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Hemorheological factors play an important role in the pathogenesis of different cardiovascular diseases. The hemorheological and hemodynamic parameters in essential hypertension and their possible modification by antihypertensive treatment were examined in the following two studies. In the first study the fundus appearance and hemorheological parameters (plasma and whole blood viscosity (WBV), fibrinogen level) of 33 hypertensive patients (mean age: 55 years) were examined. The fundus appearance showed retinopathy in all the cases between stages I-III. All the measured hemorheological parameters of the examined patients were in the pathological range (WBV at 90 s(-1): 5.18 mPa s) and were significantly (p < 0.01) higher than in healthy controls (WBV at 90 s(-1): 4.18 mPa s). The hemorheological factors showed a parallel deterioration with the fundus appearance, namely their values were significantly (p < 0.01) higher in patients with a fundus appearance stage III (WBV at 90 s(-1): 6.02 mPa s) than stage I (WBV at 90 s(-1): 4.51 mPa s). These results show that there is a correlation between hemorheological parameters and fundus appearance in hypertensives, and this suggests that hemorheological factors may play a role in the development of hypertensive retinopathy. In the second study the hemorheological and hemodynamical effects of Doxazosin, a selective alpha-1-adrenoreceptor blocker agent, was examined in twenty patients (mean age: 54 years) with essential hypertension. Hemorheologic (hematocrit, fibrinogen, plasma and whole blood viscosity) and hemodynamic (cardiac output and index, total peripheral resistance) parameters and plasma lipids were determined. The measurements were carried out before the beginning of the treatment, after 1 week and after 12 weeks treatment periods. Besides significant reduction of blood pressure and total peripheral resistance (p < 0.001), a decrease in cholesterol (p < 0.001) and triglycerides (p < 0.01) levels and a beneficial effect on hemorheological parameters was detected. Fibrinogen and plasma viscosity decreased significantly (p < 0.01). Hematocrit value was also lower after one week (p < 0.001), then an increase could be seen. Whole blood viscosity showed similar changes as hematocrit, but the degree of its final increase was slighter, which was supported by the significantly lower value of corrected blood viscosity (p < 0.05). All these findings indicate that hemorheological factors may play a role in the pathogenesis and in the development of organ damages in hypertension.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10711745&dopt=Abstract
Hypertension. 1987 Jun;9(6 Pt 2):III210-2.
Role of alpha 1- and alpha 2-adrenergic receptors in the human hypertensive kidney.
de Leeuw PW, van Es PN, de Bos R, Birkenhager WH.
Since it is not known for certain which alpha-adrenergic receptors mediate renal vasoconstriction in human essential hypertension, we infused either doxazosin (n = 7) or yohimbine (n = 7) into the renal arteries of hypertensive subjects immediately prior to diagnostic angiography. Both agents caused an increment in renal blood flow as assessed with the xenon-washout technique. Doxazosin increased renal flow from 342 +/- 36 to 360 +/- 55 ml/min per 100 g (0.05 less than p less than 0.10). Yohimbine enhanced flow from 380 +/- 41 to 485 +/- 63 ml/min per 100 g (p less than 0.01). The effect of yohimbine was significantly greater than that of doxazosin. In a control group (n = 7) receiving only saline, no changes in renal blood flow occurred. Doxazosin enhanced renin secretion in the kidney by 10 +/- 4% over levels in controls (0.05 less than p less than 0.10), whereas yohimbine increased renin release by 80 +/- 23% (p less than 0.01). The latter increase was apparently not due to alterations in flow alone, since the arteriovenous gradient for renin also widened. We conclude that in resting conditions, neurogenic vascular tone in the kidney depends mainly upon activation of alpha 2-adrenergic receptors. Moreover, these receptors exert a tonic inhibitory influence on renin release.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2885275&dopt=Abstract
Clin Exp Hypertens A. 1987;9 Suppl 1:281-92.
Efferent renal nerve activity in hypertensive man.
de Leeuw PW, Birkenhager WH.
Dept. of Medicine, Zuiderziekenhuis, Rotterdam, The Netherlands.
In a series of investigations we have evaluated efferent renal nerve activity in hypertensive man. Net renal release of noradrenaline, calculated as the arterio-venous gradient for noradrenaline across the kidney times flow, was taken as an index of local adrenergic activity. Renal blood flow, under various circumstances, was determined by xenon-washout. At rest noradrenaline release was variable but enhanced release, indicative of increased sympathetic activity, invariably was found during isometric exercise. The latter was associated with renal vasoconstriction. Further studies, employing intrarenal infusions of either the alpha-1 antagonist doxazosin or the alpha-2 antagonist yohimbine in doses that do not produce systemic effects, demonstrate that adrenergic vasoconstriction both at rest and during isometric exercise is accomplished mainly through alpha-2 receptors. It may be that an alpha- adrenoceptor mediated vascular response also determines the efficacy of chronic beta-blockade.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2890453&dopt=Abstract
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