Modulation of Baroreflexes in Hypertensive Rats / 대한신장학회지

PURPOSE: Baroreceptor reflex regulation has been shown to reset towards a higher blood pressure level. This study was designed to assess alterations of chronotropic baroreflexes in two-kidney, one clip (2K1C) and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. METHODS: Arterial pressure and heart rate (HR) were monitored continuously during intravenous infusions of phenylephrine or sodium nitroprusside. Ensuing reflex HR responses during each drug infusion were determined in two ways: (a) at 10 s intervals (time analysis), and (b) with every 10 mmHg change in pressure (pressure analysis). RESULTS: Both pressor and depressor responses produced by phenylephrine or sodium nitroprusside were comparable between normotensive and hypertensive rats. Both reflex tachycardia and bradycardia were attenuated in 2K1C hypertensive rats as compared with normotensive rats, whereas no significant differences were shown in DOCA-salt hypertensive rats. CONCLUSION: These results indicate that chronotropic baroreflexes are impaired in 2K1C hypertensive rats, but not in DOCA-salt hypertensive rats.

Effects of Atrial Natriuretic Peptide on the Arterial Basal Tone in Renovascular Hypertensive Rats / 대한신장학회지

PURPOSE: Hypertension may be involved an alteration of intrinsic basal tone in vascular smooth muscle. The purpose of this study was to investigate the vasorelaxant effect of atrial natriuretic peptide (ANP) on isolated non-contracted aorta from two-kidney, one clip (2K1C) renovascular hypertensive rats. METHODS: 2K1C hypertension was induced by clipping the left renal artery and were used 6 weeks later. Age-matched rats receiving a sham treatment, which served as controls. The thoracic aortae were mounted in tissue baths to measure the isometric tension. RESULTS: ANP diminished basal tone in previously unstimulated thoracic aortic rings from 2K1C hypertensive rats, while it had no effect in the control rats. Endothelial destruction potentiated the vasorelaxant effect of ANP on basal tone in 2K1C rats. A similar potentiation of the ANP response was observed by pre-treatment with N omega-nitro-L-arginine methyl ester (L-NAME) or methylene blue in aortic rings with endothelium. Treatment with calcium-free Krebs decreased basal tone and abolished ANPresponse. These effects were observed only in aortic rings from 2K1C rats. Similarly, staurosporine and calphostin C, inhibitors of protein kinase C (PKC), lowered basal tone and abolished ANP-response in hypertensive rats. CONCLUSION: These results demonstrate that ANP has a vasorelaxant effect on basal tone in 2K1C renovascular hypertension. Inhibition of ANP effects on basal tone by calcium-free Krebs and PKC antagonists suggests that altered Ca2+ -active tone is involved in hypertension, that modifies the response of vascular smooth muscle to the ANP.