Growth hormone receptors in the porcine testis during prepuberty

Supplementation of exogenous growth hormone (GH) during prepuberty advances onset of spermatogenesis in boars, but the mechanism of action is unknown. The present study is an investigation of the presence and characteristics of testicular growth hormone receptors (GHR). A total of 36 boars were castrated, three boars every 10 days, between the ages of 10 and 120 days. Testicular membrane preparations of 10, 20, 30, 50, 70, 100 and 120-day-old boars were used to determine ¹²⁵I-bGH binding and Scatchard analysis. Liver from a 60-kg barrow was used for comparison. Specific ¹²⁵I-bGH binding to testicular membrane preparations occurred in all age groups with the exception of 20-day-old boars at levels of 30-40% of liver binding. At 30 days of age the unlabelled bGH at 1.1 ng/tube achieved half maximal inhibition (ID₅₀). Results of Scatchard analysis indicated a single class of binding sites. Binding affinity was 2.89 x 10⁹ M with a binding capacity of 12 fmole/mg membrane protein. The results from this study suggest that GH may act directly on the cells of the prepubertal boar testis.