The influence of short photoperiod on testicular and circulating levels of testosterone precursors in the adult golden hamster

The in vivo effects of short photoperiod (SPP, 6L:18D) for 8 and 12 wk on plasma and testicular levels of testosterone (T) precursors in adult golden hamsters were evaluated. Plasma and testicular progesterone (P), 17 alpha-hydroxyprogesterone (17 alpha-OHP), androstenedione (A-dione), and T were measured after 5 injections of saline or human chorionic gonadotropin (hCG) (5 or 25 IU/day). The basal levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) in circulation were also determined. There were significant reductions in the weight of the testes in animals exposed to SPP. After 12 wk in SPP, circulating levels and testicular content of 17 alpha-OHP, A-dione, and T were significantly reduced, suggesting that the decrease in T secretion may be associated with the impairment of synthesis and/or action of 17 alpha-steroid hydroxylase, C17-20 steroid lyase, and 17 beta-hydroxysteroid dehydrogenase enzymes in the testes. Exposure to SPP for 8 wk resulted in decreased plasma and testicular content of T. Although there were reductions in testicular content of 17 alpha-OHP and A-dione, this was not reflected in plasma levels of these steroids. After 8 and 12 wk of exposure to SPP, hCG treatment increased the total amounts of T precursors (except P at 8 wk) in the testes, but the values attained in animals exposed to 12 wk of SPP remained below those observed in hamsters kept in a long photoperiod (14L:10D), suggesting that gonadotropin replacement alone may be insufficient to normalize testicular steroidogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of photoperiod and hCG on the regulation of testicular LH/hCG receptors in Syrian hamsters (Mesocricetus auratus)

The regulation of testicular LH/hCG receptors was studied in Syrian (golden) hamsters with testicular atrophy induced by exposure to short photoperiod (5L:19D) and in gonadally active hamsters kept in a long photoperiod (14L:10D). By 24 h after injection of hCG, long-photoperiod hamsters showed a dose-related decrease in the number of testicular LH/hCG receptors. At 48 and 72 h, there was a recovery from this 'down-regulation'. The recovery was much faster than has been reported for the rat and mouse, and it resulted in elevation of testicular LH/hCG receptor concentrations above basal values. Hamsters with short photoperiod-induced testicular atrophy showed an increase in testicular LH/hCG receptors after injection of hCG, except for animals injected with a very high dose. The hCG-induced increase in testicular LH/hCG binding in these animals was associated with reappearance of testosterone responses to subsequent hCG stimulation. Response of testicular LH/hCG receptors to hCG in prepubertal hamsters resembled that measured in animals with short photoperiod-induced gonadal atrophy.     

Cyclic adenosine monophosphate (cAMP) does not mediate the stimulatory action of norepinephrine on testosterone production by the testis of the golden hamster.

The role of cAMP in mediating the stimulatory effects of norepinephrine (NE) on testosterone (T) production by hamster testes in vitro was examined using tissue from both gonadally active and gonadally regressed hamsters. As expected from our previous studies, the NE-induced increase in T accumulation in this system was prevented by alpha-adrenoreceptor antagonist prazosin, but not by beta-adrenoreceptor antagonist propranolol. In incubations of regressed testes from short photoperiod-exposed hamsters, NE stimulated accumulation of cAMP in media and tissue. These effects were prevented by propranolol but not by prazosin. In incubations of active testes from long photoperiod-exposed animals, NE stimulated cAMP in the media but not in the tissue, and potentiated the effect of hCG on the accumulation of cAMP only in tissue. When added to incubations with NE and hCG, propranolol, but not prazosin, reduced cAMP levels in media and tissue. Thus, functional alpha- and beta-adrenoreceptors are present in active and regressed testes and can be activated by NE. NE stimulates cAMP production via its action at the beta-receptors and T production via its action at the alpha-receptors. These results imply that cAMP does not mediate the stimulatory action of NE on T production in hamster testes.     

