The morphology and in-vivo function of the Leydig cells were studied in rams when spermatogenesis had been disrupted by a single exposure of the testes 20 days earlier to a temperature of about 42 °C for 45 min. To avoid complications due to changed negative feedback from the testes to the pituitary with consequent changes in the degree of gonadotrophic stimulation, ten of the animals (five heated and five unheated) were surgically hypophysectomized when the testes were heated and then treated twice daily with pituitary extract. Six intact rams (three heated and three unheated) were also studied. The heat-affected testes were about half the size of the unheated testes, and blood plasma flow was closely related to testis weight. There were no differences in the testosterone concentrations in spermatic venous blood, testicular lymph or rete testis fluid, or in oestradiol in spermatic venous plasma from heated or unheated testes. Consequently, testosterone secretion by the heat-affected testes was markedly reduced, and the concentrations in jugular blood were also lower in the heat-affected rams than in controls. The volume of the interstitial tissue was less in absolute terms in the heat-affected rams, but it made up a greater fraction of the testes. The absolute volume of the blood plus lymph vessels, and their fraction of the interstitial tissue were lower in the heat-affected testes, although there was no effect on their volume as a fraction of the whole testis. The heat-affected testes of the hormone-treated rams had fewer Leydig cells, but each cell was larger; no equivalent difference was found in the intact rams. However, the dose of pituitary extract chosen was somewhat excessive, as there were higher than normal concentrations of FSH, LH and testosterone in jugular blood plasma, of testosterone and oestradiol in testicular venous blood plasma and of testosterone in rete testis fluid in the hormone-treated hypophysectomized rams. The testes of the unheated hypophysectomized rams increased in size by about 20% during treatment with pituitary extract, although testicular blood plasma flow was lower per unit weight of testis. The absolute volume of each Leydig cell and the total volume in absolute terms and as a fraction of the interstitial tissue was greater in the hormone-treated than in the untreated rams, but not the volume as a fraction of the whole testis. The total number of Leydig cells was higher in the hormone-treated unheated rams than in all the other rams taken together. It would therefore appear that when spermatogenesis was disrupted following heating of the testes and the gonadotrophic stimulation was kept constant, the Leydig cells underwent hypertrophy, presumably because of a change in the secretion of paracrine factor(s) by the tubules. However, there was also a decrease in testosterone secretion, which was closely related to decreases in blood plasma flow through the testes, and bore little or no relation to the number, total volume or size of the Leydig cells, or the concentration of testosterone in the testicular venous blood.
Journal of Endocrinology (1991) 131, 101–112
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