Salt-induced hypertension in the 'Sabra' rat strain: influence of nifedipine treatment

A comparative study of morphological changes in spontaneously hypertensive rats and normotensive Wistar Kyoto rats treated with an angiotensin-converting enzyme inhibitor or a calcium-channel blocker

It is not clear whether some pathological changes in hypertension are directly pressure-dependent, or hormonally induced, or both. The aortic arch has apparently never before been studied for those changes. The aim of this study was to compare the effects of controlling angiotensin II (Ang II) and/or blood pressure (BP), directly at the inception of hypertension, on the aortic arch, the left ventricle of the heart (LV), and the kidneys of spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto (WKY) rats. An angiotensin-converting enzyme inhibitor (ACEI, enalapril) and a calcium-channel blocker (nifedipine) were used for 21 weeks. After treatment, rats were assessed for arterial plasma renin activity (PRA). The LV, aortic arch, and kidneys were then excised for the determination of organ and tissue weight in some of the animals, while in others the aortic arch was fixed in situ and processed for microscopic analysis. Both enalapril and nifedipine levelled BP in the SHRs to almost normal values. Enalapril was able to prevent the increase in LV and kidney weights (p=0.04 wet, p<0.001 dry; p<0.001 wet and dry, respectively) and the increase in the weight of the aortic arch and in the thickness of its media (p<0.001 wet and dry; p<0.001, respectively) seen in untreated SHRs. This was associated with a larger lumen diameter (p<0.001) and a lower media to lumen ratio (p=0.01). In contrast, nifedipine did not prevent any of the changes described. Neither nifedipine nor enalapril treatment had any effects on PRA in either rat strain. Our results support previous observations that BP is not the only factor causing some of the pathological changes in hypertension; tissue Ang II level may also play a major role.

Type 1 angiotensin II receptor subtypes in kidney of normal and salt-sensitive hypertensive rats

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.