Does enhanced sympathetic tone contribute to angiotensin II hypertension in rats?
To determine whether enhanced sympathetic tone contributes to the maintenance of chronic angiotensin II (A II, 10 ng/min i.v. for 10 days) hypertension in rats, sympathetic activity was assessed in hypertensive and control rats by measuring norepinephrine (NE) turnover (alpha-methyl-p-tyrosine) in peripheral organs and by measuring depressor responses to ganglionic blockade in conscious rats. Pressor responses to methoxamine (1-8 micrograms/min) and arginine vasopressin (0.5-4 ng/min) were also obtained in rats with ganglionic blockade. Chronic A II infusion produced significant hypertension (mean +/- S.E. tail cuff pressure: 176 +/- 5 vs. 134 +/- 2 mm Hg in controls; n = 23 each group) but there were no significant differences in NE turnover in heart, kidney, skeletal muscle, or intestine in hypertensive rats compared with controls. Ganglionic blockade produced a significantly larger decrease in mean arterial pressure in A II-treated rats when compared with controls (73 +/- 7 vs. 38 +/- 2 mm Hg, n = 18 for each group). Dose-response curves for methoxamine and vasopressin were not significantly different between groups. The results suggest that the maintenance of chronic A II hypertension does not involve postsynaptic interactions between A II and the sympathetic system. The NE turnover data do not support the hypothesis that rats with chronic A II hypertension have enhanced sympathetic tone.
Kline
R L
RL
Department of Physiology, Health Sciences Centre, University of Western Ontario, Canada.
Chow
K Y
KY
Mercer
P F
PF
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000804:Angiotensin II / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D005730:Ganglionic Blockers / Q000494:pharmacology; D006439:Hemodynamics / Q000187:drug effects; D006973:Hypertension / Q000139:chemically induced* / Q000503:physiopathology; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D008781:Methyltyrosines / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014882:Water-Electrolyte Balance / Q000187:drug effects; D019805:alpha-Methyltyrosine
D000316:Adrenergic alpha-Agonists; D005730:Ganglionic Blockers; D008781:Methyltyrosines; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D001127:Arginine Vasopressin; D019805:alpha-Methyltyrosine; D014446:Tyrosine 3-Monooxygenase; D008729:Methoxamine; D009638:Norepinephrine