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The differentiation of rat seminiferous tubules have been studied in 13 to 19 days old. Testicular weight and tubular cross-sectional area were more than doubled during this period. The percentage of tubules with more than 10 primary spermatocytes increased from 4% to 90%, and the lanthanum excluding ability of the inter-Sertoli cell junctions (the blood-testis barrier) showed a similar increase but two days later. ABP production in vitro increased more than twentyfold from day 13 to day 19 of age. It is concluded that the differentiation of Sertoli cell function and the appearance of primary spermatocytes are temporally correlated which supports the assumption that the function of the Sertoli cells is important for initiation and maintenance of spermatogenesis.

Using a new experimental model of cryptorchism in rats, where testicular descent was prevented, testicular development and function were studied in bilateral and unilateral cryptorchid animals Morphometric and radioimmunological techniques were used. Up to 30 days after birth testicular development was identical in the two types of abdominal testes but in adult rats differences were observed. In these rats spermatogenesis was damaged to a similar extent, but total tubular length and testicular weight were increased in the bilateral abdominal testes. Moreover, in these testes, the volume density of Leydig cells, the total Leydig cell mass, the average Leydig cell size and the testis testosterone concentration were larger than in unilateral abdominal testes. It is suggested that the impaired spermatogenesis seen in both kinds of abdominal testes may be unrelated to Leydig cell function.

Exposure of one or both testes of rats to heating at 43 degrees C for 30 min resulted in a significant reduction in blood flow per testis, as measured using microspheres. The effects on the testes of unilateral and bilateral heating were similar, although the changes in FSH levels in peripheral blood were in general less marked after unilateral heating. Testicular blood flow fell, along with testicular weight, beginning at 2-4 days and reaching minimum values 14-21 days after heating. Both blood flow per testis and testicular weight were beginning to recover 35 days post-heating and blood flow per testis was normal by 56 days following heat treatment, although testicular weight was still slightly reduced at that time. Heating one or both testes to 42 degrees C produced similar but smaller responses 21 days later, whereas temperatures of 41 degrees C or lower were without effect on the parameters measured, except for some rises in serum LH and FSH. With slight reductions in blood flow, there were corresponding increases in testicular venous testosterone concentration so that testosterone secretion was unaffected. Further reductions in blood flow at 14 and 21 days after heating to 43 degrees C were not fully compensated by an increase in the concentration of testosterone in testicular venous blood, with the result that testosterone secretion fell.

Prostaglandin F2α (PGF2α) incorporated in Silastic-PVP tubes 2 cm long and one end sealed induced temporary sterility when placed intrascrotally in fertile male rabbits. A significant reduction in sperm number per ejaculate, testicular weight and the number of epididymal sperm accompanied the incidence of sterility which occurred 2–5 weeks after starting the treatment and persisted for 6–10 weeks. During the experimental period, no significant deviation in libido or ejaculate volume compared to sham controls was observed. Prostaglandin F2α might have a local effect on the testis and epididymis, causing disintegration and depletion of the sperm reserve resulting in temporary sterility.