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.