Increased alpha-adrenergic receptor affinity in resistance vessels from hypertensive rats.

Abstract

SUMMARY a-Adrenergic receptor-related properties, specifically, norepinephrine affinity, occupancy and reserve during contraction, were determined in segments of rat resistance arteries. These were obtained from the superior mesenteric bed of spontaneously hypertensive rats and Wistar-Kyoto strain controls. Receptor affinity for norepinephrine in the spontaneously hypertensive rats was significantly greater than that for the Wistar-Kyoto controls. There were no differences in the estimates of receptor occupancy and reserve. This finding taken together with other studies is consistent with the conclusion that increased a-adrenergic receptor-mediated sensitivity of vascular smooth muscle of the spontaneously hypertensive rat reflects differences in the agonist site on the a-adrenergic receptor. (Hypertension 11: 635-638, 1988) KEY WORDS • receptor vascular smooth muscle affinity • norepinephrine • spontaneously hypertensive rats I NCREASED sensitivity of vascular smooth muscle to norepinephrine (NE) has been proposed as a factor responsible at least in part for the increased blood pressure of the spontaneously hypertensive rat (SHR).1 " 3 This increased sensitivity may result from differences in a number of factors, including cell membrane properties, level of membrane potential, receptor density, type of receptor, and excitation-contraction coupling. Although vascular smooth muscle cells from SHR are less polarized in their resting state, 1 and this may contribute to the increased sensitivity of receptor-mediated contraction, attempts to characterize features of the postjunctional a-adrenergic receptor itself have failed to establish notable differences using conventional in vitro analysis by receptor antagonists 4 or radioligand binding. 56The sensitivity of the contraction of a blood vessel to NE has been shown to be influenced by a-adrenergic receptor number and affinity. -8 These studies suggest that these receptor variables are cell-regulated attributes. Thus, they may not necessarily be identical in the same artery from different strains, such as the SHR and

Dietary enrichment with wild blueberries (Vaccinium angustifolium) affects the vascular reactivity in the aorta of young spontaneously hypertensive rats☆

“…While incubation with a COX inhibitor failed to restore -and in fact decreased -the vasodilator response to Ach of aortas from blueberry-fed SHR, in Phe-induced vasoconstriction, the suppression of vasoconstriction in SHR-BB aortas was greater, in comparison to SHR-C, when MFA was present. Even though there is functional evidence of α-adrenergic receptors in the vasculature of young SHRs, their effect is limited compared to aged SHRs [30,31]. In the current study, we support that there is no significant effect of our blueberry-enriched diet on the vessel sensitivity to the adrenoreceptor, unless NOS and COX enzyme synthesis is inhibited.…”

Changes in α2-Adrenoceptors on Vascular Smooth Muscle and Neural Membranes following Hypertension Induced by Renal Ischemia

“…As pointed out by Nyborg and Bevan [40], none of these results are necessarily at odds with the current study. They reported that mesenteric resistance arteries from spontaneously hypertensive rats are more sensitive to norepinephrine than those from NT rats.…”

Alpha-adrenergic receptors and 45Ca2+ efflux in arteries from deoxycorticosterone acetate hypertensive rats.

“…In the present study, the dissociation constant for norepinephrine in DOCA hypertensive rats (1.29xlO~7 M) is similar to that determined by Smith et al 4 in aldosterone hypertensive rats (4.8xlO~7 M) but is 10-fold less than the dissociation constant for the agonist in mesenteric arterioles from SHR (1.29xl(r 6 M). 10 Although we found no evidence of a change in agonist affinity, a decrease in receptor affinity for the ai-antagonist 125 I-(±) BE, the radiolabeled derivative of 2-[5(4hydroxy-phenyl)-ethyl aminomethyl] tetralone or HEAT, has been reported in mesenteric arteries from DOCA hypertensive rats. 1 This disparity may be related to methodological differences but also suggests that affinity may differ between agonists and antagonists, supporting postulated differences in receptor recognition sites for these two classes of compounds.…”