular growth (in the stereological parameters analyzed). In contrast, the effect of a moderately short photoperiod (10.5L:13.5D) was comparable to the effect of a long (14L:10D) or increasing photoperiod (7L:17D to 14L:10D) on the stereological parameters examined. With the exception of the short photoperiod, all other photoperiods used in this study induced comparable early testicular maturation, with maximum testis weight at 29-35 weeks of age. As the males got older, there was a progressive, linear decline in testis weight through 60 weeks, at which time there were no significant differences among photoperiods. In conclusion, the duration of meiosis in the turkey was similar to that observed in the fowl and guinea-fowl. The existence of a threshold of photosensitivity to gonad stimulation in male turkeys is suggested to be between 7.0 and 10.5 h of light.     

Absence of an increase in gonad-independent drive to pulsatile luteinizing hormone secretion during photoperiod-induced puberty

This study was conducted to determine if photoperiod can influence the pattern of luteinizing hormone (LH) secretion in the absence of the ovaries in the developing female sheep. Lambs were raised in a photoperiod sequence (short, long, short days) known to induce puberty between 30 and 35 wk of age, or in a photoperiod (only short days) that prevents puberty during the first year. Their ovaries were removed at 10 wk of age, and the detailed pattern of LH was assessed (samples at 12-min intervals for 4 h) each 3- to 5-wk period between 9 and 45 wk of age. Rapid LH pulses (40- to 50-min interpulse interval) were evident within a few weeks after ovariectomy in both groups of females. Those exposed to the artificial photoperiod sequence that induces normal sexual maturity did not increase their pulse frequency further during the pubertal period. Moreover, their LH pulse frequencies were not greater than those in agonadal females exposed to the photoperiod that delays puberty. These findings indicate that photoperiodic induction of puberty in the sheep does not require steroid-independent modulation of pulsatile LH secretion.     

Changes in the testicular binding of luteinizing hormone and plasma testosterone concentrations in the Djungarian hamster subjected to different photoperiods and temperatures and effects of long-term testosterone treatment on the binding

The effects of artificial photoperiod, temperature, and long-term testosterone treatment on testicular luteinizing hormone (LH) binding were studied in adult male Djungarian hamsters. In hamsters transferred to long-day (LD; 16 hr light, 8 hr dark) photoperiod 8 weeks after adaptation in short-day (SD; 8 hr light, 16 hr dark) photoperiod of 25 degrees C, testicular growth was associated with an increase in the total LH binding per two testes and a decrease in LH binding per unit testicular weight. Plasma testosterone levels reached a peak 47 days after transfer to LD and tended to decrease thereafter, while the testes continued growing. In contrast, when hamsters reared under LD conditions at 25 degrees C for 12 weeks were transferred to SD, testicular regression was associated with a decrease in plasma testosterone and the total LH binding per two testes and an increase in LH binding per unit testicular weight. A significant decrease in LH binding per unit weight compared to SD controls was observed in those hamsters exposed to SD with continuous testosterone treatment. The testosterone treatment tended to induce decrease in the total LH binding. Scatchard plot analyses of the binding suggested that changes in LH binding were due to changes in the number of binding sites. When sexually mature male hamsters were subjected for 8 weeks to two different ambient temperatures (7 degrees C and 25 degrees C) and photoperiods (LD and SD), the difference between the two temperature groups was statistically not significant regarding the weights of testes, epididymides, and prostates; plasma testosterone levels; and LH binding in either LD or SD group. These results suggest that photoperiod is a more important environmental factor than temperature for the regulation of testicular activity and LH receptors and that testosterone reduces the number of LH receptors per unit testicular weight in adult male Djungarian hamsters.     

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)     

Timing of testicular recrudescence in siberian hamsters is unaffected by pinealectomy or long-day photoperiod after 9 weeks in short days

