GABA receptor binding and hemodynamic responses to ICV GABA in adult spontaneously hypertensive rats

Blood pressure and heart rate responses after central administration of GABA (100-1000 micrograms, ICV) and after ganglionic blockade with hexamethonium (25 mg/kg, i.a.) were compared in conscious 12 week-old spontaneously hypertensive (SH) and age-matched Wistar-Kyoto (WKY) rats. Ganglionic blockade produced an equivalent change in mean arterial pressure between SH and WKY rats. Thus, the total functional sympathetic nervous system contribution to blood pressure is equivalent in these two strains. Intraventricularly-administered GABA produced a greater absolute decrease in mean arterial pressure in the SHR compared to the WKY. However, the percent changes in arterial pressure produced by GABA were not different between these strains. This greater absolute depressor effect of GABA does not appear to be due to differences in GABA receptor binding constants since GABA receptor affinity and number of binding sites were not significantly different in the forebrain, cerebellum or pons-medulla between SH and WKY rats.