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Biomedical subjects

T J Resink

Publications and source records attributed to T J Resink.

At least 91 records · Page 5Linked to original sources
PubMed1987

Increased proliferation fate and phosphoinositide turnover in cultured smooth muscle cells from spontaneously hypertensive rats.

We cultured smooth muscle cells from matched sections of thoracic aortas of 20-week-old, male, spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats and compared their rates of proliferation and phosphoinositide metabolism. After seeding at initially identical densities, smooth muscle cells from SHR grow at significantly faster (P less than 0.001) rates than those from WKY rats, so that after 10 days in culture, the cell density of SHR-derived cells (3.10 +/- 0.32 x 10(5) cells/cm2) was double that of WKY-derived cells (1.59 +/- 0.28 x 10(5) cells/cm2). Following prolonged steady-state labelling in culture, incorporation of [3H]-myo-inositol into phosphatidylinositolbiphosphate (PIP2) was greater (P less than 0.01) in SHR smooth muscle cells (10.3 +/- 1.4%) than in those from WKY (6.9 +/- 1.4%). Incorporation of [3H]-myo-inositol into inositol triphosphate was also increased (P less than 0.01) in SHR (20.2 +/- 7.3%) relative to WKY cells (11.5 +/- 5.2%), while that into glycerophosphoinositol was lower (P less than 0.01) in SHR (46.5 +/- 8.0%) than in WKY (51.3 +/- 7.8%). Enhanced smooth muscle cell growth and altered phosphoinositide metabolism may be causally or consequentially involved in enhanced vasoconstriction and vascular hypertrophy in SHR.

Animals↗
PubMed1987

Greater vasodilator responsiveness to atrial natriuretic peptide in low-renin essential hypertensives.

Forearm vasodilator responses to atrial natriuretic peptide (ANP) were studied in twelve untreated patients with essential hypertension and twelve normotensive subjects. Alpha-human ANP (0.005 to 1.5 micrograms/min per 100 ml forearm volume) infused into the brachial artery increased forearm blood flow dose-dependently. This was paralleled by a decrease in forearm vascular resistance (FVR) which, at lower doses, was greater in essential hypertensives than in normotensives (P less than 0.001), and showed a lower ED50 for ANP in essential hypertensives (P less than 0.01). At higher doses of ANP the difference in vasodilator response between hypertension and normotension disappeared; the response to ANP was associated with a fall (P less than 0.01) in systemic blood pressure in hypertensives but not normotensives. At lower doses, the decreases in FVR were correlated directly with plasma renin activity in hypertensives (r = 0.656; P less than 0.05) but not normotensives. These data suggest greater vasodilator responsiveness to infusions of low doses of ANP in essential hypertensives, which is greater in low-renin states and blunted in high-renin states.

Adult↗
PubMed1986

[Secretion of atrial natriuretic peptide: relation to atrial pressure and systemic blood pressure].

To determine the influence of atrial pressure, heart rate and loss of atrial-ventricular synchrony in the release of atrial natriuretic peptide (ANP), plasma ANP concentrations were measured by radio-receptor assay in 12 patients during diagnostic cardiac catheterization and in patients with atrial fibrillation and during cardiac pacing. There was a relationship between right atrial pressure and right atrial ANP concentration (r = 0.813, p less than 0.01). Acute loss of atrial-ventricular pacing mode induced an increase in plasma ANP concentration from 44 +/- 8 to 104 +/- 13 pmol/l (n = 11, p less than 0.01) provided that systemic blood pressure was maintained. In contrast, if hypotension developed during ventricular pacing, the ANP levels fell from 68 +/- 11 to 14 +/- 7 pmol/l (n = 5, p less than 0.05) within five minutes despite elevation of atrial pressure. We therefore conclude that atrial pressure and the loss of atrioventricular synchrony may profoundly alter ANP release. The fall in plasma ANP concentration in acute hypotension suggests that, in addition to atrial pressure, ANP release is controlled by a peripheral negative feedback mechanism.

Aged↗
PubMed1986

Isolation of a mutant LLC-PK1 cell line defective in hormonal responsiveness. A pleiotropic lesion in receptor function.

