Evidence that estrogen regulation of testosterone secretion in adult rams is mediated by both indirect (gonadotropin dependent) and direct (gonadotropin independent) means

Monitoring chlorinated persistent organic pollutants in adolescents in Flanders (Belgium): concentrations, trends and dose-effect relationships (FLEHS II)

BACKGROUND

In 2007, the second cycle of the Flemish human biomonitoring survey started, with a main focus on 14-15 year-old adolescents.

OBJECTIVES

The main objectives were generating reference values for exposure markers, determining the pollution pressure in industrial hotspots and establishing dose-effect relationships between exposure to pollutants and hormone levels, sexual development, asthma and allergy, genotoxic and hematological markers.

METHODS

Geometric means with 95% confidence intervals (CI) were calculated for a reference population of 200 14-15 year-old adolescents. Stepwise multiple regression analyses with correction for confounders and covariates were performed to establish dose-effect relationships.

RESULTS

Geometric mean concentrations (with 95% CI) of 49.6 (45.7, 53.8), 70.8 (63.6, 78.8) and 8.34 (7.76, 8.97) n gg(-1) lipid for the sum of PCB 138, 153 and 180, p,p'-DDE and HCB were respectively 23%, 26% and 60% lower than those obtained five years earlier. Geometric mean concentrations of 108 (101, 114) and 32.1 (30.1, 34.2) pgCALUX-BEQg(-1) lipid were observed for the PCDD/Fs and dioxin-like PCBs, respectively. Multiple dose-effect relationships were observed between POPs and several effect markers, including positive (boys) and negative (girls) associations with data on sexual development and positive associations with asthma, animal allergy and free thyroxine (boys and girls).

CONCLUSIONS

Our findings suggest that chlorinated POP concentrations are decreasing over time and that even relatively low concentrations are associated with biological effects.

Internal exposure to pollutants and sex hormone levels in Flemish male adolescents in a cross-sectional study: associations and dose-response relationships

Flanders is densely populated with much industry and intensive farming. Hormonal status of 14- to 15-year-old male adolescents was studied in relation to internal exposure to pollutants. A total of 887 participants were selected as a random sample of the adolescents residing in the study areas. Confounding factors and significant covariates were taken into account. Serum levels of testosterone, free testosterone and estradiol, and the aromatase index showed significant positive associations with serum levels of marker polychlorobiphenyls (sum of PCBs 138, 153, and 180) and of hexachlorobenzene (HCB) and a negative association with urinary cadmium concentration. Serum levels of estradiol also showed a positive association with serum levels of dichlorodiphenyldichloroethylene (DDE). A doubling of serum concentrations of marker PCBs and HCB and of urinary concentration of cadmium were, respectively, associated with an increase of 16.4% (P<0.00001) and 16.6% (P<0.001) and a decrease of 9.6% (P<0.001) in serum testosterone concentration. Similar findings were made after additional adjustment for concurrent exposures. Associations between biological effects and internal exposures were, in terms of the regression coefficient, often stronger at exposures below the median. Environmental exposures to pollutants resulting in "normal" levels of internal exposure were associated with quite substantial differences in hormone concentrations.

Prolactin regulation of testosterone secretion and testes growth in DLS rams at the onset of seasonal testicular recrudescence

Our objective was to test the hypothesis that prolactin (PRL) acts at both the pituitary and testis levels to regulate testosterone secretion in the adult ram. The focus was on the mid-regression to mid-redevelopment stages of a photoperiod-condensed ‘seasonal’ testicular cycle. DLS rams (six per group) were given daily s.c. injections of bromocriptine (4 mg) or vehicle during the entire period. Serum PRL concentration in control rams peaked at 103.4±22.1 ng/ml in late regression and then steadily declined (P<0.01) to 19.5±4.3 ng/ml, whereas PRL in treated rams was always ≤4.0 ng/ml. Suppression of PRL tended (P<0.10) to increase the amplitude of natural LH pulses (transition stages) or reduce the number of LH receptors in the testis (regressed stage), although neither change disturbed testosterone levels in peripheral blood. These subtle changes were accompanied by significant (P<0.05) alterations in the capability of the pituitary to release LH (85% more) and of the testes to secrete testosterone (20% less). These effects of PRL were unmasked when rams were given highly stimulative i.v. injections of GNRH (single 3 μg dose) and NIH-oLH-S24 (three 5 μg doses given 20 min apart) respectively. PRL insufficiency also appeared to slow down the ‘seasonal’ rise in FSH secretion and slightly delayed (2 weeks) the times when the testes began to grow and were first significantly (P<0.05) enlarged from the regressed state. We conclude that PRL is an important part of the intricate regulation of the pituitary–gonadal system in moderately seasonal DLS rams.

