Male orangutan subadulthood: a new twist on the relationship between chronic stress and developmental arrest

Both in the wild and in captivity, a marked and enduring arrest of secondary sexual developmental occurs in some male orangutans (Pongo pygmaeus) (Kingsley [1982] The Orang-Utan: Its Biology and Conservation, The Hague: Junk; Utami [2000]). Researchers have hypothesized that chronic stress, perhaps related to aggression from mature males, causes endocrine changes altering growth and maturation rates in these males (Maple [1980] Orangutan Behavior, New York: Van Nostrand Reinhold; Graham [1988] Orangutan Biology, Oxford: Oxford University Press). In this study, urine samples were collected over a 3-year period from 23 captive male orangutans to test the hypothesis that developmentally arrested male orangutans have an endocrine profile consistent with chronic stress. Three study males were juveniles, seven were arrested adolescents, six were developing adolescents, and seven were mature adults. Morning samples were analyzed by radioimmunoassay for levels of the stress hormones cortisol and prolactin, and group hormone profiles were compared by analysis of variance. Results indicate that developing adolescent male orangutans have a significantly higher stress hormone profile than juvenile, developmentally arrested adolescent, or adult males. These results imply that the arrest of secondary sexual development in some male orangutans is not stress-induced, but instead perhaps an adaptation for stress avoidance during the adolescent or "subadult" period. These data, together with previously reported data on levels of gonadotropins, testicular steroids, and growth-related hormones, define endocrine profiles associated with alternative reproductive strategies for males with and males without secondary sexual features (Maggioncalda et al. [1999], [2000].     

Growth hormone and thyroid stimulating hormone concentrations in captive male orangutans: implications for understanding developmental arrest

There are two morphs of reproductive male in orangutans. Both morphs span the age range from adolescent to adult, but "subadult" males are smaller in size and lack secondary sexual features. In this study, urine samples were collected over a 2 year period from 23 captive male orangutans in order to define the endocrinology of this apparent arrest of secondary sexual development. Three males were juveniles, 3 to 5 years of age; seven males showed no secondary sexual trait development and were over 7 years of age; six males were in the process of developing secondary sexual features, with the youngest male being 6 years of age; and seven males were fully mature adults. Morning samples were analyzed by radioimmunoassay for levels of growth hormone (GH) and thyroid-stimulating hormone (TSH) and group hormone profiles were compared by analysis of variance. GH is the primary hormone of growth and development and its increase in teenage boys is associated with the adolescent growth spurt. TSH stimulates the thyroid to produce and secrete hormones that have metabolic effects and required for normal growth and development. Results show that arrested adolescent male orangutans have a GH level about 1/3 that of developing adolescents (P = .0006). TSH levels do not differ significantly between arrested and developing adolescents. These data complement other endocrine data showing significantly lower levels of sex steroids and luteinizing hormone (LH) in arrested males than developing males [Maggioncalda, 1995a,b; Maggioncalda et al., 1999]. Together with documented behavioral differences between reproductive males with and without secondary sexual features, these endocrine data support the hypothesis that in male orangutans there are alternative developmental pathways and corresponding alternative reproductive strategies.     

Seasonally and experimentally induced changes in testicular function of the Australian bush rat (Rattus fuscipes)

Serum concentrations of LH, FSH and testosterone were measured monthly throughout the year in male bush rats. Testicular size and ultrastructure, LH/hCG, FSH and oestradiol receptors and the response of the pituitary to LHRH were also recorded. LH and FSH rose in parallel with an increase in testicular size after the winter solstice with peak gonadotrophin levels in the spring (September). The subsequent fall in LH and FSH levels was associated with a rise in serum testosterone which reached peak levels during summer (December and January). In February serum testosterone levels and testicular size declined in parallel, while the pituitary response to an LHRH injection was maximal during late summer. The number of LH/hCG, FSH and oestradiol receptors per testis were all greatly reduced in the regressed testes when compared to active testes. In a controlled environment of decreased lighting (shortened photoperiod), temperature and food quality, the testes of sexually active adult males regressed at any time of the year, the resultant testicular morphology and endocrine status being identical to that of wild rats in the non-breeding season. Full testicular regression was achieved only when the photoperiod, temperature and food quality were changed: experiments in which only one or two of these factors were altered failed to produce complete sexual regression.     

