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PubMed1983

Changes in the pituitary-gonadal axis associated with puberty in Holstein bulls.

The temporal pattern of the endocrine changes associated with puberty were studied using 52 bulls born in October or April. Blood samples were taken weekly and at 30-min intervals for 5 h every 4-wk. Bulls were castrated at one of six 4-wk intervals between 12 and 32 wk and blood samples were taken. Season of birth affected concentrations of testosterone (greater for spring-born) in intact bulls, but not luteinizing hormone (LH) or follicle stimulating hormone (FSH). The concentration of FSH increased about 30% between 4 and 32 wk, without evidence of pulsatile discharge. Basal concentration of LH was low and pulsatile discharges were infrequent at 4 or 8 wk. At 12, 16 and 20 wk, however, basal LH concentration was elevated and LH discharges were at less than 2-h intervals. Testosterone concentration did not rise until 18 to 20 wk, but then continued to rise; LH discharge was suppressed concomitantly. Bulls castrated at 16 or 20 wk had higher concentrations of LH in their blood both before and shortly after castration values for bulls, but by 21 d after castration values for bulls of all ages were similar. It was concluded that elimination of an unidentified suppressive factor allows frequent discharges of LH between 12 an 16 wk, but the testes do not respond by secreting more testosterone until 18 to 20 wk. By 24 wk, the testes are secreting more testosterone and pituitary production of LH is restored to a lower level; LH discharges decline in frequency and basal LH level declines. The high frequency discharges of LH between 12 and 20 wk are postulated to induce responsiveness of Leydig cells to LH and, thus, enable elevation of intratesticular testosterone to levels necessary for Sertoli cell differentiation and initiation of spermatogenesis.

Age Factors↗
PubMed1991

Ontogenesis of the in vitro response of rat testis to gonadotropin-releasing hormone.

The age-related evolution of the in vitro effects of a gonadotropin releasing hormone agonist ([D-Trp6]-GnRH) on the secretion of testosterone by the testis, cultured during 3 days on a Millipore filter floating on M199 medium, was studied during the perinatal period in the rat. The basal and luteinizing hormone (LH)-stimulated secretions by testes explanted on fetal day 14.5 were unaffected by the agonist. With fetal testes explanted on days 16.5 and 18.5 post-conception, the agonist inhibited, in a concentration-dependent manner, both basal and LH-stimulated secretions from the second or the third day of treatment onwards. With fetal and neonatal testes explanted on days 20.5, 21.5 and 31.5 post-conception, the GnRH agonist also had a long-term inhibitory effect on LH-stimulated secretion, but increased basal secretion. This stimulatory effect was already observed after 4 h of culture, and was maintained for 3 days. These results suggest that, during fetal development, the cellular mechanisms involved in the negative testicular response to GnRH are differentiated 3-5 days before those involved in the positive response. Lastly, after 3 days of preculture in hormone-free medium, fetal testes explanted on day 14.5 displayed long-term GnRH agonist inhibition of in vitro basal secretion of testosterone. This observation points out a spontaneous differentiation of the negative responsiveness to GnRH in the cultured fetal testis.

Animals↗
PubMed1985

Short-term changes in plasma levels of hormones during establishment and defense of a breeding territory in male song sparrows, Melospiza melodia.

When territorial male song sparrows are captured and removed from their territories, previously unmated and nonterritorial males will take over those vacant territories within 12-72 hr. Plasma levels of testosterone are elevated in these replacement males as well as in their neighbors. Since the latter already have territories, it is suggested that the agonistic interactions over territory boundaries, or behavioral stimuli from challenging males, rather than ownership of a territory per se, stimulates secretion of testosterone. To test this hypothesis further, male song sparrows were challenged by experimental simulation of a territorial intrusion. This procedure involved placing a caged male song sparrow in the center of the subject's territory and playing tape recorded conspecific song through an adjacent speaker. Responding males were then captured at intervals after onset of the intrusion. Plasma levels of testosterone were significantly higher in males exposed to experimental territorial intrusion than they were in controls, supporting the hypothesis that behavioral stimuli emanating from an intruding male can act as supplementary information stimulating secretion of testosterone.

