CATECHOLAMINES STIMULATE TESTICULAR STEROIDOGENESIS INVITRO IN THE SIBERIAN HAMSTER, PHODOPUS-SUNGORUS

We have examined direct effects of catecholamines on testicular testosterone production in a seasonally breeding species, the Siberian hamster, Phodopus sungorus. Testicular parenchyma from gonadally active long photoperiod (LD)-exposed and gonadally regressed short photoperiod (SD)-exposed animals was incubated for 6 h with norepinephrine, epinephrine, beta-adrenoreceptor agonist isoproterenol, or alpha-adrenoreceptor agonist phenylephrine (all at 10 muM), as well as with various concentrations of norepinephrine (10 nM-10 muM), and 10 muM norepinephrine with or without hCG (0.7, 3.1, and 12.5 mIU/ml). In addition, effects of alpha-adrenoreceptor antagonist prazosin and beta-adrenoreceptor antagonist propranolol (50 muM) were tested in the incubations containing 10 muM norepinephrine. In the incubations of testes from both LD and SD Siberian hamsters, norepinephrine was most effective in stimulating testosterone production, followed by epinephrine and phenylephrine, while isoproterenol failed to increase testosterone accumulation. The stimulatory effects of norepinephrine were dose-dependent and were prevented by coincubation with prazosin, but not affected by coincubation with propranolol. In combination with various doses of hCG, norepinephrine failed to stimulate testosterone production above the levels obtained with hCG alone. These data indicate that the testicular receptors mediating the action of catecholamines on testicular steroidogenesis in Phodopus sungorus are of the alpha 1-subtype, a result in accordance with a previous study in the golden hamster. However, the results of the present study are strikingly different from the findings obtained in the golden hamster in terms of the effects of photoperiod on the responsiveness of testicular steroidogenesis to catecholamines. Thus, in the golden hamster, the seasonal photoperiod-related transition from gonadal activity to quiescence is accompanied by an acquisition of responsiveness of testicular steroidogenesis to catecholamines. In contrast, the testes of both LD-exposed and SD-exposed testes of Phodopus are equally able to respond to catecholaminergic stimuli. However, this catecholamine effect may be of only minor importance in the LD animal, in which hCG has a very strong stimulatory action on testosterone production with increases 70-90-fold over basal levels, while the effects of catecholamines are an order of magnitude smaller. In contrast, in the incubations of testes from SD animals, the stimulatory action of hCG (approximately 5-10 times basal values) was in the same range as the effect of norepinephrine (4 times basal production). Thus, the relative impact of catecholaminergic stimuli in the SD testis is by far greater than in the LD testis. Perhaps catecholaminergic input in the testis could be viewed as a back-up system for LH during the time of physiological suppression of LH release. Moreover, regardless of the functional state of the testis, catecholamines may participate in the regulation of testosterone production in the Siberian hamster by exerting a constant ''fine-tuning'' effect on testicular Leydig cells, which could be either direct or indirect via paracrine interactions with Sertoli cells or other testicular cell types.