The contribution of the sympathetic nervous system and
vasopressin to the maintenance of arterial pressure was investigated in high
sodium-fed rats 4 weeks after the induction of one-kidney, figure-8 renal wrap
hypertension. Arterial pressure was significantly greater in renal-wrapped rats than in
sham-operated animals. The contribution of the sympathetic nervous system was assessed functionally by measuring the arterial pressure response to ganglionic blockade and estimating the apparent rate of release of
norepinephrine. The contribution of
vasopressin was assessed by administration of the vascular antagonist d(CH2)5Tyr(Me)-AVP. Whole-animal vascular responsiveness and cardiac baroreceptor reflex sensitivity were determined by graded intravenous bolus
injections of
angiotensin II,
vasopressin, and
phenylephrine. Hypertensive rats demonstrated an exaggerated reduction in arterial pressure to autonomic blockade before and after blockade of vascular
vasopressin receptors. There was a significant 27% increase in the apparent rate of release of
norepinephrine into the plasma. Administration of d(CH2)5Tyr(Me)-AVP did not affect arterial pressure when given alone. However, after ganglionic blockade, inhibition of the
vasopressin system elicited similar falls in blood pressure in both normotensive and hypertensive rats. Arterial pressure dose-response effects of
phenylephrine,
angiotensin II, and
vasopressin were similar between renal-wrapped and
sham-operated animals; however, cardiac baroreceptor reflex sensitivity was suppressed in the hypertensive rats. These studies indicate that the maintenance of arterial pressure in chronic, high
sodium renal-wrap
hypertension is associated with an augmented sympathetic nervous system function.