A comparison of moment to moment and diurnal changes in circulating inhibin and testosterone concentrations in male rhesus monkeys (Macaca mulatta)

Daily and seasonal rhythmic secretary pattern of endocrinological profiles in mithun bull

Mithun (Bos frontalis) is a unique domestic free-range bovine species available in North Eastern hilly (NEH) regions of India and is reared for its protein rich meat. Mithun suffers severe non-cyclical population fluctuations; however, it is not yet declared as endangered species. Mithun follows some sort of seasonality based on the calving trend and semen production, although it is a perennial breeder. However, there is need to study the rhythmic changes of endocrine profiles to understand the hormone flow pattern in mithun to select the suitable time for blood collection to assess the exact endocrine profiles and to select the suitable time for natural breeding or semen collection by artificial methods for further research, conservation and propagation of its germplasm. Therefore, the present study was designed to evaluate the reproductive as well as metabolic endocrinological profiles in 24:00 h in intact adult mithun bulls during different seasons (winter, spring, summer and autumn) to know the rhythmic changes and flow pattern of the endocrinological profiles to improve its reproductive efficiency. Experimental mithun bulls (n = 6; age: 5-6 years; body condition score: 5-6 out of 10, classified as good) were selected for the study. Endocrinological profiles, follicle stimulating hormone (FSH), luteinizing hormone/interstitial cell stimulating hormone (LH/ICSH), testosterone, cortisol, thyroxine (T4), insulin like growth factor-1 (IGF-1), prolactin and melatonin (MT) were estimated at 04:00 h interval for one whole day in four seasons. The analysis was completed in two different ways as different times of collection (08:00, 12:00, 16:00, 20:00, 24:00 and 04:00 h) and day (08:00 to 16:00 h) & night time (20:00 to 04:00 h) collections. Repeated measures ANOVA analysis revealed that the bulls in winter and spring had significantly (p < 0.05) higher FSH, LH, testosterone, T4, IGF-1 and MT than those in summer whereas the bulls in summer had significantly higher cortisol and prolactin than those in winter and spring seasons. Similarly FSH, LH, testosterone, T4, IGF-1 and MT were significantly (p < 0.05) higher in night than in day time collections whereas cortisol and prolactin were significantly (p < 0.05) higher in day than in night time collections in different seasons. Correlation analysis revealed that FSH, LH, testosterone, T4, IGF-1 and MT had significant (p < 0.05) positive correlation with each other whereas these had significant (p < 0.05) negative correlation with cortisol and prolactin. The study concludes that season and time of blood collection had significant effect on the endocrinological profiles in mithun bulls. Estimation of FSH, LH, testosterone, T4, IGF-1 and MT during night time and cortisol and prolactin during day time was more appropriate to get correct value of the endocrinological profiles. Spring and winter have significantly greater beneficial effects than summer on reproduction and artificial breeding programs in mithun species in the semi-intensive management in the present location.

Short-term energy deprivation alters activin a and follistatin but not inhibin B levels of lean healthy women in a leptin-independent manner

CONTEXT

Leptin is a potent modulator of the hypothalamic-pituitary-gonadal axis mediating the effect of energy deprivation on several hypothalamic-pituitary-peripheral axes. Activin A, inhibin B, and follistatin (FST) also regulate the hypothalamic-pituitary-gonadal axis in humans. It remains unknown whether energy deprivation affects these hormone levels in a leptin-dependent or -independent manner.

OBJECTIVE

We investigated 1) day-night variability patterns of activin, inhibin, and FST in the fed state, 2) whether their levels are affected by fasting, and 3) whether such an effect is mediated by leptin in physiological replacement or pharmacological doses.

DESIGN

We conducted two studies in healthy, eumenorrheic females, each comprising three separate admissions. In study 1, six women were maintained for 72 h 1) on isocaloric diet, 2) fasting while receiving placebo, or 3) fasting while receiving metreleptin in physiological replacement doses. In study 2, five women were administered physiological or pharmacological metreleptin doses (0.01, 0.1, or 0.3 mg/kg i.v. four times daily).

RESULTS

Neither activin A nor FST had a pulsatile or day-night variability pattern. Inhibin B levels were also nonpulsatile, but a trend toward a day-night pattern was noted. When compared with the fed state, inhibin B levels remained unchanged, whereas FST levels increased (P = 0.01) and activin A decreased (P = 0.01) in the fasting state. These changes were not corrected with metreleptin administered in replacement or pharmacological doses.