A mutant LLC-PK1 cell line, M18, was isolated after a single treatment of the parent culture with N-methyl-N'-nitro-N-nitroso-guanidine. In contrast to LLC-PK1 cells, the mutant did not exhibit production of urokinase-type plasminogen activator (uPA) in response to the hormones calcitonin and vasopressin, but produced the expected levels of uPA upon stimulation by the receptor-independent adenylate cyclase activators forskolin and cholera toxin, as well as by the phosphodiesterase inhibitor isobutylmethylxanthine and the 8-bromo analogue of adenosine cyclic monophosphate, Br8cAMP. The patterns of activation of cAMP-dependent protein kinase were identical to those of uPA induction: calcitonin and vasopressin were without effect, but the response to all other agents was normal. In similar fashion, mutant cell homogenates displayed normal activation of adenylate cyclase upon treatment with sodium fluoride, forskolin, or the non-hydrolyzable GTP analogue guanosine 5'-[beta, gamma-imino]triphosphate, but were unresponsive to calcitonin or vasopressin. The ability of M18 cells to bind radioactively labelled calcitonin and vasopressin was measured. The mutant possessed less than 4% of the normal levels of the receptor binding activity for both hormones. Somatic cell hybrids formed between M18 and LLC-PK1 cells were found to retain normal hormone binding activity and responsiveness to hormones, indicating that the defect in M18 cells was recessive. M18 was concluded most probably to contain a single mutation impairing the function of two distinct polypeptide hormone receptors.

Adenylyl Cyclases↗
PubMed1986

The influence of activating hormones on human platelet membrane Ca2+-ATPase activity.

Intact platelets were pretreated with hormones and thereafter membranes were prepared and Ca2+-ATPase activity determined. Thrombin decreased the Vmax of Ca2+-ATPase after pretreatment of intact platelets. Platelet activating factor, vasopressin and ADP also decreased Ca2+-ATPase activity. 12-O-tetradecanoylphorbol-13-acetate (TPA) or A23187 or ionomycin alone had no effect, whilst the simultaneous pretreatment with TPA and Ca2+-ionophore decreased Ca2+-ATPase activity. cAMP elevating agents prostaglandin E1 (PGE1) and forskolin had no influence per se on Ca2+-ATPase, but antagonized the inhibitory effect of thrombin. The data suggest a close connection between phosphoinositide metabolism and the Ca2+-ATPase system.

Adenosine Diphosphate↗
PubMed1986

Biphasic Ca2+ response of adenylate cyclase. The role of calmodulin in its activation by Ca2+ ions.

The Ca2+-dependent regulation of human platelet membrane adenylate cyclase has been studied. This enzyme exhibited a biphasic response to Ca2+ within a narrow range of Ca2+ concentrations (0.1-1.0 microM). At low Ca2+ (0.08-0.3 microM) adenylate cyclase was stimulated (Ka = 0.10 microM), whereas at higher Ca2+ (greater than 0.3 microM) the enzyme was inhibited to 70-80% control (Ki = 0.8 microM). Membrane fractions, prepared by washing in the presence of LaCl3 to remove endogenous calmodulin (approximately equal to 70-80% depletion), exhibited no stimulation of adenylate cyclase by Ca2+ but did show the inhibitory phase (Ki = 0.4 microM). The activation phase could be restored to La3+-washed membranes by addition of calmodulin (Ka = 3.0 nM). Under these conditions it was apparent that calmodulin reduced the sensitivity of adenylate cyclase to Ca2+ (Ki = 0.8 microM). Prostaglandin E1 (PGE1) did not alter Ki or Ka values for Ca2+. Calmodulin did not alter the EC50 for PGE1 stimulation of adenylate cyclase but increased the Vmax (1.5-fold). The calmodulin antagonist trifluoperazine potently inhibited adenylate cyclase in native membranes (80%) and to a much lesser extent in La3+-washed membranes (15%). This inhibition was due to interaction of trifluoperazine with endogenous calmodulin since trifluoperazine competitively antagonized the stimulatory effect of calmodulin on adenylate cyclase in La3+-washed membranes. We propose that biphasic Ca2+ regulation of platelet adenylate cyclase functions to both dampen (low Ca2+) and facilitate (high Ca2+) the haemostatic function of platelets.

