Effect of chronic nicotine treatment and its withdrawal on the vasopressinergic system in rats

Abstract We have studied the effect of chronic nicotine treatment and its withdrawal on the hypothalamo-neurohypophyseal Vasopressinergic system in male Sprague-Dawley rats. They were subcutaneously infused with low and high doses of nicotine, free base (0.6 and 6.0 mg/kg/day, respectively) for 28 days, via Alzet osmotic pumps. The studies were carried out immediately after the period of infusion and 1, 7, 14 and 28 (the latter in high dose only) days later. Basal, high K(+)-stimulated and total vasopressin release from the superfused neural lobes, the residual vasopressin content in the neural lobes, and hypothalamus and plasma vasopressin concentration were measured by radioimmunoassay. Treatment with the high dose of chronic nicotine alone decreased vasopressin content in and release from the neural lobe and its plasma concentration, but it did not change significantly the vasopressin content in the hypothalamus. A similar pattern of changes in vasopressin release and plasma concentration, though less pronounced, was observed in the rats infused with the low dose of nicotine. The withdrawal of the high dose of chronic nicotine gradually returned the decreased plasma vasopressin concentration, and its content in and release from the neural lobe to control values within 2 weeks. However, vasopressin content in the hypothalamus started to decline 1 week after nicotine withdrawal and persisted to decline for at least 3 subsequent weeks. The withdrawal of the high dose was associated with a marked suppression of high K(+)-stimulated vasopressin release from the neural lobe for a period of 4 weeks. The withdrawal of the low dose of nicotine exhibited a significant decline in plasma vasopressin concentration for up to 2 weeks only following chronic nicotine withdrawal, tending to return subsequently to control levels.