ABSTRACT
Microinjections into the nucleus of the tractus solitarius (NTS) of mu- and delta-selective opioid agonists increases both arterial pressure and heart rate in artificially respirated rats, while kappa receptor activation evokes tachycardia with no effect on blood pressure. Although opioid drugs are among the oldest pharmacologically active substances known, it was not until the latter part of the 19th century that the cardiovascular actions of opioid derivatives were studied in any detail. Among the earliest reported and most prominent of the cardiovascular effects produced by high doses of peripherally administered opioids was orthostatic hypotension. Nevertheless, many studies have suggested that central opioids and/or opioid receptors might modulate baroreflex function. The NTS is the site of the first central synapse of peripheral baroreceptor afferent nerves. In addition to opioid effects on blood pressure and heart rate, many investigators have examined the effect of opioid receptor stimulation and blockade on the function of baroreceptor reflexes.
