Changes in urine volume and urinary electrolyte excretion after intracerebroventricular injection of arecoline and hemicholinium-3

Activation of cholinergic neurons in specific brain regions evokes a hypernatriuretic response, which appears to be atropine-sensitive and, perhaps, independent from the renal innervation. However the role of cholinergic neurons in central control of renal function is not well understood. The purpose of this study was to further investigate whether brain acetylcholine stores are able to influence kaliuresis and natriuresis in conscious rats. Therefore, the renal response to cholinergic drugs was examined in Wistar rats which underwent to a 0.15 M NaCl solution (saline) load administered by gavage. Central injection of arecoline, a muscarinic agonist, produced a dose-dependent reduction in water diuresis and a highly significant increase in sodium excretion within two hours from the oral saline load. An intracerebroventricular (ICV) injection of methylatropine completely blocked both the antidiuretic and the natriuretic response induced by arecoline. Hemicholinium-3 (HC), centrally administered at a dose (34.8 nmol) known to be capable of inducing a maximal depletion of brain acetylcholine, elicited a time-dependent antidiuretic effect accompanied by a highly significant reduction in potassium and sodium urinary excretion. Therefore, we suggest that brain cholinergic neurons are involved in the regulation of the electrolyte balance.