Functional relevance of luteinizing hormone receptor in mouse uterus

Abstract

Mukherjee D, Manna PR, Bhattacharya S. Functional relevance of luteinizing hormone receptor in mouse uterus. Eur J Endocrinol 1994;131:103–8. ISSN 0804–4643 The presence of high-affinity luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors has been reported in porcine, rabbit, rat and human uteri. We have demonstrated binding of [125I]LH to mouse uterus, which was saturable. Scatchard plot analysis indicated Kd to be 1.37 × 10−10 mol/l and the maximum binding capacity to be 5.24 nmol/kg protein. Attempts have been made to observe the functional relevance of gonadotropin receptor in the mouse uterus. The size and weight of the uterus remarkably decreased as a result of ovariectomy; administration of LH to ovariectomized (OVX) mice significantly increased the uterine weight in comparison to the OVX control (p < 0.01), indicating a direct effect of LH on the uterus. There was a two-fold decrease of uterine ascorbic acid content in LH-treated OVX mice as compared to the intact control. The gain in uterine weight of OVX mice by LH was due to the increase in uterine protein synthesis. The stimulatory effect of LH on OVX mice uterus appears to be mediated via steroid hormones because it significantly augmented uterine mitochondrial steroidogenesis. Since 17β-estradiol (E2) is known to stimulate uterine protein synthesis, the circulatory level of E2 was determined in intact, OVX and OVX + LHtreated mice. A fall in the circulatory level of E2 occurred in OVX mice as compared to the control, while treatment of LH for 7 days (three injections) significantly elevated E2 levels in OVX mice (p < 0.001). This higher level of E2 in OVX mice remains unaltered on adrenalectomy, indicating that adrenals are not the source for increased E2 levels. Data therefore imply that LH can stimulate uterine E2 formation. Results from an in vitro incubation of uterine tissue from intact, OVX and OVX + LHtreated mice showed that ovariectomy caused a sharp drop of E2, while treatment with LH significantly increased E2 release and the uterine contents. Hence, it may be suggested that LH has a direct effect on the uterus of OVX mice: by occupying a high-affinity binding site it stimulates steroidogenesis, resulting in higher E2 formation, which, in turn, dramatically increases uterine weight by stimulating protein synthesis. S Bhattacharya, School of Life Science, Department of Zoology, Visva-Bharati University, Santiniketan 731 235, West Bengal, India