Sympathoadrenal activity and sympathoinhibitory hormones during acute and chronic nicotine application in dogs

Though acute nicotine administration results in increased blood pressure and heart rate, previous work has shown that chronic nicotine treatment does not result in significant hypertension. In fact, surprisingly it has been shown to produce hypotension. We performed the present experiments to further analyze the effects of chronic nicotine treatment. In untreated dogs (n = 7) under pentobarbital anesthesia (with adrenal hormone release measured directly by cannulation of the adrenolumbar veins) cumulative nicotine infusions (1-24 micrograms/kg/min i.v.) caused dose-dependent release of epinephrine (from 3.0 +/- 0.7 to 111 +/- 30 micrograms/kg/min) and norepinephrine (from 0.4 +/- 0.1 to 11.2 +/- 3.1). However, significant release of leu-enkephalin and met-enkephalin immunoreactivity was observed only with the highest nicotine infusion (24 micrograms/kg/min). In untreated conscious dogs (n = 12), nicotine test infusions (3 and 10 micrograms/kg/min), 15 min, yielded smoking relevant plasma nicotine levels and augmented heart rate, mean arterial pressure, plasma catecholamine levels, and adrenal epinephrine release. Plasma-enkephalin immunoreactivities were only marginally elevated with the higher nicotine test infusion. Chronic nicotine treatment (1.5 micrograms/kg/min s.c. for 5 weeks, n = 7), only transiently (first 1-2 weeks) augmented mean arterial pressure, heart rate, and epinephrine release, but during the plateau phase of treatment, hemodynamics and catecholamine parameters were identical to the pretreatment period. Acute responses of hemodynamics and catecholamines to nicotine test infusions declined progressively during chronic treatment, but the time course of this attenuation seemed not related to the reversal of the transient hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)