Hypernoradrenergic innervation of the caudal artery of the spontaneously hypertensive rat: an influence upon neuroeffector mechanisms.

In the present studies we have established that the perfused caudal artery from spontaneously hypertensive (SH) rats responds to pharmacological and physiological stimuli in a manner similar to that described for other blood vessels from the SH rat. In addition, the responses of caudal arteries from SH rats to exogenous norepinephrine were similar to those of arteries removed from normotensive Kyoto Wistar rats. However, responses to sympathetic nerve stimulation at high, but not low, frequencies of stimulation were increased in arteries from the SH rat. In addition, impairment of neuronal uptake with cocaine unmasked a greater responsiveness of arteries from SH rats to sympathetic nerve stimulation. Consistent with the latter finding the neuronal uptake and neuronal deamination of norepinephrine was larger in caudal arteries from SH rats. A histofluorescent and electron microscopic analysis of the sympathetic innervation of caudal arteries from SH and Kyoto Wistar rats demonstrated that the vessels from SH animals had a greater number of nerve axon bundles and a greater area of adventitia occupied by nerve bundles. It is concluded that the ability of high rates of nerve stimulation and cocaine to unmask an enhanced responsiveness of caudal arteries from SH rats is related to an enhanced innervation of the artery. It is suggested that in the SH rat model of hypertension future research into the causes of the augmented blood pressure should be directed toward factors regulating the density of the sympathetic innervation of the vasculature.