Adenylyl Cyclase Inhibitors↗
PubMed1986

Calmodulin regulation of adenylate cyclase activity in human platelet membranes.

The mechanism of calmodulin dependent regulation of adenylate cyclase has been studied in human platelet membranes. Calmodulin activated adenylate cyclase exhibited a biphasic response to both Mg2+ and Ca2+. A stimulatory effect of Mg2 on adenylate cyclase was observed at all Mg2+ concentrations employed, although the degree of activation by calmodulin was progressively decreased with increasing concentrations of Mg2+. These results demonstrate that the Vmax of calmodulin dependent platelet adenylate cyclase can be manipulated by varying the relative concentrations of Mg2+ and Ca2+. The activity of calmodulin stimulated adenylate cyclase was always increased 2-fold above respective levels of activity induced by GTP, Gpp(NH)p and/or PGE. The stimulatory influence of calmodulin was not additive but synergistic to the effects of PGE1, GTP and Gpp(NH)p. GDP beta S inhibited GTP-and Gpp(NH)p stimulation of adenylate cyclase but was without effect on calmodulin stimulation. Since the inhibitory effects of GDP beta S have been ascribed to apparent reduction of active N-protein-catalytic unit (C) complex formation, these results suggest that the magnitude of calmodulin dependent adenylate cyclase activity is proportional to the number of N-protein-C complexes, and that calmodulin interacts with preformed N-protein-C complex to increase its catalytic turnover. Our data do not support existence of two isoenzymes of adenylate cyclase (calmodulin sensitive and calmodulin insensitive) in human platelets.

Adenylyl Cyclases↗
PubMed1986

Abnormal cellular calcium regulation in essential hypertension.

The plasticity of cellular Ca2+ control and the events regulated by [Ca2+]i and other messengers make it difficult to assign causative or consequential roles to deranged platelet Ca2+-linked processes in the pathophysiology of essential hypertension. Our studies in human platelets support an underlying membrane pathology as being causative since observed derangements including partial membrane depolarization and enhanced calcium influx, enhanced hormone responsiveness and coupling to adenylate cyclase, increased phosphoinositide metabolism, as well as stimulated Ca2+-ATPase extrusion activity are membrane associated systems. Modification of phosphoinositide metabolism may be a key factor accounting for the multifaceted membrane abnormalities and eventually contribute to the elevated cytosolic [Ca2+]i concentration in essential hypertension. Whether these membrane abnormalities can also be found in human smooth muscle cells has yet to be determined.

Blood Platelets↗
PubMed1986

Platelet membrane calmodulin-stimulated calcium-adenosine triphosphatase. Altered activity in essential hypertension.

Platelet free Ca2+ concentration has been found to be elevated in essential hypertension and to correlate with blood pressure level. Free cytoplasmic calcium concentration is determined by calcium influx, pooling, and efflux. The present study found a Ca2+-ATPase in platelet membranes that has a high affinity for Ca2+ (Km approximately 1 microM), is inhibited by low concentrations of orthovanadate (Ki approximately 1 microM), and can be stimulated by calmodulin (Km approximately 5 nM). The absolute increase in calmodulin-stimulated Ca2+-ATPase activity was not different between normotensive and hypertensive subjects; however, the degree of stimulation of Ca2+-ATPase activity at saturating calmodulin concentrations apparently was diminished in calmodulin-deficient membranes from subjects with established essential hypertension (40%) as compared to that in normotensive subjects of similar age (135%; p less than 0.001). Affinities for calmodulin and Ca2+ were comparable between the two groups, while the capacity for Ca2+-ATPase activity (basal and calmodulin-stimulated) was markedly greater (1.5- to 1.8-fold) in both native and calmodulin-deficient membranes from hypertensive subjects. On the other hand, the defective calcium efflux pump activity, as assessed by a decreased degree of calmodulin stimulation, may have contributed to elevated cytoplasmic calcium concentrations and the associated enhanced hormone sensitivity in platelets from essential hypertensive subjects. This may represent an adaptive negative feedback control mechanism to protect the cell against Ca2+ overload.

