TIME-COURSE OF CHANGES IN RENAL TISSUE COMPOSITION DURING LYSINE VASOPRESSIN INFUSION IN RAT

The corticomedullary osmolal gradient, largely dissipated by sustained water-diuresis, was progressively repleted by continuous i.v. ADH infusion (lysine-vasopressin, 15 mU/min/100 g body weight) in conscious rats for up to 41/2 hr. A marked increase in sodium content was essentially complete by 1/2 hr in the papillary tip; smaller, but more progressive increases occurred in the papillary base and inner medulla. Increases in medullary urea content occurred mainly in the first 21/2 hr, especially in the papillary tip. A progressive decrease in water content of all medullary segments was preceded by a significant papillary tip increase at 1/2 hr. Papillary tip-urine osmotic equilibration was slowly achieved after about 21/2 hr. The small, but significant, tip-urinary urea concentration difference of water diuresis was more rapidly replaced by a substantial difference in the reverse direction. It is concluded that the changes can be explained, adequately, by ADH-induced modifications in water and urea permeabilities of distal nephron segments and, possibly, by changes in inner medullary blood flow; that the evidence of direct ADH stimulation of sodium transport is inconclusive; and that there was no evidence of active urea transport. © 1969 Springer-Verlag.