phosphorus-radioisotopes and Hypertension

We studied vascular sodium pump activity and its regulation by vasoactive agents and endothelium in cultured aortic vascular smooth muscle cells from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Baseline sodium pump activity (ouabain-inhibitable 86Rb+ uptake) was similar in cells from both rat strains. Angiotensin II and endothelin-1 increased ouabain-inhibitable 86Rb+ uptake more in SHR than WKY cells, whereas no effects were obtained with sodium nitroprusside, 8-bromo-cGMP, or iloprost. We examined the influence of endothelium on vascular sodium pump activity either by coculturing smooth muscle and endothelial cells or by using conditioned medium. Both coculture for 24 hours with endothelial cells and treatment with conditioned medium increased smooth muscle cell sodium pump activity, this effect being higher in SHR cells. These results suggest that the endothelium may modulate sodium pump activity in the underlying smooth muscle by releasing a diffusible compound, which is more active on SHR smooth muscle. The conditioned medium obtained in the presence of inhibitors of angiotensin-converting enzyme, endothelin-1-converting enzyme, cyclooxygenase, lipoxygenase, and nitric oxide synthase had no effect on the ability of conditioned medium to increase sodium pump activity, suggesting that angiotensin II, endothelin-1, eicosanoids, and nitric oxide are not involved in this stimulatory effect. The nature of the possible endothelial factor involved is still unknown, but it possesses a molecular weight between 25 and 50 kD, is heat stable, and is sensitive to trypsin treatment. We propose it could be a growth factor.

Topics: Animals; Aorta; Cattle; Cells, Cultured; Culture Media; Endothelium, Vascular; Hypertension; Male; Muscle, Smooth, Vascular; Ouabain; Phosphorus Radioisotopes; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rubidium Radioisotopes; Sodium; Sodium-Potassium-Exchanging ATPase

In spontaneously hypertensive rats (SHR), cardiac adenylate cyclase is desensitized owing to down-regulation of myocardial beta-adrenoceptors and an increase in Gi alpha. We wished to determine whether these biochemical alterations in the beta-adrenoceptor-adenylate cyclase system precede development of hypertensive cardiac hypertrophy or whether this increase occurs only in later stages of the syndrome and represents a secondary phenomenon. Myocardial samples from 5- and 13-week-old SHR and age-matched Wistar Kyoto rats (WKY) as controls were studied. Cardiac beta-adrenoceptors were studied with [125I]cyanopindolol ([125I]ICYP] as radiolabeled ligand. beta-Adrenoceptor subtypes were determined with the beta 1- and beta 2-selective antagonists CGP 207.12A and ICI 118.551, respectively. Gi alpha proteins were measured with the pertussis toxin-catalysed [32P]ADP ribosylation. Myocardial norepinephrine (NE) content was investigated with high pressure liquid chromatography. In myocardial membranes of 13-week-old SHR, the number of total beta-adrenoceptors as well as beta 1- and beta 2-adrenoceptors was reduced. No difference was observed between SHR and WKY, at age 5 weeks. The nonionic detergent Lubrol PX at 0.5% (vol/vol) increased the amount of detectable Gi alpha by a factor of 14. Under these optimal conditions, Gi alpha was increased by 30% in 13-week-old SHR, but not 5-week-old SHR as compared with WKY. Myocardial NE content was increased by 25-35% in both 5- and 13-week-old SHR as compared with WKY. The results showed that nonspecific beta-adrenoceptor downregulation and an increase in Gi alpha occurs in hypertensive cardiac hypertrophy of SHR. In the prehypertensive stage, these changes were not observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Diphosphate; Adenylate Cyclase Toxin; Animals; Cardiomegaly; Down-Regulation; GTP-Binding Proteins; Hypertension; Male; Myocardium; Norepinephrine; Pertussis Toxin; Phosphorus Radioisotopes; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Adrenergic, beta; Ribose; Virulence Factors, Bordetella

The effects of prostaglandin E2 (PGE2) infusions on the beta 2-adrenoceptor-dependent adenylate cyclase (beta 2ARAC) system of lymphocytes were studied in 26 patients with resistant hypertension (RH). The density of beta 2-adrenoceptors and their affinity for l-isoproterenol were measured with 125ICYP, and adenylate cyclase activity was determined with alpha 32P-ATP in mononuclear lymphocytes of RH patients before and at 1, 7, and 14 days after the last PGE2 infusion. Plasma epinephrine and norepinephrine concentrations were analyzed using high-performance liquid chromatography. The patients were divided into two groups: 19 receiving clonidine (group I) and seven receiving four-drug antihypertensive therapy (group II) before and after PGE2 infusions. Resistance to antihypertensive drugs in patients of both groups was overcome by PGE2 infusions, and was correlated with a decrease in lymphocyte beta 2-adrenoceptor density, an increase in beta 2-receptor affinity for l-isoproterenol, and an increase in adenylate cyclase activation. The absence of a PGE2 effect was associated with an acute increase in plasma epinephrine content and a decrease in the sensitivity of the lymphocyte beta 2ARAC system.

