Effects of cranial cervical ganglionectomy and castration of male lambs. III. Hormonal responses following administration to gonadotrophin releasing hormone (GnRH)

Entire and castrate male lambs, which were cranial cervical ganglionectomized (GX) or untreated, were utilized in a study of responses to intravenous GnRH; 24 animals were treated at both 101 and 277 days of age. GX caused a reduction in basal LH concentrations of both wethers and rams at the first sampling, but increased pre-injection levels of this hormone in 277 day old wethers. Basal LH levels of castrates were substantially higher than those of entires, but GX had no significant influence on pretreatment testosterone secretion in rams. GnRH treatment elevated plasma LH levels in all animals, while in entires increases in testosterone concentrations also occurred. Castration significantly increased peak LH levels together with total LH output. At neither age were the LH or testosterone reponses influenced significantly by GX, nor was the interaction of castration and GX significant for LH response data. The major effect of age at GnRH treatment was that markedly higher testosterone responses were recorded from the older rams.     

A 'window of time' during which testosterone determines the opiatergic control of LH release in the adult male rat

Male rats castrated before puberty (when 26 days of age) showed a progressively decreasing susceptibility to the inhibitory effects of morphine (5 mg/kg) upon LH secretion for up to 28 days after gonadectomy (approximately 100%, 40% and 10% inhibition at 5, 12 and 28 days after castration), but thereafter morphine again caused approximately 50% reduction in serum LH values; the minimum inhibition found at 28 days after castration (age 54 days) occurred at the time at which male rats normally reach puberty. When rats were castrated at 59 days of age, morphine maximally suppressed serum LH concentrations (to less than 70%) 2 and 5 days after castration, but had no effect thereafter. In prepubertal castrates, testosterone replacement between Days 26 and 50 of life resulted in responses to morphine similar to those found in rats castrated after puberty, i.e. serum LH levels were not reduced. Morphine significantly reduced LH levels in prepubertal castrates given testosterone after 60 days of age. Treatment with morphine consistently elevated serum prolactin concentrations (greater than 100%) in castrated rats of all ages, regardless of the time elapsed after gonadectomy. These results indicate a transient fall in the inhibitory opioidergic tone upon LH secretion as the normal age of puberty approaches, that the ability of opiates to alter LH release in adulthood may depend upon testicular steroids secreted during the peripubertal period, and that the LH responses do not reflect general changes in the neuroendocrine response to opiates after castration since the prolactin response to morphine remains intact in rats castrated before and after puberty.     

Testicular involvement in peripubertal gonadotropin levels and accessory sex organ weight of male hamsters

This study evaluates the influence of testicular secretions during development in male hamsters on peripubertal gonadotropin levels. Castration or sham operations were performed on the day of birth (Day 1), Day 5, 10, or 20 of life. Repeated plasma samples on Days 20-60 at 10-day intervals were taken via orbital sinus puncture. Castrated animals received a subcutaneous testosterone capsule on Day 60 and were killed on Day 70. In addition, seminal vesicles and ventral prostate weights were taken in all animals at Day 70. Castrated animals, regardless of day of castration, had higher gonadotropin levels and suppressed sexual accessory organ weights. Animals castrated on the day of birth had lower luteinizing hormone (LH) levels than animals castrated on other days. Castration on Day 10 resulted in lower follicle stimulating hormone (FSH) levels. Males castrated on Day 20 were most sensitive to the negative feedback effect of testosterone on LH secretion, while Day 10 castrates had elevated FSH levels after testosterone exposure. Sexual accessory weights also differed depending upon the day of castration. Results point out the importance of testicular secretions on the developmental processes as well as the differing ages at which various systems may be influenced.     

Effects of intermittent pulsatile infusion of luteinizing hormone-releasing hormone on dihydrotestosterone-suppressed gonadotropin secretion in castrate rams

