Biomedical subjects

M Tepel

Publications and source records attributed to M Tepel.

133 records · Page 8Linked to original sources

PubMed1991

Erythropoietin increases cytosolic free calcium concentration and thrombin induced changes in cytosolic free calcium in platelets from spontaneously hypertensive rats.

Using fura-2 cytosolic free calcium concentrations were measured in intact washed platelets from 9 spontaneously hypertensive rats (SHR) and from 9 age-matched normotensive Wistar-Kyoto rats (WKY). In resting platelets cytosolic free calcium concentration was significantly higher in SHR than in WKY (171.8 +/- 64.4 nM vs 93.1 +/- 59.0 nM, p less than 0.05). After preincubation with erythropoietin cytosolic free calcium concentration was significantly higher in SHR than in WKY (197.5 +/- 83.2 vs 93.0 +/- 60.1, p less than 0.01). Using platelets from SHR erythropoietin increased mean resting cytosolic free calcium concentration by 14.9% (p less than 0.05) and mean thrombin induced changes of cytosolic free calcium by 58.3% (p less than 0.01). In contrast, erythropoietin caused no significant increase in the resting calcium concentration or in thrombin induced changes of cytosolic free calcium in platelets from WKY. It is concluded that erythropoietin is involved in the pathogenesis of hypertension by elevating cytosolic free calcium concentration.

Animals↗

PubMedDate not supplied

Long-term effects of vitamin B(12), folate, and vitamin B(6) supplements in elderly people with normal serum vitamin B(12) concentrations.

BACKGROUND: In the elderly, deficiencies of folate, cobalamin (vitamin B(12)) and pyridoxal phosphate (vitamin B(6)) are common. The metabolites homocysteine, methylmalonic acid, 2-methylcitric acid and cystathionine have been reported to be sensitive markers of these vitamin deficiencies. OBJECTIVE: The long-term (269 days) effect of an intramuscular vitamin supplement containing 1 mg vitamin B(12), 1.1 mg folate, and 5 mg vitamin B(6) on serum concentrations of homocysteine (tHcy), methylmalonic acid (MMA), 2-methylcitric acid (2-MCA), and cystathionine (Cysta) was studied in 49 elderly subjects with normal levels of vitamin B(12). METHODS: Vitamin supplement was administered 8 times over a 21-day period, metabolite concentrations were measured until day 269 (e.g. 248 days after the end of vitamin supplementation). RESULTS: From day 0 to 21, the serum levels of the 3 vitamins increased significantly, after cessation of supplementation the levels returned to baseline within the follow-up period. The MMA, 2-MCA and tHcy levels decreased during the treatment period significantly and did not reach baseline values within the 248-day period. Cysta levels did not differ significantly from baseline, either during or after treatment. CONCLUSION: MMA and 2-MCA levels rather reflect the availability of vitamins, especially cobalamin, than the actual serum levels. Since deficiencies of folate, cobalamin and pyridoxal phosphate in the elderly may cause hyerhomocysteinemia and hence may have unfavorable effects on mental performance, determination of MMA and 2-MCA levels in elderly patients with mental disturbances may be a cost-effective measure to improve or maintain mental performance.

Aged↗

PubMedDate not supplied

A novel platelet-derived renal vasoconstrictor agent in normotensives and essential hypertensives.

Platelet homogenates from 200 ml blood of essential hypertensives (n = 28) and normotensives (n = 13) were deproteinized and separated by gel chromatography. The fractions obtained were then tested for vasopressor activity in the isolated perfused rat kidney. In both normotensives and hypertensives, two vasopressor fractions appeared. There was no difference in vasopressor activity in the first vasoactive fraction between normotensives and hypertensives. In the second vasoactive fraction, the hypertensive patients showed a significant higher activity than the normotensive subjects (increase in perfusion pressure by 35.9 +/- 11.5 vs. 6.8 +/- 5.3 mmHg, p less than 0.01). This vasopressor fraction was not inhibited by saralasin, phentolamine, ketanserin, nitroprusside and daltroban and was effective after pretreatment with indomethacin and reserpine and in enzymatically deendothelialized kidneys. The effect was reduced by nifedipine and unchanged by heating the fraction at 100 degrees C and by incubation with proteinase K. It is concluded that a yet unidentified platelet-derived vasopressor agent may contribute to the enhanced vasoconstriction in essential hypertension.

Adenosine Triphosphate↗

PubMedDate not supplied

Effects of protein kinase C activation on intracellular Ca2+ distribution in vascular smooth muscle cells of spontaneously hypertensive rats.

Protein kinase C is known to influence contraction in vascular smooth muscle cells by Ca(2+)-dependent and Ca(2+)-independent mechanisms. In the present study, the effect of protein kinase C activation by phorbol 12-myristate 13-acetate on resting cytosolic free Ca2+ and on cellular Ca2+ pools was assessed in cultured rat aortic muscle cells using fura 2. Cellular Ca2+ pools were evaluated with the selective inhibitor of the sarcoplasmic Ca2+ ATPase, thapsigargin. In normotensive vascular smooth muscle cells, protein kinase C activation caused a redistribution of Ca2+ from the thapsigargin-sensitive pool into the cytoplasm, whereas, in hypertensive cells, no significant effect of protein kinase C activity on cellular Ca2+ distribution was found. It is concluded that protein kinase C modulates the amount of Ca2+ stored in the thapsigargin-sensitive calcium stores. In hypertensive cells, the regulation of Ca2+ pools by protein kinase C is disturbed.

Animals↗

PubMedDate not supplied

Mechanism of the action of angiotensin-converting enzyme inhibitors on agonist-induced Ca2+ influx.

To evaluate the direct effects of the angiotensin-converting enzyme (ACE) inhibitors, captopril, enalaprilat, enalapril (a prodrug without therapeutically significant ACE inhibitory effect) and ramiprilat, on cellular calcium metabolism, the cytosolic free calcium concentration was measured in cultured rat vascular smooth muscle cells using the fluorescent dye, fura-2. Preincubation with captopril, enalaprilat, enalapril, or ramiprilat for 40 min significantly reduced the angiotensin II-induced transplasma membrane calcium influx but did not influence the angiotension II-induced calcium release from internal stores. Captopril and ramiprilat also inhibited arginine vasopressin, but not the thapsigargin-, norepinephrine-, or the BayK 8644-induced changes in cytosolic calcium. Phorbol 12-myristate 13-acetate pretreatment for 30 s caused an increase in the angiotensin II-induced rise in cytosolic calcium. Although both captopril and verapamil reduced responses to angiotensin II to similar extents, only verapamil blocked the ability of phorbol 12-myristate 13-acetate to enhance responses to angiotensin II. It is concluded that ACE inhibitors modulate the effects of some but not all agonist-induced transplasma membrane calcium influx.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMedDate not supplied

Diadenosine polyphosphates increase cytosolic calcium and attenuate angiotensin-II-induced changes of calcium in vascular smooth muscle cells.

The effects of diadenosine tetraphosphate (AP4A), diadenosine pentaphosphate (AP5A), and diadenosine hexaphosphate (AP6A) on the cytosolic free calcium concentration ([Ca2+]i) were evaluated in cultured rat vascular smooth muscle cells (VSMC) using the fluorescent dye technique. A concentration-dependent increase of [Ca2+]i by AP4A, AP5A, and AP6A was observed in VSMC. Additions of 10 micromol/l AP4A, AP5A, and AP6A significantly increased [Ca2+]i in VSMC by 224 +/- 98 nmol/l (n = 6; p < 0.01, 205 +/- 27 nmol/l (n = 14; p < 0.01), and 269 +/- 98 nmol/l (n = 5; p < 0.05), respectively. Additions of AP4A, AP5A, and AP6A only 120 s prior to angiotensin II (Ang II) administration significantly attenuated the Ang-II-induced changes of [Ca2+]i in VSMC from 1,053 +/- 174 nmol/l to 283 +/- 42 nmol/l, 591 +/- 112 nmol/l, and 477 +/- 79 nmol/l, respectively (each p<0.01) as compared to the control). The AP6A-induced changes of [Ca2+]i were inhibited by the blockers of P2 purinoceptors, suramin and pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid, but not by the inhibitor of P2y purinoceptors, reactive blue. Adenosine triphosphate (ATP) also increased [Ca2+]i in VSMC, whereas the purinoceptor P2x agonist, alpha,beta-methylene-ATP, had no effect on [Ca2+]i in VSMC. Therefore diadenosine polyphosphates may induce changes of [Ca2+]i by interacting with purinoceptors and may be involved in local regulation of vascular resistance evoked by the Ca(2+)-dependent contractile response of VSMC.

Adenosine Triphosphate↗

PubMedDate not supplied

Proscillaridin A immunoreactivity: its purification, transport in blood by a specific binding protein and its correlation with blood pressure.

A material crossreacting with antibodies against the bufadienolide proscillaridin A and inhibiting the sodium pump was found in human blood plasma. The concentration of the material with a retention time similar to ouabain in a reversed phase HPLC correlated to systolic blood pressure and pulse pressure. Affinity purification of this compound from bovine adrenals resulted in the isolation of a compound with molecular mass of 600 Da that was not identical with ouabain. Consistent with the postulate that endogenous ouabain and proscillaridin A immunoreactivities may belong to a new class of cardiotonic steroid hormones, a protein of Mr = 60 kDa has been found in bovine serum by affinity-labeling with N-hydroxysuccimidyl digoxigenin-3-O-methylcarbonyl-epsilon-aminocaproate.

Adrenal Glands↗