Aggression↗
PubMed1993

The in vitro perifused rat ovary: IV. Modulation of ovarian steroid secretion by insulin.

Insulin has been implicated as a regulatory factor in ovarian steroidogenesis. To assess this issue, we examined the role of insulin on steroid secretion by whole ovaries from pregnant mare serum gonadotropin (PMSG)-pretreated rats, using an in vitro perifusion ovarian model. Three concentrations of insulin were perifused in the absence and presence of gonadotropin pulse-stimulation. Bioactive insulin concentrations after perifusion of ovarian tissue were 4, 40 and 400 mIU/ml. In the absence of gonadotropin-pulse stimulation, acute perifusion with insulin had no effect on ovarian steroid secretion. During stimulation with luteinizing hormone (LH) plus follicle stimulating hormone (FSH), insulin significantly decreased the secretion of testosterone and estradiol but increased the output of progesterone. This effect was only evident after 180 min perifusion and with the highest concentration of insulin. We conclude that acute elevation of insulin concentration has no effect on basal ovarian secretion of progesterone, testosterone, or estradiol in gonadotropin-pretreated rats. However, insulin has a moderate effect on steroid secretion in ovaries exposed to LH/FSH pulsatile stimulation, resulting in a decrease in estradiol and testosterone release, and stimulation of progesterone secretion.

Animals↗
PubMed1985

Patterns of secretion of luteinizing hormone, follicle stimulating hormone and testosterone in stallions during the summer and winter.

Samples of jugular blood were drawn from each of five stallions every 15 min for 12 h during the summer and winter to determine the short-term fluctuations in plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone. Concentrations of LH and FSH were generally not pulsatile, although one stallion exhibited three distinct pulses in these hormones during the winter. In general, patterns of secretion of all three hormones were similar in both seasons and the number of significant rises in hormonal concentrations did not differ between seasons. Concentrations of LH and FSH were positively correlated (P less than .05) for eight of the ten sampling periods, indicating a close relationship between the secretion rates of these two gonadotropins. Testosterone concentrations varied in an episodic manner during the 12-h period, and all stallions exhibited at least one episode of high testosterone secretion regardless of the pattern of LH concentrations. The response in testosterone concentrations to the three LH pulses exhibited by the one stallion in winter was not the same for each pulse. The correlations between a single random sample and mean concentrations over the 12-h period were high (r between .88 and .99) for all three hormones, indicating that a single sample of blood would be representative of overall concentrations. It appears that the stallion differs from males of other domestic species in that concentrations of gonadotropins and testosterone vary in a much less pulsatile manner.

Animals↗
PubMed2000

Reproductive responses of cattle to GnRH agonists.

The response in cattle to treatment with gonadotrophin releasing hormone (GnRH) agonist includes downregulation of GnRH receptors on gonadotrophe cells, desensitisation of the anterior pituitary gland to endogenous GnRH, and the abolition of pulsatile release of LH. In bulls, a tonic pattern of LH release is associated with increased secretion of testosterone, which persists for the duration of treatment with GnRH agonist. The mechanism for this response in bulls has not been elucidated, but clearly pulsatile release of LH is not required to stimulate the synthesis of steroidogenic enzymes that sustain elevated secretion of testosterone. In heifers, desensitisation to endogenous GnRH prevents the occurrence of the pre-ovulatory surge release of LH, thus blocking ovulation. The latter provided the opportunity to evaluate the potential of a GnRH agonist bioimplant to control fertility in heifers under extensive management. Bioimplants that contained graded amounts of GnRH agonist prevented pregnancies in heifers for periods of 3 to 12 months. Zebu crossbred heifers treated with GnRH agonist from 14 to 23 months of age failed to conceive, but showed normal conception patterns when introduced into mating herds at around 26 months of age. After treatment with GnRH agonist for 4 to 6 weeks, ovarian follicular growth in heifers is restricted to relatively small (2-4 mm) antral follicles. Suppressed follicular growth in heifers treated long-term with GnRH agonist is due to a lack of gonadotrophin support, rather than a direct action of agonist at the ovaries. This was demonstrated by the ability to induce apparently normal follicular growth and ovulation by acute treatment with FSH for 4 days, followed by an injection of LH, in heifers that had been exposed to GnRH agonist for around 6 months, and which had only small (2-4 mm) antral follicles at the start of FSH treatment. GnRH agonist bioimplants have been incorporated into new multiple ovulation and embryo transfer protocols that allow control of the time of ovulation subsequent to superstimulation of ovarian follicular growth with FSH. In these protocols, the endogenous surge release of LH is blocked by treatment with agonist and ovulation is timed by injection of exogenous LH, allowing fixed-time AI. It can be concluded from recent studies that GnRH agonist bioimplants have considerable potential for both pro-fertility and anti-fertility applications in cattle. It is likely that commercial bioimplants will be available within the next 3 to 5 years.