Adult↗
PubMed1986

Enhanced platelet cyclic AMP response to prostaglandin E1 in essential hypertension.

Platelets provide an accessible and homogeneous cellular system for investigative studies on hypertension. Hypertension-associated abnormalities of cyclic adenosine 3',5'-monophosphate (AMP) metabolism were studied in human platelets. Platelets from hypertensive subjects had an enhanced cyclic AMP accumulation response to prostaglandin E1 (twofold increase in prostaglandin E1 sensitivity). The degree of adenylate cyclase activation in response to both prostaglandin E1 (receptor-mediated) and forskolin (non-receptor-mediated) was greater in hypertensive than normotensive subjects, and prostaglandin E1-stimulated and forskolin-stimulated adenylate cyclase activity correlated directly (r = 0.71, p less than 0.001, n = 26). This finding suggests that the catalytic subunit of the enzyme is the rate-limiting step of this hormonal information transduction. Platelets from hypertensive subjects were more sensitive to epinephrine-induced inhibition of the stimulatory effects of prostaglandin E1 on both cyclic AMP accumulation (fourfold) and activation of cyclic AMP-dependent protein kinase. These findings suggest that the enhanced cyclic AMP metabolic response to prostaglandin E1 in platelets from subjects with established essential hypertension may function as a negative feedback mechanism to protect the cells against calcium overload and to reduce their stimulated participation in hemostatic and thrombotic processes.

Adult↗
PubMed1986

Vasodilating agents and platelet function: intracellular free calcium concentration, cyclic nucleotides, and shape-change response.

The adenylate-cyclase activator forskolin, the guanylate-cyclase stimulator sodium nitroprusside, the phosphodiesterase inhibitor Ro 15-2041, different Ca-entry blockers, as well as various vasodilators, and the atrial natriuretic peptide were tested for antiplatelet activity. Thrombin, vasopressin, ADP, arachidonic acid, and the dihydropyridine Ca agonist CGP 28392 were used as platelet activators. The physiological and biochemical parameters of platelet function studied included shape-change reaction, intracellular free-Ca modulation, and cyclic nucleotide formation. When inhibition of the shape-change response occurred, it was accompanied by inhibition of the increase in intracellular free Ca. Furthermore, the results suggest a possible intracellular site of action of Ca entry blockers in platelets, and confirm the importance of modulation of cyclic nucleotides in the regulation of platelet function, regardless of the mechanism of platelet activation. Additional antiplatelet activity of antihypertensive agents may have a beneficial effect in reducing the associated risk of thrombo-embolic complications in essential hypertension.

Adenosine Diphosphate↗
PubMed1986

Atrial antipressor natriuretic peptide: release mechanisms and vascular action in man.

Atrial natriuretic peptide (ANP) release into the human circulation, responses to cardiopulmonary volume changes and natriuretic and vasorelaxant effects were studied in 45 normal subjects and in 12 patients during diagnostic cardiac catheterization. A new radioreceptor assay with a detection limit of 2 fmol/tube for alpha-human ANP (alpha-hANP) was used. In normal subjects plasma ANP was 27.2 +/- 4 pmol/l (n = 45, range 2-80). Right atrial plasma ANP correlated with right atrial pressure (r = 0.813, P less than 0.01), and in four of the patients increases in ANP paralleled the rise in atrial pressure during bicycle ergometry. Reducing venous return by bilateral thigh-cuff occlusion decreased atrial ANP from 66.8 +/- 17.9 to 19.6 +/- 8.0 pmol/l (n = 6, P less than 0.05). Increasing cardiopulmonary volume during 3-h head-out water immersion was associated with an increase in ANP from 16.0 +/- 5.6 to 92.6 +/- 21.5 pmol/l (n = 7, P less than 0.01) followed by transient urinary sodium excretion. The natriuretic threshold plasma ANP concentration during intravenous ANP infusion was 70-80 pmol/l. Atrial natriuretic peptide infused intra-arterially at a maximal forearm vasodilator dose (0.75 micrograms/min per 100 ml forearm tissue) increased forearm blood flow by 7.0 +/- 1.44 ml/min per 100 ml whereas the increase in sodium nitroprusside was 11.1 +/- 1.47 ml/min per 100 ml. Thus, ANP is rapidly released in response to atrial volume and pressure changes and represents a powerful vasodilating and, at high concentrations, natriuretic hormone in man.

