Developmental changes and differential regulation by testosterone and estradiol of growth hormone receptor expression in the rabbit

Abstract

To investigate the effects of testosterone and estradiol (E2) on growth hormone receptor (GH-R) gene expression, we measured GH-R mRNA levels in relation to the changes of sex steroid concentrations in the normal male rabbits aged 1-12 months and after administration of testosterone or E2 to castrated male rabbits. In the normal animals. E2 levels were below the detection limit in all age groups, and testosterone levels were below the detection limit at 1 month, increased at 2 months and reached the plateau of the adult levels after 4 months. Liver GH-R mRNA levels were low at 1 month, reached a peak at 2 months and then decreased slightly thereafter. In the castrated animals, liver and growth plate GH-R mRNA levels were increased in the testosterone-treated group (162.0 ± 12.0%, p <0.025; 128.4 ± 7.6%; p< 0.025) and reduced in the E2-treated group (29.6 ± 6.2%, p < 0.005; 53.6 ± 11.3%, p < 0.025). Sex steroid administration did not result in any significant change in GH-R mRNA levels