ROLE OF THE ROSTRAL VENTROLATERAL MEDULLA IN MAINTENANCE OF BLOOD-PRESSURE IN RATS WITH GOLDBLATT HYPERTENSION

The aim of the present study was to examine the participation of the r ostral ventrolateral medulla (RVLM) in the maintenance of hypertension in rats submitted to the renovascular Goldblatt (two-kidney, one clip ) procedure. We inhibited or stimulated this area with the use of drug s such as glycine, L-glutamate, or kynurenic acid. (1) Bilateral micro injection of glycine (100 nmol, 200 nL, n=13) into the RVLM of hyperte nsive rats produced a decrease in mean arterial blood pressure (MAP) f rom 177.2+/-29.3 to 102.3+/-20.9 mm Hg (P<.05), which was similar to t he decrease produced by intravenous administration of hexamethonium. T he inhibition of RVLM with glycine in normotensive rats produced a dec rease in MAP from 106+/-17.1 to 59.7+/-7.3 mm Hg (P<.05, n=9). (2) An impressive increase in MAP from 153.3+/-16.3 to 228+/-34.9 mm Hg (P<.0 5) occurred in hypertensive rats after microinjection of L-glutamate ( 50 nmol, 200 nL, n=6) into the RVLM. The same procedure caused a signi ficant but less intense increase in MAP from 105+/-13.8 to 148.3+/-24. 9 mm Hg in normotensive rats (P<.05, n=6). (3) A decrease in MAP from 151.6+/-25.3 to 96.8+/-22.5 mm Hg occurred in hypertensive rats after microinjection of the broad-spectrum glutamate antagonist kynurenic ac id (4 nmol, 200 nL, n=6) into the RVLM, whereas the same procedure did not change MAP in normotensive animals (n=6). Heart rate was not sign ificantly affected in any group. Together these results show that the activity of RVLM neurons is important in the maintenance of arterial b lood pressure in Goldblatt hypertensive rats and probably indicate a c hange in the sensitivity and/or number of glutamatergic receptors in t his area after the development of hypertension.