Morphometric studies on hamster testes in gonadally active and inactive states: light microscope findings

This study provides quantitative information on the testes of seasonally breeding golden hamsters during active and regressed states of gonadal activity. Seminiferous tubules occupied 92.5% of testis volume in adult gonadally active animals. Leydig cells constituted 1.4% of the testicular volume. The mean volume of an individual Leydig cell was 1092 microns 3, and each testis contained about 25.4 million Leydig cells. The volume of an average Sertoli cell nucleus during stage VII-VIII of the cycle was 502 microns 3. A gram of hamster testis during the active state of gonadal activity contained 44.5 million Sertoli cells, and the entire testis contained approximately 73.8 million Sertoli cells. Testes of the hamsters exposed to short photoperiods for 12-13 wk displayed a 90% reduction in testis volume that was associated with a decrease in the volume of seminiferous tubules (90.8% reduction), tubular lumena (98.8%), interstitium (72.7%), Leydig cell compartment (79.3%), individual Leydig cells (69.7%), Leydig cell nuclei (50.0%), blood vessels (85.5%), macrophages (68.9%), and Sertoli cell nuclei (34.1%). The diameter (61.1%) and the length (36.8%) of the seminiferous tubules were also decreased. Although the number of Leydig cells per testis was significantly lower (p less than 0.02) after short-photoperiod exposure, the number of Sertoli cells per testis remained unchanged. The individual Sertoli cell in gonadally active hamsters accommodated, on the average, 2.27 pre-leptotene spermatocytes, 2.46 pachytene spermatocytes, and 8.17 round spermatids; the corresponding numbers in the regressed testes were 0.96, 0.20, and 0.04, respectively. The striking differences in the testicular structure between the active and regressed states of gonadal activity follow photoperiod-induced changes in endocrine function and suggest that the golden hamster may be used as a model to study structure-function relationships in the testis.     

Effect of GABA and benzodiazepines on testicular androgen production

We have evaluated the effect of Ro5-4864, a selective probe to label peripheral type benzodiazepine receptor, on "in vitro" testicular androgen production. Decapsulated testes from adult rats showed a significant increase in the basal and hCG-stimulated testosterone secretion into the medium in response to 10(-5) M, 10(-6) M, and 10(-7) M Ro5-4864. In addition, we have studied the changes in testicular GABA content at three different ages and we found its highest concentration at 31 days of age. When we evaluated the effect of GABA on "in vitro" androgen production at different stages of gonadal maturation we observed that the highest concentration of GABA (10(-6) M) was able to modify the basal and hCG-stimulated androgen production from adult (60 days) and pubertal (45 days) testes. In addition, when prepubertal testes (31 days) were incubated under basal conditions, 10(-6) M GABA induced a significant increment of androstanediol production, while the stimulatory effect of hCG was reduced in the presence of the same GABA concentration. The present results suggest that GABA plays a physiological role in the regulation of rat testicular androgen production depending on the stage of sexual maturation.     

Changes in the response to adrenergic drugs on mouse uterine contractions during pregnancy

The effect of isoproterenol (ISO), norepinephrine (NE) and phenylephrine (PHE) on electrically-induced contractions of mice uterine horns was studied during pregnancy. At the different times of gestation adrenergic agonists always inhibited uterine contractions in the following rank order of potency: ISO greater than NE greater than PHE. Cumulative dose-response curves constructed for the effect of these amines during diestrous, and at days 3-7, 10-15, 17-21 of gestation, showed that EC50 values increased gradually as term approached, which could imply a lower capacity of the uterus to respond to adrenergic drugs. Some likely explanations for this phenomenon are proposed. It is suggested that this lower response to catecholamines at the end of pregnancy could be a cause for the reduced success of beta 2-adrenergic drugs to stop premature labor.     

