Bradykinin stimulates tissue plasminogen activator release in human vasculature.
(9/721)
Bradykinin stimulates tissue plasminogen activator (tPA) release in isolated perfused animal tissues. The present study tests the hypothesis that bradykinin increases tPA release in humans through local effects on the vasculature. Graded doses of sodium nitroprusside (0.8 to 3.2 micrograms/min), acetylcholine (ACh) (7.5 to 60 micrograms/min), and bradykinin (100 to 400 ng/min) were administered intra-arterially in random order in 10 salt-depleted (10 mmol/d of Na) normotensive volunteers. None of the drugs altered mean arterial pressure or heart rate. Forearm blood flow (FBF) was measured by strain-gauge plethysmography. All 3 drugs caused a dose-dependent increase in FBF, although ACh was less potent than either nitroprusside or bradykinin (maximum FBF 7.5+/-2.4 versus 10.0+/-1.5 and 11.9+/-2.1 mL. 100 mL-1. min-1, respectively). Bradykinin caused a significant, dose-dependent increase in venous (effect of dose F=9. 9, P=0.028 by ANOVA), but not arterial (F=0.154, P=0.92) tPA antigen in the infused arm. Thus, net tPA release increased significantly in response to bradykinin (50.6+/-13.3 at the highest dose versus 0. 9+/-0.4 ng. 100 mL-1. min -1 at baseline, P=0.014). In contrast, bradykinin did not affect plasminogen activator inhibitor antigen. Neither nitroprusside nor ACh altered plasma levels of tPA or plasminogen activator inhibitor antigen. Bradykinin increased tPA release across the forearm in the absence of systemic effects. This effect could not be attributed to changes in blood flow because doses of equivalent potency of the vasodilator nitroprusside did not increase tPA. These data demonstrate that bradykinin stimulates tPA release in the human vasculature. (+info)
Inhibition of phosphodiesterase III with milrinone increases renin secretion in human subjects.
(10/721)
One of the major signaling molecules involved in the regulation of renin secretion is cyclic AMP (cAMP). The concentration of cAMP in cells is determined in part by the rate of cAMP hydrolysis by several families of phosphodiesterases, especially the phosphodiesterase III family, but little is known about the roles of these enzymes in the control of renin secretion, particularly in humans. The aim of the present study was to investigate the effect of the phosphodiesterase III inhibitor milrinone on renin secretion in human subjects. Milrinone was infused i.v. in eight healthy normotensive subjects in a dose of 100 microgram/kg. Immediately after the infusion, there was a transient increase in systolic pressure from 107 +/- 5 to 116 +/- 5 mm Hg (p <.01), but no significant change in diastolic or mean arterial pressure. Heart rate increased from 67 +/- 2 to 86 +/- 4 beats/min (p <.01) and remained elevated. Plasma renin activity increased in all subjects, the mean value increasing from 3.0 +/- 0.5 to 6.0 +/- 1.1 ng/ml/h at 15 min (p <.01). These results demonstrate that milrinone increases renin secretion in human subjects, thus providing evidence that phosphodiesterase III family participates in the control of renin secretion in humans. The increase in renin secretion does not appear to be mediated by major mechanisms that control renin secretion, and likely results from an increase in cAMP concentration in the juxtaglomerular cells. (+info)
Modulation of effect of dietary salt on prehepatic first-pass metabolism: effects of beta-blockade and intravenous salt loading.
