Adrenergic neurotransmission in tail arteries from two-kidney, one clip, renal hypertensive rats

The goal of this study was to determine if increased vascular smooth muscle sensitivity to norepinephrine in two-kidney, one clip (2K1C) hypertensive rats is the result of a decrease in adrenergic nerve function. Vascular sensitivity to norepinephrine was measured in isolated tail artery strips from 2K1C hypertensive and normotensive rats and in various arterial strip preparations from normotensive rats that exhibit varying degrees of adrenergic innervation. In each case, the characteristic of the vascular smooth muscle response in the vessel with the least amount of adrenergic innervation simulated the response of the vascular smooth muscle from the 2K1C hypertensive rats. Release or displacement of endogenous norepinephrine by electrical stimulation, tyramine, potassium-free solution, and potassium excess, and measurement of tissue content of norepinephrine suggest that the blood vessels of 2K1C hypertensive animals are depleted of catecholamine stores. Based on these observations it is concluded that the increased sensitivity of vascular smooth muscle to norepinephrine in 2K1C hypertensive rats is the result of a diminished adrenergic innervation. This increased sensitivity of the vasculature may be a response of the smooth muscle cells to a decrease in innervation or the consequence of vascular wall hypertrophy leading to an increased number of smooth muscle cells that are remote from their adrenergic supply.