Type 1 Angiotensin II Receptor Subtypes in Kidney of Normal and Salt-Sensitive Hypertensive Rats

Abstract

Abstract We studied the localization and regulation of the two type 1 angiotensin II receptor subtypes AT 1A and AT 1B in different renal zones of the rat kidney by a reverse transcription–polymerase chain reaction amplification method. The yield of the reaction was quantified with an internal standard that was a 63-bp deleted mutant cRNA of the AT 1A receptor. In kidneys of male Sprague-Dawley rats (n=4), the levels of AT 1A and AT 1B receptor mRNAs were highest in the inner stripe of the outer medulla, lowest in the inner medulla, and intermediate in the cortex and outer stripe of the outer medulla. Results (mean±SE) expressed in 10 5 molecules per microgram total RNA were for cortex, outer stripe, inner stripe, and inner medulla, respectively, 171±15, 152±27, 322±10, and 73±3 for AT 1A , and 35±9, 26±1, 71±10, and 53±11 for AT 1B . In Sabra rats sensitive (n=6) or resistant (n=6) to salt-induced hypertension and maintained on a normal salt diet, the percentage and level of each receptor subtype mRNA in cortex and outer stripe were similar in the two strains and comparable to those observed in Sprague-Dawley rats. However, AT 1A of the inner stripe was significantly decreased in salt-resistant compared with salt-sensitive rats (166±28 and 318±58 10 5 molecules per microgram total RNA, respectively). These modifications were organ specific because no difference in the level of the receptor mRNAs was observed in the liver of the two Sabra rat strains, whereas a twofold increase in AT 1A mRNA level but not in AT 1B mRNA level was apparent in adrenal and in one renal zone, the inner stripe of the outer medulla, of hypertension-prone Sabra rats.