Regional blood flow in conscious spontaneously hypertensive rats

In spontaneously hypertensive and normal control rats in the conscious state, blood flow was observed in the carotid artery, superior mesenteric artery, renal artery, and terminal aorta with a chronically implanted electromagnetic flow probe. At rest, flow per body weight was not different between the two groups except at the terminal aorta where it was significantly smaller in hypertensive rats (P less than 0.05). Regional peripheral resistance was higher in hypertensive rats than in normal rats in all the four arteries, but its elevation in the former was not uniform but most marked in the hindquarter area supplied by the terminal aorta. Quantitatively, this area was estimated to contribute about 40% of the total conductance decrease in hypertensive rats in comparison with the control. This suggests the importance of elevation of resistance in muscle blood vessels in hypertension. The contributions from the superior mesenteric area and the bilateral kidneys were estimated to be about 15% each. In the transposition response induced by transposing rats from their home cage to a new cage, the increase in hindquarter flow was significantly greater in hypertensive rats than in normal rats (P less than 0.01). The sum of the mean flows of the four arteries, a measure of cardiac output, was not different between hypertensive and normal rats at rest but greater in the former during transposition response. Elevation of arterial pressure in the response in hypertensive rats but not in the normal rats was ascribable largely to a greater increase in cardiac output in the former than the latter.