The findings about mechanisms regulating production and excretion of urodilatin [ANP-(95-126)], a member of the atrial natriuretic peptide (ANP) family, are controversial. To elucidate a possible relationship between arterial blood pressure and renal urodilatin excretion, we studied the effects of different perfusion pressures on urine flow (UV), urinary sodium (U(Na)V), urinary potassium (U(K)V), and urodilatin excretion (U(URO)V), and the concentration of urodilatin in the perfusate (P(URO)) of isolated perfused rat kidneys. Kidneys were perfused for 180 min with constant perfusion pressures (80 and 120 mmHg, respectively; each, n = 4) in a closed circuit system. Samples of urine and perfusate were taken every 30 min. Mean UV, U(Na)V, U(K)V, and U(URO)V values were significantly higher with a perfusion pressure of 120 mmHg than with 80 mmHg, whereas P(URO) did not change significantly. Serial measurements revealed no direct relation of U(URO)V with either U(Na)V or UV. This suggests that renal perfusion pressure is a determinant of U(URO)V and that urinary and venous effluent concentrations of urodilatin (probably production) are not coupled directly and that U(URO)V and U(Na)V may dissociate during acute variations of sodium excretion and UV.
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