FURTHER STUDIES ON THE NEUROGENIC CONTROL OF THE ESTROUS CYCLE BY UTERINE DISTENTION1

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Abstract
Previous results were confirmed and extended to show that the presence of a foreign body in the ovine uterus can significantly modify the estrous cycle. When an 8 mm bead was introduced on day 3 (early luteal phase) the intervals between heats were significantly shortened to 13.0 days (P< 0.05). When the bead was introduced on day 8 (late luteal phase) the cycles were lengthened to 23.1 days (P < 0.01). Histological examination of ovaries and of uterine endometria showed that the corpora lutea were maintained and their functional life was prolonged. When the bead was inserted on day 13 (follicular phase) the cycles remained normal (16.1 days). Both shortening and lengthening of the cycles could be prevented by surgical resection of the uterine segment containing the bead. This indicates that the mechanism involved is neural or neurohumoral. Beads 4 mm in diameter caused a shortening of the cycle when inserted into the uterus on day 3, but this shortening was not statistically significant perhaps because of the small number of observations. Beads 2 mm in diameter caused no modification in mean cycle length at any insertion time, but there was evidence that they had some physiological effect, such as causing ovulation without heat.