Sympathetic nerve function and vascular reactivity in Doca-salt hypertensive rats

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Abstract
The present study was conducted to measure norepinephrine release during sympathetic nerve stimulation and to evaluate vascular reactivity in the isolated perfused mesenteric vasculature of normotensive and DOCA[deoxycorticosterone acetate]-salt hypertensive rats. Significantly greater vasoconstrictor responses to periarterial nerve stimulation, norepinephrine and vasopressin, but not to BaCl2, were observed in the mesenteric vasculature of the hypertensive rats in comparison with the control normotensive group. Norepinephrine release, measured as total 3H overflow, during periarterial nerve stimulation at 4 Hz for 2 min, was identical in both normotensive and hypertensive animals. Phentolamine (5.3 .mu.M) significantly increased 3H overflow, but to the same extent in the normotensive and the hypertensive mesenteric vasculature, suggesting that the negative feedback presynaptic .alpha.-adrenoceptor mechanism, which was proposed to modulate transmitter release, was unaltered in this form of hypertension. Hyperresponsiveness of the mesenteric vasculature to periarterial nerve stimulation in the hypertensive rats is due to increased sensitivity of the vascular .alpha.-adrenoceptor and not facilitation of the transmitter release. The increased vascular reactivity to norepinephrine and vasopressin may be involved in the maintenance of DOCA-salt hypertension.