CONCLUSIONS

Short-term energy deprivation alters levels of activin A and FST, but these effects are not mediated by leptin.

The interrealtionship between locally applied heat, ageing and skin blood flow on heat transfer into and from the skin

In response to a thermal stress, skin blood flow (BF) increases to protect the skin from damage. When a very warm, noxious, heat source (44 °C) is applied to the skin, the BF increases disproportionately faster than the heat stress that was applied, creating a safety mechanism for protecting the skin. In the present investigation, the rate of rise of BF in response to applied heat at temperatures between 32 °C and 40 °C was examined as well as the thermal transfer to and from the skin with and without BF in younger and older subjects to see how the skin responds to a non-noxious heat source. Twenty male and female subjects (10 - 20-35 years, 10 - 40-70 years) were examined. The arms of the subjects were passively heated for 6 min with and without vascular occlusion by a thermode at temperatures of 32, 36, 38 or 40 °C. When occlusion was not used during the 6 min exposure to heat, there was an exponential rise in skin temperature and BF in both groups of subjects over the 6-min period. However, the older subjects achieved similar skin temperatures but with the expenditure of fewer calories from the thermode than was seen for the younger subjects (p<0.05). BF was significantly less in the older group than the younger group at rest and after exposure to each of the three warmest thermode temperatures (p<0.05). As was seen for noxious temperatures, after a delay, the rate of rise of BF at the three warmest thermode temperatures was faster than the rise in skin temperature in the younger group but less in the older group of subjects. Thus, a consequence of ageing is reduced excess BF in response to thermal stress increasing susceptibility to thermal damage. This must be considered in modelling of BF.

Circadian clock and output genes are rhythmically expressed in extratesticular ducts and accessory organs of mice

Circadian clocks regulate multiple rhythms in mammalian tissues. In most organs core clock gene expression is oscillatory, with negative components Per and Cry peaking in antiphase to Bmal1. A notable exception is the testis, where clock genes seem nonrhythmic. Earlier mammalian studies, however, did not examine clock expression patterns in accessory ductal tissue required for sperm maturation and transport. Previous studies in insects demonstrated control of sperm maturation in vas deferens by a local circadian system. Sperm ducts express clock genes and display circadian pH changes controlled by vacuolar-type H(+)-ATPase and carbonic anhydrase (CA-II). It is unknown whether sperm-processing rhythms are conserved beyond insects. To address this question in mice housed in a light-dark environment, we examined temporal patterns of mPer1 and Bmal1 gene expression and protein abundance in epididymis, vas deferens, seminal vesicles, and prostate. Results demonstrate variable tissue-specific patterns of expression of the two genes, with variations in levels of clock proteins and their nucleo-cytoplasmic cycling observed among examined tissues. Strikingly, mPer1 and Bmal1 mRNA and proteins oscillate in antiphase in the prostate, with similar peak-trough patterns as observed in the suprachiasmatic nuclei, the brain's central clock. Genes encoding CA and a V-ATPase subunit, which are rhythmically expressed in sperm ducts of moths, are also rhythmic in some segments of murine sperm ducts. Our data suggest that some sperm duct segments may contain peripheral circadian systems whereas others may express clock genes in a pleiotropic manner.

Age-related changes in diurnal rhythms and levels of gonadotropins, testosterone, and inhibin B in male rhesus monkeys (Macaca mulatta)

Testosterone shows circadian rhythms in monkeys with low serum levels in the morning hours. The decline relies on a diminished frequency of LH pulses. Inhibin B shows no diurnal patterns. In elderly men, the diurnal rhythm of testosterone is blunted and inhibin levels fall. Here we explore whether aging exerts similar effects in the rhesus monkey. We collected blood samples from groups of young (6-9 yr) and old (12-16 yr) male rhesus monkeys at 20-min intervals for a period of 24 h under remote sampling via a venous catheter. We determined moment-to-moment changes in plasma levels of testosterone, FSH, and LH by RIA, and of inhibin B by ELISA. We found significant diurnal patterns of testosterone in both groups. The circadian rhythm in testosterone was enhanced in older monkeys. Testosterone levels and pulse frequencies dropped significantly below those of young monkeys during midday hours. Diminished pulse frequency of LH appeared to be responsible for the midday testosterone decrease in old monkeys, while LH and testosterone pulse frequency did not change in young monkeys at corresponding time points. Old monkeys showed extended periods of LH-pulse quiescence in the morning and midday hours. Inhibin B and FSH levels were generally lower in old monkeys compared with the young group, but neither inhibin B nor FSH showed circadian rhythms. We conclude from these data that old rhesus monkeys have a more prominent circadian rhythm of LH and testosterone resulting from an extended midday period of quiescence in the hypothalamus-pituitary-gonadal axis.

