Changes in the messenger ribonucleic acid for insulin-like growth factor- I and -II in the porcine testis during and between two waves of testicular development

The boar testis was used as a model for examining the possible role of production of the insulin-like growth factors (IGF) in steroidogenesis and/or testicular growth as testicular development occurs in waves. Blood and testes were sampled from boars at different ages (100-102 days of gestation; 7, 19, and 30 days; and 10 and 25 wk), selected to occur during and between the last two waves of testicular development. Serum was analyzed for testosterone and RNA was extracted from the testes for Northern and dot-blot analysis of IGF mRNA. Testosterone concentrations declined (p = 0.01) from 7 days to 10 wk of age and rebounded at 25 wk, indicating completion of the second and third waves of testicular development. The quantity of testicular mRNA for IGF-I increased gradually with age, and that for IGF-II decreased. We therefore conclude that regulation of the expression of the mRNAs for IGF-I and -II in the pig testis is not a function of either the waves of testicular development or the level of steroidogenesis.