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EFFECTS OF NITRIC OXIDE SYNTHASE INHIBITION AND ENDOTHELIN ET A RECEPTOR BLOCKADE ON HAEMODYNAMICS IN HYPERTENSIVE RATS
Author(s) -
Granstam SO,
Lind L.,
Granstam E.,
Fellström B.
Publication year - 1998
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1998.tb02278.x
Subject(s) - endocrinology , medicine , vasodilation , omega n methylarginine , vascular resistance , nitric oxide synthase , nitric oxide , hemodynamics , endothelin 1 , endothelin receptor , renal blood flow , acetylcholine , chemistry , receptor
SUMMARY 1. The objectives of the present study were to study regional differences in haemodynamics between spontaneously hypertensive (SHR) and normotensive Wistar‐Kyoto (WKY) rats induced by the nitric oxide synthase (NOS) inhibitor N G ‐monomethyl ‐ l ‐arginine ( l ‐NMMA) and the endothelin ET A receptor antagonist BQ123 in vivo in tissues known to be important for blood pressure (BP) regulation (heart, kidney and skeletal muscle). Furthermore, the effect of acetylcholine (ACh) infusion (2 μg/kg per min) was examined after l ‐NMMA or BQ 123. The microsphere method was used for determinations of cardiac index (CI) and regional haemodynamics. 2. N G ‐Monomethyl‐ l ‐arginine (20mg/kg) increased BP (26–48%; P < 0.01) and reduced CI in both rat strains. BQ 123 (1 mg/kg) reduced BP slightly (‐4 to 11 %; P < 0.05). 3. N G ‐Monomethyl‐ l ‐arginine significantly increased myocardial and skeletal muscle vascular resistance in SHR only; however, in the kidney, l ‐NMMA reduced blood flow and increased vascular resistance in both rat strains. 4. BQ 123 induced minor changes in regional haemodynamics that were not significantly different between the two strains. 5. Acetylcholine following BQ123 induced an increase in myocardial blood flow in WKY rats, but decreased blood flow in SHR. Acetylcholine following l ‐NMMA reduced myocardial blood flow in both strains. 6. Acetylcholine following BQ 123 induced renal vasodilation in WKY rats but, following l ‐NMMA, ACh did not induce renal vasodilation in either rat strain. In contrast, l ‐NMMA did not abolish the vasodilation of acetylcholine in skeletal muscle in WKY rats. 7. In conclusion, the contribution of nitric oxide to basal vessel tone was not impaired in the heart, skeletal muscle and kidney in SHR. Antagonism of ET A receptors caused similar haemodynamic responses in both rat strains in these organs. Furthermore, NOS inhibition, but not ET A blockade, blunted the expected ACh‐induced vasodilation in the heart and kidney in WKY rats, but not in skeletal muscle in both strains.