Topics: Adenosine Triphosphate; Adenylyl Cyclases; Adult; Chromatography, High Pressure Liquid; Dinoprostone; Epinephrine; Humans; Hypertension; Infusions, Intravenous; Isoproterenol; Lymphocytes; Male; Middle Aged; Norepinephrine; Phosphorus Radioisotopes; Receptors, Adrenergic, beta

Platelet intracellular free calcium concentration [Ca2+]i from patients with essential hypertension has been found to be elevated, but the intracellular effects of this increase are still unclear. As protein phosphorylation is an important regulatory step in cell activation and increased protein phosphorylation has been demonstrated in platelets from hypertensive animals, we investigated protein phosphorylation and [Ca2+]i in platelets from patients with essential hypertension and age-matched normotensives. We measured the 32P incorporation into a 20 kDa protein and a 47 kDa protein in 17 hypertensive patients and 20 normotensive, age-matched subjects. The [Ca2+]i was measured with the fluorescent dye fura-2. Protein phosphorylation and [Ca2+]i were assessed in unstimulated platelets and after exposure of the cells to 0.1 and 0.25 U/mL thrombin at 20, 60, and 300 sec. In addition we assessed the activity of protein kinase C by incubating the platelets with phorbol-ester TPA at 20, 60, and 300 sec. Basal phosphorylation of the two proteins was not different between the two groups. After exposure of the platelets to thrombin 32P, incorporation into the 20 kDa protein and the 47 kDa protein was significantly increased in platelets from hypertensive patients at all times. Furthermore, the specific stimulation of protein kinase C with TPA resulted in a significantly higher phosphorylation of the 47 kDa protein, whereas the 20 kDa protein was not phosphorylated after incubation with TPA for 1 min. Basal [Ca2+]i was higher in platelets from hypertensive patients (124 +/- 7 nmol/L v 104 +/- 5 nmol/L, P less than .05), although there was a wide overlap between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Blood Platelets; Calcium; Female; Humans; Hypertension; Male; Middle Aged; Phosphorus Radioisotopes; Phosphorylation; Protein Kinase C; Proteins; Tetradecanoylphorbol Acetate; Thrombin; Time Factors

In various models of hypertension of genetic origin, a hypersensitivity of phospholipase C has been demonstrated to participate in the hyperreactivity of platelets toward a variety of vasoactive agents. Since this abnormality could not be observed in the absence of cell stimulation, it could not account for the increase in free Ca2+ which has been reported in resting platelets in primary hypertension. Likewise, in hypertensive subjects, platelets behave hyperactive when stimulated by ADP, although the stimulus has been demonstrated to be a poor activator of phospholipase C. In order to gain insight into the membrane alteration that could account for the cellular hyperactivity which characterizes hypertensive subjects, we investigated, in resting platelets, the kinetics of radioactive labeling of major membrane phospholipids. Isolated platelets were prepared from SHR (4w and 17w of age), SHR-SP, Dahl salt-resistant and salt-sensitive rats fed either a low or a high salt diet, DOCA-salt hypertensive rats and from the appropriate normotensive controls. Irrespective of the radioactive precursor used (32P-orthophosphate, 3H-glycerol, 3H-choline), the labeling of phosphatidylcholine (PC) was markedly (up to 20 fold) enhanced in SHR (whichever their age) and SHR-SP compared with WKY. This increase, specific of PC, could not be accounted for by differences either in the actual amount of PC or in the uptake of various labels, suggesting an increased PC turnover. Such an increase was also observed in platelets of Dahl hypertensive rats but not in those of DOCA-salt hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Platelets; Cell Membrane; Disease Models, Animal; Hypertension; Phosphatidylcholines; Phosphorus Radioisotopes; Rats; Rats, Inbred SHR; Rats, Inbred WKY

