Attenuation of alkalizing effect of thrombin by S-nitrosoglutathione in human platelets.

S-Nitrosoglutathione and sodium nitroprusside, two activators of the soluble guanylate cyclase, inhibit the intracellular calcium rise evoked by thrombin at an early step of the activation cascade. A similar effect is obtained with prostaglandin E1, a drug that increases cAMP. We have found that in human platelets thrombin 0.1 IU/ml (approximately 1 nmol/l) produced a transient increase of [Ca2+]i. After a 10-min preincubation at 37 degrees C in 100 mumol/l S-nitrosoglutathione the peak value was reduced by 79 +/- 4% (mean and SEM, percentage of the parallel control). The [Ca2+]i peak was reduced by 66 +/- 4% after preincubation in 100 mumol/l sodium nitroprusside, and by 90 +/- 2% after preincubation in 10 mumol/l prostaglandin E1. Thrombin has a slow alkalizing effect. After a 10-min preincubation at 37 degrees C in 100 mumol/l S-nitrosoglutathione the change in pHi produced by thrombin was reduced by 35 +/- 5%, but only 12 +/- 4% after preincubation in 100 mumol/l sodium nitroprusside. The alkalizing effect of thrombin was also blunted by 10 mumol/l prostaglandin E1: the change of intracellular pH was decreased by 39 +/- 5%. As a conclusion, these drugs in addition to the reduction of rise in [Ca2+]i have an inhibitory effect on the alkalizing response induced by thrombin.

Lithium opens store-operated channels in human platelets.

Ca(2+) release from internal stores as a result of activation of phospholipase C or inhibition of the endoplasmic reticulum pump is accompanied by Ca(2+) influx from the extracellular space. Measurement of intracellular calcium concentration and fluorescence quenching in Fura2-loaded cells showed that platelets preincubated in lithium have significantly higher basal, but lower agonist-stimulated influx of Mn(2+) (acting as a surrogate of Ca(2+) influx), than platelets reloaded with calcium in a normal sodium medium. There is no difference in the basal entry of divalent ion in platelets preincubated in sodium, lithium, or N-methyl glucamine in the absence of calcium. In platelets preincubated in lithium there is a higher basal Mn(2+) entry without further increase upon store depletion by thapsigargin. In contrast, a significant increase in the divalent ion influx was found in sodium or N-methyl glucamine attributable to the opening of channels sensitive to store depletion. In the absence of extracellular calcium, the empty store opens channels and Li(+) did not have additional effect on channels that are already open. The refilling of the stores with Ca(2+) suppresses Mn(2+) entry after sodium or NMG preincubation, but not after lithium preincubation. We propose that lithium induces a calcium influx throughout store-operated channels. This hypothesis may explain the lack of additivity, in cell preincubated in lithium, of basal entry and thapsigargin-triggered entry of calcium.

Genistein inhibits osmotic activation of Na(+) /H( +) exchange in human platelets.

The osmotic shrinkage is an important activator of the Na(+)/H( *) exchanger. The intracellular signaling mechanisms by which shrinkage changes intracellular pH have not been fully elucidated. In human platelets, the removal of calcium did not prevent the osmotic activation of the exchanger. The increase of pH(i) after an hyperosmotic stress was reduced by W-7 (63 micromol l(-1)), and by ML-7 (25 micromol l(-1)), inhibitors of responses mediated by calmodulin or by myosin light chain kinase, but the high concentrations needed suggested that non-specific effects could be involved. Although the exchanger was quiescent during preincubation in hypertonic sodium free solutions, some steps of the signal transduction chain that links the shrinkage to the exchanger activation suffers a modification. Therefore, upon exposure to isotonic sodium-containing media, the rate of recovery from acid loads was increased. The presence of genistein (100 micromol l( -1)) during the preincubation inhibited this activation of Na(+)/H( +) exchanger. We propose that shrinkage induce activation of tyrosine kinases, which in turn leads to the activation of Na(+)/H(+) exchanger and contributes to the restoration of cell volume in human platelets.

