Animals with bilateral cannulas in the paraventricular nucleus were made hypertensive by a one-kidney, figure eight renal wrap procedure or
sham operated. Femoral artery and vein
catheters were inserted for arterial pressure measurement and plasma
catecholamine determination. After recovery and 4 days after
hypertension surgery,
bicuculline methiodide or
muscimol was microinjected into the paraventricular nucleus. In some rats,
nitroprusside was infused intravenously to reflexly stimulate the sympathetic nervous system. In control rats,
bicuculline increased blood pressure, heart rate, and plasma
norepinephrine and
epinephrine concentrations. In contrast, in hypertensive rats blood pressure did not change while the heart rate response was maintained. Plasma
norepinephrine and
epinephrine responses were reduced 75 and 68%, respectively.
Muscimol injections decreased arterial pressure in the hypertensive rats. Heart rate responses to
nitroprusside were similar in the two groups of rats, while the plasma
catecholamine responses were attenuated in the hypertensive animals. These data suggest that
GABA function in the paraventricular nucleus is reduced in renal wrap
hypertension.