Regional distribution of sympathetic vasoconstrictor tone in conscious spontaneously hypertensive rats.

An electromagnetic flow probe was chronically implanted around the common carotid, superior mesenteric, or renal artery in spontaneously hypertensive rats (SHR). An indwelling catheter was inserted into the terminal aorta for measurement of arterial pressure. Peripheral resistance was calculated by dividing arterial pressure by flow. Decrease in peripheral resistance on ganglion blockade with hexa-methonium bromide was assumed to indicate the presence of vasoconstrictor tone to regional resistance vessels. In the conscious, resting state, peripheral resistance decreased significantly on ganglion blockade in the carotid and renal areas but not in the superior mesenteric area. The magnitudes of the decrease in peripheral resistance in the carotid and renal areas were not greater than the respective, corresponding values in normal rats. Presumably, vasoconstrictor tone in these three vascular regions, being quite different from that in the hindquarters, is not higher in SHR than in normal rats. Venomotor tone does not seem to be elevated in conscious SHR either, because the decrease in the sum of the mean peripheral flows on ganglion blockade, which was assumed to reflect the decrease in cardiac output, was not larger in SHR than in normal rats. Pentobarbital anesthesia did not abolish renal vasoconstrictor tone in SHR as it does in normal rats.