Differential Response of Hamster Cheek Pouch Microvessels to Vasoactive Stimuli during the Early Development of Hypertension

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Arteriolar responses in the hamster cheek pouch to direct microapplications of norepinephrine (NE), angiotensin n (A II), and potassium chloride (KC1) were investigated during the early developmental phase of hypertension. After determination of arterial pressure in 12 hamsters, control luminal and wall diameters and the response of arterioles (second order branching, 28-60 jun diameters) to microapplications of NE (0.5, 1.0, 5.0 ng), A II (0.5 ng), KC1 (22.2 min) and the vehicle (Tris-buffered Ringer's solution) were determined. Then using a figure-eight ligature around each kidney hypertension was induced in nine animals, and three were sham-operated. Measurements were repeated on the same hamsters 4, 8, and 13 days later. Four of the nine animals developed a sustained hypertension (HT-S) and the remaining five developed a transient hypertension (HT-T), only on day 4. The sham-operated hamsters remained normotensive. The arteriolar response to KC1 was increased significantly in the HT-S group on days 4 and 8 whereas the arteriolar response to NE and A II was increased significantly on days 8 and 13. There were no significant differences in the arteriolar responses of either the HT-T or normotensive group to any agent at any time. Futhennore, there were no significant changes in arteriolar wall/lumen ratios for any group at any time. Thus, the transient nature of the arteriolar response to potassium combined with the delayed Increase in the arteriolar response to NE and A II implies that there are two vascular phases associated with the early development of hypertension in this model. The first phase may be an ionic alteration which in turn may initiate the second or humoral phase. Ore Res 44: 512-517, 1979

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