Collagen Content of the Nonpregnant Rat Uterus as Related to the Functional Responses to Estrogen and Progesterone

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Abstract
CoUagen content has been estimated by the hydroxyproline method on uteri in 95- to 105-day-old rats from an inbred colony. The influence of cyclic ovarian activity, of castration, and of estrogen and progesterone administration to castrates has been investigated. Results, expressed both as total collagen per uterus and as g/100 g wet and dry tissue, were statistically compared to litter mate controls. In the normal intact rat the lowest values for collagen were found just before ovulation, when the animals were in early estrus and uterine weights were at their highest levels. Following ovulation, an increase in total collagen was accompanied by an increase in collagen concentration, reaching a peak in the metestrous phase and declining as the corpora lutea regressed. This postovulatory increase in collagen formation was prolonged and exaggerated when the luteal phase was prolonged by the administration of HCG. A rapid and continued drop in uterine weight and total collagen for 21 days following oophorectomy was associated with an increase in collagen concentration which attained a constant level by the 10th day. Injections of estradiol started 4–7 days after castration caused a fall in collagen concentration. When given in amounts just sufficient to produce vaginal estrus, this drop counteracted the increase in uterine weights, so that total collagen remained unchanged. Progesterone, when given to such estrogen-primed animals, increased both the total collagen per uterus and the g/100 g of tissue. This finding was in keeping with the changes noted after ovulation in the normal cycle. It is suggested that the physiologic response of the rat uterus to the combined action of estrogen and progesterone is associated with a more rapid accumulation of collagen than of other tissue proteins. The findings are discussed in relation to those of other investigators.