The feedback effects of dihydrotestosterone (DHT) on gonadotropin secretion in rams were investigated using DHT-implanted castrate rams (wethers) infused with intermittent pulsatile luteinizing hormone-releasing hormone (LHRH) for 14 days. Castration, as anticipated, reduced both serum testosterone and DHT but elevated serum LH and follicle-stimulating hormone (FSH). Dihydrotestosterone implants raised serum DHT in wethers to intact ram levels and blocked the LH and FSH response to castration. The secretory profile of these individuals failed to show an endogenous LH pulse during any of the scheduled blood sampling periods, but a small LH pulse was observed following a 5-ng/kg LHRH challenge injection. Dihydrotestosterone-implanted wethers given repeated LHRH injections beginning at the time of castration increased serum FSH and yielded LH pulses that were temporally coupled to exogenous LHRH administration. While the frequency of these secretory episodes was comparable to that observed for castrates, amplitudes of the induced LH pulses were blunted relative to those observed for similarly infused, testosterone-implanted castrates. Dihydrotestosterone was also shown to inhibit LH and FSH secretion and serum testosterone concentrations in intact rams. In summary, it appears that DHT may normally participate in feedback regulation of LH and FSH secretion in rams. These data suggest androgen feedback is regulated by deceleration of the hypothalamic LHRH pulse generator and direct actions at the level of the adenohypophysis.     

Role of gonadal negative feedback on the gonadotrophin responses to gonadotrophin-releasing hormone (GnRH) in ram lambs from two lines of sheep selected for their luteinizing hormone response to GnRH.

Divergent selection has resulted in two lines of lambs (high and low) that have a 5-fold difference in their ability to release luteinizing hormone (LH) in response to 5 micrograms of gonadotrophin-releasing hormone (GnRH). Baseline gonadotrophin concentrations, the gonadotrophin responses to a GnRH challenge and the concentrations of testosterone and oestradiol were compared in lambs which were castrated at birth and intact lambs from both selection lines at 2, 6, 10 and 20 weeks of age. The pattern of LH and follicle-stimulating hormone (FSH) secretion was similar in the two lines, but differed between the intact and the castrated lambs. Basal LH and FSH secretion were significantly higher in the castrates than in the intact lambs from both selection lines. The high-line lambs had significantly higher basal FSH concentrations at all ages tested and significantly higher basal LH concentrations during the early postnatal period. The magnitude of the gonadotrophin responses to GnRH differed significantly between the intact and the castrated lambs within each line, the amount of gonadotrophins secreted by the castrated lambs being significantly greater. The removal of gonadal negative feedback by castration did not alter the between-line difference in either LH or the FSH response to the GnRH challenge. Throughout the experimental period, the concentration of testosterone in the intact lambs was significantly greater than in the castrated lambs in both selection lines, but no significant difference was seen in the concentrations of oestradiol. No significant between-line differences were found in the peripheral concentrations of testosterone or oestradiol in the intact lambs from the two selection lines. Therefore, despite similar amounts of gonadal negative feedback in the selection lines, there were significant between-line differences in basal gonadotrophin concentrations, at 2 and 6 weeks of age, and in the LH and FSH responses to an exogenous GnRH challenge, at all ages tested. Removal of gonadal negative feedback did not affect the magnitude of the between-line difference in the response of the lines to GnRH stimulation. The results indicate that the effects of selection on gonadotrophin secretion are primarily at the level of the hypothalamo-pituitary complex.     

Ontogeny of growth hormone, prolactin, luteinizing hormone, and testosterone secretory patterns in the ram

The ontogenetic changes that occur in secretory patterns of growth hormone (GH), prolactin (Prl), luteinizing hormone (LH), and testosterone (T) in rams maintained in constant photoperiod were examined. Nine ram lambs were moved to individual pens in a controlled environment (12L: 12D cycle; 18-24 degrees C temperature) at 66 days of age. Blood samples were collected via indwelling cannulae at 15-min intervals for an 8-h period at 80, 136, 192, 248, and 304 days of age. Plasma concentrations of GH, Prl, LH, and T were quantitated and parameters of the secretory patterns determined. Mean concentration of GH tended to decline with age, probably because the amplitude of secretory peaks was significantly reduced with age. There were no age-associated changes in basal concentration of GH or incidence of GH peaks. There was an increase in Prl secretion (as estimated by mean concentration) at 136 and after 248 days of age. Significant age-associated changes occurred in all parameters of LH and T secretion. At the younger ages, testosterone concentrations were low and LH concentrations were elevated. At the older ages the relationship was reversed, with LH low and testosterone high. There were no significant correlations between frequency and magnitude of LH and T peaks. The significant correlations present among parameters of LH and T secretion were between basal concentration of LH and overall mean concentration and basal concentration of T. These results suggest that LH may not be the sole tropic stimulator of acute T secretion.     

