Rete mirabile of goat: its flow-damping effect on cerebral circulation.

This work was designed to characterize in anesthetized goats the hemodynamic response of the carotid rete during pharmacologically induced changes in systemic blood pressure or blood flow to the brain. Under control conditions, mean blood pressure in the middle cerebral artery (distal to rete) was 18% lower than that measured in the internal maxillary artery (proximal to rete). Pressure gradient and calculated resistance across the rete were unchanged when systemic arterial pressure was increased or decreased by intravenous administration of norepinephrine or isoproterenol, respectively. Hypercapnia or injections of isoproterenol and acetylcholine into the internal maxillary arteries increased blood flow and decreased middle cerebral arterial pressure, whereas injections of norepinephrine decreased blood flow and increased postrete pressure. Calculated resistance across the rete was unchanged. These observations indicate that the response of the carotid rete to the substances tested is negligible; they also suggest that the carotid rete may have a flow-damping effect by maintaining resistance to blood flow when a change in the caliber of brain vessels occurs.