Inhibin B levels in adolescents and young adults with type 1 diabetes

OBJECTIVE/METHODS: To assess exocrine and endocrine testicular function in subjects with diabetes, we evaluated serum inhibin B, gonadotrophins and testosterone levels in 33 male adolescent and young adult patients affected by type-1 diabetes (age 21.0 +/- 5 years; range 14.2-33.3), with a mean disease duration of 12.7 +/- 5.8 years (range 1.5-25.3) and various metabolic control (HbA1c 7.8 +/- 1.5%; range 5.5-13.2) and compared them with those of an age-matched group of 36 healthy control subjects (age 19.5 +/- 4.1 years; range 13.6-28.1). Both patients and controls had a testicular volume >or=15 ml. Inhibin B was measured by ELISA method. RESULTS/CONCLUSION: Diabetics and controls had comparable inhibin B (203 +/- 74 vs. 221 +/- 69 pg/ml, respectively) and follicle-stimulating hormone (FSH) levels, while luteinizing hormone (LH) and testosterone levels were significantly higher in the diabetic group. Inhibin B was negatively correlated both in patients and controls with FSH, while a negative correlation with LH was found only in the diabetic group. We conclude that our young diabetic males, after a mean disease duration of 12 years and various metabolic control, had inhibin B and FSH levels comparable to those of normal subjects. Therefore, they seem to have a regular testicular function and in particular a normal seminiferous tubule/Sertoli cell activity despite sustained hyperglycemia.     

Effects of exogenous testosterone on testicular luteinizing hormone and follicle-stimulating hormone receptors during aging

During aging, the male Japanese quail exhibits a loss of fertility, increased morphological abnormalities in the testes, and a higher incidence of Sertoli cell tumors. Although there is a coincident loss of reproductive behavior, plasma androgen levels remain high until testicular regression occurs in association with senescence. The purpose of this study was to compare mean specific binding of chicken luteinizing hormone (LH) and follicle-stimulating hormone (FSH) as a measure of testicular receptors during identified stages during aging. Males were categorized according to age (young = 9 months, middle aged = 24 months, or old = 36+ months) and sexual behavior (active or inactive). Testicular samples were collected immediately after perfusion with 4% paraformaldehyde from the following groups: young active (n = 8), young photoregressed (n = 5), young photoregressed plus testosterone implant (n = 4), middle-aged active (n = 8), middle-aged inactive (n = 4), old inactive (n = 5), and old inactive plus testosterone implant (n = 6). A crude plasma membrane fraction was prepared from the testes of each bird and an aliquot deriving from 10 mg of testicular tissue was used for binding assay. Specific binding of labeled LH or FSH was expressed as percentage of total radioactive hormone. Results showed significant (P < 0.05) age-related decreases in both FSH and LH receptor numbers. The highest FSH binding was found in young and middle-aged active males, with low binding in old inactive males. Testicular LH binding decreased during aging, with a sharp decrease in middle-aged males, which was similar to old males. Testosterone implants weakly stimulated FSH and LH binding in old males. Both LH and FSH binding decreased in photoregressed young males. However, testosterone implants stimulated increased LH binding, but did not affect FSH binding in young photoregressed males. These results provide evidence for separate regulation of testicular LH and FSH receptors, with testosterone stimulation of LH receptor, but not FSH receptor number in young males. However, during aging there appears to be a loss of this response, potentially because of the reduced efficacy of testosterone stimulation, thereby implying a diminished capacity for response with aging.     