Neonatal castration of male and female rats affects luteinizing hormone responses to estrogen during adulthood

We examined the positive and negative feedback effects of estradiol (E2) on luteinizing hormone (LH) and prolactin (Prl) secretion in adult male and female rats which were gonadectomized within 24 h after birth (long-term castrates) and compared these responses to those elicited by E2 in short-term castrated (7 days) adult males and females. The high serum E2 did not reduce the elevated serum LH concentrations in long-term castrates until 4 days of treatment. Also, only after negative feedback was established were the positive feedback actions of E2 observed. In contrast, Prl surges were observed after 2 days of E2, and baseline Prl serum levels were elevated by Day 3 of E2 in long-term castrated male and female rats. Some long-term castrates lacked both LH and Prl surges, and E2 was ineffective in altering basal gonadotropin secretion in these animals. Short-term castrated males had elevated serum Prl levels but no Prl surges. Seemingly, when the hypothalamus is deprived of estrogen or androgen from birth to adulthood, an equal percentage of males and females become refractory to the positive feedback effects of estrogen during adulthood. Thus, it is difficult to separate castration effects from those which may be produced by the endogenous androgen secreted during the first 26 h of life.     

Effects of hyperprolactinemia on the control of luteinizing hormone and follicle-stimulating hormone secretion in the male rat

Experiments were conducted to determine the effects of acute hyperprolactinemia (hyperPRL) on the control of luteinizing hormone and follicle-stimulating hormone secretion in male rats. Exposure to elevated levels of prolactin from the time of castration (1 mg ovine prolactin 2 X daily) greatly attenuated the post-castration rise in LH observed 3 days after castration. By 7 days after castration, LH concentrations in the prolactin-treated animals approached the levels observed in control animals. HyperPRL had no effect on the postcastration rise in FSH. Pituitary responsiveness to gonadotropin hormone-releasing hormone (GnRH), as assessed by LH responses to an i.v. bolus of 25 ng GnRH, was only minimally effected by hperPRL at 3 and 7 days postcastration. LH responses were similar at all time points after GnRH in control and prolactin-treated animals, except for the peak LH responses, which were significantly smaller in the prolactin-treated animals. The effects of hyperPRL were examined further by exposing hemipituitaries in vitro from male rats to 6-min pulses of GnRH (5 ng/ml) every 30 min for 4 h. HyperPRL had no effect on basal LH release in vitro, on GnRH-stimulated LH release, or on pituitary LH concentrations in hemipituitaries from animals that were intact, 3 days postcastration, or 7 days postcastration. However, net GnRH-stimulated release of FSH was significantly higher by pituitaries from hyperprolactinemic, castrated males. To assess indirectly the effects of hyperPRL on GnRH release, males were subjected to electrical stimulation of the arcuate nucleus/median eminence (ARC/ME) 3 days postcastration. The presence of elevated levels of prolactin not only suppressed basal LH secretion but reduced the LH responses to electrical stimulation by 50% when compared to the LH responses in control castrated males. These results suggest that acute hyperPRL suppresses LH secretion but not FSH secretion. Although pituitary responsiveness is somewhat attenuated in hyperprolactinemic males, as assessed in vivo, it is normal when pituitaries are exposed to adequate amounts of GnRH in vitro. Thus, the effects of hyperPRL on pituitary responsiveness appear to be minimal, especially if the pituitary is exposed to an adequate GnRH stimulus. The suppression of basal LH secretion in vivo most likely reflects inadequate endogenous GnRH secretion. The greatly reduced LH responses after electrical stimulation in hyperprolactinemic males exposed to prolactin suggest further that hyperPRL suppresses GnRH secretion.     

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.     

