Chemical renal medullectomy. Effect on urinary prostaglandin E2 and plasma renin in response to variations in sodium intake and in relation to blood pressure.

Abstract

We have studied the possible vasodepressor role of the renal medulla by chemical medullectomy. Bromoethylamine hydrobromide (200 mg/kg) was injected to induce selective renal medullary necrosis in rats. The acute effects on sodium balance and long-term effects on blood pressure, plasma renin concentration (PRC) and urinary prostaglandin E2 (PGE2) were studied and compared with saline injected controls. There was an immediate and sustained increase in urine volume of low osmolality. Direct blood pressure in conscious free-moving animals was higher at 2 and 10 weeks after injection in medullary-damaged rats, although this was only significant at 10 weeks (136 +/- 3.3 vs 118 +/- 4.5 mm Hg, p less than 0.01). An initial negative sodium balance returned to normal by 7 days and rats with established medullary damage tolerated a wide range of sodium intakes. Although there was no evidence of sodium retention on the normal diet, with very high sodium loads some sodium retention was apparent since PRC was suppressed and body weight increased. Plasma creatinine and creatinine clearance were normal. PRC in rats with medullary damage was unchanged on normal diet and rose to similar levels as in control rats on low sodium intake. Urinary PGE2 was markedly reduced (148 +/- 54 vs 536 +/- 71 ng/day, p less than 0.01) in medullary damaged rats, consistent with the renal medulla being the major source of urinary PGE2. High salt intake increased urinary PGE2 in normal and proportionally in medullary damaged rats, whereas on a low sodium intake, urinary PGE2 was not different from that on the normal diet in either group.(ABSTRACT TRUNCATED AT 250 WORDS)