Mecamylamine pretreatment counteracts cigarette smoke induced changes in hypothalamic catecholamine neuron systems and in anterior pituitary function.

We have studied the effects of acute, intermittent exposure to tobacco smoke on discrete hypothalamic CA nerve terminal networks and on neuroendocrine function by means of quantitative histofluorimetrical determinations of catecholamine (CA) fluorescence in sections of rat brain and by radioimmunoassay procedures for hormones. Acute intermittent exposure to cigarette smoke induced a lowering of NA levels and increased NA turnover in discrete hypothalamic nerve terminal regions. This exposure also induced increases in DA turnover in the median eminence. The cigarette smoke lowered TSH, prolactin, LH and FSH serum levels, but induced an increase in serum corticosterone concentrations. To determine if the above mentioned changes in neuroendocrine function were nicotine mediated, a cholinergic nicotine-like blocking agent, mecamylamine, was administered prior to exposure to cigarette smoke. Pretreatment with mecamylamine (1.0 mg kg-1) counteracted the cigarette smoke induced changes in CA levels and turnover in all hypothalamic CA nerve terminal regions as well as the changes in serum levels of the pituitary hormones and corticosterone. It is suggested that acute intermittent exposure to cigarette smoke, via its nicotine component, lowers TSH, prolactin, LH and FSH secretion at least in part through activation of the tubero-infundibular DA neurons. Furthermore, the nicotine component of the cigarette smoke is suggested to induce the increase in corticosterone serum levels via increasing NA turnover in the paraventricular hypothalamic nucleus.