Sympathetic activation in rats with L-NAME-induced hypertension.
We evaluated the hemodynamic pattern and the contribution of the sympathetic nervous system in conscious and anesthetized (1.4 g/kg urethane, iv) Wistar rats with L-NAME-induced hypertension (20 mg/kg daily). The basal hemodynamic profile was similar for hypertensive animals, conscious (N = 12) or anesthetized (N = 12) treated with L-NAME for 2 or 7 days: increase of total peripheral resistance associated with a decrease of cardiac output (CO) compared to normotensive animals, conscious (N = 14) or anesthetized (N = 14). Sympathetic blockade with hexamethonium essentially caused a decrease in total peripheral resistance in hypertensive animals (conscious, 2 days: from (means +/- SEM) 2.47 +/- 0.08 to 2.14 +/- 0.07; conscious, 7 days: from 2.85 +/- 0.13 to 2.07 +/- 0.33; anesthetized, 2 days: from 3.00 +/- 0.09 to 1.83 +/- 0.25 and anesthetized, 7 days: from 3.56 +/- 0.11 to 1.53 +/- 0.10 mmHg mL-1 min-1) with no change in CO in either group. However, in the normotensive group a fall in CO (conscious: from 125 +/- 4.5 to 96 +/- 4; anesthetized: from 118 +/- 1.5 to 104 +/- 5.5 mL/min) was observed. The responses after hexamethonium were more prominent in the hypertensive anesthetized group. However, no difference was observed between conscious and anesthetized normotensive rats in response to sympathetic blockade. The present study shows that the vasoconstriction in response to L-NAME was mediated by the sympathetic drive. The sympathetic tone plays an important role in the initiation and maintenance of hypertension.
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Disciplina de Fisiologia Cardiovascular e Respiratória, Departamento de Fisiologia, Escola Paulista de Medicina, Universidade Federal de São Paulo, Rua Botucatu 862, 04023-060 São Paulo, SP, Brazil.
Bergamaschi
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D000818:Animals; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology*; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors; D006973:Hypertension / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology*
D004791:Enzyme Inhibitors; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester