Changes in regional blood flow and cardiac output after L-glutamate stimulation of A5 cell group.

Changes in regional blood flow and cardiac output were measured by the reference organ method in pentobarbital-anesthetized rats with radioactive microspheres (15 microns) before and after chemical stimulation of the A5 cell group with the excitatory amino acid L-glutamate an agent that excites cell bodies but not fibers of passage. This stimulation caused a decrease in mean arterial pressure, heart rate, cardiac output, and calculated stroke volume. The limb skeletal muscles showed a large increase in blood flow and decrease in vascular resistance, whereas the trunk musculature showed no change in flow or resistance. The blood flow of the entire gastrointestinal tract decreased. Blood flow in the skin decreased with no change in resistance. The cardiac muscle of the ventricles showed a decrease in flow without a change in resistance. The ipsilateral half of the brain showed a decrease in blood flow, while the contralateral side showed no change. The kidneys exhibited no change in blood flow and a decrease in resistance. A5 stimulation in guanethidine-sympathectomized rats caused no change in regional blood flow. In contrast, an increase in cardiac output was observed, and the possible interpretations for this change are discussed. Rats treated with intraventricular injections of 6-hydroxydopamine showed no changes in regional blood flow or cardiac output, indicating that catecholamine neurons are involved in these responses.