Differential effects of short photoperiod on the release of progesterone and testosterone by hamster testes in vitro

Suppression of testicular activity in hamsters and voles exposed to constant darkness or short photoperiod is associated with reduced ability of the testes to convert C21 steroid precursors to C19 androgens. In the present study, we have examined the time course of changes in testicular secretion of progesterone and testosterone in vitro in adult male golden hamsters exposed to short photoperiod. Gradual decrease in testicular weight after 1, 2, and 3 months of exposure to short photoperiod was accompanied by significant increase in the amount of progesterone released per milligram of testicular tissue in response to gonadotropin stimulation. In contrast, testosterone response to gonadotropic stimulus progressively decreased. These results suggest that photoperiod-related gonadal atrophy may be accompanied by reduced activity of the 17 alpha-hydroxylase: C17,20-lyase enzyme complex in the testes, and that seasonal transitions between the states of reproductive activity and quiescence involve changes in both the amount of steroids produced by the testes and the relative proportions of testosterone and its precursors.     

Effect of photoperiod on the size of the Leydig cell population and the rate of recruitment of Leydig cells in adult Syrian hamsters

The number of Leydig cells was determined by stereologic procedures in adult Syrian hamsters housed in long days (14L:10D) to maintain testicular activity (active), in short days (5L:19D) for 12-13 wk to induce testicular regression (photoperiod-induced regressed), or in short days for a period of 21 wk or more to allow spontaneous gonadal recrudescence (spontaneously recrudesced). Testes were removed, sliced, fixed, embedded in Epon 812, and observed by bright-field microscopy. Testicular and seminal vesicle weights, plasma testosterone concentration, total Leydig cell volume per testis, and volume of single Leydig cell were greater (p less than 0.01) in active and recrudesced animals than in regressed animals. The density of Leydig cells was greater in the regressed testes, but the total number per testis was not influenced by photoperiod. In Experiment 2, the rate of recruitment of Leydig cells was determined in 5 adult hamsters exposed to long days (active) or 5 hamsters whose testes were regressed by exposure of animals to short days for 13 wk followed by long-day exposure to initiate testicular growth (photoperiod-induced recrudescing). Hamsters were injected for 3 days/wk for 3 wk with tritiated thymidine, 0.5 or 1 microCi/g body weight. Testes were fixed and tissues prepared, as above, and processed for autoradiography. Again, the photoperiod did not influence the number of Leydig cells per testis. Labeling of Leydig cell nuclei revealed that recruitment of new Leydig cells occurred at approximately 1.3% per day in recrudescing testes but also occurred at approximately 0.6% per day in active testes. Without change in the total number of Leydig cells, new Leydig cells were added continually to the existing population in adult hamsters with either recrudescing or active testes.     

Limb-specific differences in the skin vascular responsiveness to adrenergic agonists

In this study, to test the hypothesis that adrenergic vasoconstrictor responses of the legs are greater compared with the arms in human skin, cutaneous vascular conductance (CVC) in the forearm and calf were compared during the infusion of adrenergic agonists in healthy young volunteers. Under normothermic conditions, norepinephrine (NE, α- and β-agonist, 1 × 10(-8) to 1 × 10(-2) M), phenylephrine (PHE, α(1)-agonist, 1 × 10(-8) to 1 × 10(-2) M), dexmedetomidine (DEX, α(2)-agonist, 1 × 10(-9) to 1 × 10(-4) M), and isoproterenol (ISO, β-agonist, 1 × 10(-8) to 1 × 10(-3) M) were administered by intradermal microdialysis. Skin blood flow (SkBF) was measured by laser-Doppler flowmetry, and the local temperature at SkBF-measuring sites was maintained at 34°C throughout the experiments. CVC was calculated as the ratio of SkBF to blood pressure and expressed relative to the baseline value before drug infusion. The dose of NE at the onset of vasoconstriction and the effective dose (ED(50)) resulting in 50% of the maximal vasoconstrictor response for NE were lower (P < 0.001) in the calf than forearm. The ED(50) for PHE and DEX was also lower (P < 0.05) in the calf than forearm. Increases in CVC in response to ISO were potentially smaller in the calf, but the statistical differences in the responses were dependent on the expressions of CVC. These findings suggest that the cutaneous vasoconstrictor responsiveness to exogenous NE is greater in the legs than in the arms due to a higher α(1)- and α(2)-adrenoceptor reactivity, while the β-adrenoceptor function plays a minor role in regional differences in adrenergic vasoconstriction in normothermic humans.     

Testicular responsiveness to hCG of the ovine fetus in the last third of gestation

The in vivo and in vitro testicular responsiveness to hCG of hemicastrated lamb fetuses 95-99, 110-118 and 130-141 days of gestational age was studied. Basal plasma testosterone (T) levels were similar at all ages (less than 0.25 ng/ml), while the mean testicular concentrations of dehydroepiandrosterone sulfate (DHA-S), 17 alpha-hydroxyprogesterone (17-OHP) and T were higher in 95- to 99-day-fold fetuses. Plasma T levels and the concentration of T, DHA-S, 17-OHP, androstenedione (A) and cyclic adenosine 3'5'-monophosphate (cAMP) were increased by hCG in the hemicastrated animal at all ages. cAMP and T production by enriched preparations of dispersed interstitial cells from control testes was increased by hCG in all groups. In fetuses pretreated with hCG in vivo the addition of hCG in vitro failed to modify cAMP and T production. 100 micrograms of LHRH to a 130-day-old fetus increased plasma LH and T levels. From these experiments, it is suggested that the low plasma LH and T levels found throughout the last trimester of fetal life reflect a relative lack of endogenous LHRH synthesis and/or release, rather than reduced testicular steroidogenic capacity.     

Effects of testosterone, estradiol, aromatase inhibitor, gonadotropin and prolactin on the response of mouse testes to acute gonadotropin stimulation

These studies determined the local acute responsiveness of the testis to intratesticular administration of human chorionic gonadotropin (hCG) under basal, stimulated (systemic hCG pre-treated), hypogonadotropic (steroid pre-treatment) and hyperprolactinemic conditions in male mice. In addition, testicular testosterone (T) levels were determined after intratesticular administration of the aromatase inhibitor, 4-hydroxyandrostenedione (4-OHA) or progesterone under basal or hCG-stimulated conditions. Intratesticular administration of 0.025, 0.25, 2.5 or 25 mIU hCG resulted in a dose-dependent (3- to 14-fold) increase in testicular T concentrations in hCG compared to vehicle-injected testes. Systemic (i.p.) pre-treatment with 5 IU hCG 24 h before prevented any further increases in the already elevated (10-fold basal) T levels after direct intratesticular hCG injection. Pretreatment with 250 micrograms testosterone propionate (TP) reduced basal testicular T concentrations, but resulted in increased responsiveness to intratesticular hCG administration. In contrast, estradiol benzoate (EB) pretreatment, which also reduced basal testicular T concentrations, did not affect the testicular responsiveness to hCG. Hyperprolactinemia reduced testicular responsiveness to intratesticular administration of 0.025, 0.25 or 2.5 mIU hCG, but basal levels of testicular T were elevated. One hour after intratesticular injections of an aromatase inhibitor, 4-OHA; (0.25 micrograms) testis, T levels were increased in males pre-treated with 5 IU hCG (i.p.) 24 h earlier. Higher doses of 4-OHA (2.5, 25 or 250 micrograms) resulted in significant, dose-related increases in basal testicular T levels which were attenuated by hCG-pre-treatment. Intratesticular administration of 20 micrograms progesterone increased testicular T concentrations 2.7-fold, but this effect was attenuated (1.5-fold) in hCG-pre-treated mice, suggesting that enzymatic lesions beyond progesterone may be involved in hCG-induced testicular desensitization. These results indicate that testicular responsiveness to hCG depends on the existing levels of gonadotropic stimulation. However, it is evident that estrogens and prolactin also influence the sensitivity of the testis to gonadotropin.     

