Calcium Modulation of Microvascular Sensitivity during Renovascular Hypertension

Abstract

Abstract

The effects of in vivo alterations in local calcium concentration on small vessel responses to norepinephrine were obtained for a first order arteriole and venule in the cremaster muscle of normotensive and one-kidney, one-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 first-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 (pD ₂) of first-order arterioles in normotensive rats was significantly increased by a change in bath [Ca²⁺] from 1.3 to 2.6 mM; however, the norepinephrine sensitivity of comparable arterioles in hypertensive rats was not affected by this change in bath [Ca²⁺]. These data indicate that mechanisms for calcium modulation of vasoconstriction are attenuated for large arterioles in the cremaster muscle of one-kidney, one-clip Goldblatt hypertensive rats.