OSMOTICALLY INDUCED DRINKING IN THE GOAT: AN OSMORECEPTOR OR A SODIUM RECEPTOR MECHANISM?

¹ A.F.R.C. Institute of Animal Physiology, Babraham, Cambridge CB2 4AT

Changes in sodium concentration and osmolality in lateral ventricle cerebrospinal fluid (c.s.f.) caused by intracarotid infusion of hypertonic solutions were measured in conscious goats. Intracarotid infusion (1·5 ml.min^-1) of 1·0 or 2·0 mol.kg^-1 or urea 4·0 mol.kg^-1 produced significant increases in osmolality and increases in sodium concentration of the c.s.f. 5 and 10 min after the beginning of the infusion. No significant effect was seen following intracarotid infusion of 0·15 M-NaCl. Only intracarotid NaCl 1·0 or 2·0 mol.kg^-1 caused significant drinking. Blood osmolality was significantly increased by the two hypertonic NaCl solutions as well as by hypertonic urea. In conclusion, drinking in goats following peripheral administration of hypertonic solutions is probably due to an osmoreceptor mechanism. A c.s.f. sodium receptor mechanism is unlikely because hypertonic NaCl or urea both increased the sodium concentration in c.s.f. but only the osmotically effective NaCl solution produced significant drinking.