[Prevalence of hypertension in 3154 young students]. / Prevalencia de hipertensión arterial en 3154 jóvenes estudiantes.

Blood pressure (BP) levels were evaluated in 3154 students (mean age 21 years old) of La Plata University, School of Medicine. BP was registered three times in each student and the mean was used for all the analyses. Systolic (SBP) and diastolic pressure (DBP) were significantly higher in men. Mean SBP was 126 +/- 13 mm Hg for men and 115 +/- 11 mm Hg for women. Mean DBP was 77 +/- 10 mm Hg and 74 +/- 9 mmHg for men and women, respectively. The global prevalence of HBP (BP > or = 140 and/or 90 mm Hg) was 12% when both sexes were considered together, but it was significantly higher in men than in women (20% and 6% respectively; p < 0.001). Mean BP corresponding to the 95th percentile in each sex was also estimated. Taking these values to define high blood pressure (HBP) the cut-off point between normal and HBP will be different for each sex (148/93 mm Hg for men and 133/88 mm Hg for women). The prevalence of HBP in this survey is high if we compare with that of the NHANES III (1988-91, USA, 2%) for a group of the same age. However, it is very similar to that of NHANES II (1976-80, USA, 12%), before the intensification of educational and primary prevention programs took place. The global prevalence of optimal BP (BP < 120/80 mm Hg) was just 44%. The relation between Body Mass Index (BMI) and BP levels was also studied, and the result was a positive correlation, statistically significant. Mean BP increased 1.16 mm Hg per unit of increase of BMI. When asking about family history (only mother or father) of HBP we could not find any significant difference between the students with HBP and the others. Cardiovascular diseases are the first cause of death in our country and HBP is one of the most important risk factors. The high prevalence of HBP in this young population must be considered when planning health care programs.

Calcium-calmodulin modulation of the activity of Na+/H+ exchanger in human platelets.

This study aimed at establishing the role of calmodulin in regulating pHi of human platelets under acid loads and in stimulated states. The response of human platelets to thrombin was an initial drop of pHi followed by a recovery with a significant increase above the pre-stimulation level in control experiments and a recovery to initial values in platelets maintained in the presence of 19 mmol/l TFP (trifluoperazine = 2 trifluoromethyl-10 [3'-(1 methyl-4-piperazinyl) propyl] phenothiazine). The change in pHi after 8 min was 0.130 +/- 0.030 in the control and 0.001 +/- 0.011 pH units in TFP (P < 0.05). The initial velocity of recovery from an acid load was reduced to 56.7 +/- 6% of the control (n = 6, P < 0.05) with 50 mumol/l W7 (N-(6 aminohexyl)-5-chloro-l-naphthalene sulphonamide), and to 29.7 +/- 4.3% of the control (n = 8, P < 0.05) with 19 mumol/l TFP. The initial velocity of recovery was significantly greater in recalcified platelets than in the preparations kept in the nominal absence of extracellular calcium (1.08 +/- 0.12 vs 0.66 +/- 0.12 pH units per min, P < 0.05). Lower concentration of TFP had an inhibitory effect only in the presence of calcium. The velocities of recovery reached similar values at higher TFP concentration. The significant interaction between Ca2+ and TFP concentrations indicates that the Ca-calmodulin complex, rather than an unspecified direct action of TFP, is responsible for the modulation of the Na+/H+ exchanger. These findings indicate that calcium-calmodulin participates in both the recovery of pH after an acid load and the increase of pHi in stimulated states of human platelets.

Chelerythrine inhibits Na(+)-H+ exchange in platelets from spontaneously hypertensive rats.

