Immunochemical and cytochemical studies of relaxin-containing cells in the guinea pig uterus

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Abstract
Uteri and ovaries from cycling, pregnant, and lactating guinea pigs were studied for immunolocalization of relaxin with the light microscope. Endometrial gland cells (EGC) from the same group of animals were examined in the electron microscope for the presence of secretory granules. Those EGC that exhibited high numbers of granules were stained either for relaxin with the protein A colloidal gold method or for carbohydrate with the thiocarbohydrazide technique. Relaxin was found in EGC from middle and late pregnant animals but was not detected in ovaries or uteri from cycling animals. While cytoplasmic granules were noted in most EGC from cycling animals examined, the number of granules was greatest in uteri from estrus and proestrus animals. Granules in EGC from estrus animals contained a carbohydrate‐rich material but did not contain relaxin. Endometrial gland cells from animals in early to middle stages of pregnancy (days 15 and 30) contained limited numbers of granules, almost all of which contained carbohydrate. At day 45 of pregnancy, EGC containing many granules were noted. The majority of granules contained relaxin; however, a significant number of EGC contained carbohydrate‐rich granules. Infrequently, EGC were noted that contained two populations of granules, and these two populations were assumed to be made up of relaxin‐containing and carbohydrate‐rich granules. EGC from animals on day 60 of pregnancy typically contained granules, and the majority of these contained relaxin. Carbohydrate‐rich granules were observed in EGC of the day 60 animals but were smaller in diameter and were noted in much lower numbers than the relaxin‐containing granules. Endometrial gland cells from lactating animals infrequently contained granules. These studies are consistent with the hypothesis that the uterus is the primary source of relaxin in the guinea pig and that relaxin plays an important role in pregnancy and parturition of this species. The observations implicate endometrial glands and their products in the physiology of the cycling animal as well as the pregnant and parturient animal.