Negative feedback regulation of gonadotropin secretion by androgens in fetal rhesus macaques

Previously we described sex differences in circulating gonadotropin concentrations (greater in females) in fetal rhesus macaques, and demonstrated that these sex differences relate, at least in part, to the negative feedback actions of testicular secretions. A fully functional gonadal-hypothalamic-pituitary feedback relationship is present as early as Day 100 of gestation in fetal males because castration at this time results in a dramatic increase (greater than 10-fold) in fetal luteinizing hormone (LH) concentrations. Although short-term (6-h) treatment of fetuses with testosterone (T) 3 wk after gonadectomy (GX) does not lower LH levels in males, it is completely effective in females. These data suggest that either T is not the primary testicular factor responsible for feedback suppression of LH in fetal males, or the hypothalamic-pituitary axis becomes insensitive to T after GX. To determine if immediate treatment with T after GX is effective in maintaining LH levels, we gonadectomized five fetal rhesus males on Days 98-104 of gestation and immediately implanted crystalline-T-containing intraabdominal Silastic capsules. An additional five fetuses were treated with the nonaromatizable androgen dihydrotestosterone (DHT). Umbilical arterial samples for hormone analysis were obtained prior to GX and again approximately 3 wk later. Serum from control males (n = 11) castrated in utero on Day 100 of gestation contained significantly greater concentrations of LH and follicle-stimulating hormone (FSH) 3 wk after the operation than before GX. Five sham-operated male fetuses did not have elevated levels of either LH or FSH in their serum on Day 120 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age-related changes in testicular development and reproductive endocrinology associated with aflatoxicosis in the male chicken

A study was conducted to investigate endocrine and testicular changes in the male chicken associated with the ingestion of 10 or 20 ppm aflatoxin at 3 different stages of development. Weekly body weight gain, absolute and relative combined testes weights, and plasma testosterone concentrations were reduced in aflatoxin-fed males as compared to controls, with the greatest differences seen at 12 wk of age. The effect of dietary aflatoxin on levels of plasma luteinizing hormone (LH) was dependent on age at exposure. Concentrations of plasma LH in 6-wk-old control males were significantly higher than in aflatoxin-fed birds, whereas no treatment differences were observed in older males. Additionally, few changes were observed in static levels of monoamines in any of the brain regions assayed, regardless of age at exposure. The delay in peak levels of LH, as well as the suppression of plasma testosterone and testicular weight, indicate a possible delay in the onset of sexual maturation associated with aflatoxicosis in this species.     

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.     

Sexual Differentiation of Gonadotropin Patterns

The original experiments, done by Witschi and his associates,on sexual differentiation of pituitary gonadotropins weie interpietedas demonstrating the contrasting effects of testes on the subsequentoutput of luteimzing hormone (LH) and interstitial cell stimulatinghormone (ICSH). The subsequent demonstration that these twohormones were identical has led to a theory that testes alterthe hypothala mic centeis which control the cyclic release ofLH "Masculinization of the female hypothalamic pituitary axishas been claimed following neonatal treatment with steroids".However, true sex reversal of gonadotiopin patterns has neitherbeen demon stiated, the male pattern has not yet been clearlydenned Consistent high levels of blood and pituitary folliclestimulating hormone (FSH) appear to be at least two characteristicsof the male pattern, and neither can be induced in lemales byneonatal treatment with testosterone propionate. Furthermore,castration of males at bnth with concomitant ovanan implinldtion,does not appear to remove the male pattern of high FSH. Consideringthat we understand so little regarding gonadotropin patternsin males, we cannot assume that this pattern can be inducedsimply by pie or postnatal steroid trealment. Considerably moredata on the positive and negative feedback effects of steroids,and steroid combinations, on TSH, LH, and piolictin in bothmales and females, will be requned before a meaningful conceptof sexual differentiation cin be formulated     

The role of testicular hormones and luteinizing hormone in spatial memory in adult male rats

