Effects of Thermal Stimulation, Applied to the Hindpaw via a Hot Water Bath, upon Ovarian Blood Flow in Anesthetized Nonpregnant Rats

The effects of thermal stimulation, applied to the hindpaw via a hot bath set to either 40°C (non-noxious) or 49°C (noxious), upon ovarian blood flow were examined in nonpregnant anesthetized rats. Ovarian blood flow was measured using a laser Doppler flowmeter. Blood pressure was markedly increased following 49°C stimulation. Ovarian blood flow, however, showed no obvious change during stimulation, although a small increase was observed after stimulation. Ovarian blood flow and blood pressure responses to 49°C stimulation were abolished after hindlimb somatic nerves proximal to the stimuli were cut. Heat stimulation (49°C) resulted in remarkable increases in both ovarian blood flow and blood pressure in rats in which the sympathetic nerves supplying the ovary were cut but the hindlimb somatic nerves remained intact. The efferent activity of the ovarian plexus nerve was increased during stimulation at 49°C. Stimulation at 40°C had no effect upon ovarian blood flow, blood pressure or ovarian plexus nerve activity. Electrical stimulation of the distal part of the severed ovarian plexus nerve resulted in a decrease in both the diameter of ovarian arterioles, observed using a digital video microscope, and ovarian blood flow.The present results demonstrate that noxious heat, but not non-noxious warm, stimulation of the hindpaw skin in anesthetized rats influences ovarian blood flow in a manner that is attributed to reflex responses in ovarian sympathetic nerve activity and blood pressure.