A POSITIVE AND REVERSIBLE RELATIONSHIP BETWEEN ADRENERGIC-NERVES AND ALPHA-1A ADRENOCEPTORS IN RAT ARTERIES

We evaluated the relationship between the presence of adrenergic nerve s and the presence of alpha-1 adrenoceptors (alpha-1 AR) in the arteri al tree of the rat. The thoracic aorta and the carotid, mammary, renal and femoral arteries were isolated from 20-week-old male WKY rats, al ong with the superior mesenteric artery and small (first order) and re sistance-sized (third order) side branches of this vessel. Norepinephr ine content ([NE]) and specific binding of 300 pM [H-3]prazosin were d etermined. To estimate the total density of alpha-1A AR ([alpha-1 AR]) as well as the density of alpha-1A AR ([alpha-1A AR]), binding experi ments were performed with and without pretreatment of the preparations with the irreversible alpha-1B AR and alpha-1D AR antagonist chloroet hylclonidine and in the absence and presence of the alpha-1A AR select ive ligand (+)-niguldipine (30 nM). Also the presence of mRNA for alph a-1A AR was evaluated by use of reverse transcriptase-polymerase chain reaction (RT-PCR). In intact rats, arterial [NE] ranged between 0.1 a nd 15 ng/mu g DNA, arterial [alpha-1A AR] ranged between 12.4 and 46.8 fmol/mg protein and [alpha-1A AR] ranged between 0.05 and 27.9 fmol/m g protein. There was no significant correlation between [alpha-1 AR] a nd [NE]. However, with respect to the [alpha-1A AR] a significant corr elation between [NE] and [alpha-1A AR] was observed. RT-PCR analysis c onfirmed the expression of alpha-1A AR in the densely innervated mesen teric resistance-sized arteries. Two weeks after chemical sympathectom y of the rats with 6-hydroxydopamine (i) arterial [NE] was markedly re duced, and (ii) a distinct reduction in the [alpha-1A AR] as percentag e of the total [alpha-1 AR] density in mesenteric artery side branches was noted. These findings indicate that there is a positive and rever sible relationship between the presence of adrenergic nerves and that of alpha-1A AR in rat arteries.