Attempts to determine the influence of testicular hormones on learning and memory in males have yielded contradictory results. The present studies examined whether testicular hormones are important for maximal levels of spatial memory in young adult male rats. To minimize any effect of stress, we used the Object Location Task which is a spatial working memory task that does not involve food or water deprivation or aversive stimuli for motivation. In Experiment 1 sham gonadectomized male rats demonstrated robust spatial memory, but gonadectomized males showed diminished spatial memory. In Experiment 2 subcutaneous testosterone (T) capsules restored spatial memory performance in gonadectomized male rats, while rats with blank capsules demonstrated compromised spatial memory. In Experiment 3, gonadectomized male rats implanted with blank capsules again showed compromised spatial memory, while those with T, dihydrotestosterone (DHT), or estradiol (E) capsules demonstrated robust spatial memory, indicating that T's effects may be mediated by its conversion to E or to DHT. Gonadectomized male rats injected with Antide, a gonadotropin-releasing hormone receptor antagonist which lowers luteinizing hormone levels, also demonstrated spatial memory, comparable to that shown by T-, E-, or DHT-treated males. These data indicate that testicular androgens are important for maximal levels of spatial working memory in male rats, that testosterone may be converted to E and/or DHT to exert its effects, and that some of the effects of these steroid hormones may occur via negative feedback effects on LH.     

Effects of sympathetic denervation on follicular distribution,oestradiol and progesterone serum levels in prepubertal hemi-ovariectomized female guinea pig

The aim of this study was to determine the effects of maternal undernutrition during pregnancy on adult reproductive function in male and female offspring. Groups of ewes were fed rations providing either 100% (High, H) or 50% (Low, L) of estimated metabolisable energy (ME) requirements for pregnancy, from mating until day 95 of gestation, and thereafter were conventionally managed. At 20 months of age, LH and FSH profiles, and LH responses to exogenous GnRH were measured in male and female offspring and, in males, testicular responses to exogenous LH (as measured by testosterone concentrations) were also measured. Undernutrition had no effect on the mean birth weights of lambs of either sex, or on testicular size in male animals at either 6 weeks or 20 months of age. L males exhibited significantly higher FSH concentrations than H males (P < 0.05) but there were no differences with treatment in FSH profiles in females, basal LH profiles or gonadotrophin responses to GnRH in offspring of either sex, and no difference in basal testosterone concentrations or in the testosterone response to exogenous LH administration in males. Semen quality at 20 months of age was unaffected by pre-natal undernutrition but ovulation rate was significantly reduced in L compared to H female offspring (P < 0.05). It is concluded that pre-natal undernutrition had no effect on male reproductive development and adult function, but reduced ovulation rate in female progeny. This effect was not associated with a change in gonadotrophin profiles or pituitary responsiveness.     

Pituitary-gonadal axis before puberty: evaluation of testicular steroids in the male rat

Orchidectomy was performed on 26-day-old rats via a single midscrotal incision following which 1 of 6 steroids was administered subcutaneously twice daily for 7 days. Each hormone treatment set had its own controls both castrate and intact. Levels of serum LH and FSH were measured by radioimmunoassay. It was found that LH was suppressed to intact levels by testosterone or its active metabolites at doses within the "physiologic dosage range" (equivalent in biological activity to endogenously secreted androgens). FSH suppression with androgens occurred at considerably higher doses; only testosterone could maintain FSH at intact levels with a physiologic dosage. Both 5alpha-dihydrotestosterone, and 3alpha-androstanediol suppressed LH well and FSH partially; 3beta-androstanediol and fluoxymesterone were ineffective over the same dosage range. Estradiol suppressed both LH and FSH. It was concluded that LH is more easily suppressed than FSH by androgens, that there is poor correlation between biologic potency and their gonadotropin-suppression ability, and that testosterone is almost certainly not the final active intracellular androgenic hormone. It was suggested that while a small amount of testicular androgen can maintain the low levels of LH, complete control of FSH secretion may require conversion of testosterone to estrogens.     

