FUROSEMIDE STIMULATES RENIN EXPRESSION IN THE KIDNEYS OF SALT-SUPPLEMENTED RATS

This study was conducted to obtain information about a possible influe nce of salt transport by the thick ascending limb of Henle (TALH) and the macula densa on the expression of renin in the kidney. To this end , adult male rats were subcutaneously infused with furosemide (12 mg/2 4 h), an established inhibitor of TALH and macula densa salt transport , or with vehicle for 6 days. The animals had free access to chow, wat er and salt water (0.8% NaCl, 0.1% KCl) to maintain salt and water bal ance. Chronic furosemide treatment led to a 20-fold increase in urine flow rates and 50% increase in kidney weights, while urine osmolality decreased by 60% and body weight gain decreased by 40% in the furosemi de-treated animals. Plasma renin activities increased from 2.9 +/- 0.5 ng angiotensin I h-1 ml-1 in controls to 10.6 +/- 2.2 ng angiotensin I h-1 ml-1 in furosemide-treated rats. In parallel, kidney areas immun oreactive for renin increased by 80% and the renal content of renin mR NA increased by 120% in the animals receiving furosemide. Under the as sumption that the effects seen on renal renin expression were primaril y due to the inhibition of TALH and macula densa function by furosemid e, our findings suggest that salt transport across the TALH and macula densa exerts a negative control function not only on the secretion bu t also on the expression of renin in the kidney.