Received for publication July 3, 2003.
Revised August 1, 2003.
Accepted for publication September 30, 2003.

Increased Reactivity of Murine Mesenteric Veins to Adrenergic Agonists: Functional Evidence Supporting Increased Alpha-1 Adrenoceptor Reserve in Veins Compared to Arteries

Abstract

These studies examined adrenergic reactivity of mesenteric arteries and veins from DOCA-salt hypertensive and SHAM control mice. We measured constrictions in unpressurized arteries and veins by monitoring vessel diameter using computer-assisted video microscopy in vitro. Veins were more sensitive than arteries to the constricting effects of norepinephrine (NE) and phenylephrine (PE) but the ₂ agonists clonidine and UK 14,304 did not constrict arteries or veins. Reactivity was not altered in arteries or veins from DOCA-salt mice. We next investigated the mechanism of increased venous reactivity to NE and PE by studying desensitization to maximum concentrations of NE and PE. SHAM arteries desensitized to NE and PE more than DOCA-salt arteries while DOCA-salt and SHAM veins maintained 80% of the initial NE and PE constriction. To determine if the increased reactivity and resistance to desensitization in veins was due to a greater - adrenoceptor reserve, vessels were incubated with the alkylating agent phenoxybenzamine (PBZ; 0.3, 3, 10, 30 nM). The NE-elicited initial constriction was reduced by PBZ (3, 10, 30 nM) in SHAM but only by PBZ (30 nM) in DOCA-salt veins. All doses of PBZ blocked NE responses in SHAM and DOCA-salt arteries. These data suggest that mesenteric veins express more ₁ -adrenoceptors than arteries accounting for greater reactivity and resistance to desensitization compared to arteries.

Key words: DOCA-salt hypertension, alpha adrenergic receptors, alpha adrenoceptor reserve, alpha-1 adrenoceptors, mesenteric vasculature, vascular reactivity

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