Responses of hypogastric nerve afferent fibers to uterine distension in estrous or metestrous rats.

The response of afferent fibers in the distal end of the cut hypogastric nerve to distension of the uterus to various pressure levels was investigated in anesthetized virgin female rats on two different days of the estrous cycle (estrus or metestrus). Whereas relatively intense levels of uterine distension produced an increase in afferent activity in a pressure-dependent manner in both stages of the estrous cycle, the minimal pressure necessary to activate the fibers was significantly less on the day of estrus. These results suggest that hypogastric nerve afferent fibers are more likely to respond to potentially damaging uterine stimuli during the time when such responsiveness would be most important for reproductive success.