EFFECTS OF DIETARY SALT ON ANGIOTENSIN PEPTIDES IN KIDNEY

This study used a novel simple method for the extraction, separation, identification, and quantitation of angiotensin-like immunoactivity fr om tissue to examine the effects of altering dietary NaCl intake on in trarenal angiotensin I, Il, and III levels in salt-sensitive, spontane ously hypertensive rats, salt-resistant Wistar-Kyoto rats, and Sprague -Dawley rats. Seven-week-old male spontaneously hypertensive rats, Wis tar-Kyoto rats, and Sprague-Dawley rats were assigned randomly to a di et containing either 8% (high) or 1% (basal) salt and were maintained on these diets for 3 wk. Rats were then decapitated without prior anes thesia, and kidneys were rapidly (< 30 s) removed, snap frozen in liqu id nitrogen, and stored at -80 degrees C. Frozen tissue was extracted in 2 M acetic acid and then subjected to solid-phase extraction with t he cation exchange resin AG 50W X4. Angiotensin peptides were separate d by reversed-phase high-performance liquid chromatography on a phenyl silica gel column with an eluent consisting of 20% acetonitrile in 0. 1 M ammonium phosphate buffer, pH 4.9, and quantitated by radioimmunoa ssay. The elution of standard peptides under isocratic conditions reve aled clear resolution of angiotensin I, II, and III and the (1-7) and (3-8) peptides. Recoveries of both labeled and unlabeled angiotensin p eptide standards from the extraction step were >90%. Renal angiotensin II stores were significantly higher in spontaneously hypertensive rat s than in Wistar-Kyoto or Sprague-Dawley rats, independent of diet. Re nal angiotensin II and III were further suppressed during dietary salt supplementation in both salt-resistant strains but not in the spontan eously hypertensive rat, These findings are consistent with an enhance d (compared with Wistar-Kyoto and Sprague-Dawley rats) role for angiot ensin II in the kidney of the salt-sensitive, spontaneously hypertensi ve rat, particularly under conditions of dietary salt supplementation.