Steroidal modulation of in vitro gonadotropin secretion in prepubertal and adult male Siberian hamsters

The effects of exogenous gonadal steroids, testosterone (T), and 17beta-estradiol (E(2)) upon the hypothalamo-pituitary-gonadal axis were reported to be different between prepubertal and adult Siberian hamsters. Utilizing an in vitro static culture system, we investigated if age-related differences in steroid responsiveness occurs at the pituitary. Prepubertal (20 days old) or adult (140 days old) male Siberian hamsters were implanted with 1 mm silastic capsules containing undiluted T, E(2) or cholesterol (Ch, control). After 15 days, pituitaries were removed, incubated in vitro, and subjected to the following treatments: two baseline measurements, one challenge with 10ng/ml of D-Lys(6)-gonadotropin-releasing hormone (GnRH), and three post-challenge washes. Fractions were collected every 30 minutes and measured for follicle-stimulating hormone (FSH) and luteinizing hormone (LH). T and E(2 )reduced basal secretion of LH and FSH in juveniles but not adults. In juveniles, E(2) increased GnRH-induced FSH and LH secretion, while T augmented GnRH-induced FSH secretion but attenuated GnRH-induced LH secretion. Steroid treatment had no effect on GnRH-stimulated LH or FSH release in adults. The only effect of steroid hormones upon adult pituitaries was the more rapid return of gonadotropin secretion to baseline levels following a GnRH challenge. These data suggest both basal and GnRH-induced gonadotropin secretion are more sensitive to steroid treatment in juvenile hamsters than adults. Further, differential steroidal regulation of FSH and LH at the level of the pituitary in juveniles might be a mechanism for the change in sensitivity to the negative effects of steroid hormones that occurs during the pubertal transition.     

Measurement of dimeric inhibins and effects of active immunization against inhibin alpha-subunit on plasma hormones and testis morphology in the developing cockerel

Inhibins and activins are implicated as endocrine regulators of follicle-stimulating hormone production and of testicular steroidogenesis and spermatogenesis in mammals. The potential involvement of these proteins in cockerels was investigated by measurement of circulating inhibin A, inhibin B, total inhibin alpha-subunit immunoreactivity (ir-alpha), activin A, LH, FSH, and testosterone from the juvenile state through to sexual maturity. Plasma inhibin A remained low between 6 to 12 wk of age and increased approximately threefold (P < 0.05) to a prepubertal peak between Weeks 14 to 18, followed by a gradual decline to the end of the study (Week 24). Although plasma FSH levels were not correlated to inhibin A before Week 16 (r = -0.17), they were negatively correlated from Week 18 (r = -0.49; P < 0.005). Inhibin B levels were below the assay detection limit until 16 wk of age but thereafter rose steadily in parallel with FSH (r = 0.27; P < 0.02) and testosterone (r = 0.35; P < 0.005). Thus, inhibins A and B showed divergent profiles during sexual maturation. Plasma ir-alpha levels were much higher than dimeric inhibin levels throughout, although the relative difference varied with age. Plasma activin A levels were below the assay detection at all times. Juvenile cockerels were actively immunized against a synthetic chicken inhibin alpha-subunit peptide conjugate to determine effects on plasma hormones and on testicular weight, morphology, and activin A content. Immunization generated circulating antibodies that bound (125)I-bovine 32-kDa inhibin but did not affect plasma FSH or testosterone levels at any stage of development. However, immunization reduced postpubertal plasma LH levels (P < 0.05) and promoted increased testicular weight (24%; P < 0.01) and total testicular activin A content (42%; P < 0.001) at 24 wk. Testis weight of immunized birds was positively correlated with inhibin antibody titer (r = 0.61; P < 0.05). Live weight gain was not affected by immunization. Morphometric analysis of testis sections showed that inhibin immunization had no effect on the fractional volume of the seminiferous tubule wall, seminiferous tubule lumen, or interstitial tissue area. Likewise, seminiferous tubule surface area and surface area:volume ratios were not different from controls. These findings support differential roles for inhibins A and B in regulating the pituitary-testicular axis during sexual maturation in the cockerel but highlight the need for more detailed studies to distinguish between potential endocrine and local intragonadal roles of inhibin-related peptides and to elucidate the mechanism by which immunization against inhibin alpha-subunit promotes testis enlargement without raising plasma FSH.     