In this study, the authors asked whether pinealectomy or temporary exposure to a stimulatory photoperiod affects the timing of spontaneous testicular recrudescence in adult Siberian hamsters chronically exposed to short days (9:15 light:dark). In Experiment 1, hamsters were pinealectomized after 6, 9, or 12 weeks in short days. Pinealectomy after 9 or 12 weeks did not affect the timing of spontaneous gonadal growth (27.7 +/- 1.9 and 25.4 +/- 1.3 weeks, respectively) compared to sham-operated controls (28.6 +/- 0.9 weeks). Enlarged testes occurred earlier in animals that were pinealectomized after 6 weeks in short days (21.8 +/- 2.1 weeks). In Experiment 2, adult hamsters were exposed to short days for 9 weeks, transferred to long days (16:8 light:dark) for 4 weeks, and then returned to short days for 23 additional weeks. Although long-day interruption caused gonadal growth in 15 out of 19 hamsters, the temporary long-day exposure did not affect the timing of spontaneous gonadal growth following return to short days (28.2 +/- 0.9 weeks) in 10 of the 15, relative to the timing observed in control hamsters continuously maintained in short days (28.2 +/- 1.1 weeks). Four out of 19 hamsters did not show gonadal growth following long-day exposure. Spontaneous gonadal growth in these hamsters (28.0 +/- 1.4 weeks) also occurred at the same time as controls. The remaining 5 hamsters exhibited enlarged testes following long-day exposure (12.0 +/- 0.0 weeks) but were refractory to the second short-day exposure. All hamsters exhibited entrainment of wheel-running activity following the change in photoperiod. A final group of 13 animals were pinealectomized before long-day transfer. They exhibited gonadal growth (at 17.2 +/- 0.8 weeks) but failed to regress a second time when returned to short days. The timing of gonadal growth in these animals was delayed relative to the sham-operated hamsters temporarily transferred to long days (Experiment 2) but accelerated relative to the hamsters pinealectomized at 9 weeks, which remained continuously in short days (Experiment 1). The results of both experiments suggest that a pineal-independent process mediates the timing of spontaneous gonadal growth in Siberian hamsters chronically exposed to a short-day photoperiod.     

Photoperiod modulates pubertal shifts in behavioral responsiveness to testosterone.

This study examined the effect of photoperiod on pubertal maturation of steroid-dependent reproductive behaviors in male European ferrets (Mustela putorius furo). In the first experiment, levels of neck gripping, mounting, and pelvic thrusting in gonadally intact prepubertal (PRE) ferrets were compared with those of adults that had undergone puberty either while housed in short days (8 hr light/16 hr darkness per day; SD), or after transfer from SD to long days (18 hr light/6 hr darkness per day; LD) at 12 weeks of age. Both LD and SD adults demonstrated significantly greater amounts of neck gripping and mounting than PRE males. In addition, a significantly greater proportion of adults in both SD and LD displayed at least one incidence of the three behaviors compared to PRE ferrets. There were no statistically significant differences in behavior of the gonadally intact LD and SD adults. In the second experiment, dose-response curves for behavioral responses to subcutaneous injections of 0, 0.5, 1.25, 2.5, 5, and 10 mg/kg testosterone propionate (TP) in oil were generated in castrated PRE, SD, and LD males. The lowest dose of TP elicited significantly greater amounts of all three behaviors in LD adults than in PRE ferrets. In addition, levels of mounting and thrusting elicited by the lowest dose of TP were significantly greater in LD adults than in SD adults. These data indicate that pubertal activation of male sexual behavior in male ferrets is accompanied by a pubertal increase in responsiveness to the behavioral effects of testosterone. Furthermore, the degree of behavioral responsiveness of adult ferrets to testosterone is modulated by environmental photoperiod experienced during reproductive maturation.     

Release of luteinizing hormone and growth hormone after recovery from maximal exercise

Pulsatile properties of luteinizing hormone (LH) and growth hormone (GH) release were evaluated in 19 eumenorrheic untrained females [mean age 31.1 +/- 1.1 yr, height 165.2 +/- 1.4 cm, weight 64.8 +/- 2.1 kg, peak oxygen uptake (Vo2) 41.6 +/- 1.4 (SE) ml.kg-1.min-1] during the early follicular phase of the menstrual cycle (days 3-4 after the onset of menses). Each subject was studied during two consecutive menstrual cycles under each of two conditions in random order: 1) no formal exercise for 72 h (C) and 2) 12-24 h after two maximal exercise bouts (peak Vo2/lactate threshold treadmill evaluation and a 3,200-m time-trial run or a maximal Vo2 inclined treadmill test) performed on consecutive days (EX). Blood sampling was performed every 10 min for 12 h. LH and GH pulsatile parameters were identified and characterized by the Cluster pulse detection algorithm. No significant differences were noted in the number of peaks, peak amplitude, interpeak interval, peak increment, or 12-h integrated concentrations between C and EX for LH or GH. We conclude that maximal exercise protocols typically used for exercise evaluation do not have an effect on the pulsatile characteristics of LH or GH release in untrained women during the early follicular phase of the menstrual cycle if 12-24 h of recovery are allowed before evaluation of the pulsatile secretion of gonadotropins or GH.