Size Dependence of Functional Alterations in Mesenteric Arteries from the Aldosterone-Salt Hypertensive Rat

Abstract

We tested the hypothesis that an elevated potassium-42 (⁴²K⁺) efflux (highly dependent on Ca²⁺) and an increase in the sensitivity of contraction and ⁴²K⁺ efflux to norepinephrine (NE) in conduit arteries of aldosterone-salt hypertensive rats (AHR) exended to smaller, distributing arteries. Functional endpoints were compared in two sizes of arteries from the mesenteric bed: second-order branches of the superior mesenteric artery (SMA branches) and the SMA. Contraction and free cytosolic Ca²⁺ concentration ([Ca²⁺]_c; fura-2 microfluorometry) were measured simultaneously and ⁴²K⁺ efflux was measured separately in SMA branches. Contraction and ⁴²K⁺ efflux were measured separately in SMA. Basal tone, [Ca²⁺]_c, and ⁴²K⁺ efflux were similar in SMA branches from AHR and control-salt rats (CSR). However, basal ⁴²K⁺ efflux was elevated in SMA from AHR compared to CSR. The sensitivity of the contractile, [Ca²⁺]_c, and ⁴²K⁺ efflux responses to NE was similar in SMA branches. In contrast, the sensitivity of the contractile and ⁴²K⁺ efflux responses to NE was enhanced in SMA from AHR compared to CSR. Inhibiton of endothelium-derived vasoactive substances by pretreatment with N_ω-nitro-L-arginine methyl ester and indomethacin significantly shifted the NE concentration-response relationships to the left for contraction, [Ca²⁺]_c, and ⁴²K⁺ efflux in both SMA branches and SMA from CSR. A similar shift to the left was observed in AHR for contraction but not consistently for [Ca²⁺]_c and ⁴²K⁺ efflux. We conclude that SMA branches from AHR demonstrate neither the elevated basal ⁴²K⁺ efflux, nor the NE supersensitivity exhibited by SMA. Endothelial function was not impaired both in SMA and SMA branches.

Pharmacological evidence for the activation of potassium channels as the mechanism involved in the hypotensive and vasorelaxant effect of dioclein in rat small resistance arteries

“…(1996) suggested that the resistance vasculature, which is critical to the control of peripheral resistance, might not show the same functional alterations as those expressed in large conductance arteries. Thus, considering that in our previous study ( Lemos et al ., 1999 ) we employed aortic preparations which are conductance arteries ( Magliola & Jones, 1999 ) and likely would contribute little to the decrease in peripheral resistance seen after dioclein, it is plausible to propose that the hypotensive effect produced by the flavonoid in conscious normotensive rats is, at least, secondary to a vasorelaxant effect on resistance vessels.…”