Hypertension has been associated with increased activity of the Na(+)-H+ exchanger. To study the role played by protein kinase C in this process, we used chelerythrine, a potent and specific inhibitor of the kinase. After an acid load by ammonium chloride preincubation, platelets isolated from spontaneously hypertensive rats showed a faster and larger increase in intracellular pH than platelets from Wistar-Kyoto rats. The initial rate of intracellular pH recovery was 2.46 +/- 0.26 pH units per minute in spontaneously hypertensive rats and 1.74 +/- 0.19 in Wistar-Kyoto rats. For protein kinase C inhibition, platelets were incubated for 30 minutes with 10 mumol/L chelerythrine. This treatment induced a significant reduction in the recovery rate only in spontaneously hypertensive rat platelets, indicating that a pathway involving protein kinase C participates in the prestimulation of the exchanger in cells from this rat strain. Addition of chelerythrine reduced the baseline intracellular pH of platelets. No significant difference was found between the decrease of steady-state intracellular pH induced by chelerythrine in either rat strain. These findings indicate that this model of hypertension is characterized by increased Na(+)-H+ activity mediated by protein kinase C stimulation.

[Blood pressure levels in young students. Correlation between body mass and metabolic and hemodynamic factors]. / Niveles de presion arterial en jovenes estudiantes. Correlacion con la masa corporal, factores metabolicos y hemodinamicos.

Blood pressure (BP) levels were measured in 450 students (mean age 20.8 +/- .11 years old) and were correlated with different parameters. Prevalence of arterial hypertension was, according to the JNC-V, 13% in males and 3% in females. The correlations between Body Mass Index (BMI) and BP levels were statistically significant either in males and females. Mean BP (MBP) increased 1.17 mmHg per unit of increase of BMI in males and 0.97 mmHg in females. According to the BP levels proposed by the JNC-V the male individuals were classified in three groups: optimal BP (OBP), high normal BP (HNBP) and hypertensives stage 1 (Hypert.). These groups had different BMI; OBP: 22.74 +/- 2; HNBP 24.4 +/- 0.48; Hypert. 25.06 +/- 0.66 kg/m2 (P < 0.05 Hypert. and HNBP as regards PAO; HNBP and Hypert. were not statistically different). Samples of each of these groups were taken in order to analyze other parameters such as: cardiac index (CI), total peripheral resistance (TPR), plasma glucose, plasma insulin, glucose/insulin ratio and intracellular pH in platelets. No significant differences were found in the three groups as regards plasma glucose, plasma insulin and glucose/insulin ratio. The different BP levels among the groups were due to an increase in CI: OBP 3.25 +/- 0.13; HNBP 3.76 +/- 0.2; Hypert. 4.76 +/- 36 ml/min/m2 (P < 0.05) but with TPR numerically "normal": OBP: 2139 +/- 106; HNBP 2170 +/- 114; Hypert. 1858 +/- 146 dynes sec. cm-5 m2 (NS). The intracellular pH in platelets was: 7.15 +/- 0.07 in the OBP, 7.21 +/- 0.05 in the HNBP and 7.33 +/- 0.04 in the Hypert. (P < 0.05 in the Hypert. as regards the PAO). The increase of the pHi in the Hypert. suggests hyperactive Na+/H+ exchanger.

Identification of a sodium-bicarbonate symport in human platelets.

Intracellular pH (pH(i)) was measured in human platelets using fluorescent probes. Basal pH(i) was higher in HC(O3-)- buffered solutions (7(7.33 +/- 0.01) than in nominally HCO3- free, Hepes buffered solutions (7.16 +/- 0.01, P < 0.05). Addition of EIPA caused to fall in Hepes, but did not inhibit the increase of pH(i) when platelets maintained in Hepes were transferred to a CO2/HCO3- buffer. After an intracellular acidosis induced by an NH4Cl prepulse, the initial velocity of recovery (d(pH)/dt(i), in pH units/min) was 3.32 +/- 0.69 in Hepes-buffered solution and 2.85 +/- 0.88 in HCO3- media. Taking into account the differences in buffer capacity, the efflux of acid equivalents after 1.2 min was twice as much in the presence of bicarbonate. The addition of 30 mumol/1 EIPA effectively blocked acid efflux (d(pH)/dt(i) = 0.08 +/ 0.04) in a nominally HCO3- free solution, whereas the recovery was reduced but not abolished (d(pH)/dt(i) = 0.37 +/- 0.10, P < 0.05) in the presence of bicarbonate. The stilbene derivative SITS further inhibited the EIPA-resistant pH(i) recovery. Removal of external Na+ inhibited the HCO(3-)-dependent recovery whereas depletion of internal Cl-, did not suppress it. Depolarization of the membrane had no effect on this recovery. The results suggest the contribution of an electroneutral Na+/HCO3- cotransport in the recovery of pH(i) following an acid load. Both the Na+/H+ antiport and the HCO(3-)-dependent mechanism contribute approx. 50% each to the total acid equivalent efflux during the recovery from a pH(i) 6.46 +/- 0.14 to the basal pH(i) in human platelets.

