Effect of chronic preoptic lesions on the renal excretion of sodium in rats

Rats with bilateral lesions in the preoptic area showed a normal pattern of urineand electrolyte excretion under resting conditions but complete absence of a natriuretic response to unilateral carotid baroreceptor stimulation and also a significant reduction in the rate of sodium excretion after saline loading and after a high-sodium intake. Measurements of renal clearance did not show any significant differences in glomerular filtration rate, renal plasma flow, or filtration fraction between normal and preoptic-lesion rats. Apart from the test situations used above, rats with preoptic lesions were apparently able to regulate their sodium metabolism normally because after 3 wk on a high-sodium intake their plasma and extracellular fluid volumes, plasma electrolytes, osmolaity, and mean arterial pressures were indistinguishable from normal rats.It is suggested that the preoptic component of the baroreceptor reflex pathway mighthave an input into a hypothalamic area controlling sodium excretion.