Endogenous Opioids and Blood Pressure in Man
Effects on the cardiovascular system have been recognized as part of the pharmacological profile of opiate drugs since the end of the nineteenth century when orthostatic hypotension was documented in dogs . The early clinical studies performed with pethidine in man showed that this drug too can lower blood pressure at doses used clinically . Knowledge in this area increased substantially following the publication of an extensive study into the mechanism by which morphine lowers blood pressure in man . Fifteen milligrams of morphine given intravenously significantly reduced hand vein venous pressure during temporary circulatory arrest, and there is a similar reduction in forearm venous tone. Forearm blood flow also increases significantly following morphine. These investigators presented evidence suggesting that the action of morphine was central rather than peripheral. Morphine had no effect on the arteriolar or venoconstrictor actions of noradrenaline when administered intraarterially, and conversely the actions of morphine on arterioles were unimpaired by beta-adrenoceptor, cholinoceptor, or histamine receptor blockade. Also, when morphine was given into a brachial artery there were no changes in forearm blood flow. These observations have taken on new relevance with the identification of endogenous opioids.
KeywordsPlacebo Morphine Histamine Noradrenaline Methionine
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