bq-485 and Hypertension

The physiological and pathophysiological functions of endothelin-1 in modulating the regional blood flow of normal and spontaneously hypertensive rats (SHR) were studied in the perfused mesenteric vascular bed, a useful model for investigating resistance vessels.. We used 12-week-old SHR and Wistar-Kyoto (WKY) rats. Endothelin A (ETA) receptor responsiveness was evaluated by endothelin-1 (0.2-2 mumol/l) concentration-response curves, and repeated in the presence of indomethacin and the ETA and endothelin B (ETB) receptor antagonists BQ-485 and BQ-788, respectively. ETB receptor responsiveness was tested by sarafotoxin S6c concentration-response curves, obtained in the noradrenaline-precontracted mesenteric vascular bed, and repeated after treatment with BQ-788 and after endothelial denudation.. In both groups, endothelin-1 induced concentration-dependent contraction; SHR exhibited a markedly increased maximal effect compared with WKY rats (P < 0.01). BQ-485 produced a shift to the right for endothelin-1 concentration-response curves in both groups, with a higher pA2 (negative common logarithm of the antagonist that produces an agonist dose ratio of 2) value in SHR than in WKY rats (P < 0.01). The increase in the maximal effect produced by endothelin-1 in SHR was prevented by indomethacin, which also induced a significant increase in the endothelin-1 concentration producing the half-maximal response (EC50) in SHR (P < 0.05). Sarafotoxin S6c produced an ETB-dependent endothelium-mediated relaxant effect in WKY rats, which was not observed in SHR.. The higher vasoconstriction induced by endothelin-1 in SHR may be related to a greater number of available ETA receptors, due to the presence of an ETA receptor subtype. This mechanism may be linked to the production of prostanoids that add to the direct endothelin-1-evoked vasoconstriction. These results, together with the lack of relaxation in response to sarafotoxin S6c in SHR, suggest that an imbalance in the endothelin-1 ability to induce both contraction and relaxation is present in SHR with sustained hypertension, manifesting as a greater contractile effect evoked in this strain.

Topics: Animals; Antihypertensive Agents; Azepines; Blood Pressure; Cyclooxygenase Inhibitors; Disease Models, Animal; Endothelin-1; Endothelium, Vascular; Hypertension; Indomethacin; Mesenteric Arteries; Oligopeptides; Piperidines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Vascular Resistance; Vasoconstriction

To test the hypothesis that endothelin (ET) and nitric oxide (NO) interact in modulating the sympathetic nervous system in conscious rats, as they do in the endothelium, mean arterial pressure (MAP), heart rate, and renal sympathetic nerve activity (RSNA) were recorded in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) given losartan and compared before and during intravenous infusion of an NO synthase inhibitor, L-NMMA (0.25 mg/kg/min). The slope of the relation between RSNA and MAP to blood pressure reduction was increased in the presence of L-NMMA (from 0.6 +/- 0.1 to 2.8 +/- 0.2), suggesting that endogenous NO suppresses the reflex increase in RSNA. Since NO inhibits ET production in the endothelium, we speculated that the increase in MAP-RSNA slope was due partly to an unmasking of ET, and thus recorded MAP, heart rate, and RSNA during intravenous infusions of both L-NMMA and the ET-type-A-receptor antagonist BQ-485 (0.10 mg/kg/min). The slope decreased significantly in SHR when BQ-485 was added (1.5 +/- 0.2), but not in WKY, implying that unmasked ET enhanced the sympathetic increase via ETA receptors in hypertensive rats. An ETB-receptor antagonist potentiated the sympathetic response only in WKY rats. These results suggest that NO suppressed the reflex increase in RSNA to blood pressure reduction, while ET uncovered by L-NMMA enhanced the sympatho-activation, indicating an interaction between ET and NO in modulating the sympathetic nervous system in conscious hypertensive animals in vivo. In contrast, the interaction was not observed in normotensive rats.

Topics: Animals; Antihypertensive Agents; Azepines; Biphenyl Compounds; Blood Pressure; Electrodes, Implanted; Endothelin Receptor Antagonists; Endothelins; Heart Rate; Hypertension; Imidazoles; Kidney; Losartan; Male; Nitric Oxide; Oligopeptides; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Sympathetic Nervous System; Tetrazoles