Role of catecholamines in the inhibitory effect of immobilization stress on testosterone secretion in rats

Immobilization stress applied for 6 h induced, in adult male rats, a rise of epinephrine (E) and norepinephrine (NE) plasma levels and a decrease of baseline plasma testosterone (T) values and of human chorionic gonadotropin (hCG)-induced T response. Treatment of the animals for 5 weeks with guanethidine (G), a sympathetic neuron toxic agent, significantly decreased E and NE responses to stress and partly antagonized the inhibitory effects exerted by immobilization on T biosynthesis. Adrenalectomy totally suppressed circulating E and reduced the stress-induced NE increase while partly antagonizing the inhibitory effects exerted on T biosynthesis. Combined G and adrenalectomy treatments totally suppressed plasma E and NE, and completely blocked the effects of immobilization on T levels. Treatment of the animals with the alpha 1-adrenergic blocker, prazosin, and the beta 1-adrenergic blocker, metoprolol, did not modify the effects of stress on T biosynthesis. Treatment with propranolol or with butoxamine, a nonspecific beta- and a specific beta 2-adrenergic receptor blocker, respectively, antagonized the testicular hyposensitivity to hCG induced by stress. Stress- or treatment-induced changes of plasma luteinizing hormone (LH) and hCG levels were not consistently correlated with plasma T modifications. These findings suggest that at least part of the inhibitory effects of immobilization stress on T biosynthesis is exerted by catecholamines through a beta 2-adrenergic receptor.     

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.     

Interspecies differences in the effects of HCG on testicular function among rodents

Adult mice, rats and hamsters were injected with 0 or 0.3 IU hCG/g BW, 24 h before sacrifice. Basal LH receptor concentration was highest in rats and lowest in hamsters (rats greater than mice greater than hamsters). Injection of hCG caused LH receptor down-regulation in rats and mice, and up-regulation in hamsters. Basal plasma progesterone was highest in hamsters and lowest in rats (hamsters greater than mice greater than rats), however, hCG increased plasma progesterone levels in mice and rats, but not in hamsters. Mice had much higher plasma and testicular testosterone levels than other species, but hCG did not induce a relatively more dramatic increase in any species. When testes fragments were incubated with 0 or 12.5 mIU hCG/ml for 4 h, hCG increased media progesterone levels in rats and control mice, but not in hamsters and hCG-injected mice. Also, hCG elevated media testosterone levels in control but not in hCG-injected animals. Furthermore, addition of hCG in vitro partially prevented the elevation of media testosterone induced by in vivo hCG. The present results indicate that the mechanisms for the transduction of the gonadotropic signal by the Leydig cells are species-defined.     

Gonadal regression despite light pulses coincident with locomotor activity in the Syrian hamster

Feedback lighting (LDFB), which illuminates an animal cage in response to active wheel running, exposes only the photosensitive portion of the phase-response curve to light. In the hamster, the photoinducible zone of the circadian rhythm of photoperiodic photosensitivity occurs during the interval of active wheel running. Since LDFB exposes the photoinducible zone almost as much as constant light (LL), we predicted that LDFB would maintain gonadal function just as LL does. Surprisingly, 10 male hamsters exposed to 1-sec pulses of LDFB for 8 wk had regressed testes similar to those of hamsters in continuous darkness (DD) and significantly smaller than hamsters exposed to LL (P less than 0.01). Two of 5 male hamsters exposed to 2-min pulses of LDFB underwent complete testicular regression and two had partially regressed testes. All females exposed to LDFB or to DD ceased showing cyclic signs of ovulation within 20 days, whereas most hamsters exposed to LL continued to show signs of cyclic ovulation. Six of the 8 hamsters exposed to LL had ova in their oviducts at autopsy, and also had significantly larger uteri (P less than 0.01) than hamsters exposed to DD or LDFB. None of the latter two groups (n = 6 and 9, respectively) had oviductal ova at autopsy. These results demonstrate that considerable exposure of the photoinducible zone to light does not necessarily maintain gonadal function. Light delivered to the photoinducible zone by LDFB may disrupt the normal alignment (internal coincidence) of circadian rhythms, thereby causing gonadal regression. Gonadal induction can occur when the photoinducible zone is exposed to light; however, it may not be the light itself, but rather the action of the light to alter the phase relationships of several oscillators, that causes induction and maintenance of the gonads.     

