Relaxin concentrations in endometrial, placental, and ovarian tissues and in sera from ewes during middle and late pregnancy.

These studies were designed to determine the tissue source of ovine relaxin and to determine the feasibility of using the pregnant ewe for study of relaxin production and secretion. On Day 4 of gestation, ewes were laparotomized, the nonpregnant uterine horn was ligated, and the ovary not containing the corpus luteum was removed. During a second surgery at Day 45 (n = 8) or 140 (n = 9) of gestation, 10-ml blood samples were drawn from a uterine artery, the ovarian vein, and veins draining the pregnant and nonpregnant uterine horns. Endometrial, placental, and luteal tissues were obtained for immunocytochemistry and extraction. Relaxin was detected by a heterologous porcine radioimmunoassay (RIA) in 3 of 54 serum samples (701.3 +/- 25.4 pg/ml, mean +/- SEM). Relaxin was not detected in crude tissue extracts, but low quantities were detected by RIA following Sephadex G-50 column chromatography of tissue extracts. Total relaxin activity for all tissues was equivalent to 0.57 +/- 0.13 ng of porcine relaxin/g tissue (w.w.). Relaxin was not detected immunocytochemically by light or electron microscopy. These data indicate that low quantities of relaxin are present in tissues and sera of pregnant ewes.