Differences in prevalence of diastolic arterial hypertension in 1423 young individuals in two different interviews.

OBJECTIVES: To determine prevalence of diastolic arterial hypertension (DAH) in young individuals using different criteria. Secondly, to test the possible different blood pressure reactions to mental stress and hand grip in two groups: group A, a 'low blood pressure group', and group B, diastolic blood pressure 90 mmHg or greater in one interview and below these values in a second interview. SUBJECTS: A total of 1423 volunteer medical students was recruited at La Plata School of Medicine, average age 21 +/- 3 years. DESIGN: Systolic and diastolic blood pressure were measured three times on two different occasions separated by one week. With the values obtained, prevalence of arterial hypertension was determined according to the criteria suggested by The Joint National Committee 4 (JNC-4) and the World Health Organization (WHO), and to statistical bases. INTERVENTIONS: Mental stress and hand grip tests were performed by groups A and B. MAIN RESULTS: The prevalence of DAH when only the first determination of the first interview was considered was 14.7%, 6.7% (considering the WHO criterion) or 5% (using the statistical criterion). These values are reduced if repeated measurements are averaged. The greatest reduction was obtained when the JNC-4 criterion was used (1.6%). The reactivity of stressors did not show any relationship with the initial blood pressure of the subjects. CONCLUSIONS: In epidemiological studies, the differences among the criteria should be considered when analyzing blood pressure of populations. Stress tests (mental stress and hand grip) do not help in identifying differences between the groups studied.

Effects of adenosine on chronotropic responses of rat atria to alpha and beta adrenergic stimulation.

The chronotropic response of rat atria to beta adrenergic stimulation required higher concentrations of agonist in the presence of adenosine. This anti beta-adrenergic effect could attenuate the tachycardia induced by the increased sympathetic tone during cardiac ischemia. The sensitivity to alpha adrenergic stimulation did not change in the presence of adenosine.

Comparison between sodium-hydrogen ion and lithium-hydrogen ion exchange in human platelets.

The membrane-coupled exchange of Li+ and/or Na+ for H+ was studied in human platelets measuring intracellular pH(pHi) with a fluorescent indicator. A Li(+)-containing medium restored the internal pH of preacidified platelets to their prior pHi control value. When Na+ was replaced by Li+, similar steady-state values were attained in this system, although it was transported more slowly. The Km and Vmax were both higher with Na+ than with Li+. Exchanges of Li+ or Na+ with H+ were both blocked by ethylisopropylamiloride (EIPA) achieving half-maximal inhibition at submicromolar concentrations. The efflux Li+ or Na+ and resuspended in a choline medium exhibited an influx of H+ sensitive to EIPA. Thrombin, an activator of Na+/H+ exchange, induced a rapid increase in platelet internal pH in the presence of exogenous Li+. Thus: (1) Li+ can be substituted for Na+ in both the forward and the reverse exchange reaction; (2) Li+, while having a higher affinity than Na+ for the external site of the membrane carrier, has a lower Km and (3) Li+ as well as Na+ exchange are activated by thrombin.

[Definition of hypertension based on a prevalence study of 1,423 young adults]. / Consideraciones sobre la definición de hipertensión arterial a partir de un estudio de prevalencia en 1423 jóvenes.

