Hypertension
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Heme oxygenase is a mammalian enzyme that converts heme to biliverdin and carbon monoxide. Carbon monoxide activates soluble guanylate cyclase and relaxes vascular smooth muscle, and it has been implicated as a potential neuromessenger. The regulatory functions of endogenous carbon monoxide on hemodynamics are not known. ⋯ After pretreatment with chlorisondamine (5 mg/kg IP) or prazosin (5 mg/kg IP) to inhibit autonomic ganglionic or alpha 1-adrenoceptor functions, respectively, ZnDPBG did not affect arterial pressure or heart rate. This suggests that ZnDPBG-induced increases in blood pressure rely on autonomic nervous function. We conclude that the pressor response to heme oxygenase inhibitors results from withdrawal of the inhibitory influence of endogenous carbon monoxide on a pressor mechanism mediated by the autonomic nervous system.
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Comparative Study
Angiotensin II exerts differential actions on renal nerve activity and heart rate.
Angiotensin II (Ang II) exerts complex actions on sympathetic nerve activity and heart rate, but these actions are incompletely understood. We performed three series of experiments in conscious rabbits to analyze the actions of exogenous and endogenous Ang II on renal sympathetic nerve activity and heart rate. (1) Graded intravenous doses of phenylephrine and Ang II suppressed renal sympathetic nerve activity to the same degree, whereas Ang II decreased heart rate much less than phenylephrine. (2) Ang II infusion at 10 ng/kg per minute increased mean arterial pressure by 13 +/- 2 mm Hg (P < .01) and decreased renal sympathetic nerve activity by 67 +/- 13% (P < .01) but did not change heart rate. ⋯ Losartan shifted the heart rate-mean arterial pressure curve to the left but did not alter the renal nerve activity-mean arterial pressure curve. These results demonstrate that whereas exogenous Ang II resets the baroreceptor reflex control of heart rate to a higher pressure, it does not increase resting renal sympathetic nerve activity or alter the baroreceptor reflex control of renal nerve activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Time course of changes in sigmoidal-fitting baroreceptor curves in one-kidney, one clip hypertensive rats.
The present study examined the time course of changes in baroreceptor reflex function by means of sigmoidal curve-fitting analysis in conscious, unrestrained renovascular one-kidney, one clip (1K1C) rats at 1, 3, 7, 15, 30, and 60 days after renal artery clipping. The reflex heart rate responses were elicited by alternate intravenous bolus injections of phenylephrine (change, +5 to +50 mm Hg) and sodium nitroprusside (change, -5 to -50 mmHg). Atropine methylnitrate and atenolol were given to evaluate the responses mediated by the cardiac sympathetic or vagal component, respectively. ⋯ The data showed a decreased vagal activity contributing to the attenuation of the baroreceptor gain only in the 30-day 1K1C group. In contrast, the cardiac sympathetic component of the baroreceptor reflex was significantly decreased in all 1K1C groups (from 2.10 +/- 0.4 to 0.50 +/- 0.2 bpm/mm Hg) compared with the respective sham groups (from 3.80 +/- 0.3 to 3.10 +/- 0.4 bpm/mm Hg). These results suggest that a reduced contribution of the sympathetic component to the baroreceptor heart rate reflex may be the main cause of the progressive attenuation of the baroreceptor reflex sensitivity observed in conscious 1K1C hypertensive rats.
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We tested Portapres, an innovative portable, battery-operated device for the continuous, noninvasive, 24-hour ambulatory measurement of blood pressure in the finger. Portapres is based on Finapres, a stationary device for the measurement of finger arterial pressure. Systems were added to record signals on tape, to alternate measurements between fingers automatically each 30 minutes, and to correct for the hydrostatic height of the hand. ⋯ There were no major limitations in behavior, and no discomfort that originated from continuous monitoring was reported. Measurements continued normally during physical exercise. Portapres provides for the first time continuous 24-hour, noninvasive ambulatory blood pressure waveform monitoring and offers real and obvious advantages over current noninvasive and invasive devices.
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Review Case Reports
Hypertension, the endothelial cell, and the vascular complications of diabetes mellitus.
Hypertension is a major factor that contributes to the development of the vascular complications of diabetes mellitus, which primarily include atherosclerosis, nephropathy, and retinopathy. The mechanism of the pathophysiological effects of hypertension lies at the cellular level in the blood vessel wall, which intimately involves the function and interaction of the endothelial and vascular smooth muscle cells. Both hypertension and diabetes mellitus alter endothelial cell structure and function. ⋯ In diabetic retinopathy, damage and altered growth of retinal capillary endothelial cells is the major pathophysiological insult leading to proliferative lesions of the retina. Thus, the endothelium emerges as a key target organ of damage in diabetes mellitus; this damage is enhanced in the presence of hypertension. An overall approach to the understanding and treatment of diabetes mellitus and its complications will be to elucidate the mechanisms of vascular disease and endothelial cell dysfunction that occur in the setting of hypertension and diabetes.