Animals↗
PubMed1981

Use of a cloned double stranded cDNA coding for a major androgen dependent protein in rat seminal vesicle secretion: the effect of testosterone in gene expression.

The abundant class of poly(A+)RNA [poly(A+)RNA11S] from rat seminal vesicle was used to synthesize ds-cDNA11S. The ds-cDNA11S was inserted and cloned into the Pst I site of pBR-322 using E. coli RR1 as host. Colony filter hybridization and restriction mapping was used to demonstrate that a 620 NTP long insert in a plasmid clone (pSV2) represents the almost full length structural gene coding for a precursor to the seminal vesicle secretion protein IV (SVS IV). The entire insert was sequenced and the coding region was matched with the known amino acid sequence. Most of the signal peptide sequence was derived from the DNA sequence. The insert in pSV2 was labelled and used to study the effect of testosterone on the accumulation of mRNA SVS IV. Administration of testosterone to castrated rats resulted in the induction of mRNA SVS IV from a few molecules per cell to levels of over 100,000 after 96 h of hormone treatment.

Animals↗
PubMed1975

[Secretion into the plasma of testosterone and estradiol 17 beta by the human testicle. Value of the study in male sterility].

The levels of oestradiol and of testosterone were estimated in the spermatic and in the perpheral veins in two series of 13 subjects. The one was a control group and the other stimulated with 10,000 International Units of chorionic gonadontrophir (II.C.G). The follwing conclusions can be drawn. --the first is that the testis secretes simultaneously testosterone and oestradiol 17 beta --the second is that the level of oestradiol is significantly raised after the administration of II.C.G. whereas the level of testosterone hardly alters. This leads on to the supposition that oestradiol does not arise from the same source in the testis as testosterone.

Chorionic Gonadotropin↗
PubMed1994

Steroidogenic and morphogenic characteristics of human peritubular cells in culture.