Low aromatase activity and gene expression in human fetal testes

Because of previous indications that estradiol (E2) plays a role in the regulation of testicular testosterone (T) production in some species, the production of E2 and aromatase gene expression in human fetal testes were investigated. Testicular minces from 14 fetuses (fetal age 15-23 weeks) were incubated with and without 200 ng/ml highly purified hCG, and the production of E2 and T was measured by RIA. Basal T production was high at 15-18 weeks of gestation and decreased thereafter. Estradiol production was low in all testes. Aromatase mRNA (P-450 arom messenger ribonucleic acid) was not detectable in fetal testicular tissues when studied by Northern and dot blot techniques. Placenta and fetal liver expressed aromatase mRNA, but fetal ovary contained only miniscule amounts. HCG significantly stimulated the production of both T and E2 in the testes of older fetuses (19-23 weeks), but the testicular E2 production of the youngest fetuses (15-18 weeks) did not increase significantly after hCG stimulation. These results indicate that aromatase activity and gene expression are very low in human fetal testes. These findings suggest that E2 may not play a major role in testicular T production in the human fetus.     

Testicular recrudescence in intermediate day lengths reflects loss of photoperiodic memory in Siberian hamsters

Siberian hamsters transferred from a long (16 h light/day [16 L]) to an intermediate (13.5 L) day length (DL) undergo testicular regression within 2 months followed approximately 2 months later by "spontaneous" testicular recrudescence. Recovery of gonadal function after prolonged exposure to intermediate DLs is thought to reflect development of neuroendocrine refractoriness to intermediate-duration melatonin signals. The authors tested the alternative hypothesis that testicular recrudescence in 13.5 L occurs when the "memory" for the 16-L photoperiod fades and hamsters can no longer compare the 13.5-L to the prior 16-L day length. Adult hamsters transferred from 16 L to 13.5 L that underwent testicular involution were either maintained continuously in 13.5 L for 41 weeks or given a supplementary 2-week treatment of 16 L before being returned to 13.5 L. The supplementary treatment was administered either after hamsters had been in 13.5 L for 10 weeks and had involuted testes, or after 24 weeks, when the gonads had undergone recrudescence. The authors found that 16 L treatment administered at week 10 delayed final gonadal recrudescence by approximately 12 weeks; similar 16-L treatment at week 24 induced a second gonadal regression when animals were returned to 13.5 L. The most parsimonious hypothesis to account for these findings is that gonadal recrudescence in intermediate DLs reflects fading of the "memory" for prior long DLs rather than induction of refractoriness to melatonin signals generated in intermediate DLs.     

Catecholamine inhibition of luteinizing hormone secretion in isolated pig pituitary cells

This study investigated the direct effect of catecholamines, epinephrine (EPI), and norepinephrine (NE) on basal and gonadotropin-releasing hormone (GnRH)-stimulated secretion of luteinizing hormone (LH) from dispersed pig pituitary cells in vitro. Pig pituitaries were dispersed into cells with collagenase and DNAase and then cultured in McCoy's 5a medium containing horse serum (10%) and fetal calf serum (2.5%) pretreated with dextran-coated charcoal for 3 days. EPI and NE did not affect basal LH secretion after 4 h of incubation. When pituitary cells were incubated with EPI or NE (1 microgram/ml) for longer than 30 min, GnRH-stimulated LH secretion was reduced. The degree of this reduction was dependent on EPI and NE, and a concentration of EPI and NE higher than 1 ng/ml and 100 ng/ml, respectively, was needed. L-isoproterenol, a nonselective beta-agonist, also inhibited the LH response to GnRH. Propranolol, a beta-antagonist, blocked the inhibitory effect of EPI, whereas phentolamine, an alpha-antagonist, had no effect. These results suggest that catecholamines, acting by a beta 2-adrenergic receptor, may play a role in the control of the porcine pituitary gonadotrope's response to GnRH.     