Effects of gonadectomy and steroids on pituitary gonadotropin secretion in a frog, Rana pipiens

Secretory dynamics of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured at various times following gonadectomy in adult male grass frogs, Rana pipiens. Plasma levels and in vitro initial secretory rates of both LH and FSH increased significantly within 1 wk and remained elevated for 3-4 wk of castration. Pituitary FSH and LH content were unchanged. However, dissociation between the two gonadotropins (Gth) occurred thereafter: Secretion of FSH remained elevated for 70 days, but those of LH declined to control levels after 30 days. In vitro secretion of Gth from gonadectomized (gonadx) frogs declined progressively over time reaching control levels after 24 h incubation. The results indicate that elevated pituitary secretion contributes to the observed circulating LH and FSH levels in gonadx frogs, and that FSH and LH may be controlled independently. Replacement therapy with 17 beta-estradiol (E2) suppressed post-gonadectomy increases in plasma Gth and in vitro responses to GnRH, whereas 5 alpha-dihydrotestosterone (DHT) had little effect in vivo and augmented GnRH responses in long-term castrates. In vitro, E2 also inhibited, while 48 h of DHT treatment had no effect on GnRH responsiveness of pituitaries from gonadx frogs. The actions of these steroids were opposite to those typically observed in mammals (and birds), and support the hypothesis that E2 may contribute to seasonal testicular regression in ranid frogs.     

Effects of melatonin implants in ram lambs

Sixteen pinealectomized and 19 unoperated ewes were exposed to constant light for about 4 weeks before and 4 weeks after lambing. Six ram lambs born to unoperated ewes were implanted s.c. with melatonin sachets while 8 ram lambs were implanted with empty sachets. The 8 ram lambs born to pinealectomized dams also received empty implants. Ewes and lambs were then returned to the field. Analysis of weekly blood samples indicated that prolactin secretion was significantly decreased in the ram lambs with empty implants between 44-51 weeks of age whereas lambs treated with melatonin failed to show a significant change during development. All 3 groups of rams had elevated LH levels between 7 and 17 weeks of age, and a second period of high LH between 27 and 40 weeks. There were no significant differences between groups in the patterns of FSH secretion; FSH was highest between 7 and 17 weeks of age, and again between 27 and 40 weeks of age. Plasma testosterone levels in all groups increased gradually between 4 and 35 weeks. Between 38 and 48 weeks of age testosterone concentrations were markedly elevated in all groups. Growth was not affected by melatonin treatment. These results indicate that neonatal melatonin treatment has subtle endocrine effects; whether these effects are sufficient to compromise fertility in the ram, however, remains to be established.     

Selective increase in plasma luteinising hormone concentrations in drug free young men with mania.

The hypothalamic-pituitary-gonadal system was investigated in drug free young men with either mania or acute schizophrenia and in age matched controls by measuring, at frequent intervals during a 17 hour "neuroendocrine day," plasma concentrations of luteinising hormone (LH), follicle stimulating hormone, prolactin, testosterone, sex hormone binding globulin (SHBG), and cortisol. Plasma LH in mania was significantly increased compared with the control value at all time periods and increased in the morning and evening samples compared with values in the schizophrenic patients. Plasma prolactin and cortisol concentrations were significantly greater in mania and schizophrenia compared with control values at several times during the day, but there were no significant between group differences in plasma testosterone or SHBG. These results show that in young men with mania there is a major disturbance in the central mechanisms that control the release of LH, the control of prolactin and cortisol secretion is abnormal in mania and acute schizophrenia, and plasma LH concentrations may provide a useful hormonal diagnostic test for mania.     

Effect of 2-bromo-alpha-ergocryptine (CB 154) on plasma prolactin, LH and testosterone levels, accessory reproductive glands and spermatogenesis in lambs during puberty

Effects of 2-bromo-alpha-ergocryptine (CB 154) on plasma prolactin, luteinizing hormone (LH), and testosterone levels, accessory reproductive glands, and spermatogenesis were studied in lambs during puberty. 18 lambs born during normal lambing season (February and 10 lambs born during the nonlambing period (October) and received a daily injection of CB 154 (2 gm) from the 10th week after birth until the 21st week. Treatment resulted in a highly significant (p less than .001) decrease in the concentration of plasma prolactin, but did not affect LH or testosterone levels. There was no marked decrease in testis weight in the treated animals and the establishment of spermatogenesis was not delayed by the treatment. However, there was a significant decrease in the weight of the seminal vesicles (p less than .01) and in their fructose concentration (p less than .01 and p less than .05). These results indicate that prolactin may play a role in the secretory activity of these glands in the male lamb.     

