A Positive and Reversible Relationship Between Adrenergic Nerves and Alpha-1A Adrenoceptors in Rat Arteries1

Abstract

We evaluated the relationship between the presence of adrenergic nerves and the presence of alpha-1 adrenoceptors (alpha-1 AR) in the arterial tree of the rat. The thoracic aorta and the carotid, mammary, renal and femoral arteries were isolated from 20-week-old male WKY rats, along with the superior mesenteric artery and small (first order) and resistance-sized (third order) side branches of this vessel. Norepinephrine content ([NE]) and specific binding of 300 pM [³H]prazosin were determined. To estimate the total density of alpha-1 AR ([alpha-1 AR]) as well as the density ofalpha-1A AR ([alpha-1A AR]), binding experiments were performed with and without pretreatment of the preparations with the irreversible alpha-1B AR andalpha-1D AR antagonist chloroethylclonidine and in the absence and presence of the alpha-1A AR selective ligand (+)-niguldipine (30 nM). Also the presence of mRNA foralpha-1A AR was evaluated by use of reverse transcriptase-polymerase chain reaction (RT-PCR). In intact rats, arterial [NE] ranged between 0.1 and 15 ng/μg DNA, arterial [alpha-1 AR] ranged between 12.4 and 46.8 fmol/mg protein and [alpha-1A AR] ranged between 0.05 and 27.9 fmol/mg protein. There was no significant correlation between [alpha-1 AR] and [NE]. However, with respect to the [alpha-1A AR] a significant correlation between [NE] and [alpha-1A AR] was observed. RT-PCR analysis confirmed the expression of alpha-1A AR in the densely innervated mesenteric resistance-sized arteries. Two weeks after chemical sympathectomy of the rats with 6-hydroxydopamine (i) arterial [NE] was markedly reduced, and (ii) a distinct reduction in the [alpha-1A AR] as percentage of the total [alpha-1 AR] density in mesenteric artery side branches was noted. These findings indicate that there is a positive and reversible relationship between the presence of adrenergic nerves and that of alpha-1A AR in rat arteries.