Central organization of androgen-sensitive pathways to the hypothalamic-pituitary-adrenal axis: implications for individual differences in responses to homeostatic threat and predisposition to disease

Despite clear evidence of the potency by which sex steroids operate on the hypothalamic-pituitary-adrenal (HPA) axis and genuine sex differences in disorders related to HPA dysfunction, the biological significance of this remains largely ignored. Stress-induced increases in circulating glucocorticoid levels serve to meet the metabolic demands of homeostatic threat head-on. Thus, the nature of the stress-adrenal axis is to protect the organism. As one develops, matures, and ages, still newer and competing physiological and environmental demands are encountered. These changing constraints are also met by shifts in sex steroid release, placing this class of steroids beyond the traditional realm of reproductive function. Here we focus on the dose-related and glucocorticoid-interactive nature by which testosterone operates on stress-induced HPA activation. This provides an overview on how to exploit these characteristics towards developing an anatomical framework of testosterone's actions in the brain, and expands upon the idea that centrally projecting arginine vasopressin circuits in the brain act to register and couple testosterone's effects on neuroendocrine and behavioural responses to stress. More generally, the work presented here underscores how a dual adrenal and gonadal systems approach assist in unmasking the bases by which individuals resist or succumb to stress.

Partial characterization of circulating inhibin-B and pro-alphaC during development in the male rhesus monkey

Gel filtration chromatography and ELISAs for inhibin-B and pro-alphaC were used to examine the circulating forms of inhibin in the neonatal (age 2-6 weeks), juvenile (age 1-2 yr), and adult male rhesus monkey. In all samples, isoforms of inhibin-B of 26-36K and 150K were found. Both forms were significantly greater in the adult. The alpha-subunit assay detected major peaks at 45-60 and 29-31K, and a minor peak of greater than 100K. As for inhibin-B, the major forms of inhibin pro-alphaC were highest in adulthood. Inhibin-B and pro-alphaC were measurable in peripheral plasma at age 1 week, increased with the neonatal rise in plasma FSH, and then decreased but remained detectable through age 1 yr. Values in adult males were higher than at any time during the first year of life. Finally, mean values of plasma inhibin-B and pro-alphaC in five monkeys, based on multiple blood samples drawn between age 1 week and 1 yr, were rank ordered and were found to be highly positively correlated (r = 0.96), suggesting that inhibin levels in the first year of life may be a marker of Sertoli cell number, and may predict the spermatogenic capacity of the testis in adulthood.

The time course of follicle-stimulating hormone suppression by recombinant human inhibin A in the adult male rhesus monkey (Macaca mulatta)

In higher primates, FSH secretion appears to be regulated by a control system consistent with that described by the classical inhibin hypothesis. The purpose of the present experiment was to examine the time course of inhibin's action to suppress FSH secretion in the intact adult male rhesus monkey. To this end, five adult males implanted with indwelling venous catheters and exhibiting typical episodic patterns of LH and testosterone (T) secretion received a 4-day i.v. infusion of recombinant human (rh) inhibin A (832 ng/h x kg) followed, after a 4-week interval, by vehicle infusion of similar duration. Changes in circulating FSH concentrations during the inhibin and vehicle infusions were determined using a sensitive homologous macaque RIA, whereas enzyme-linked immunosorbent assays were employed to track inhibin A, inhibin B, and inhibin pro-alpha-C levels during the experiment. Normal pulsatile activity in the hypothalamic-pituitary-Leydig cell axis was confirmed by monitoring changes in circulating concentrations of LH and T in 12-h windows of sequential blood collection (1200-2400 h; every 20 min) before, during, and after the rh inhibin A and vehicle infusions. Although infusion of rh inhibin A, which led to a 12 ng/ml square wave increment in circulating levels of this inhibin dimer, produced a marked decline in circulating FSH concentrations, significant suppression of the secretion of this gonadotropin was not manifest until 54 h after initiation of the infusion. Despite the marked decline in FSH secretion during the last 24 h of the 4-day infusion of recombinant hormone, circulating inhibin B and pro-alpha-C concentrations were maintained at preinfusion control levels (1 ng/ml). The finding that imposition of an exaggerated circulating inhibin signal led to suppression of FSH secretion in the male monkey only after 2 days of exposure to the hormone indicates that in this species the feedback action of testicular inhibin on FSH secretion is heavily lagged. Moreover, as the decrease in FSH did not lead to changes in native inhibin secretion, it seems reasonable to propose that the FSH-inhibin feedback loop that governs testicular function in higher primates operates with considerable hysteresis at both the pituitary and gonadal levels. The failure of dramatically elevated inhibin A levels to influence the pulsatile secretion of LH in the monkey reinforces the idea that in this species the pituitary action of testicular inhibin is specific for FSH and does not involve modulation of GnRH receptor levels.

