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 rostral 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 drugs such as glycine, L-glutamate, or kynurenic acid. (1) Bilateral microinjection of glycine (100 nmol, 200 nL, n=13) into the RVLM of hypertensive rats produced a decrease in mean arterial blood pressure (MAP) from 177.2+/-29.3 to 102.3+/-20.9 mm Hg (P<.05), which was similar to the decrease produced by intravenous administration of hexamethonium. The inhibition of RVLM with glycine in normotensive rats produced a decrease 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<.05) occurred in hypertensive rats after microinjection of L-glutamate (50 nmol, 200 nL, n=6) into the RVLM. The same procedure caused a significant 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 acid (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 significantly affected in any group. Together these results show that the activity of RVLM neurons is important in the maintenance of arterial blood pressure in Goldblatt hypertensive rats and probably indicate a change in the sensitivity and/or number of glutamatergic receptors in this area after the development of hypertension.