We have explored the morphogenic and functional characteristics of human peritubular cells originating from seminiferous tubule (ST) fragments isolated from the testes of two prepubertal patients with the androgen insensitivity syndrome. These ST were cultured in Dulbecco's Modified Eagle's Medium-Ham's F-12 supplemented with antibiotics, transferrin, hydrocortisone, vitamin E, and 3% fetal bovine serum. A centrifugal growth of elongated fibroblast-like cells peripheral to the ST explants was observed. Muscle-specific actin and 3 beta-hydroxysteroid dehydrogenase were evident in the peritubular area and in the elongated cells growing from the tubules. Histochemistry was negative in the tubules themselves, revealing the mixed nature of these cultures. The ST fragments were lost after subculturing, leaving a homogeneous monolayer of fibroblast-like cells. The steroidogenic potential of these cells was demonstrated by the secretion of testosterone (T) to the culture medium. T secretion was stimulated by hCG in a time-dependent fashion (patient 1: Day 11, 84% and Day 15, 200%; patient 2: Day 8, 73% and Day 11, 32% over basal). FSH also stimulated T secretion (patient 1: Day 5, 136% and Day 8, 89%; patient 2: Day 8, 117% and Day 11, 129% over basal). Furthermore, T secretion by these cultures was 100% higher than that observed in mesenchymal cells obtained from the testicular intertubular space in the same patient. Spontaneous T secretion and hormone responses declined progressively to cease by 25 days in culture. These results suggested the involvement of Sertoli cell (SC)-secreted factor(s) in the regulation of T secretion by peritubular cells. In order to further explore possible paracrine interactions between peritubular and Sertoli cells, we carried out heterologous cocultures with rat SC. After 72 h a striking redistribution of both cell types was observed with the formation of cord-like structures. Ultrastructural examination of these cords showed the formation of a basement membrane between epithelial (Sertoli) and mesenchymal cells of peritubular origin. No resumption of T secretion was observed, but an increase in androgen-binding protein (ABP) production by rat SC under basal (37%) and FSH-stimulated (52%) conditions was evident. Our results show that in the human peritubular compartment, cells exist that can alternatively express steroidogenic functions, associate with SC in a specific mesenchymal-epithelial interaction, and exert regulatory influences on ABP secretion by SC. In addition they indicate that communicating events in the testis are preserved throughout evolution.

3-Hydroxysteroid Dehydrogenases↗
PubMed1991

Pig Leydig cell culture: a useful in vitro test for evaluating the testicular toxicity of compounds.

In vivo studies have shown that the testis is a target organ for drugs and chemicals. In order to evaluate the testicular toxicity of compounds and to identify the mechanisms of their toxicity, we have developed a miniaturized primary culture of immature pig Leydig cells. Five well-known drugs with differing mechanisms of toxicity on testicular functions were tested to validate the model. Testosterone and progesterone secretion were measured to evaluate testicular function. Cell viability was assessed quantitatively using a colorimetric assay based on the reduction of a tetrazolium salt (3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide) which stains viable cells only, thus allowing discrimination between specific inhibitors of Leydig cell function and nonspecific cytotoxic drugs. Ketoconazole and aminoglutethimide inhibited both testosterone and progesterone secretion, but without modifying cell viability. Spironolactone specifically blocked testosterone secretion and increased progesterone concentration without inducing cell mortality. Cycloheximide altered testicular steroid secretion by another mechanism of action. Chlorpromazine, which interferes with the secretion of gonadotropins in vivo, produced a significant inhibition of progesterone and testosterone secretion as a result of the cytotoxic effects of the drug. In conclusion, this in vitro test enables one to discriminate accurately between specific and nonspecific inhibitors of steroidogenesis and could reduce the number of false positives when screening for potential testicular toxins.

Aminoglutethimide↗
PubMed2006

Low testosterone levels and unimpaired melatonin secretion in young males with metabolic syndrome.

The interrelations between testosterone, insulin and melatonin levels in males with metabolic syndrome (MS) are still not clarified, especially in young age groups. The aim of the present study was to compare the testosterone serum levels in young men with MS to those in healthy controls, and to determine the possible changes in their melatonin rhythm, as well as the relation between melatonin, insulin and lipid profile. Fasting insulin and testosterone concentrations were measured in 10 healthy nonobese and 10 MS patients. Blood samples for melatonin, insulin and luteinizing hormone (LH) were collected at 19.00, 03.00 and 11.00 hours. A significant difference was found between the testosterone levels in controls and patients. Luteinizing hormone levels in both groups were similar, however, higher night LH levels in MS patients were observed. No changes in the melatonin concentrations of the two groups were found. In conclusion, total testosterone levels were significantly lower in young men with MS compared with healthy age-matched controls. Mild hypoandrogenia in hyperinsulinaemic patients was not related with changes in their melatonin levels. No alterations in the endogenous melatonin rhythm of the MS patients were found.