Absence of photoperiodic modulation of gonadotrophin secretion in HPD rams following chronic pulsatile infusion of GnRH

Hypothalamo-pituitary disconnected Soay rams (HPD rams) were treated chronically with a pulsatile infusion of GnRH (250 ng/2 h) for 10 weeks to reactivate the pituitary-gonadal axis under long days (16L:8D; LD group n=8) and short days (8L:16D, SD group n=8). The aim was to establish whether photoperiod modulates the secretion of gonadotrophins (presumably through the daily melatonin signal) by an action at the level of the pituitary gland. The treatment of the HPD rams with GnRH induced a marked, long-term increase in the peripheral blood concentrations of FSH, LH and testosterone, growth of the testes and reappearance of the androgen-dependent sexual skin colouration. There were parallel changes in the short-term, pulsatile fluctuations in the blood concentrations of LH and FSH, the pituitary responsiveness to GnRH and the testicular responsiveness to a standardized injection of oLH, as observed previously in normal intact rams during reactivation of the reproductive axis induced by a switch from long to short days. There were no significant differences in any of the reproductive parameters between the LD and SD HPD groups, although the blood concentrations of prolactin were significantly higher in the LD group, and GnRH provoked a chronic increase in the blood concentrations of prolactin, particularly in the SD group. Overall, the results support the conclusion that (i) melatonin does not act within the pituitary gland to mediate effects of photoperiod on GnRH-induced gonadotrophin secretion; and (ii) changes in prolactin secretion which result from the local action of melatonin in the pituitary gland do not affect gonadotrophin secretion in the ram.

A re-evaluation of the effects of gonadal steroids on neuronal activity in the male rat

Single unit activity (SUA) was recorded from 77 cells located in the arcuate nucleus (ARC) and medial preoptic area (MPA) of anesthetized, intact male rats. Animals were administered vehicle, testosterone (T; 5 or 50 micrograms) or 17 beta-estradiol (E; 0.5 microgram) intravenously and SUA was monitored for 8-12 min. T (50 micrograms) reduced SUA in 50% of ARC units and 44% of MPA units within 2.1 +/- 0.46 and 3.3 +/- 0.92 min, respectively. Inhibition of ARC SUA was more pronounced than MPA SUA. A small percentage (9%) of ARC units were excited by T. E reduced SUA in 29% of ARC units and 27% of MPA units. Single doses of 5 micrograms T did not affect ARC activity. However, when followed within 10 min by an additional dose of 5 or 50 micrograms T, 30% and 43% of ARC units were inhibited, respectively. Doses (10 micrograms) of T produced plasma T concentrations within physiological limits, although 50 micrograms doses produced supraphysiological T levels. Neither dose affected circulating LH concentrations. We conclude that physiological and supraphysiological concentrations of T can rapidly affect SUA within the ARC.

Pubertal changes in the secretion of gonadotropic hormones, testicular gonadotropic receptors and testicular function in the ram

Developmental changes in pituitary content and secretory patterns of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL), testicular size and steroidogenic function, testicular LH- and FSH-binding activity, and growth of the accessory sex organs were examined for 24 Dorset X Leicester X Suffolk rams (born in March) every 30 days from 30 to 150 days of age, and again at 200 days. Pituitary LH and FSH contents increased between 30 and 60 days of age and remained constant until 150 days, when contents were somewhat greater than on either 120 or 200 days. LH-pulse amplitude and frequency, and mean FSH concentration, were highest at 60 and (or) 90 days of age. Testicular growth increased dramatically between 90 and 150 days of age in association with increases in the number of LH- (100-fold) and FSH- (33-fold) binding sites in the testis and a small increase in blood testosterone concentration (1 ng/ml). During the same period, pituitary content and blood concentration of PRL increased to maximal values, epididymal, vesicular gland and bulbourethral gland weights increased 6-fold, and body weight doubled. Between 150 and 200 days of age, testosterone concentration increased considerably (8 ng/ml), as did LH-pulse frequency and the amount of LH- and FSH- binding in the testis; the reproductive organs continued to grow at a rate faster than that of the body as a whole. Testicular development of ram lambs was accompanied by increases in the secretion of all three pituitary hormones with gonadotropic properties, and in the number of LH and FSH receptors.