In primary hypertension, phospholipase C (PLC) is hypersensitive in several target tissues (platelets, vascular smooth muscle cells, aortic fibroblasts). Protein kinase C (PKC) and myosin light chain kinase (MLCK), which are physiologically activated by PLC-triggered second messengers (diacylglycerol and Ca2+ ions, respectively), phosphorylate specific proteins closely involved in the cell functional responses. In this study, we have examined and compared between platelets of spontaneously hypertensive rats (SHR) and their normotensive controls Wistar-Kyoto (WKY), the patterns of protein phosphorylation obtained either with the receptor-mediated agonist thrombin (i.e. which acts via PLC) or with direct activators of the protein kinases, PKC and MLCK. Activation by thrombin of 32P-prelabeled platelets induced incorporation of radioactivity into two proteins, P20 (myosin light chain) and P47. The curves obtained when platelets were challenged with either increasing doses of thrombin (0.025-0.3 U/ml) for 20 sec or with a low dose of the agent (0.1 U/ml) for up to 1 min, revealed that phosphorylation of the target proteins of PKC (P47) and of MLCK (P20) were significantly enhanced in platelets of SHR compared to WKY. In contrast, direct activation of PKC by phorbol ester and of MLCK by the calcium ionophore A23187 evoked the selective phosphorylation of the respective target proteins, P47 and P20, to a similar extent in platelets of SHR and WKY. Taken together, these results demonstrate that a physiological agonist (thrombin) induces an enhanced phosphorylation of intracellular proteins in platelets of SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Platelets; Blood Proteins; Enzyme Activation; Hypertension; Myosin-Light-Chain Kinase; Phosphorus Radioisotopes; Phosphorylation; Protein Kinases; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Thrombin; Type C Phospholipases

The effects of substance P on inositol phospholipids of adrenal medulla slices from spontaneously hypertensive and normotensive Wistar-Kyoto rats were investigated. Substance P reduces [32P] incorporation into inositol phospholipids of both rat strains. This effect was most expressed in hypertensive rats, which showed a higher basal 32P incorporation into phosphatidylinositol phosphates compared to normotensive control rats (probably due to the higher turnover of monoester-phosphate groups). Substance P causes a less potent diesteratic hydrolysis of [3H]inositol prelabelled phospholipids in spontaneously hypertensive rats compared with Wistar-Kyoto rats. A possible consequence of the reduced diesteratic hydrolysis by endogenous substance P and related substances of inositol phospholipids in adrenal medulla from spontaneously hypertensive rats is discussed.

Topics: Adrenal Medulla; Animals; Hydrolysis; Hypertension; Inositol; Male; Phosphates; Phosphatidic Acids; Phosphatidylcholines; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositol Phosphates; Phosphatidylinositols; Phosphatidylserines; Phosphorus Radioisotopes; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Substance P

Thrombin-induced aggregation and serotonin release were markedly enhanced in platelets from spontaneously hypertensive rats (SHR) when compared with those from normotensive Wistar-Kyoto rats (WKY). Since phosphoinositides are involved in calcium-mediated platelet responses, the metabolism of these lipids was investigated in SHR and WKY by using 32P-labeled quiescent platelets. In unstimulated cells, both the rate and extent of 32P incorporation into individual inositol-containing phospholipids and phosphatidic acid were identical in SHR and WKY. This finding suggests that the pool size and basal turnover of phosphoinositides did not differ between the two strains. In contrast, early thrombin-induced phosphoinositide metabolism, when monitored as changes in [32P]phosphatidic acid, was significantly higher in SHR than in WKY. For example, a 20-second exposure to thrombin, 0.3 U/ml, induced the formation of 1.6 times more [32P]phosphatidic acid in SHR than in WKY. These results provide evidence for a leftward shift of the dose-response and time-course curves of thrombin-induced [32P]phosphatidic acid formation in SHR. Moreover, the extent of the difference between SHR and WKY was independent of the extracellular calcium concentration. Following thrombin stimulation, [32P]phosphatidic acid formation likely reflects the initial agonist-receptor interaction; therefore, these results suggest that phospholipase C activity is enhanced in platelets of SHR and that the hypersensitivity of phospholipase C in SHR may play a role in the overall alteration of cell calcium handling and, hence, in the platelet responses of SHR.

Topics: Animals; Blood Platelets; Calcium; Hypertension; Male; Phosphatidylinositols; Phosphorus Radioisotopes; Platelet Aggregation; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Serotonin; Type C Phospholipases

A study of orthophosphate incorporation into erythrocyte membrane proteins and lipids of spontaneously-hypertensive rats (SHR) at incubation of erythrocytes with 32PO4 and that of erythrocyte ghosts with 32P-gamma-ATP showed basal phosphorylation of proteins as well as polyphosphoinositides of erythrocyte ghosts to be essentially increased in SHRs as compared to normotensive animals, the differences being eliminated by the addition of protein kinase C activator (4 beta-phorbol-12 beta-myristate-13 alpha-acetate, PMA). After PMA-stimulated protein phosphorylation most of the label was incorporated into proteins of Band 4.1. There was no difference in basal phosphorylation of membrane proteins in case of intact erythrocytes. Under PMA stimulation, most of the label was incorporated into proteins of band 4.1 similarly to labelling of erythrocyte ghosts and a significant increment of radioactivity could only be seen in the control animals.

