Localization of relaxin in endometrial gland cells of pregnant, lactating, and ovariectomized hormone‐treated guinea pigs

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Abstract
Uteri taken from guinea pigs in different stages of pregnancy and during lactation, as well as animals that had been ovariectomized and treated with hormones, were examined for relaxin with the peroxidase‐antiperoxidase (PAP) technique employing an antiserum produced against porcine relaxin. While relaxin was not detected in uteri of day 15 pregnant animals, small amounts were noted in a few endometrial glands in day 30 pregnant animals. Uteri from day 45, day 60, and late‐pregnant animals exhibited heavy amounts of relaxin; however, endometrial gland cells from lactating animals contained very little or no relaxin. Injections of estrogen and progesterone that brought a relaxation of the pelvic ligaments in ovariectomized guinea pigs also induced an accumulation of relaxin in the endometrial glands. Relaxin was not detected in nonendometrial portions of the uterus, endometrial stromal components, luminal surface epithelium, or uterine cervical glands. Extracts prepared from uteri of day 45, day 60, and late‐pregnant animals showed positive responses for relaxin in the mouse uterus bioassay.