Effects of estradiol and progesterone on accumulation of relaxin‐ and carbohydrate‐containing granules in endometrial gland cells of the guinea pig

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Abstract
Guinea pigs were spayed and given various regimens of injections of estradiol and progesterone. The following were monitored in each animal: pubic separation (relaxin stimulation), resorption of the vaginal membrane (estrogen priming), and the presence of PAS‐positive granules and/or relaxin in endometrial gland cells (EGC). Injections of estradiol alone resulted in resorption of the vaginal membrane, accumulation of PAS‐positive granules in EGC of all animals, and accumulation of relaxin in EGC of two of four animals; but they did not cause pubic separation. Progesterone injections did not result in resorption of the vaginal membrane, separation of pubes, or accumulation of PAS‐positive granules; however, one of three animals demonstrated a few EGC that contained relaxin. Animals that received both estradiol and progesterone exhibited PAS‐positive granules and relaxin in EGC as well as separated pubes, but did not have resorbed vaginal membranes.Upon examination with the electron microscope, EGC from animals that received estradiol alone exhibited remarkable numbers of secretory granules that contained a carbohydrate‐rich material. Secretory granules were not prominent in EGC from animals that received progesterone alone. Estradiol and progesterone injections resulted in accumulation of secretory granules in EGC that contained relaxin and a carbohydrate‐rich material.The observations that estradiol and progesterone induce relaxin production in EGC support the hypothesis that uterine relaxin plays an important role in pregnancy and/or parturition in the guinea pig.