Abstract: 63

IN VIVO EFFECTS OF LUTEINIZING HORMONE ON TESTICULAR ENDOCRINE FUNCTION IN GROWTH HORMONE RECEPTOR GENE DISRUPTED MICE.

V. Chandrashekar^{1 *}, A. Bartke,^{1 *}, JJ. Kopchick²
Departmet of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, ¹
Department of Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Athens, Ohio. ²

A number of in vitro studies have shown that insulin-like growth factor-I (IGF-I) influences testosterone (T) secretion. However, the in vivo role of IGF-I in the control of Leydig cell function is poorly understood. Growth hormone gene knockout (GHR-KO) mice with IGF-I deficiency are good experimental animals to assess the in vivo role of IGF-I in testicular endocrine function. Therefore, groups of adult GHR-KO mice and their normal siblings were divided into two subgroups (7-9 mice/subgroup) and were treated ip with either saline or oLH (0.3 µg/g BW; NIH-26) in saline. One hour later, blood was obtained via heart puncture. Plasma IGF-I, LH, androstenedione (A-dione) and T levels were measured by RIAs. Unlike in normal siblings, IGF-I was not detectable in circulation in GHR-KO mice. Plasma LH, basal and LH-induced A-dione secretions were similar in GHR-KO mice and in their normal siblings. The basal circulating T levels were also not different in GHR-KO mice than in normal animals. Treatment with LH significantly (p<0.001) increased plasma T levels in both groups of mice. However, this plasma T response to LH treatment was significantly (p<0.01) attenuated in GHR-KO mice. This suggests that within the testes of GHR-KO mice, the key enzyme, 17-hydroxysteroid dehydrogenase that converts A-dione to T is defective and/or less responsive to exogenous LH. This indicates that IGF-I is required for the normal LH action on Leydig cell function and IGF-I plays an important role in testicular steroidogenesis in mice. Our previous study has shown that GHR-KO mice are hyperprolactinemic (Endocrinology, in press). Therefore, chronic hyperprolactinemia might have also contributed to the attenuated LH effect on T secretion in GHR-KO mice (Supported by NIH Grant HD-20001).

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.