Topics: Animals; Blood Proteins; Enzyme Activation; Erythrocyte Membrane; Female; Hypertension; Membrane Proteins; Methods; Phospholipids; Phosphorus Radioisotopes; Phosphorylation; Protein Kinase C; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Tetradecanoylphorbol Acetate

The rapid turnover of phosphoinositides within membranes suggests that these lipids play an important role in membrane function. Since various abnormalities have been described in the erythrocyte membrane of the spontaneously hypertensive rat (SHR) we have studied the turnover of phosphoinositides in the erythrocyte of SHR and age-matched normotensive Wistar-Kyoto rat (WKY). This was achieved by measuring the incorporation of 32P into inositol lipids after incubation of 1) intact erythrocytes with [32P]orthophosphate and 2) isolated ghost membranes with [gamma-32P]ATP. In both series of experiments more than 99% of the radioactivity incorporated into lipids was into the polyphosphoinositides diphosphoinositide (DPI) and triphosphoinositide (TPI). In both intact erythrocytes and ghost membranes, the levels of 32P incorporated into DPI and TPI were significantly different in SHR than in WKY. Further analysis of factors known to influence the labeling of DPI and TPI indicated that this could be ascribed to decreased activities of phosphatidylinositol kinase and/or DPI kinase, with respect to ATP as substrate. Moreover comparison of data obtained in intact cells with those obtained with ghost membranes suggests that within the SHR erythrocyte, membrane-cytosol interactions may occur that could also be responsible for the alteration of phosphoinositide labeling observed in hypertensive animals. Since phosphoinositides have been reported to be involved in the Ca2+-gating system of membrane, our findings could be associated with the abnormal Ca2+ binding and transport recently described in SHR erythrocyte.

Topics: Animals; Erythrocyte Membrane; Erythrocytes; Hypertension; Kinetics; Male; Membrane Lipids; Membrane Proteins; Phospholipids; Phosphorus Radioisotopes; Phosphorylation; Rats; Rats, Inbred Strains

The level of polyphosphoinositides (PPI) and the incorporation rate of 32P into PPI of erythrocytes from essential hypertensive patients was studied. The PPI were found to have a decreased level and an increased 32P incorporation rate compared with the controls.

Topics: Adult; Erythrocytes; Humans; Hypertension; Middle Aged; Phosphatidylinositol Phosphates; Phosphatidylinositols; Phosphorus Radioisotopes; Polymers

During the past decade the diagnostic use of blood volume determinations has declined as a result of the generation of largely inaccurate results and inappropriate normalization and interpretation. After historical development of more than 50 years, current methodology employs 125I-labeled human serum albumin and 51Cr-labeled red blood cells to determine plasma volume and red cell volume, respectively. Accurate blood volume determinations require (1) abandoning the use of the mean body hematocrit:venous hematocrit ratio and using simultaneous independent measurements of both volumes; (2) delaying multiple postinjection patient samples until complete mixing and equilibration are complete; (3) backextrapolation of plasma concentrations of 125I to account for albumin loss from the plasma, and, rarely, back-extrapolation of red cell concentrations to account for dilution by red cells transfused during the procedure; (4) normalization of volumes by adjusting patient weight to normal correspondence with lean tissue mass, whenever necessary. A rapid, routine method that fulfills these four requirements is presented. A number of surgical and medical conditions in which blood volume determinations are very useful in diagnosis and therapy are discussed. Recently developed techniques for blood volume measurements include neutron acativation analysis and fluorescent excitation analysis. Correct normalization of accurate blood volume measurements will provide a valuable service to the entire medical community.

Topics: Aged; Blood Volume Determination; Body Constitution; Carbon Monoxide; Central Venous Pressure; Chromium Radioisotopes; Diagnostic Errors; Erythrocytes; Hematocrit; Hormones, Ectopic; Humans; Hyperaldosteronism; Hypertension; Indium; Iron Radioisotopes; Male; Phosphorus Radioisotopes; Plasma Volume; Polycythemia; Postoperative Complications; Potassium Radioisotopes; Radioisotope Dilution Technique; Serum Albumin, Radio-Iodinated; Shock; Technetium; Time Factors; Transferrin; Vasopressins