Therapeutic significance and the mechanism of action of the LH-RH agonist ICI 118630 in breast and prostate cancer

The influence of the LH-RH agonist ICI 118630 on circulating levels of the pituitary gonadotrophins LH and FSH and the gonadal steroids oestradiol, progesterone, 17-hydroxyprogesterone and testosterone has been studied in phase I clinical trials of the drug in patients with advanced breast or prostate cancer. ICI 118630 initially stimulated plasma levels of LH and FSH. On continued treatment however, the drug reversed this response and produced a rapid decline in plasma testosterone and progesterone in male and female patients respectively. Plasma oestradiol concentrations equivalent to those seen in oophorectomised or postmenopausal women were eventually produced in all 5 female patients treated with ICI 118630. In one patient however persistent follicular activity occurred until her third menstrual cycle. No appreciable side effects of the drug were observed. These data indicate that ICI 118630 initiates a castration-like endocrine response and has potential in the treatment of hormone dependent tumours of the breast and prostate.     

Low Testosterone Correlates with Delayed Development in Male Orangutans

Male orangutans (Pongo spp.) display an unusual characteristic for mammals in that some adult males advance quickly to full secondary sexual development while others can remain in an adolescent-like form for a decade or more past the age of sexual maturity. Remarkably little is understood about how and why differences in developmental timing occur. While fully-developed males are known to produce higher androgen levels than arrested males, the longer-term role of steroid hormones in male life history variation has not been examined. We examined variation in testosterone and cortisol production among 18 fully-developed (“flanged”) male orangutans in U.S. captive facilities. Our study revealed that while testosterone levels did not vary significantly according to current age, housing condition, and species origin, males that had undergone precocious development had higher testosterone levels than males that had experienced developmental arrest. While androgen variation had previously been viewed as a state-dependent characteristic of male developmental status, our study reveals that differences in the physiology of early and late developing males are detectable long past the developmental transition and may instead be trait-level characteristics associated with a male’s life history strategy. Further studies are needed to determine how early in life differences in testosterone levels emerge and what consequences this variation may have for male behavioral strategies.     

The effects of methyltestosteone on reproductive function in male greyhounds

Oral administration of methyltestosterone (MT) at 50 mg/dog/day to intact adult male greyhounds for 90 d resulted in decreased (P < 0.05) mean daily sperm output and mean testicular length. Additionally, the mean diameter of seminiferous tubules in MT-treated dogs tended to decrease (P = 0.08). Mean concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) and concentrations of testosterone in serum were also decreased or tended to decrease (P = 0.0003 to 0.059) at various sampling periods during MT treatment, suggesting alterations in spermatogenesis resulted from decreased serum concentrations of gonadotropins and steroids. Mean daily sperm output, mean testicular length, mean seminiferous tubule diameter and mean concentrations of FSH in serum were not decreased (P > 0.05) at the end of a 90-d recovery period. However, mean concentrations of serum LH and concentrations of testosterone were still lower (P < 0.05) during five of six and one of six sampling times, respectively, during the recovery period than the pretreatment levels, suggesting a prolonged effect of MT treatment on the pituitary/gonadal axis.     

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.     

Paramethasone acetate (PA): corticosteroid potency vs hypothalamic pituitary-gonadal axis

Because paramethasone acetate (PA) suppresses basal and midcycle LH surge and blocks estrogen synthesis in the female, its possible effect upon testicular physiology was evaluated in 13 healthy men by measuring the circulating levels of FSH, LH, prolactin (PRL), testosterone (T), dihydrotestosterone (DHT), androstenedione (A), estradiol (E2) and cortisol (C) every 4 h throughout the day, before (control) and after PA (6 mg/d/7 d). The total concentrations of each hormone, as well as the PA-induced suppressibility (measured as percent decrease in the mean 24 h plasma level) were analyzed. PA suppressed neither the basal nor circadian rhythm of T and had no effect on LH, FSH or PRL output. DHT, A, E2 were significantly reduced and the basal concentrations and circadian variations of C were abolished. PA showed a dual control on the pituitary gonadal axis and while causing a maximal suppressed adrenocortical activity it had no interference in testosterone synthesis.     

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.