Effects of growth hormone and insulin-like factor 1 on testosterone secretion in premature male rats

Growht hormone (GH) and Insulin-like growth factor-1 (IGF-1) may be related to the secretion of gonadal hormones. Some reports show that GH therapy promoted puberty. It seems that GH and its related factors such as IGF-1 enhance the promotion of puberty by increasing leydig cells’ ability to secret testosterone. With regard to the high percentage of people with gonadal hormonal disease in the present study, the effects of GH and IGF-1 on the stimulation of gonads for testosterone production in premature male rats were observed. Premature wistar rats in 10 separate groups were studied. GH, IGF-1 and HCG were injected intraperitoneally together as separately. On the other hand, one mL of leydig cell suspensions that had been extracted from the testis of the four groups of the rats was incubated with GH, IGF-1 and HCG together or separately. Blood samples were collected from the treated rats and testosterone concentrations were estimated in the serums. Testosterone concentrations in treated leydig cell suspensions were also measured. GH administration increased the testosterone production (p=0.001) but GH together with IGF-1 and HCG did not significantly increase the secretion of testosterone in the rats. Injection of IGF-1 and hCG reduced the testosterone production compared with those received hCG alone (p=0.02). Leydig cells incubated with GH secreted more testosterone (p<0.0001). Testosterone secreted by the cells incubated with IGF-1 or GH and IGF-1 was increased but was not different (p<0.001). It seems that the direct effect of GH on testosterone production is more than its indirect effect through hypothalamus. LH (or HCG) is a major hormone in testosterone production and promotion of puberty, conversely, IGF-1 has no significant effect on the testosterone secretion.