The prevalence of arterial hypertension (AH) was studied in 1423 individuals (702 males and 721 females) aged 21 years (Fig. 1, Table 1). Systolic (SBP) and diastolic (DBP) blood pressures and heart rate (HR) were measured three times on two different occasions separated by at least one week. Three different criteria were used to define AH (Table 3): 1) World Health Organization (WHO) [PAD > or = 95 mmHg in one casual determination]; Joint National Committee IV (JNC-4) [PAD > or = 90 mmHg on two different occasions]; and 3) Statistical [PAD > percentile 95 of the respective distribution]. BP was distributed normally in both males and females (Fig. 4). DBP decreased progressively along the six measurements (Fig. 2, Table 2), with the average of DBP determinations 4-6 being significantly lower than the average of determinations 1-3 (p < 0.05). SBP behaved in the same way (Fig. 2, Table 2), but in this case the 2nd and 3rd determinations within each occasion (2-3 and 5-6) were significantly lower than determinations 1 and 4, respectively (p < 0.05). As a result, the percentage of individuals of either sex with DBP > 90 mmHg was 14.7% based on the 1st determination (Fig. 5), but if the averages of determinations 1 to 3 or 1 to 6 were considered, these percentages decreased to 8.7% and 4% respectively (Fig. 5). With the WHO criterion (PAD > or = 160/95 mmHg based on the first determination) there were 3.3% of individuals with AH. With the statistical criterion the prevalence of AH was always 5%, but the actual value of percentile 95 was progressively lower as we took into account the 1st. determination, the average of 1-3 or the average of 1-6: 100, 95 and 90 mmHg in males and 90, 88 and 84 mmHg in females, respectively (Fig. 6). With the JNC-4 criterion there were 1.6% of individuals with AH (Fig. 5). These low figures were caused by the lack of repeatability of DBP readings in the second determination, since 79% of the individuals with DBP > or = 90 mmHg on the first occasion were normotensive on the second one, whereas more than 95% of those being initially normotensive remained in that category on the second visit (Fig. 7). The FC did not show important changes (Fig. 8), and the percentage of individuals with systolic AH was low (Table 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Consideraciones sobre la definicion de hipertension arterial a partir de un estudio de prevalencia de 1423 jovenes / Hypertension definition based on a prevalence study in 1.423 young adults

Se estudió la prevalencia de hipertensión arterial (HA) en una muestra de 1423 jóvenes (702 varones y 721 mujeres) de 21 años de edad promedio. En cada individuo se midió la presión arterial sistólica (PAS) y diastólica (PAD) y la frecuencia cardíaca (FC) tres veces en cada una de dos ocasiones separadas entre sí por al menos una semana. Para definir HA se utilizaron tres criterios: 1) el de la Organización Mundial de la Salud (OMS) [PAD * 95 mmHg]; 2) el del Joint National Commitee IV (JNC-4) [PAD * 90 mmHg en dos fechas distintas]; y Estadístico: PAD > al percentilo 95 de la distribucción respectiva. La PAD y PAS descendieron significativamente en la segunda ocasión con respecto a la primera (p < 0,05), y en el caso de la PAS hubo descensos significativos en la segunda y tercera tmas de cada ocasión con respecto a la primera toma (p < 0,05). Como consecuencia, el número de indivíduos con PAD * 90 mmHg fue, en ambos sexos, de 14,7% si nos basamos en la primera toma, pero bajó a 8,7% si nos basamos en el promdeio de las tomas 1 a 3; y a un 4% si nos basamos en el promdeio 1-6. Con el criterio de la OMS (basado en la medición 1) hay un 3,3% de hipertensos en ambos sexos . Con el criterio estadístico hubo siempre un 5% con HA, pero la línea de corte (percentilo 95) bajó a medida que consideramos la toma 1, el promedio 1-3 o el promedio 1-6: 100, 95 y 90 mmHg en varones y 90, 88 y 84 mmHg en mujeres. Con el criterio del JNC-4 se detectaron 1,6% de individuos con HA. En el bajo porcentaje detectado con este último criterio influyó más la falta de repetibilidad de las cifras que el mismo exige que el descenso progresivo de la PAD antes mencionado, ya que aproximadamente un 80% de los inicialmente hipertensos fueron normotensos, ya que aproximadamente un 80% de los inicialmente hipertensos fueron normotensos en la segunda fecha; mientras que más del 95% de los inciialmente nomotensos se conservaron como tales en la segunda fecha. La FC no mostró alteraciones de importancia, y el número de individuos con PASelevada fue escaso...