The pattern of LH release in the adult ram influences the testicular steroidogenic response to individual LH pulses and is regulated by testosterone negative feedback

Two experiments were conducted with adult intact rams (approximately 58 kg in body weight) in the nonbreeding season to investigate interrelationships between LH and testosterone secretion. In Experiment 1, LH pulse frequency was increased from approximately two to six peaks per 8 hours (for 56 hours) by injecting (iv) 10 micrograms NIH-LH-S18 every 80 minutes. Induction of a breeding season peak frequency produced a progressive 3-fold increase (P less than 0.01) in mean serum testosterone levels to values during the last 8 hours of treatment (12.6 +/- 1.2 ng/ml) that were 50% of those in the fall. In response to LH pulsing, testosterone peak amplitude increased (P less than 0.05) from 3.5 +/- 0.8 ng/ml to 6.7 +/- 0.7 ng/ml. In Experiment 2, the mean testosterone level was increased to breeding season values (for 96 hours) by injecting (im) 5 mg testosterone every 4 hours. Mean LH levels and LH peak frequency were decreased (approximately 70%, P less than 0.01) following 36 hours of treatment, and the LH response to exogenous GnRH was decreased (approximately 45%, P less than 0.01) by the final 4 hours Results indicate that for rams in the nonbreeding season, the testicular steroidogenic response to individual LH pulses is enhanced when pulse frequency is increased. When blood testosterone is elevated to breeding season levels, LH pulse frequency is severely impaired, while pituitary responsiveness to GnRH is diminished, as in the fall.

Endocrine parameters, hormone receptors, and functions of the testicular interstitium and seminiferous epithelium in estradiol-immunized Ile-de-France rams

The testicular response of Ile-de-France rams actively immunized against estradiol (E2) was evaluated during both the ovine nonbreeding season (spring) and breeding season (autumn). Plasma concentrations of LH, FSH and testosterone were elevated in E2-immunized rams during both spring and autumn when compared with BSA-immunized controls. Testis weights were significantly elevated by E2 immunization and were characterized by greater interstitial cell volume, including Leydig cells, blood and lymph vessels, greater seminiferous tubule length, and greater numbers of leptotene spermatocytes and round spermatids. Neither Sertoli cell number, Sertoli cell nuclear volume nor testicular FSH receptor number were affected by E2 immunization, but testis weight, Sertoli cell nuclear area, FSH receptor number and LH receptor number were significantly greater in autumn than in spring. A positive effect of E2 immunization on testicular LH receptors was evident in spring but not in autumn. Testicular androgen receptors were suppressed by E2 immunization but were not affected by season. It was concluded that E2 immunization results in moderate stimulation of the ovine testis to increase testosterone secretion and to enhance total daily spermatid production. This effect appears to result from a change in E2 negative feedback and increased pituitary gonadotropin secretion.

Testicular involution in elderly men: comparison of histologic quantitative studies with hormone patterns

An endocrinologic and quantitative histologic study was carried out in 64 elderly men who underwent orchidectomy owing to prostatic carcinoma. The men were classified into age groups (decade of life), and each group was subdivided into group A (testes with complete spermatogenesis in most tubules) and group B (testes showing maturation arrest of spermatogenesis in most tubules). Up to 80 years of age, men of group A showed hormone levels and testicular parameters similar to those of young control men. From 50 to 60 years of age, men of group B showed a significant decrease in testicular volume, tubular volume, tubular length, number of germ cells, Sertoli cells and Leydig cells per testis, and plasma testosterone levels, whereas the tunica propria thickness and plasma levels of both follicle-stimulating hormone and luteinizing hormone were increased.

Follicle stimulating hormone, luteinizing hormone and testicular Leydig cell responses to estradiol immunization in Ile-de-France rams

Active immunization of Ile-de-France rams against estradiol (E2) resulted in the production of E2-neutralizing antibodies and an elevation in the plasma concentrations of FSH, LH, and testosterone. The presence of E2 antibodies did not affect the testosterone metabolic clearance rate, indicating that the immunization-mediated 10-fold increase in plasma testosterone was the result of a 10-fold increase in testicular testosterone production. Testis weights, as well as nuclear and cytoplasmic volumes of individual peritubular and perivascular Leydig cells, were greater in E2-immunized rams than in albumin-immunized controls. Leydig cell numbers were not affected by treatment. The E2 antibodies were capable not only of neutralizing the inhibitory effects of endogenous E2 on gonadotropin levels in intact rams, but were able to block the effects of exogenously administered E2 on their FSH and LH secretory response to castration. It is concluded that circulating E2 in the ram is involved in pituitary-testicular endocrine homeostasis and that E2 immunoneutralization can be employed to enhance testosterone secretion in this species.