Influence of prostaglandins on papillary blood flow and pressure-natriuretic response.

The present study examined whether renal prostaglandins influence the pressure-natriuretic response by altering medullary hemodynamics or renal interstitial pressure. The diuretic and natriuretic responses to changes in renal perfusion pressure were compared in control rats (n = 15) and in rats receiving either meclofenamate (2 mg/kg, n = 9) or indomethacin (2 mg/kg, n = 4). In control rats, urine flow and sodium excretion increased from 10 +/- 2 to 118 +/- 10 microliters/min/g kidney wt and from 1.8 +/- 0.3 to 21.0 +/- 1.5 mueq/min/g kidney wt, respectively, when renal perfusion pressure was increased from 109 to 167 mm Hg. Urinary excretion of prostaglandin E2 and thromboxane B2 increased significantly by 152% and 190%, respectively. Meclofenamate lowered thromboxane B2 and prostaglandin E2 excretion and prevented the increase in eicosanoid excretion produced by elevations in perfusion pressure. The pressure-diuretic and pressure-natriuretic responses of rats given meclofenamate or indomethacin were approximately half of those observed in the control rats. Papillary blood flow increased 21% and renal interstitial pressure rose from 5.0 +/- 0.7 to 8.2 +/- 0.7 mm Hg in control rats when pressure was elevated from 100 to 150 mm Hg. Meclofenamate and indomethacin lowered papillary blood flow and renal interstitial pressure and blunted the increases in these values produced by elevations in perfusion pressure. These results support the view that renal prostaglandins modulate the pressure-natriuresis relation by altering renal medullary hemodynamics and suggest that an intact renal prostaglandin system is necessary for the full expression of the medullary hemodynamic and natriuretic responses to increases in renal perfusion pressure.