Circulating concentrations of dimeric inhibin A and B in the male rhesus monkey (Macaca mulatta)

The purpose of this study was to determine the relative concentrations of inhibin A and B in peripheral serum of the adult male rhesus monkey and to examine the testicular contribution to these circulating forms of inhibin. In addition, inhibin B concentrations were also determined in peripheral sera of neonatal and juvenile males and in spermatic vein blood of adults. Immunoradiometric assays specific for the measurement of inhibin A and B were used. These assays also provided an opportunity to reexamine the physiological significance of a replacement infusion of recombinant human (rh)-inhibin A previously employed to study the role of this hormone in regulating FSH secretion in the monkey. In intact adults, the mean (+/-SE) serum concentration of inhibin B was 1008 +/- 184 pg/mL. In contrast, circulating inhibin A concentrations were very low (< 46 pg/mL). Inhibin B was consistently detected in neonatal monkey serum (275 +/- 57 pg/mL), and concentrations of this inhibin dimer increased throughout postnatal development, reaching maximum values in adulthood. Circulating inhibin A concentrations in neonatal and juvenile monkeys were undetectable (< 7 pg/mL). Both forms of inhibin were generally undetectable in castrate sera. The ratio of inhibin B concentrations in testicular venous blood to those in the peripheral circulation was 1.4:1. These findings indicate that, in the male monkey, inhibin B is the principal form of circulating dimeric inhibin, and that this hormone is derived exclusively from the testis. The elevated levels of circulating inhibin B in the juvenile male monkey suggest that, during this phase of development, testicular inhibin B secretion is relatively gonadotropin independent. Additionally, we found that the concentration of circulating inhibin A in castrate animals that had earlier received an iv infusion of rh-inhibin A (832 ng/h/kg BW) was 9881 +/- 2135 pg/mL, indicating that this mode of inhibin replacement may not have been entirely physiological.

A study of the relative roles of follicle-stimulating hormone and luteinizing hormone in the regulation of testicular inhibin secretion in the rhesus monkey (Macaca mulatta)

The purpose of this study was to examine the relative roles of FSH and LH in stimulating testicular inhibin secretion in the male rhesus monkey. Recombinant human (rh) FSH and rhCG were used as the gonadotropic stimuli, and juvenile rhesus monkeys, in which the endocrine activity of the pituitary-testicular axis was being driven in an adult manner with an intermittent i.v. GnRH infusion, were studied. Immunoactive inhibin levels were measured by the Monash RIA. Initiation of an intermittent i.v. infusion of rhFSH (10 IU every 3 h) resulted, after a delay of 5-6 h, in a progressive increase in the concentrations of immunoactive inhibin, which achieved, after 48 h of stimulation, a value twice that observed during vehicle treatment. Gel filtration chromatography revealed that the FSH-induced elevation in immunoactive inhibin was the result of an increase in three distinct mol wt fractions: peak I (100 kDa), peak II (50-60 kDa), and peak III (31 kDa). Although peak III accounted for most of the inhibin immunoactivity in vehicle-treated animals, peaks I and II were most responsive to FSH stimulation. Application of recently developed enzyme-linked immunosorbent assays for inhibin B and pro-alpha-C-related peptides provided additional insights into the nature of the FSH-sensitive forms of circulating immunoactive inhibin. Most notably, the 31-kDa fraction (peak III) was comprised of inhibin B and pro-alpha-C. In contrast to FSH stimulation, an intermittent infusion of rhCG (40 IU every 3 h), which markedly elevated testicular testosterone secretion, failed to increase immunoactive inhibin concentrations. These findings indicate that various forms of immunoactive inhibin are present in the circulation of the rhesus monkey, and that in this species, FSH is the principal stimulus of the secretion of testicular inhibins, including inhibin B. Additionally, they further underline the importance of the FSH-inhibin feedback loop in governing testicular function in primates.

