Preoptic hypothalamic control of arteriolar vasodilatory responses.

Arteriolar responses to hemorrhage were directly observed in the skeletal muscle and intestinal circulations of two groups of animals. In one group, the periventricular tissue surrounding the anteroventral portion of the third cerebral ventricle (AV3V) was electrolytically lesioned 7-10 days before an acute experiment. In the other group, control surgical procedures were performed. Hemorrhage resulted in similar decreases in arterial blood pressure (30-60% prehemorrhage level) and intestinal blood flow (20-60% prehemorrhage level) in both groups. In contrast, arteriolar diameter significantly increased following hemorrhage in the spinotrapezius muscle of control-operated animals (141 +/- 9% prehemorrhage level) but did not change in animals with AV3V lesions (97 +/- 7% prehemorrhage level). In a previous study, electrical stimulation of intact AV3V tissue was shown to cause a sustained decrease in blood pressure (80-90% of control level) and a vasodilation in skeletal muscle arterioles (120-140% control level). Since stimulation of intact AV3V tissue evokes vasodilation and AV3V tissue ablation reduces hemorrhage-induced vasodilation, this region of the hypothalamus may play an important role in the regulation or modulation of some responses in the peripheral microcirculation.