Testicular steroidogenesis in the rhesus monkey (Macaca mulatta

A simple technique for collecting blood of testicular origin: application to in vivo studies on testicular steroidogenesis in rats and Macaca fascicularis

A technique for rapidly collecting blood of testicular origin is described, one which can provide sufficient plasma amounts to investigate some steps of testicular steroid biogenesis in vivo in 2 species. In adult male rats, testosterone (T), androstenedione (4A) and 5-androstenediol (5AD) were determined in pampiniform plexus testicular venous blood (PPTV) and peripheral (PV) blood samples before and 2 h after human Chorionic Gonadotropin (hCG). PPTV concentration of 5AD was 0.83 +/- 0.1 ng/ml (mean +/- SEM) with a PPTV/PV ratio of 7.0 +/- 1.0, comparable to a PPTV/PV ratio for 4A of 5.8 +/- 1.8. After hCG, PPTV concentration of 5AD significantly increased to 1.28 +/- 0.15 ng/ml (P less than 0.05). Those data are in favor of a participation of 5-ene pathway to testicular biogenesis of T associated to a 4-ene pathway which is predominant. In adult male Macaca fascicularis, spermatic vein (SV) concentrations of 5AD and 4A were comparable (3.0 +/- 1.2 vs 4.3 +/- 1.0 ng/ml) as well as SV/PV ratios under basal conditions (3.5 +/- 0.9 vs 5.1 +/- 0.1), as well as 48 h after hCG, confirming in vivo that both 5-ene and 4-ene pathways are involved in testicular T biogenesis. Testicular production of estradiol (E2), estrone (E1) and their sulfates E2S and E1S showed a SV/PV ratio significantly higher than 1 (3.4 +/- 0.6; 2.4 +/- 0.1; 1.7 +/- 0.2 and 1.6 +/- 0.2, respectively).

In vitro 16 alpha-hydroxylation of progesterone by testes of crab-eating monkey (Macaca irus): a characteristic of primates?

Radioactive 16 alpha-hydroxyprogesterone was obtained as one of the major metabolites of [14C]pregnenolone and progesterone by testicular homogenates of an adult crab-eating monkey (Macaca irus). 16 alpha-hydroxylation of progesterone occurred by incubation of testes of men and and the monkey, but not by those of rodents and other vertebrates examined.

Steroidogenesis in the monkey testis: relationship of enzyme organization to endogenous steroids, steroidogenesis and gonadotropin treatment

To explore testicular factors which determine steroidogenesis, circulating and intratesticular steroid levels were measured and in vitro steroidogenesis in testicular mines and microsomes was investigated using adult rhesus monkeys before and after treatment with pharmacological doses of hCG or hCG together with hMG. After gonadotropin treatment serum and intratesticular levels of 17 alpha-hydroxyprogesterone as well as end product testosterone were markedly elevated. Dynamic studies revealed that 17 alpha-hydroxyprogesterone produced from pregnenolone was partly metabolized to C19-steroids but almost no 17 alpha-hydroxyprogesterone produced from progesterone was utilized by C17-20 lyase. Androstenedione levels increased in serum after both treatments and were elevated in testis tissue after hCG treatment. Androstenedione accumulated in vitro during incubation of untreated and hCG-treated testes with [3H]pregnenolone and [14C]progesterone. The major portion of the accumulated androstenedione was produced from pregnenolone through dehydroepiandrosterone rather than through 17 alpha-hydroxyprogesterone, indicating differential availability of androstenedione to 17 beta-hydroxysteroid oxidoreductase according to its origin. The 3H/14C ratio in product androstenedione was much greater than the ration in product testosterone in both untreated and hCG-treated testis; in testes of animals treated with hCG together with hMG, the ratios in both products were closely linked. Among the enzymes examined, 17 alpha-hydroxylase and C17-20 lyase activities for 5-ene-C21-steroids were increased and 17 beta-hydroxysteroid oxidoreductase activity were decreased by gonadotropin treatment. Our findings confirm the phenomenon of unequal substrate availability to enzymes depending upon the provenance of the substrate and demonstrate that gonadotropin(s) change substrate availability as do direct changes in enzyme activities. The unequal substrate availability validates the assumption, previously proposed by others, that microsome enzymes have an organized arrangement as enzyme complexes.

Seasonal changes in steroidogenesis in the testis of the rhesus monkey (Macaca mulatta)

To investigate the influence of seasonal changes from breeding to nonbreeding season on testicular steroidogenesis in the adult rhesus monkey, two animals were hemiorchidectomized in November and the second testis of each was removed the following April. Intratesticular steroid concentrations related to the formation of testosterone from pregnenolone were measured by radioimmunoassay. Related steroidogenic enzyme activities were also assayed and dynamic studies of the bioconversion of radiolabeled precursor steroids by testicular microsomes were performed. Testosterone was synthesized from pregnenolone through both dehydroepiandrosterone and 17 alpha-hydroxyprogesterone. No distinct differences were found in the testosterone biosynthetic pathway between testes in breeding and nonbreeding seasons. In the breeding season, intratesticular testosterone concentrations, the sum of intratesticular steroids measured, and the ratio of testosterone to the steroid sum were increased when compared to those in the nonbreeding season. No major seasonal changes in microsome enzyme activities were found, although enzyme activities, except for delta 5-3 beta-hydroxysteroid dehydrogenase for C21-steroids, were slightly higher in the breeding season. We conclude that increased testosterone production in the testis during the breeding season is due primarily to increased pregnenolone supply from Leydig cell mitochondria and, to a lesser extent, to an enhanced pregnenolone bioconversion to testosterone in the microsomes.