Adolescent↗
PubMed1986

Altered platelet phosphatidylinositol metabolism in essential hypertension.

The metabolism of phosphoinositides was investigated in platelet membranes from nine patients with essential hypertension (EHT) and from 10 age/sex-matched normotensive subjects. 32P-labelling or phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2) was measured in lipid extracts prepared from resting 32P-prelabelled platelets. There were no differences in 32P-PA between subject groups. In platelets of hypertensive patients, 32P-incorporation into both PIP and PIP2 was greater (P at least less than 0.01). This increase apparently occurred at the expense of lower 32P-incorporation into PI (P less than 0.001). An alteration in the interconversion equilibrium between phosphoinositides which is directed towards polyphosphoinositide formation may lead to altered membrane ionic fluxes.

Adult↗
PubMed1985

The influence of CGP 28392, a 1,4-dihydropyridine, on human platelet calcium and cyclic AMP metabolism.

Use of Ca2+ ionophores (e.g. ionophore A 23187) and Ca2+ channel antagonists (e.g. dihydropyridines, phenylalkamines) has provided some insight into the molecular events involved in platelet activation. Recent structural modification of dihydropyridines has generated a novel class of compounds (e.g. CGP 28393) which apparently exert opposing functional effects. We report that CGP 28392 induced an elevation in free intracellular calcium concentrations [( Ca2+]i) via both calcium influx and mobilization of intracellular stores. Treatment of washed human platelets with this Ca2+ agonist resulted in typical Ca2+-linked activation phenomena such as shape change and phosphorylation of Mr 47 000 and Mr 20 000 proteins. CGP 28392 also negatively influenced platelet cyclic AMP metabolism, and appears to exert this effect as a consequence of elevated [Ca2+]i. The data suggest that the mechanisms of action of CGP 28392 involve dihydropyridine-susceptible structures on the cell membrane and intracellular Ca2+ binding sites.

Alprostadil↗
PubMed1985

Platelets and hypertension.

Various physiological changes of platelets and the vascular smooth muscle cell are intimately related. For this reason, in addition to the number of features in common between platelets and vascular smooth muscle and the increased risk for thromboembolic complication in essential hypertension, the platelet was used as an experimental model for the investigation of calcium-dependent functional anomalies associated with hypertension. It is demonstrated, by a sequential analysis of receptor and postreceptor events, that platelets in hypertension exhibit (a) a greater adenylate cyclase-activation and c-AMP-accumulation response to PGE1, (b) an enhanced epinephrine-induced phosphorylation response, and (c) an increased shape change sensitivity to serotonin and epinephrine. The anomalies in these calcium-dependent processes are linked to elevated free calcium concentrations in platelets from hypertensive subjects.

Adenylyl Cyclases↗
PubMed1985

Platelet membrane Ca(2+)-ATPase: blunted calmodulin-stimulation in essential hypertension.

To determine whether defective calcium-efflux pump activity may be responsible for calcium overload in platelets from patients with essential hypertension, the properties of a calmodulin-stimulated Ca(2+)-ATPase in membranes from 25 normotensive and 27 hypertensive subjects were compared. Calcium-ATPase did not differ in affinity for calmodulin or Ca2+ between groups. Stimulation of Ca(2+)-ATPase activity at saturating calmodulin concentrations is diminished in calmodulin-deficient membranes from established essential hypertensive patients (64%) compared with normotensive subjects (125%) (P < 0.01). The capacity for Ca(2+)-ATPase activity (basal and calmodulin-activated) is markedly greater (1.5 to 1.8-fold) in both native and calmodulin-deficient platelet membranes from hypertensive compared with normotensive subjects. The data suggest that calmodulin-stimulation of Ca(2+)-ATPase in platelets from patients with established essential hypertension does not effectively maintain Ca2+ homeostasis, and that the increased Ca(2+)-ATPase capacity may reflect an adaptation to increased intracellular calcium concentration.

Adult↗