Effect of GABA agonist and antagonists on cardiovascular and sympathetic responses in SHR and WKY rats.

Injection of muscimol (4 mg/kg, i.a.) to unanesthetized SHR rats reduced the arterial blood pressure and heart rate more than in WKY rats. These cardiovascular responses were accompanied by a moderate increase in plasma norepinephrine level and a marked increase in plasma epinephrine level, in the SHR rats. In the WKY rats, only a moderate increase in plasma epinephrine level was seen. Injection of subconvulsive doses of picrotoxin (2 mg/kg, i.a.) or bicuculline (1 mg/kg, i.a.) to SHR rats, elicited a higher and a more prolonged increase of the arterial blood pressure than in WKY rats. Plasma norepinephrine and epinephrine levels increased to the same extent in both the SHR and WKY rats following picrotoxin injection. These results suggest that the SHR rats differ from the WKY rats in the reactivity of GABAergic responses in cardiovascular centers which also modulate the peripheral sympathetic tone.