Growth hormone (GH) regulation of circulating insulin-like growth factor-I levels during sexual maturation of the GH-deficient dwarf (dw/dw) male rat.

In many mammalian species, circulating levels of insulin-like growth factor-I (IGF-I) rise during puberty. Previous studies manipulating testosterone levels in rats with normal GH secretion suggested that the pubertal IGF-I rise is regulated by an interaction between GH and sex steroids. Therefore, in a reciprocal study, IGF-I levels were examined during sexual maturation of the GH-deficient dwarf (dw/dw) rat which has a selective genetic deficiency of GH but normal sex steroid levels. Male dw/dw rats were treated with daily injections of recombinant human GH (200 μg/100 g body weight) or saline vehicle, from 28 to 70 days of age