Effect on gonadotrophin secretion of blockage of the ductuli efferentes in the normal and androgen-deprived rat

Leydig cell function in the pubertal rat following local testicular irradiation

Dose- and time-response relationships were measured after irradiation of the pubertal rat testis with between 1 and 20 Gy of 300 kVp X-rays. The threshold dose for Leydig cell dysfunction was about 5 Gy. Dysfunction after higher doses was observed by 2 weeks post-irradiation as a dose-dependent decrease in serum testosterone (T) concentrations, and the levels were undetectable after 15 or 20 Gy. Despite the recovery of serum T by 24 and 36 weeks, dysfunction of the Leydig cell population was still observed as an increase in luteinizing hormone (LH) secretion (1.5 to 2-fold increase after 15 or 20 Gy at 24 weeks; 2 to 3-fold increase after 10 or 20 Gy at 36 weeks). The endocrine changes were probably due to the observed loss of Leydig cells following irradiation. These results indicate that the Leydig cells of pubertal rats are more radioresponsive than those of the adult.

Dose and time relationships in the endocrine response of the irradiated adult rat testis

The dose- and time-dependent responses for the interstitial and tubular compartments in irradiated adult rat testes are described. Leydig cell dysfunction, as indicated by increased serum LH (to a maximum of 385% of control after 5 Gy) and decreased serum T (to a minimum of 30% of control after 10 Gy), was observed at 8 weeks postirradiation. Subsequent recovery of Leydig cell function was then observed, so that after 9 months serum T was normal but LH was still marginally elevated. The dysfunction, with a threshold of about 4 to 5 Gy, was associated with a loss of Leydig cells from the testis. Spermatogenic damage was observed; after doses of 3 Gy and above a marked dose-response was recorded as assessed by counts of tubule cross sections exhibiting spermatogenesis. Reduced serum levels of androgen binding protein indicated Sertoli cell dysfunction at 8 weeks after 3 Gy and above, with values of less than one half of those seen in the controls. Serum FSH also was elevated to between 150% and 200% of control, and after 9 months closely reflected androgen binding protein changes. Unlike the Leydig cell, no recovery with time was observed for this aspect of Sertoli cell function.

Dose and time related responses of the irradiated prepubertal rat testis. II. Seminiferous epithelial function

Dose-related effects of radiation upon the seminiferous epithelium were examined in the prepubertal rat. Marked damage to the spermatogenic cell populations was produced by doses of 5 Gy and above. As a result serum levels of FSH were increased, maximum changes being observed at 2 weeks, but levels remaining high even at 36 weeks after irradiation. Serum levels of androgen binding protein (ABP) were inversely related to serum FSH. Above a threshold dose of 5 Gy, serum ABP levels were reduced to between 30-50% of control values, possibly indicating damage to the Sertoli cells. Progression in the degree of testicular failure was indicated at 36 weeks after a dose of 15 Gy by further increases in serum gonadotrophins when compared to earlier times and by the absence of spermatogenesis.

Dose and time related responses of the irradiated prepubertal rat testis. I. Leydig cell function

The testes of prepubertal rats were locally irradiated with 300 kVp x-rays to doses of between 1 and 15 Gy. Leydig cell function was assessed between 2 and 36 weeks post-irradiation. Dysfunction was observed at two weeks as evidenced by a reduction in serum levels of testosterone to between 40 and 70% of control, with a threshold dose of about 5 Gy. Endocrine deficiencies in the Leydig cell population were indicated at later times by increased serum levels of LH, although serum testosterone concentrations recovered to control levels. The elevations in serum LH increased with time suggesting progressive Leydig cell failure.

The release of pituitary gonadotrophins by luteinizing hormone releasing hormone in the intact, castrated and aspermatogenic rat

The change in serum gonadotrophin concentration in response to synthetic Luteinizing Hormone Releasing Hormone (LHRH - 400 ng i.v.) was investigated under barbiturate anaesthesia in adult male rats either chronically castrated, rendered aspermatogenic by the administration of alpha-chlorohydrin 12-16 weeks previously (to remove inhibin), or treated with vehicle. A single injection of LHRH increased serum LH and FSH concentrations similarly in both intact and aspermatogenic rats. In castrated rats the amount of LH released was much greater and the FSH secretion sustained. A second injection produced a similar increase although a second peak of FSH could not be detected in castrated rats as the FSH level was still elevated. The increase in LH levels was two to three times larger in response to the second injection of LHRH than to the first in all groups. The results do not support the hypothesis that the enhanced gonadotropin response to castration in the aspermatogenic rat is due to increased pituitary sensitivity to LHRH.

Vasculature of the mouse, rat, and rabbit testis-epididymis

The arrangement of blood vessels serving the testis-epididymis vas investigated microscopically in the mouse, rat, and rabbit. Blood vessels were visualized by infusing liquid silicone rubber into the vessels and subsequently clearing the surrounding tissue. Comprehensive illustrations of the vasculature were prepared from three-dimensional examinations. Arterial and venous vessels serving the testis-epididymis follow similar routes in all three species. However, the arrangements and characteristics of the blood vessels demonstrate dramatic species differences. For example, arteries within the testes have tight coils in the mouse and artery-artery anastomoses in the rat. Veins form vascular pathways that connect the testis and efferent ductules in all three species but also form a connection between the testis and cauda epididymidis in the rabbit only. Testosterone concentrations were determined in blood obtained by micropuncture of selected testis-epididymal veins. The measurements establish that the highest levels of testosterone are found in testicular surface veins. Also, vas deferential veins of the rabbit had significant amounts of testosterone. Studies of the blood-vessel volumes suggested that the volumes of arteries and veins in the testis are similar, whereas venous volumes exceed arterial volumes in all of the other organs examined. The studies provide comprehensive information about the architecture and physiology of blood vessels serving the testis-epididymis in the mouse, rat, and rabbit. Each species exhibits diversity in the vasculature and testosterone content of the veins. Veins connecting the testis to the efferent ductules and cauda epididymidis may provide for the preferential delivery of testicular secretions to androgen-dependent organs before the secretions are metabolized or diluted in the systemic blood.