RECOMBINANT GROWTH-HORMONE AND INSULIN-LIKE GROWTH-FACTOR-I DO NOT ALTER GONADOTROPIN STIMULATION OF THE BABOON TESTIS IN-VIVO

In vitro studies indicate a physiological role for insulin-like growth factor I (IGF-I) in paracrine regulation of testicular function and r ecent clinical studies suggest a potential role for growth hormone (GH ) and/or IGF-I in the treatment of hypogonadotrophic states in males. This study aimed to examine the effects of pretreatment with recombina nt human GH (rhGH) or rhIGF-I on the response to gonadotrophins of the non-human primate testis in vivo. Using a balanced Latin square desig n with repeated measures, six prepubertal male hamadryas baboons (Papi o hamadryas hamadryas) were treated in a cross-over sequence for perio ds of 18 days with daily im injections of rhGH (0.4 IU.kg(-1).day(-1)) , rhIGF-I (0.1mg.kg(-1).day(-1)) or saline with a 2-week washout perio d between each treatment. A single im injection of hCG (1500 IU) incre ased serum testosterone (p = 0.0002) but neither rhGH nor rhIGF-I infl uenced the timing or magnitude of this response (p > 0.5). A single im dose of FSH (75 IU) stimulated immunoreactive inhibin (p = 0.01) but also was unaffected in magnitude or timing by pretreatment with rhGH o r rhIGF-I (p > 0.2). Circulating IGF-T levels were increased independe ntly by hCG (p = 0.01) and FSH (p < 0.0001) administration. These find ings indicate that neither GH nor IGF-I pre-treatment enhance acute go nadal responses to gonadotrophin stimulation of the prepubertal non-hu man primate testis in vivo. These findings suggest that GH or IGF-I tr eatment of hypogonadotrophic men without somatotrophin deficiency is u nlikely to be beneficial.