A NOVEL ROLE FOR TESTICULAR DESCENT - TEMPERATURE-DEPENDENT INDUCTION OF PERTUSSIS-TOXIN-SENSITIVE G(I) PROTEIN FUNCTION IN POSTNATAL RAT LEYDIG-CELLS

The role of temperature and testicular descent in postnatal appearance of inhibitory guanine nucleotide-binding regulatory protein (G(i)) function was studied in the rat testis. Dispersed testicular cells of 5-day-old rats were incubated for 24 h at: 32 or 37 C, then for another 24 h at the same temperatures in the presence and absence of pertussis toxin (PT; 100 mu g/liter), and finally for a third 24-h period with cholera toxin (CT; 500 ng/liter) with or without PT. At both temperatures, PT treatment significantly (P < 0.05) increased the CT-stimulated cAMP output, but had no effect on basal cAMP production. When testosterone (T) production, as an indicator of Leydig cell function, was measured in the same incubation, CT-stimulated T production was greater at 32 C, but PT had no effect at either temperature. A similar finding was made when hCG (10 mu g/liter), instead of CT, was used as the stimulus of T production. Hence, a functional G(i) protein is present in seminiferous tubules of 5-day-old testes cultured for 3 days at 32 and 37 C, but not in Leydig cells. We then examined the effects of longer exposure of 5-day-old testes to the two temperatures. After culture for 7 days with 0.1 mu g/liter ovine LH, the presence of PT at 32 C significantly (P < 0.01) enhanced CT-stimulated T production during the last 24 h of culture, but the PT effect was not observed when the culture was carried out at 37 C. Hence, G(1)-mediated modulation of Leydig cell function appears to require several days of induction at the lower temperature of 32 C. As the postnatal descent also changes the ambient testicular temperature, we next studied whether this event alters the G(i) protein function of Leydig cells. Five-day-old rats were rendered bilaterally cryptorchid or sham operated, and studied after 12 days. Testis weights did not differ between the abdominal and scrotal testes. In contrast, the basal and hCG-stimulated rates of T production were significantly (P < 0.01-0.05) higher in the scrotal testes. When dispersed cells of the scrotal and abdominal testes were incubated for 24 h at 37 C in the presence of CT with or without PT, enhancement of T production by PT was only observed in cells of the scrotal testes. Immunohistochemical studies on frozen testicular sections showed that the G(i)1/2 and G(i)3 proteins were detectable in the same fashion in testes of 1- and 16-day-old rats in both Leydig cells and seminiferous tubules, including the Sertoli cells. Hence, there is immunoreactive G(i) protein in neonatal Leydig cells, but it is apparently unresponsive to PT inactivation. In conclusion, this study reveals a new role for testicular descent in the postnatal acquisition of PT sensitive G(i) protein modulation of Leydig cell steroidogenesis.