Reproductive endocrinology of free-living nestling and juvenile starlings, Sturnus vulgaris; an altricial species

Plasma concentrations of luteinizing hormone (LH), prolactin and testosterone, and pituitary content of LH and prolactin, were measured in free-living starlings, Sturnus vulgaris , from hatching until 12 weeks of age.
Plasma LH concentrations were elevated in both sexes until four days after hatching, then they decreased. Throughout the period, plasma LH levels were low compared to those in breeding adults but were comparable to levels in post-breeding photorefractory adults. Pituitary LH content increased until 12 days after hatching, but this increase was due to physical growth during this period. Plasma prolactin concentration and pituitary prolactin content increased dramatically during the nestling period. The increase in pituitary prolactin content was in excess of that accounted for by increasing size. Plasma prolactin remained high during the immediate post-fledging period, but had started to decrease by 12 weeks after hatching. Plasma testosterone concentrations were lower than those in breeding adults, but generally higher than in post-breeding photorefractory adults. The gonads of both sexes remained regressed.
These results suggest that the reproductive system of nestling and juvenile starlings is in a similar state to that of post-breeding photorefractory adult starlings. The comparatively high levels of testosterone may reflect involvement in sexual differentiation.     

The response of the anterior pituitary and testes to synthetic luteinizing hormone-releasing hormone (LHRH) and the effect of castration on pituitary responsiveness in the maturing chicken fed aflatoxin

The responsiveness of the anterior pituitary to exogenous luteinizing hormone-releasing hormone (LHRH; 20 micrograms/kg body weight) and the subsequent stimulation of testosterone secretion by the testes was studied after administration of dietary aflatoxin (10 ppm) to 9-wk-old male chickens. In both control and aflatoxin-treated males, there were significant (p less than 0.05) increases in plasma luteinizing hormone (LH) concentrations following LHRH administration, which peaked at 5 min post injection and declined thereafter. Plasma testosterone levels increased soon after the LHRH injection in control males, secondary to elevated LH levels in the peripheral circulation, and continued to increase throughout the experimental period. In contrast, this LH-induced elevation in plasma testosterone was delayed in aflatoxin-treated males, with no substantial increase until 20 min post-LHRH injection. In a subsequent experiment, castration of aflatoxin-fed males resulted in an altered response to exogenous LHRH, as compared to their intact counterparts. Based on these data, it appeared that while the LH-secretory capacity of the anterior pituitary was not diminished in birds receiving aflatoxin, the testicular response to exogenous LHRH was altered during aflatoxicosis. Additionally, the effect of castration on plasma LH profiles after LHRH administration provides preliminary evidence for extra-testicular effects of dietary aflatoxin on reproduction in the avian male.     

Opioidergic control of luteinizing hormone secretion in the female rabbit: influence of age on the response to naloxone

To examine the role of opioid neurons on luteinizing hormone (LH) secretion in the female rabbit, we determined LH release at timed intervals after naloxone administration to rabbits aged 25-150 days. The LH response to naloxone (10 mg/kg) was not significantly elevated until day 43 when LH rose 76-113% above basal levels at 40-80 min. In 56-day-old females the corresponding increase was 160% at 15 min and in 65- to 67-day-olds it was 154%. From 70 to 80 days of age the LH response was blunted and no significant elevations could be elicited. By contrast, naloxone-induced LH increases were again evident when rabbits were older than 100 days. At all ages no significant change in FSH concentrations was observed. In the adult females, naloxone at 2.5, 5, and 10 mg/kg caused increases in LH secretion which occasionally were high enough to induce ovulation as exemplified by elevated serum progesterone 4 days later. These data suggest that opioid peptides may be involved in the prepubertal rise in LH and in the normal inhibition of adult secretion in the female rabbit.     

Luteinizing hormone release by gonadotropin releasing hormone before and after castration in bulls

The magnitude of gonadotropin releasing hormone (GnRH) induced lutei nizing hormone (LH) release prior to castration, following castration, a nd during testosterone replacement in males, was compared, using 6 9-mon th-old Holstein bulls. Also, the effects of castration and testosterone replacement on patterns of episodic changes in serum LH were studied. Blood samples were collected at hourly intervals for 24 hours prior to castration, at 21 days after castration, and at 23 days postcastration a fter testosterone, 20 mg thrice daily, has been given for 24 hours. Each animal was given GnRH, 40 mcg iv, at 24 hours before castration, at 7 and 14 days after castration, and at 28 days postcastration following 6 days of testosterone treatment. GnRH caused LH release before and after castration. The LH increase was 2.5-fold at 14 days postcastratio n. Testosterone replacement did not reduce the magnitude of LH response to GnRH to precastration levels. The number of episodic increases in serum LH prior to castration averaged 3.7 daily and increased to 6.5 daily at 21 days after castration (p less than .05). The magnitude of increase in LH concentration in these epidsodic events was not affected by castration. Testosterone replacement failed to restore either the average number or change the magniture of LH increase above precastratio n levels. It was shown that LH is normally released episodically in bulls. The peaks of LH release were followed by increased testosterone in serum. Results suggest that LH release in bulls is controlled by gonadic factors other than testosterone.     

