British Journal of Anaesthesia, Vol 79, Issue 1 84-87, Copyright © 1997 by The Board of Management and Trustees of the British Journal of Anaesthesia
P. Kirstetter, F. Lagneau, O. Lucas, Y. Krupa and J. Marty
The mechanisms by which endothelium attenuates vasodilation caused by
isoflurane are not well understood. We examined the role of endothelium-
derived substances, nitric oxide (NO), endothelium-derived hyperpolarizing
factors (EDHF), prostanoids and endothelins in the response to isoflurane
in rat thoracic aorta. Increasing cumulative concentrations of isoflurane
were administered to aortic rings suspended in Hepes solution and
preconstricted with either phenylephrine 10(-6) mol litre-1 or KCl 40 mmol
litre-1 (which inhibit EDHF). Rings were intact, denuded or incubated with
an inhibitor of nitric oxide synthesis (N omega-nitro-L-arginine (LNNA 5 x
10(-5) mol litre-1), an inhibitor of prostanoid synthesis (indomethacin
10(-5) mol litre-1) or a blocker of the vascular receptors to endothelins
(cyclo (- D-trp-D-Asp-Pro-D-Val-Leu (BQ 123 10(-5) mol litre-1)-
Endothelium attenuated isoflurane-induced vasodilation in KCl-constricted
rings at concentrations of 4% (mean 95 (SEM 4)% vs 72 (4)%; P = 0.0005) and
5% (100 (4)% vs 80 (4)%; P = 0.0008) and in phenylephrine constricted rings
at concentrations of 4% (54 (8)% vs 35 (3)%; P = 0.04) and 5% (78 (10)% vs
49 (5)%; P = 0.03). Relaxation was significantly greater in rings treated
with LNNA than in intact rings at concentrations of 4% (85 (4)% vs 72 (4)%;
P = 0.0005) and 5% (90 (4)% vs 80 (4)%; P = 0.0008). Indomethacin and BQ
123 did not alter isoflurane-induced vasodilation. We conclude that
endothelium attenuated the vasodilator effect of isoflurane by a mechanism
which was abolished by inhibition of nitric oxide. We hypothesize that
isoflurane inhibits the release of nitric oxide, leading to a relative
vasoconstriction counter-balancing its vasodilator effect. In contrast,
EDHF, prostanoids and endothelins were not involved in the attenuation of
isoflurane-induced vasodilatation.
LABORATORY INVESTIGATIONS
Role of endothelium in the modulation of isoflurane-induced vasodilatation in rat thoracic aorta
Department of Anaesthesia, Hopital Beaujon, Clichy and INSERM U-408, Hopital Bichat, Paris, France
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