Effects of bovine, human and rat growth hormones on immature hypophysectomized rat testis

In this study we have compared the effects of the homologous rat growth hormone with its human and bovine counterparts on the testicular development of immature hypophysectomized rats, after 7 days of treatment. Each hormone increased (12- to 13-fold) the body weight gain and IGF-I blood level (12- to 16-fold). Human GH increased testis weight (1.3-fold) the pregnenolone production (4-fold), the LH dependent steroidogenesis (7-fold), the aromatase activity (5-fold), the concentration of LH receptors (1.6-fold) and spermatogenesis. Bovine and rat growth hormones had marked effects only on pregnenolone production (2- to 3-fold). Incorporation of 5-bromodeoxyuridine in testicular cells after hGH treatment was positive (0.47 per 100 cells), an effect which was 2-fold higher than those produced by bovine and rat GHs (0.25 per 100 cells). These results have led us to conclude that the in vivo action of rat growth hormone on rat testis is comparable to bovine GH and thus might be considered as purely somatogenic. In addition to the known effects on growth promotion, rat GH affected the rate limiting step of steroidogenesis and the Leydig cell multiplication.