Effects of angiotensin II and endothelin-1 on platelet aggregation and cytosolic pH and free Ca2+ concentrations in essential hypertension.
The aims of this study were to determine the relations between platelet free calcium concentrations ([Ca2+]i), intracellular pH (pHi), and aggregation and to assess the effects of angiotensin II (Ang II) and endothelin-1 on these platelet parameters in normotensive subjects and hypertensive patients. Seventeen normotensive subjects, 25 untreated hypertensive patients, and 34 treated hypertensive patients were studied. Platelet cytosolic free [Ca2+]i and pHi were measured spectrofluorometrically using specific fluorescent probes (fura 2-AM and BCECF-AM, respectively) in unstimulated and Ang II- and endothelin-1-stimulated platelets. Aggregation was measured by a turbidometric technique. Basal [Ca2+]i (141 +/- 11 nmol/L) and pH (7.16 +/- 0.01) were higher (P < .05) in the untreated hypertensive group compared with the normotensive (118 +/- 9 nmol/L, 7.11 +/- 0.01, respectively) and treated hypertensive (121 +/- 11 nmol/L, 7.12 +/- 0.01, respectively) groups. In the combined normotensive and hypertensive groups, there were significant correlations between [Ca2+]i and mean arterial pressure (r = .75, P < .01), pHi and mean arterial pressure (r = .72, P < .01), [Ca2+]i and pHi (r = .71, P < .01), [Ca2+]i and aggregation (r = .69, P < .02), and pHi and aggregation (r = .56, P < .05). Ang II stimulation significantly increased [Ca2+]i and pHi in the untreated hypertensive and normotensive groups. The net change in [Ca2+]i induced by Ang II was significantly higher (P < .05) in the untreated hypertensive group compared with the other groups (67 +/- 6 nmol/L for the untreated hypertensive group versus 54 +/- 5 and 29 +/- 8 nmol/L for the normotensive and treated hypertensive groups, respectively). In the presence of Ang II, thrombin-induced aggregatory responses were increased in all three groups, but the maximal response was significantly higher in the untreated hypertensive group compared with the other groups (P < .05). Endothelin-1 increased pHi through endothelin A-receptors (effect blocked by the specific antagonist BQ-123) but had no significant effect on [Ca2+]i or aggregation. However, endothelin-1 blunted thrombin-induced platelet aggregation in normotensive subjects but not in hypertensive patients. In conclusion, increased Ang II-stimulated [Ca2+]i and pHi in platelets of essential hypertensive patients may be associated with increased aggregatory responses. The stimulatory effect of endothelin-1 on pHi but not on [Ca2+]i or aggregation suggests that in platelets endothelin-induced signaling pathways other than phospholipase C may be involved.(ABSTRACT TRUNCATED AT 400 WORDS)
Touyz
R M
RM
Clinical Research Institute of Montreal, University of Montreal, Quebec, Canada.
Schiffrin
E L
EL
D000328:Adult; D000368:Aged; D000584:Amiloride / Q000494:pharmacology; D000704:Analysis of Variance; D000804:Angiotensin II / Q000494:pharmacology*; D001792:Blood Platelets / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D002118:Calcium / Q000032:analysis; D003600:Cytosol / Q000737:chemistry / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006973:Hypertension / Q000097:blood*; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000378:metabolism; D012044:Regression Analysis; D012504:Saralasin / Q000494:pharmacology
D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D010456:Peptides, Cyclic; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D000804:Angiotensin II; D000584:Amiloride; D012504:Saralasin; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D002118:Calcium