Consideraciones sobre la definicion de hipertension arterial a partir de un estudio de prevalencia de 1423 jovenes / Hypertension definition based on a prevalence study in 1.423 young adults

Se estudió la prevalencia de hipertensión arterial (HA) en una muestra de 1423 jóvenes (702 varones y 721 mujeres) de 21 años de edad promedio. En cada individuo se midió la presión arterial sistólica (PAS) y diastólica (PAD) y la frecuencia cardíaca (FC) tres veces en cada una de dos ocasiones separadas entre sí por al menos una semana. Para definir HA se utilizaron tres criterios: 1) el de la Organización Mundial de la Salud (OMS) [PAD * 95 mmHg]; 2) el del Joint National Commitee IV (JNC-4) [PAD * 90 mmHg en dos fechas distintas]; y Estadístico: PAD > al percentilo 95 de la distribucción respectiva. La PAD y PAS descendieron significativamente en la segunda ocasión con respecto a la primera (p < 0,05), y en el caso de la PAS hubo descensos significativos en la segunda y tercera tmas de cada ocasión con respecto a la primera toma (p < 0,05). Como consecuencia, el número de indivíduos con PAD * 90 mmHg fue, en ambos sexos, de 14,7% si nos basamos en la primera toma, pero bajó a 8,7% si nos basamos en el promdeio de las tomas 1 a 3; y a un 4% si nos basamos en el promdeio 1-6. Con el criterio de la OMS (basado en la medición 1) hay un 3,3% de hipertensos en ambos sexos . Con el criterio estadístico hubo siempre un 5% con HA, pero la línea de corte (percentilo 95) bajó a medida que consideramos la toma 1, el promedio 1-3 o el promedio 1-6: 100, 95 y 90 mmHg en varones y 90, 88 y 84 mmHg en mujeres. Con el criterio del JNC-4 se detectaron 1,6% de individuos con HA. En el bajo porcentaje detectado con este último criterio influyó más la falta de repetibilidad de las cifras que el mismo exige que el descenso progresivo de la PAD antes mencionado, ya que aproximadamente un 80% de los inicialmente hipertensos fueron normotensos, ya que aproximadamente un 80% de los inicialmente hipertensos fueron normotensos en la segunda fecha; mientras que más del 95% de los inciialmente nomotensos se conservaron como tales en la segunda fecha. La FC no mostró alteraciones de importancia, y el número de individuos con PASelevada fue escaso...(AU)

Consideraciones sobre la definición de hipertensión arterial a partir de un estudio de prevalencia en 1423 jóvenes. / [Definition of hypertension based on a prevalence study of 1,423 young adults]

The prevalence of arterial hypertension (AH) was studied in 1423 individuals (702 males and 721 females) aged 21 years (Fig. 1, Table 1). Systolic (SBP) and diastolic (DBP) blood pressures and heart rate (HR) were measured three times on two different occasions separated by at least one week. Three different criteria were used to define AH (Table 3): 1) World Health Organization (WHO) [PAD > or = 95 mmHg in one casual determination]; Joint National Committee IV (JNC-4) [PAD > or = 90 mmHg on two different occasions]; and 3) Statistical [PAD > percentile 95 of the respective distribution]. BP was distributed normally in both males and females (Fig. 4). DBP decreased progressively along the six measurements (Fig. 2, Table 2), with the average of DBP determinations 4-6 being significantly lower than the average of determinations 1-3 (p < 0.05). SBP behaved in the same way (Fig. 2, Table 2), but in this case the 2nd and 3rd determinations within each occasion (2-3 and 5-6) were significantly lower than determinations 1 and 4, respectively (p < 0.05). As a result, the percentage of individuals of either sex with DBP > 90 mmHg was 14.7

based on the 1st determination (Fig. 5), but if the averages of determinations 1 to 3 or 1 to 6 were considered, these percentages decreased to 8.7

and 4

respectively (Fig. 5). With the WHO criterion (PAD > or = 160/95 mmHg based on the first determination) there were 3.3

of individuals with AH. With the statistical criterion the prevalence of AH was always 5

