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.

Role of Tyrosine Kinases in 5-HT-Induced Vascular Contraction in Two-Kidney, One Clip Hypertensive Rats / 대한신장학회잡지

Tyrosine kinases have been implicated in vascular smooth muscle cell proliferation and contraction. The involvement of tyrosine kinases in 5-hydroxytryptamine (5-HT)-induced contractile response of the isolated aorta was examined in two-kidney, one clip (2K1C) hypertensive rats, 2141C hypertension was made by constricting the left renal artery and age-matched control rat received sham treatment. Thoracic aortic rings denuded of endotheliurn were mounted in tissue bath, for measurement of isometric contractile force. The putative tyrosine kinase inhibitor, genistein, shifted concentration-response curves to 5-HT toward the right in control rats The isometric force generation induced by 5-HT was also inhibited by genistein in aortic rings from 2K1C: hypertensivc rats, however genistein did not affect on the high concentration of 5-HT in hypertensive rat ;. Genistein-induced relaxations were more attenuated in aortae from hypertensive rats than those from control Genistein had no effect on contrartcion elicited by the direct protein kinase C activator, phorbol 12, 13 dibutyrate (PDBu) either in 2KlC hypertensive or in control Group. These findings indicate that genistein-sensitive tyrosine kinases paeticipate in 5-HT-induced contraction of rat aortic smooth muscle, of which role is apparent in 2K1C: hypertension.

Pressor Responses to Intracerebroventricular Infusion of Hypertonic NaCl in Renal Hypertensive Rats

BACKGROUND: The sodium concentration in the central nervous system may play an important role in cardiovascular function and body fluid regulation. The purpose of this investigation was to examine the effects of intracerebroventricular (ICV) infusion of hypertonic NaCl solutions on the cardiovascular responses in normotensive and 2-kidney, 1 clip (2K1C) renal hypertensive rats. METHODS: 2K1C hypertension was made by clipping the left renal artery and were used 4 weeks later. Age-matched control rats received a sham treatment. Under thiopental (50 mg/kg, IP) anesthesia, both isotonic and hypertonic NaCl solutions (0.15 M, 0.6 M and 1.2 M) were ICV applied, while blood pressure and heart rate (HR) responses were continuously monitored. RESULTS: Central administration of hypertonic NaCl solution caused an elevation in mean arterial pressure (MAP) and HR in both normotensive and 2K1C hypertensive rats. The response magnitude in the blood pressure was positively correlated to the NaCl concentration in normotensive rats, while the pressor responses to hypertonic NaCl were comparable regardless of the concentration of NaCl in hypertensive rats. Despite of the HR responses were similar in between two groups, the magnitude of the MAP increases were more elevated in hypertensive than in normotensive control rats. Isotonic NaCl solution, when centrally applied, caused an elevation in blood pressure only in hypertensive rats. CONCLUSION: These results indicate that the central sensitivity to sodium chloride is altered in 2K1C renal hypertensive rats.

Effects of Nitric Oxide Synthesis Inhibition on the Blood Pressure Response to Bradykinin in Rats / 대한신장학회잡지

Bradykinin has been known to elicit a pressor effect when administered centrally, and a depressor effect when administered peripherally. The present study was aimed at investigating whether the blood pressure response to bradykinin is dependent on the endogenous generation of nitric oxide (NO). Effects of NG-nitro-L-arginine methyl ester (L-NAME) on the pressor and depressor responses to intracerebroventricularly and intravenously injected bradykinin (5nmol/rat), respectively, were examined in anesthetized rats. Neither the pressor response nor the depressor response was affected by acute parenteral treatment with L-NAME. The pressor and depressor effects of bradykinin were also noted in rats chronically supplemented with L-NAME in drinking water for 4 weeks. Bradykinin caused a relaxation of the isolated thoracic aorta in vitro, which was not affected in the presence of L-NAME. However, bradykinin failed to cause a relaxation of the aorta isolated from rats chronically treated with L-NAME. These findings suggest that endogenous generation of NO may not completely account for the blood pressure responses to bradykinin in rats.