MYOMETRIAL LH HCG RECEPTORS DURING THE ESTROUS-CYCLE AND PREGNANCY INPIGS/

Receptors for luteinizing hormone/human chorionic gonadotropin (LH/hCG ) have been identified in porcine, rabbit, rat, and human myometrium. To determine the estrous cycle and pregnancy related changes in the re ceptor capacity and affinity, radioreceptor assays were performed with membrane homogenates of porcine uterine tissues. Cycling gilts were d ivided into four experimental groups: I (n = 6), day 1-2; II (n = 5), day 6-7; m (n = 5), day 11-12; and IV (n = 6), day 18-20 of the estrou s cycle. Pregnant pigs were divided into three experimental groups: I (n = 5), day 35-40; II (n = 5), day 65-70; and m (n = 4), day 95-105 o f pregnancy. The concentrations [femtomoles/mg protein (fmol/mg protei n)] and affinities of unoccupied LH/hCG binding sites were characteriz ed in all samples of myometrium. Receptor concentrations were highest (P < 0.01) in groups II and III (19.3 +/- 2.5 and 35.8 +/- 2.1 fmol/mg protein, respectively), and was lowest in groups I and IV (5.3 +/- 1. 4 and 7.5 +/- 0.7 fmol/mg protein, respectively). Receptor affinity co nstants (K-a) were consistent (P > 0.05) throughout the estrous cycle [I, (5.1 +/- 1.5) x 10(9); II, (3.0 +/- 0.8) x 10(9); m, (3.2 +/- 0.9) x 10(9); IV, 5.5 +/- 0.7 x 10(9) lm(-1)]. Plasma hormone concentratio ns of progesterone, estrogen and LH were typical of values noted at th ese times. During pregnancy, receptor concentrations were greatest (P < 0.05) in group II (85.4 +/- 18.5 fmol/mg protein). In groups I and m receptor numbers were 10.8 +/- 2.3 and 26.7 +/- 6.6 fmol/mg protein, respectively. The K-a in group I was 10 times greater (P < 0.05) than K, in groups II and III, (I, 3.1 +/- 0.9 x 10(10) lm(-1); II, 3.4 +/- 0.3 x 10(9) lm(-1); m, 3.3 +/- 1.1 x 109 lm(-1)). Plasma hormone conce ntrations typically found during pregnancy were noted. The function of these LH/hCG binding sites remains unknown; however, changes in recep tor capacity during the estrous cycle and pregnancy support a role for modulation of the receptor by hormonal factors. (C) 1998 Elsevier Sci ence B.V. All rights reserved.