On the relationship between urinary PGE2 and PGF2 alpha excretion rates and urine flow, osmolar excretion rate and urinary osmolality in anesthetized rats.

A strong inverse relationship was found between the excretion rates of the prostaglandins PGE2 and PGF2 alpha and urine flow (and osmolar excretion rate) over a range of urine flow rates from 1.5 to 40 microliters . min-1 . g kidney weight-1, covering spontaneous variations and isotonic saline diuresis. These results suggest the operation of a negative feedback mechanism by which the diuretic action of the prostaglandins, as part of a defence system, counteracts excessive oliguria. PGE2 excretion did not correlate with either urinary kallikrein excretion or plasma renin concentration. When the concentrating mechanism was interfered with by reducing renal perfusion pressure to, or below 65 mmHg, and vasopressin was given i.v. PGE2 excretion rate roughly parallelled urine--and probably medullary interstitial osmolar activity. However, in hydropenic rats there was no correlation between urine osmolality (Uosm) and PGE2 excretion over a range of osmolalities from 500 to 2 500 mOsm . kg-1, nor any relationship between delta Uosm and delta PGE2 excretion. Thus, a high interstitial osmolar activity appears to be a prerequisite for the activation of PG-synthesis in the renal medulla, but another (other) yet undefined factor(s) play the major role as (a) determinant(s) for PG-excretion in vivo.