Evidence for a Hypothalamic Control of Renal Sodium Excretion

Abstract Slow infusions (7.5 μl/min) of hypertonic NaCl into the 3rd brain ventricle of goats maintained on a NaCl‐supplemented diet provoked natriuresis reaching maximum about 70 min after onset of the infusions. The natriuresis was less pronounced in animals receiving no dietary NaCl‐supplementation. The magnitude of the natriuretic response was dependent on the molarity of the NaCl infused and on infusion duration. A much smaller relative increase in K excretion, reaching peak values 20 min before maximum natriuresis, also occurred. Aldosterone treatment did not prevent the natriuretic response and it could be elicited in diabetes insipidus animals, showing that release of posterior pituitary hormones was not essential. Determinations of inulin clearance (CIn) indicated that glomerular filtration rat (GFR) increased and that relative reabsorption of Na+ decreased during the natriuresis. Similar intraventricular infusions of hypertonic NH4Cl resulted in greatly diminished renal Na+ excretion lasting for about 2 hrs. Such infusions also delayed by 90 min the normal natriuretic response to an intravenous NaCl load. CIn determinations indicated that a diminished GFR may have contributed to this reduction in renal Na+ excretion. The results indicate that renal Na+ excretion is under hypothalamic control in the goat. Possible mechanisms for this control are discussed.