Rat prostatic inhibin: less than 35 kDa protein(s)

An attempt was made to purify and physicochemically characterize the inhibin-like activity of rat ventral prostate based on the technique of immunosorption. It was possible to partially purify prostatic inhibin by affinity chromatography and the molecular size of inhibin-like material was shown to be less than 35 kDa.

Inhibin in normal and abnormal pregnancy: maternal serum concentration and partial characterization

OBJECTIVE

This study evaluated maternal serum inhibin concentration and molecular distribution in normal and abnormal pregnancies.

STUDY DESIGN

Serum inhibin levels were measured by radioimmunoassay in 33 abnormal pregnancies (23 singleton and 10 multiple gestations) and 33 matched controls and were compared with pregnancy variables.

RESULTS

In the controls serum inhibin concentrations rose with gestational age (correlation coefficient 0.358, p < 0.01) and were higher in mothers with female fetuses (p < 0.05). Inhibin levels were higher in the abnormal singleton pregnancies (2.69 +/- 1.41 ng/ml) than in controls (1.26 +/- 0.32 ng/ml, p < 0.0001) and increased more rapidly with gestational age in multiple pregnancies (p < 0.05). Gel filtration chromatographic analysis of immunoreactive inhibin revealed three peaks with the major form having an apparent molecular weight of 55 to 60 kd.

CONCLUSION

Maternal serum inhibin concentrations are affected by gestational age, fetal gender, and complications of pregnancy. Most of the immunoreactive inhibin in maternal circulation is a large-molecular-weight form.

Inhibin and follicle-stimulating hormone levels in gonadotroph adenomas: evidence of a positive correlation with tumour volume in men

OBJECTIVE

Gonadotroph adenomas are generally revealed by symptoms of mass effect at the stage of macroadenoma. Most of them hypersecrete FSH and/or gonadotrophin subunits. Rarely they hypersecrete LH, which could induce endocrinological symptoms. As the glycoprotein inhibin is secreted by the gonads under FSH control, we have evaluated whether high immunoreactive inhibin (iINH) levels correlated with FSH hypersecretion and whether iINH and FSH levels were related to tumour volume in subjects with gonadotroph adenomas.

PATIENTS

Forty-five patients (30 men, 15 women) were retrospectively selected on the basis of immunostaining technique using specific antibodies raised against FSH-beta, LH-beta and glycoprotein alpha-subunit.

MEASUREMENTS

Immunoreactive inhibin (iINH) was measured by radioimmunoassay using antiserum 1989 raised to bovine inhibin. Tumour volume index was the product in cm3 of length, width and height of the adenoma as assessed by computerized tomography.

RESULTS

In men (age 21-61 years), iINH levels were positively correlated with FSH levels (Spearman's r = 0.67, P < 0.001), and both iINH and FSH levels were significantly correlated with tumour volume index (Spearman's r = 0.38, P < 0.05 and r = 0.39, P < 0.05 respectively). In the subgroup of men with normal FSH levels (n = 17), the correlation of FSH with tumour volume index was high: Spearman's r = 0.56, P < 0.05. In the post-menopausal women (n = 8, age > 55 years), iINH levels were undetectable or below the follicular phase range regardless of FSH values. In the premenopausal women (n = 7, age 22-49 years, follicular phase or amenorrhoea) iINH levels were above follicular phase range in three women including one who had very high FSH levels.

CONCLUSIONS

These data show that in men with gonadotroph adenoma FSH levels are related to tumour mass and suggest that a significant part of circulating FSH in patients with normal FSH levels arises from the tumour. The significant correlation between iINH and FSH levels demonstrates that tumoral FSH is bioactive and that high iINH levels do not exert any feedback control on tumoral FSH secretion. Therefore the coexistence of high FSH levels with high iINH levels is strongly suggestive of a gonadotroph adenoma. Gonadotroph adenomas seem to represent a unique model of long-term FSH stimulation of inhibin-producing cells, in some way analogous to that created by repetitive administration of exogenous FSH.