In vivo venular changes with the development of one-kidney, one-clip hypertension in the rat

Television microscopy was used to quantify in vivo resting venular diameters and the responses to topically applied norepinephrine in the cremaster muscle of two groups of urethanchloralose anesthetized rats: normotensive rats (NT) and one-kidney, one-clip Goldblatt hypertensive rats (1K1C). Observations were made two weeks after the surgery which was used to induce renovascular hypertension. At this stage, we have previously observed an increase in arteriolar reactivity (1). In the current study, mean arterial blood pressures for 1K1C (149 +/- 5 mmHg) were significantly higher than pressures for NT (102 +/- 3 mmHg). Venules were categorized by branching order and venular diameters were measured at three different levels of the microcirculation: first (1V), second (2V), and third order (3V) venules. Reactivity to norepinephrine at all venular levels in the 1K1C group was similar to that recorded for the NT group. Resting venular luminal diameters, however, were significantly smaller (20%) for large (1V) venules of the HT group (137 +/- 9 micron) compared to those for the NT group (171 +/- 10 micron). Thus, in contrast to previously reported data for arterioles, a structural venoconstriction and not an increase in venular reactivity appears to characterize the early vascular changes associated with this form of renovascular hypertension.