Number of Mast Cells in the Rat Uterus with Special Reference to Its Relation to Hormonal Treatment and Decidual Response1

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Abstract
The number of mast cells in the uteri of rats during the estrous cycle and in ovariectomized animals treated with estrogen, progesterone or both was studied. In cyclic animals mast cells were most numerous during metestrus but declined significantly (P < 0.01) by the late evening of proestrus (50% below metestrous level). In ovariectomized animals the number of mast cells counted 15 hr after a single injection of 0.25 µg estradiol-17β was 74% below the number in control animals. Estrogen treatment also produced considerable degranulation of the mast cells. By comparison, a single injection of 5 mg progesterone resulted in less drastic changes in the mast cells than that following the estrogen treatment. When ovariectomized rats were treated with progesterone for various periods prior to administration of estradio1-17β, mast cell numbers declined well below the levels recorded following treatment with either estrogen or progesterone alone. In animals pretreated with 5 mg/day progesterone over a period of 2 days followed by estrogen then examined 15 hr thereafter, the number of mast cells in the uterus declined 87% below control levels; in addition, many degranulated mast cells were also observed. Maximal deciduomal development was induced in animals similarly treated (progesterone treatment for 2 days followed by a single injection of estrogen) only when trauma was applied 15 hr after the estrogen. It was concluded from these studies that uterine sensitivity to decidual development is dependent on adequate hormonal preparation of the endometrium, and the sensitivity so established appears to bear a parallel relationship to the population of mast cells in the uterus.

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