Adult↗
PubMed1980

Photoperiod-induced change in responsiveness of the hypothalamic-pituitary axis to exogenous 5 alpha-dihydrotestosterone and 17 beta-estradiol in castrated male hamsters.

Exposure to short day lengths for 9 weeks renders the hypothalamic-putuitary axis of the castrate hamster extremely responsive to the negative feedback effect of exogenous testosterone. The systemic and/or local conversion of testosterone to 5 alpha-dihydrotestosterone (5 alpha-DHT) or 17 beta-estradiol (E2) is considered to be an important step in its action on target tissues. The present study was designed to determine if the photoperiod can induce changes in the sensitivity of the hypothalamic-pituitary axis to the inhibitory effects of 5 alpha-DHT or E2. 5 alpha-DHT-filled Silastic capsules that were 2, 4, or 8 mm long greatly reduced serum LH and FSH levels in castrates that were exposed to a nonstimulatory LD 8:16 light cycle, but not in animals exposed to a stimulatory LD 14:10 light cycle. E2 capsules that were 1, 2, 4, or 8 mm long greatly reduced serum LH and FSH levels in castrates exposed to LD 8:16, but not in animals exposed to LD 14:10. Serum gonadotropin levels were reduced in all of the animals receiving the larger 5 alpha-DHT (20 or 50 mm long) or E2 (20 mm long) capsules, irrespective of photoperiod. Thus, the photoperiod can alter the sensitivity of the gonadotropin control center to the negative feedback effect of both the 5 alpha-reduced derivative of testosterone, 5 alpha-DHT, and the aromatized metabolite of testosterone, E2. These results suggest that testicular secretions besides testosterone and/or extratesticular conversion of testosterone to its metabolites may be involved in the photoperiodic inhibition of the hamster reproductive system.

Animals↗
PubMed1981

Long-standing virilism in a woman with hyperplasia and neoplasia of ovarian lipidic cells.

A woman with bilateral hyperplasia of ovarian hilar cells, stromal lipidic cells (hyperthecosis), and unilateral adenoma of Leydig cells is described. Her clinical course was characterized by long-standing virilism with a recent exacerbation suggesting growth of a tumor from the hyperplastic stromal lipidic cells. Evidence for this hypothesis included similar light and electron microscopic features of the hyperplastic and neoplastic cells and identical patterns of secretion of steroid hormones. Comparison of the in vivo steroid biosynthesis of the hyperplastic lipidic cells with that of testicular Leydig cells showed several similarities. These included 1) secretion of 5 and delta 4 steroids; 2) greater secretion of the delta 4 hormones, progesterone and 17-hydroxyprogesterone, than of the delta 5 steroids, pregnenolone and 17-hydroxypregnenolone; 3) prominent secretion of testosterone but not androstenedione; and 4) limited secretion of estrogens, with estradiol as the principal estrogen. These findings support prior microscopic evidence that ovarian lipidic cells and testicular Leydig cells represent cells of common function and, likely, common origin.

Adenoma↗
PubMedDate not supplied

Altered testosterone feedback in pubertal male rats raised on reduced caloric intake.

A study was conducted to explore the hypothesis that reduced caloric intake increases the negative feedback efficacy of testosterone on gonadotropin secretion. Daily subcutaneous injections of testosterone propionate in oil were administered to either age-matched (37-day-old) or weight-matched (mean = 178 g) ad libitum-fed (control) or underfed rats that received 60% of normal daily food intake from the age of 20 days. Daily doses of testosterone propionate ranged from 25 to 400 micrograms/100 g body weight. Results indicate that reduced caloric intake increases the suppression of serum LH by testosterone propionate in both age-matched and weight-matched underfed rats. On the other hand, the response of serum FSH concentrations to testosterone propionate was affected by reduced diet only in the weight-matched animals. Results suggest that the increased negative feedback of testosterone on LH secretion is a specific diet-induced effect and not merely the result of reduced growth. The altered response in FSH secretion, however, may represent age-associated changes in sensitivity to testosterone rather than diet-induced effects.

Animals↗