Calcium Modulation of Microvascular Sensitivity during Renovascular Hypertension

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Abstract
The effects of in vivo alterations in local Ca concentration on small vessel responses to norepinephrine were obtained for a 1st order arteriole and venule in the cremaster muscle of normotensive and 1 kidney, 1-clip Goldblatt hypertensive rats. The cremaster with intact circulation and innervation was suspended in a modified Krebs solution which contained either 1.3, 2.6 or 5.1 mM CaCl2. Closed-circuit television microscopy was used to measure vessel diameters. The resting lumenal diameters of 1st order arterioles in hypertensive rats were 31% smaller than lumenal diameters of the corresponding arterioles in normotensive rats. Concentration-response curves showed that the norepinephrine sensitivity (pD2) of 1st order arterioles in nomotensive rats was significantly increased by a change in bath [Ca2+] from 1.3 to 2.6 mM; the norepinephrine sensitivity of comparable arterioles in hypertensive rats was not affected by this change in bath [Ca2+]. Mechanisms for Ca modulation of vasoconstriction are attenuated for large arterioles in the cremaster muscle of 1 kidney, 1-clip Goldblatt hypertensive rats.