(11/721)
We previously demonstrated that increased dietary salt markedly decreases plasma quinidine concentrations shortly after p.o. dosing, without an effect on the drug's terminal elimination half-life or concentrations after i.v. administration. These findings suggest an effect of dietary salt on intestinal metabolism or transport of the drug. Because one effect of salt loading is sympathetic inhibition, we examined the effect of beta-adrenoceptor blockade on salt-related changes in quinidine disposition. Furthermore, we examined whether the action of salt is local or systemic by determining the effect of salt loading by the i.v. route. To assess the effect of beta-blockade, quinidine disposition was studied in eight normal volunteers after a single p.o. dose of quinidine; data were obtained after 1 week on a high-salt diet (400 mEq/day) and 1 week on a low-salt diet (10 mEq/day) during chronic nadolol and compared with those previously obtained in the same subjects without the beta-blocker. beta-Blockade had no effect on oral clearance during the high-salt diet [0.28 +/- 0.1 (quinidine + nadolol) versus 0.30 +/- 0.2 liters/h/kg (quinidine alone)] but increased clearance on the low-salt diet from 0.23 +/- 0.1 to 0.29 +/- 0.1 liters/h/kg (p <. 05). For the i.v. salt study, the disposition of single p.o. and single i.v. doses of quinidine was determined on two occasions in eight subjects: once during a low-salt diet (10 mEq/day) and once during the same diet, supplemented by 400 mEq/day NaCl i.v. for 8 days. In contrast to our findings after p.o. salt loading, i.v. salt loading did not alter the pharmacokinetics of p.o. quinidine. Taken together, these data implicate a local alteration of drug-metabolizing activity and/or drug transport in the intestinal mucosa as the major effect of dietary salt on the disposition of p.o. quinidine and further suggest that beta-adrenergic activation by a low-salt diet is one component of a signaling pathway whereby intestinal drug disposition is suppressed, resulting in increased oral bioavailability. (+info)
Effect of metoprolol administration on renal sodium handling in experimental congestive heart failure.
(12/721)
BACKGROUND: Long-term metoprolol therapy improves cardiac performance and decreases mortality in patients with chronic congestive heart failure (CHF). This study examined the effect of long-term metoprolol therapy on renal sodium handling in an experimental rat model of CHF. METHODS AND RESULTS: Rats with left coronary ligation and myocardial infarction-induced CHF were treated with metoprolol (1.5 mg. kg-1. h-1) or vehicle for 3 weeks by osmotic minipump. They were then evaluated for their ability to excrete a short-term sodium load (5% body weight isotonic saline infusion over 30 minutes) and a long-term sodium load (change from low- to high-sodium diet over 8 days). All CHF rats had left ventricular end-diastolic pressure >10 mm Hg, and heart weight/body weight ratios averaged 0.68+/-0.02% (versus control of approximately 0.40%). Compared with vehicle CHF rats (n=19), metoprolol CHF rats (n=18) had lower basal values of mean arterial pressure (122+/-3 versus 112+/-3 mm Hg) and heart rate (373+/-14 versus 315+/-9 bpm) and decreased heart rate responses to intravenous doses of isoproterenol. During short-term isotonic saline volume loading, metoprolol CHF rats excreted 54+/-4% more of the sodium load than vehicle CHF rats. During long-term dietary sodium loading, metoprolol CHF rats retained 28+/-3% less sodium than vehicle CHF rats. CONCLUSIONS: Metoprolol treatment of rats with CHF results in an improved ability to excrete both short- and long-term sodium loads. (+info)
The management of hypertensive disease in black patients.
(13/721)
The ethnic differences in the incidence, pathophysiology and management of hypertensive disease, are particularly pertinent to the Black or Afro-Caribbean populations, who have a high prevalence of hypertension and associated complications, such as strokes and renal impairment. Our understanding of the underlying pathophysiology of hypertensive disease and the optimal treatment of hypertension in Black patients continues to evolve, especially with the introduction of new drugs and the need for prognostic data in this ethnic population. We review the management of hypertensive disease in the black population, emphasizing race-related differences in the pathophysiology of hypertension and the importance of tailored management in this group of patients, including sensible application of non-pharmacological measures with effective antihypertensive agents. For example, diuretics and calcium antagonists are suitable first-line agents in black hypertensives, whilst beta-blockers and the ACE inhibitors tend to be less effective at lowering blood pressure, due to the low renin state in these patients. (+info)
Renal injury and salt-sensitive hypertension after exposure to catecholamines.
(14/721)
We investigated whether chronic infusion of phenylephrine could induce structural and functional changes in the kidney of rats with the subsequent development of salt-sensitive hypertension. Rats were infused with phenylephrine (0.15 mmol/kg per day) by minipump, resulting in a moderate increase in systolic blood pressure (BP) (17 to 25 mm Hg) and a marked increase in BP variability as measured by an internal telemetry device. After 8 weeks, the phenylephrine infusion was stopped with the return of BP to normal, and a nephrectomy was performed for histological studies. Glomeruli were largely spared, but focal tubulointerstitial fibrosis was present, with the de novo expression of osteopontin by injured tubules, macrophage and "myofibroblast" accumulation, and focal increases in mRNA for transforming growth factor beta by in situ hybridization. Peritubular capillaries at sites of injury had distorted morphology with shrinkage, rounding, and focal rarefaction, and endothelial cell proliferation was also identified. Rats were randomized to a high (8% NaCl or 1.36 mol/kg) or low (0.1% NaCl or 17 mmol/kg) salt diet. After 4 to 8 weeks, phenylephrine-treated rats on a high salt diet developed marked hypertension, which was in contrast with phenylephrine-treated rats placed on a low salt diet or vehicle-treated rats given a high salt diet. Hypertension after phenylephrine exposure correlated with the initial mean systolic BP (r(2)=0.99) and the degree of BP lability (r(2)=0.99) during the phenylephrine infusion, the amount of osteopontin expressed in the initial biopsy/nephrectomy (r(2)=0.74), and the final glomerular filtration rate (r(2)=0.58). These studies provide a mechanism by which a markedly elevated sympathetic nervous system can induce salt-dependent hypertension even when the hyperactive sympathetic state is no longer engaged. (+info)
Increased renal vasodilator prostanoids prevent hypertension in mice lacking the angiotensin subtype-2 receptor.
(15/721)
The angiotensin subtype-1 (AT(1)) receptor mediates renal prostaglandin E(2) (PGE(2)) production, and pharmacological blockade of the angiotensin subtype-2 (AT(2)) receptor potentiates the action of angiotensin II (Ang II) to increase PGE(2) levels. We investigated the role of the AT(2) receptor in prostaglandin metabolism in mice with targeted deletion of the AT(2) receptor gene. Mice lacking the AT(2) receptor (AT(2)-null) had normal blood pressure that was slightly elevated compared with that of wild-type (WT) control mice. AT(2)-null mice had higher renal interstitial fluid (RIF) 6-keto-PGF(1alpha) (a stable hydrolysis product of prostacyclin [PGI(2)]) and PGE(2) levels than did WT mice, and had similar increases in PGE(2) and 6-keto-PGF(1alpha) in response to dietary sodium restriction and Ang II infusion. In contrast, AT(2)-null mice had lower PGF(2alpha) levels compared with WT mice during basal conditions and in response to dietary sodium restriction or infusion of Ang II. RIF cAMP was markedly higher in AT(2)-null mice than in WT mice, both during basal conditions and during sodium restriction or Ang II infusion. AT(1) receptor blockade with losartan decreased PGE(2), PGI(2), and cAMP to levels observed in WT mice. To determine whether increased vasodilator prostanoids prevented hypertension in AT(2)-null mice, we treated AT(2)-null and WT mice with indomethacin for 14 days. PGI(2), PGE(2), and cAMP were markedly decreased in both WT and AT(2)-null mice. Blood pressure increased to hypertensive levels in AT(2)-null mice but was unchanged in WT. These results demonstrate that in the absence of the AT(2) receptor, increased vasodilator prostanoids protect against the development of hypertension. (+info)
Pressure-dependent renin release: effects of sodium intake and changes of total body sodium.
(16/721)
The impact of sodium intake and changes in total body sodium (TBS) for the setting of pressure-dependent renin release (PDRR) was studied in freely moving dogs. An aortic cuff allowed servo control of renal perfusion pressure (RPP) at preset values. Protocols were 1) high sodium intake (HSI), 2) low sodium intake (LSI), 3) TBS moderately increased (+3.1 mmol Na/kg body wt) by 20% reduction of RPP for 2-4 days, 4) large increase of TBS (+8.2) by combining protocol 3 with aldosterone infusion, and 5) TBS reduced (-3.1) by peritoneal dialyses. Twenty-four-hour time courses of arterial plasma renin activity (PRA) revealed that LSI increased PRA for the first 10 h only; afterward PRA did not differ between LSI and HSI. Reduced TBS increased PRA constantly, and the large increase of TBS constantly reduced PRA. PDRR stimulus-response curves (assessed 20 h after last sodium intake) revealed an exponential relationship in each protocol. PDRR was not changed by different sodium intake. Conversely, reduced TBS increased PDRR markedly, whereas the large increase of TBS suppressed it. Thus an inverse relationship between TBS and PRA, i.e., a TBS-dependent renin release, was found. This relationship was enhanced by decreasing RPP. This interplay between TBS-dependent renin release and PDRR allows the organism a differentiated reaction to changes in TBS and arterial pressure. (+info)