Renal prostanoids: physiological relevance in healthy salt-depleted women

Abstract

The effective role played by prostanoids in the control of renal function has been investigated in healthy women with salt depletion. Salt depletion (SD2 group, n = 6) was induced by low sodium chloride dietary intake (< or = 60 mmol per day) and combined treatment with natriuretic and potassium-sparing drugs. At the end of the depletive treatment, the cumulative sodium deficit was 513 +/- 56 mmol. The renal function and urinary excretions of prostaglandin (PG) E2, 6-keto-PGF1 alpha (6KPGF) and thromboxane (Tx) B2 were evaluated during hypotonic polyuria. The basal values of plasma sodium and potassium concentrations, plasma renin activity (PRA) and urinary aldosterone excretion were determined before the induction of hypotonic polyuria. Paired studies were performed in the absence (control) and presence of indomethacin both in the SD2 group and in a previously studied group (N2, n = 6) of healthy women in normal sodium and potassium balance. Women in normal balance received 100 mg i.m. of indomethacin, salt-depleted women received only 50 mg (because 100 mg of the drug produced a prolonged anuria). In the SD2 vs. N2 group in the absence of treatment the following significant differences were found: (a) higher basal values of PRA and urinary aldosterone excretion; (b) higher urinary excretions of 6KPGF and TxB2 but not of PGE2; (c) lower values of urinary flow rate, creatinine clearance, absolute and fractional excretions of sodium and chloride, plasma osmolality and plasma electrolyte concentrations. The effects of the indomethacin have been assessed as percentage variations by using paired data for each experimental group. In the SD2 vs. N2 group the reduction in urinary excretions of 6KPGF, TxB2 and potassium as well as in creatinine clearance were not significantly different. On the other hand, the following were significantly different: (a) the lower reduction in PGE2 excretion; (b) the higher reduction in urinary flow rate and in CH2O; (c) the reductions in absolute and fractional excretions of sodium and chloride, and the increase in plasma potassium concentration, significant in the SD2 group but not in the N2 group. The data suggest that: (1) when stimulated by salt depletion the renal biosynthetic pathways of PGI2 and TxA2 showed greater sensitivity to indomethacin inhibition; (2) the effects of the neurohormonal systems activated by salt depletion were either modulated or mediated by renal prostanoids.