Effects of photoperiod, beta-endorphin, and naloxone on in vitro secretion of testosterone in white-footed mouse (Peromyscus leucopus) testes

The effects of the pro-opiomelanocortin-derived beta-endorphin (B-EP) and the opioid antagonist naloxone on in vitro secretion (accumulation of testosterone (T) in the medium) of T by testicular cells were assessed in adult white-footed mice (Peromyscus leucopus). Animals were housed under long days (16L:8D) to maintain testicular function or under short days (8L:16D) to induce gonadal regression. In vitro treatment with B-EP or naloxone did not affect basal secretion of T in dispersed cells from active or regressed testes. However, B-EP caused a dose-dependent reduction in secretion of T from cells stimulated maximally with human chorionic gonadotropin (hCG) or dibutyryl cyclic adenosine 3', 5'-monophosphate (dbcAMP). Conversely, naloxone enhanced maximal hCG- and dbcAMP-stimulated secretion of T in testicular incubates from both long- (1.5-fold) and short-day (3.5-fold)-exposed mice. The finding that the addition of naloxone to maximally stimulated cells increased further the secretion of T is evidence that B-EP may act to inhibit gonadotropin-stimulated secretion of T. Also, the stimulatory effect of naloxone on cells from regressed testes indicates that B-EP may be involved in suppressing production of T during the gonadally regressed state. Testicular B-EP-like immunostaining is present within the cytoplasm of interstitial cells and is not apparent in the seminiferous tubules. Together, these results support the idea that in P. leucopus endogenous opioid peptides in the testes may aid in the regulation of testicular function throughout the yearly breeding cycle.     

Effects of photoperiod, hypophysectomy, and follicle-stimulating hormone on testicular follicle-stimulating hormone binding sites in golden hamsters

Experiments were conducted to partially characterize and to examine the regulation of unoccupied testicular follicle-stimulating hormone (FSH) binding sites in adult golden hamsters. Testicular FSH binding sites were measured in the 1800 X gav fraction of whole testicular homogenates using iodinated bovine FSH. Binding of FSH was highly specific for FSH, located primarily in the testes, was time- and temperature-dependent, initially reversible, saturable, and consistent with a model consisting of a single class of high-affinity binding sites (range of equilibrium association constants (Ka) 2-12 X 10(10) M-1). Exposure of hamsters to a short photoperiod consisting of 5L:19D was associated with an increase in concentration (fmol/mg protein), but a reduction in total content (fmol/testes) of testicular FSH binding sites. There was no appreciable 5L:19D-associated alteration in receptor affinity (average Ka = 7.83 X 10(10) M-1). Injections of ovine prolactin (oPRL), ovine luteinizing hormone (oLH), or ovine FSH (oFSH) for 3 days into hamsters housed in 5L:19D for 12 wk had no effect on photoperiod-induced changes in testicular FSH binding sites. On Days 5 and 6 post hypophysectomy, a dramatic increase in FSH binding site concentration occurred, with but marginal effects on binding site affinity. Injections of 5 micrograms oFSH on Days 2, 3, and 4 after hypophysectomy prevented the increase in binding site concentrations measured on Day 5. Injection of a combination of 5 micrograms oFSH, 50 micrograms oPRL, and 25 micrograms oLH also reduced testicular FSH binding site concentrations in hypophysectomized hamsters, but oPRL or oLH by themselves were ineffective. The data indicate a homologous down-regulation of testicular FSH binding sites, but do not exclude the involvement of other hormones.