Effects of gamma-aminobutyric acid on regional vascular resistances of conscious spontaneously hypertensive rats.

1. The regional vascular effects of a central injection of gamma-aminobutyric acid (GABA) in conscious spontaneously hypertensive rats (SHR) were compared with normotensive control rats (NCR), including Wistar-Kyoto rats (male, 10-20 weeks of age). One week or more after insertion of a cannula into the cisterna magna, an electromagnetic flow probe was implanted around one of five arteries, and a catheter for measurement of blood pressure and heart rate was inserted into the terminal aorta or common carotid artery. Cardiovascular changes were observed in the conscious animal after recovery from the surgery. Peripheral resistance was calculated as pressure divided by flow. 2. Ten min following intracisternal injection of 10 mu mol of GABA, mean arterial pressure and heart rate were significantly lowered (P < 0.05; t-test): - 29 and -16% (70 d.f.) in SHR versus -23 (116 d.f.) and -19% (112 d.f.) in NCR. Hindquarters, carotid, superior mesenteric and renal, but not coeliac, vascular resistances were significantly lowered (P < 0.05; t-test, 21, 9, 18 d.f.) in SHR. However, when comparing the effect of GABA injection in SHR and NCR, there were no significant differences in coeliac, carotid and hindquarters vascular resistances, but there were significant decreases in superior mesenteric and renal vascular resistances in SHR. 3. These results indicate that: (i) a cisternal injection of GABA in SHR decreases both peripheral vascular resistance and heart rate, and thereby lowers blood pressure; (ii) the vascular resistance of the superior mesenteric and renal vascular beds was more decreased in SHR than in NCR. This suggests that the GABAergic control of regional vascular resistance differs in the SHR and the NCR.