The Effect of the Administration of Water or Isotonic Nacl Solution on the Urinary Excretion of 5-Hydroxyindoleacetic Acid in the Rat

Abstract

Abstract Administration of tap water by stomach tube or of isotonic NaCl solution orally or subcutaneously produces a conspicuous increase in the urinary excretion of 5-hydroxyindoleacetic acid (5-hiaa) in the rat. The same increase can be observed after administration of water plus posterior-pituitary antidiuretic hormone (adh). Tap water is less effective than physiological saline; the latter, in its turn, is more effective by the subcutaneous route than by mouth. Increase of 5-hiaa may be, for short periods, as high as 3 times normal. The minimum oral dose of tap water causing a significant increase in urinary 5-hiaa is 2 ml./100 g., that of physiological saline 1 ml./100 g. Repeated doses of both tap water and physiological saline produce a more intense and long-lasting increase of 5-hiaa output than single doses. Generally, excess 5-hiaa coincides with excess urine elimination, but there is no obligatory correlation of the intensity of the two phenomena. Recovery, as urinary 5-hiaa, of exogenous 5-hiaa, 5-hydroxytryptamine (5-ht) and 5-hydroxytryptophan (5-htp) is the same in control, non-hydrated rats and in rats given single or repeated doses of tap water, tap water plus adh, or isotonic saline solution. The mechanism by which water or saline administration produces increased urinary excretion of 5-hiaa is discussed.