Pituitary and testicular function in growth hormone receptor gene knockoutmice

The role of GH in the control of pituitary and testicular function is poorl y understood. GH receptor gene knockout (GHR-KO) mice were recently produce d. As these mice are good experimental animals to assess the influence of t he effects of GH and insulin-like growth factor-I (IGF-I), the present stud ies were undertaken. Young adult male GHR-KO mice and their normal siblings were tested for fertility and subsequently injected tip) with saline or Gn RH (1 ng/g BW) in saline. Fifteen minutes later, blood was obtained via hea rt puncture. Plasma IGF-I, PRL, LH, and testosterone concentrations were me asured by RLAs. In addition, the testicular testosterone response to LH tre atment was evaluated in vitro. The results indicate that the absence of GH receptors (GHRs) was associated with an increase (P < 0.005) in plasma PRL levels, and circulating IGF-I was not detectable. Although the basal plasma LH levels were similar in GHR-KO mice relative to those in their normal si blings, the circulating LH response to GnRH treatment was significantly (P < 0.001) attenuated. Plasma testosterone levels were unaffected by disrupti on of the GHR gene. However, basal (P < 0.01) and LH-stimulated (P < 0.001) testosterone release from the isolated testes of GHR-KO mice were decreased . The rate of fertility in GHR-KO male mice was also reduced. These results indicate that the lack of GHRs (with GH resistance and lack of IGF-I secre tion) induces hyperprolactinemia and alters the effect of GnRH on LH secret ion as well as testicular function. Thus, GH and IGF-I influence pituitary and gonadal functions in male mice.