Evaluation of the involvement of nitric oxide and substance P in reducing baroreflex gain in the genetically hypertensive (GH) rat.
The attenuation of baroreflex gain associated with hereditary hypertension could involve abnormal signalling by nitric oxide or substance P. Baroreflex gain was measured in age-matched male genetically hypertensive (GH) and nonnotensive (N) anaesthetised rats from heart rate changes in response to i.v. phenylephrine or sodium nitroprusside. In subgroups of these animals, nitric oxide synthesis was inhibited using NG-nitro-L-arginine methyl ester (L-NAME, 30 mg x kg(-1) i.v.), substance P transmission was blocked using the antagonist SR 140333 (360 nmoles x kg(-1) i.v.) or substance P release was inhibited with resiniferatoxin (4 doses of 0.3 microg x kg(-1) i.v. at 4 min intervals). Baroreflex gain was markedly reduced in GH compared to N animals (N -0.37 +/- 0.04 beat x min(-1) x mm Hg(-1), GH -0.17 +/- 0.02 beat x min(-1) x mm Hg(-1), p < 0.0001). Inhibition of nitric oxide synthase increased baroreflex gain in each strain, but the inter-strain difference in gain persisted (post-treatment N -0.57 +/- 0.07 beat x min(-1) x mm Hg(-1), GH -0.24 +/- 0.05 beat x min(-1) x mm Hg(-1) (p < 0.001). Blockade of receptors or inhibition of substance P release did not affect gain in either strain. Nitric oxide, but not substance P, appears to play an inhibitory role in the rat arterial baroreflex. Impairment of baroreflex gain in GH rats is not secondary to altered nitric oxide signaling.
Brady
Felicity
F
Department of Physiology, Trinity College, Dublin, Ireland.
Bakhle
Y S
YS
Bell
C
C
D000818:Animals; D017704:Baroreflex / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D004224:Diterpenes / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006973:Hypertension / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D064729:Neurokinin-1 Receptor Antagonists; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011812:Quinuclidines / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D012146:Rest; D013373:Substance P / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D004224:Diterpenes; D004791:Enzyme Inhibitors; D064729:Neurokinin-1 Receptor Antagonists; D010880:Piperidines; D011812:Quinuclidines; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C085215:SR 140333; D009599:Nitroprusside; D010656:Phenylephrine; D009569:Nitric Oxide; D013373:Substance P; C024353:resiniferatoxin; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester