Mechanism of the Antidiuretic Effect Associated with Interruption of Parasympathetic Pathways

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Abstract
The present experiments were undertaken to investigate the mechanism whereby the parasympathetic nervous system may be involved in the renal regulation of solute-free water excretion. The effects of interruption of parasympathetic pathways by bilateral cervical vagotomy were examined in eight normal and seven hypophysectomized anesthetized dogs undergoing a water diuresis. In the normal animals cervical vagotomy decreased free-water clearance (CH2O) from 2.59±0.4 se to −0.26±0.1 ml/min (P < 0.001), and urinary osmolality (Uosm) increased from 86±7 to 396±60 mOsm/kg (P < 0.001). This antidiuretic effect was not associated with changes in cardiac output, renal perfusion pressure, glomerular filtration rate, renal vascular resistance, or filtration fraction and was not affected by renal denervation. A small but significant increase in urinary sodium and potassium excretion was observed after vagotomy in these normal animals. Pharmacological blockade of parasympathetic efferent pathways with atropine, curare, or both was not associated with an alteration in either renal hemodynamics or renal diluting capacity. In contrast to the results in normal animals, cervical vagotomy was not associated with an antidiuretic effect in hypophysectomized animals. CH2O was 2.29±0.26 ml/min before and 2.41±0.3 ml/min after vagotomy, and Uosm was 88±9.5 mOsm/kg before vagotomy and 78±8.6 mOsm/kg after vagotomy in the hypophysectomized animals. Changes in systemic or renal hemodynamics or electrolyte excretion were also not observed after vagotomy in these hypophysectomized animals. On the basis of these results, we conclude that the antidiuretic effect associated with cervical vagotomy is initiated by interruption of parasympathetic afferent pathways and is mediated by increased endogenous release of vasopressin. This antidiuresis was also demonstrated to occur in the absence of renal nerves and alterations in systemic and renal hemodynamics.