Renal concentration in the normal dog: effect of an acute reduction in salt excretion

Abstract

In normal anesthetized hydropenic dogs, the T^cH₂O-C_osm relation generated by infusing hypertonic solutions was variable. In ten dogs T^cH₂O rose as C_osm increased, attaining a maximum of 3.7–6.3 ml/min ("high curve"). In seven dogs a maximum T^cH₂O of only 1.4–2.5 ml/min was observed at low C_osm and CH₂O was often generated at moderate C_osm ("low curve"). The acute reproducibility of this T^cH₂O-C_osm relation was examined by allowing C_osm to return to low levels and again infusing the same hypertonic solution. The T^CH₂O-C_osm relation was duplicated only in dogs initially exhibiting a high curve. Therefore, the effects on T^cH₂O of acutely reduced sodium excretion were examined only in dogs with an initial high curve relation. After the first diuresis, a phlebotomy or prolonged infusion of 10% mannitol was utilized to induce salt retention. If sodium excretion was reduced to less than 40 µEq/min at low C_osm, T^cH₂O was decreased during the subsequent diuresis. This impairment in T^cH₂O generation is attributed to decreased availability of salt for transport into the medulla.