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.     

Possible involvement of inhibin in altered follicle-stimulating hormone (FSH) secretion during dissociated luteinizing hormone (LH) and FSH release: unilateral castration and experimental cryptorchidism

Male rats were either unilaterally or bilaterally castrated, or were rendered cryptorchid when they were either 15 or 45 days old. Subsequently, blood was sampled over the next several weeks and plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), and immunoreactive inhibin-alpha (irI alpha) levels were measured by specific radioimmunoassays (RIAs). At the end of the experiment, gonadal expression of inhibin-alpha, inhibin-beta A, and inhibin-beta B subunits was measured by S1 nuclease analysis and in situ hybridization. In both age groups, bilateral castration (BC) produced the expected marked (p less than or equal to 0.01) increases in plasma LH and FSH levels, and concomitant decreases in T and irI alpha secretion within 1 - 2 days after surgery. In 15-day-old animals, unilateral castration (UC) significantly increased FSH and decreased circulating levels of irI alpha, but did not measurably alter LH or androgen production. At 7 days after surgery, the level of inhibin mRNA in the remaining testis was unchanged. In 45-day-old animals, UC caused a measurable increase in FSH, with little or no changes in the circulating levels of irI alpha. Plasma T levels were lowered (p less than or equal to 0.05) by UC; however, there were no statistical changes in LH levels in these UC rats. Finally, T administration markedly reversed UC-induced increase in FSH secretion in both age groups. Androgen therapy also interfered with inhibin release in 45-day-old, but not in 15-day-old rats. In rats 15 days old at the time of surgery, cryptorchidism produced a small but measurable increase (p less than or equal to 0.05) in LH release at Week 6 only, which was accompanied by a significant (p less than or equal to 0.01) decline in T secretion. Plasma FSH levels were elevated at all times in cryptorchid rats, and at 2, 4, and 6 wk, these levels were not statistically distinguishable (p greater than 0.05) from those of castrated animals. In this group of rats, cryptorchidism caused a transient increase (p less than or equal to 0.05) in irI alpha values 1 wk after surgery, but no changes at later times. Finally, measurement of testicular inhibin-alpha subunit messenger RNA (mRNA) levels showed an approximately 2-fold increase compared to total RNA levels in the testis. However, because of the significant decrease in total RNA levels per testis caused by cryptorchidism, the absolute change in inhibin-alpha subunit mRNA levels per testis corresponded to an approximately 3-fold decrease.(ABSTRACT TRUNCATED AT 400 WORDS)     

Seasonal variations of LH, prolactin, androstenedione, testosterone and testicular FSH binding in the male blue fox (Alopex lagopus)

The seasonal changes in testicular weight in the blue fox were associated with considerable variations in plasma concentrations of LH, prolactin, androstenedione and testosterone and in FSH-binding capacity of the testis. An increase in LH secretion and a 5-fold increase in FSH-binding capacity were observed during December and January, as testis weight increased rapidly. LH levels fell during March when testicular weight was maximal. Plasma androgen concentrations reached their peak values in the second half of March (androstenedione: 0.9 +/- 0.1 ng/ml: testosterone: 3.6 +/- 0.6 ng/ml). A small temporary increase in LH was seen in May and June after the breeding season as testicular weight declined rapidly before levels returned to the basal state (0.5-7 ng/ml) that lasted until December. There were clear seasonal variations in the androgenic response of the testis to LH challenge. Plasma prolactin concentrations (2-3 ng/ml) were basal from August until the end of March when levels rose steadily to reach peak values (up to 13 ng/ml) in May and June just before maximum daylength and temperature. The circannual variations in plasma prolactin after castration were indistinguishable from those in intact animals, but LH concentrations were higher than normal for at least 1 year after castration.