The expression of heme oxygenase-1 and inducible nitric oxide synthase in aorta during the development of hypertension in spontaneously hypertensive rats

Background: The aim of this study was to observe the time-course changes of heme oxygenase-1 (HO-1) and inducible nitric oxide synthase (iNOS) induction in aorta during the development of hypertension, as well as the relationship of HO-1/carbon monoxide (CO) system and iNOS/nitric oxide (NO) system in spontaneously hypertensive rats (SHR). Methods: The systolic blood pressure (SBP) was determined in conscious rats by the tail-cuff method. The tissue HO-I and iNOS mRNA and protein levels were estimated with reverse transcription polymerase chain reaction and Western blot method. Results: The expression of HO-1 and iNOS in aorta increased with the SBP elevation during the development of SHR and was attenuated when the hypertension was lowered with the vasodilator hydralazine. At 8 weeks, only HO-1 was induced, whereas at 12 and 16 weeks, both HO-1 and iNOS were observed. The level of plasma nitrite/nitrate was associated with the change in iNOS expression in SHR. In addition, the SBP of 8-week-old SHR was significantly increased after pretreatment with zinc protoporphyrin IX for 7 consecutive days. Chronic blockade of iNOS activity by aminoguanidine resulted in significant up-regulation of HO-1, but the pressor effect was blunt. Conclusions: These results suggest that the up-regulation of HO-1 and iNOS in aorta is a compensatory mechanism for the elevation of SBP during the development of hypertension in SHR. The expression of HO-I is earlier than that of iNOS. Our data suggest that the HO-1/CO system takes over and acts as a major modulator for the regulation of SBP when the iNOS/NO system is suppressed. (C) 2004 American Journal of Hypertension, Ltd.