, but the actual value of percentile 95 was progressively lower as we took into account the 1st. determination, the average of 1-3 or the average of 1-6: 100, 95 and 90 mmHg in males and 90, 88 and 84 mmHg in females, respectively (Fig. 6). With the JNC-4 criterion there were 1.6

of individuals with AH (Fig. 5). These low figures were caused by the lack of repeatability of DBP readings in the second determination, since 79

of the individuals with DBP > or = 90 mmHg on the first occasion were normotensive on the second one, whereas more than 95

of those being initially normotensive remained in that category on the second visit (Fig. 7). The FC did not show important changes (Fig. 8), and the percentage of individuals with systolic AH was low (Table 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Consideraciones sobre la definición de hipertensión arterial a partir de un estudio de prevalencia en 1423 jóvenes. / [Definition of hypertension based on a prevalence study of 1,423 young adults]

The prevalence of arterial hypertension (AH) was studied in 1423 individuals (702 males and 721 females) aged 21 years (Fig. 1, Table 1). Systolic (SBP) and diastolic (DBP) blood pressures and heart rate (HR) were measured three times on two different occasions separated by at least one week. Three different criteria were used to define AH (Table 3): 1) World Health Organization (WHO) [PAD > or = 95 mmHg in one casual determination]; Joint National Committee IV (JNC-4) [PAD > or = 90 mmHg on two different occasions]; and 3) Statistical [PAD > percentile 95 of the respective distribution]. BP was distributed normally in both males and females (Fig. 4). DBP decreased progressively along the six measurements (Fig. 2, Table 2), with the average of DBP determinations 4-6 being significantly lower than the average of determinations 1-3 (p < 0.05). SBP behaved in the same way (Fig. 2, Table 2), but in this case the 2nd and 3rd determinations within each occasion (2-3 and 5-6) were significantly lower than determinations 1 and 4, respectively (p < 0.05). As a result, the percentage of individuals of either sex with DBP > 90 mmHg was 14.7

based on the 1st determination (Fig. 5), but if the averages of determinations 1 to 3 or 1 to 6 were considered, these percentages decreased to 8.7

and 4

respectively (Fig. 5). With the WHO criterion (PAD > or = 160/95 mmHg based on the first determination) there were 3.3

of individuals with AH. With the statistical criterion the prevalence of AH was always 5

, but the actual value of percentile 95 was progressively lower as we took into account the 1st. determination, the average of 1-3 or the average of 1-6: 100, 95 and 90 mmHg in males and 90, 88 and 84 mmHg in females, respectively (Fig. 6). With the JNC-4 criterion there were 1.6

of individuals with AH (Fig. 5). These low figures were caused by the lack of repeatability of DBP readings in the second determination, since 79

of the individuals with DBP > or = 90 mmHg on the first occasion were normotensive on the second one, whereas more than 95

of those being initially normotensive remained in that category on the second visit (Fig. 7). The FC did not show important changes (Fig. 8), and the percentage of individuals with systolic AH was low (Table 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Bay K 8644 enhances the outflow of [3H]-noradrenaline and [3H]-DOPEG from isolated rat atria.

The effect of Bay K 8644 (a dihydropyridine Ca(2+)-channel activator), was examined on spontaneous and stimulus-evoked release of tritium from isolated rat atria prelabelled with [3H]-noradrenaline. Bay K 8644 (3 mumol/l) significantly increased atrial rate from 206 +/- 7 to 259 +/- 9 beats.min-1 (P less than 0.05) and also tritium outflow (expressed as fractional rate of loss in min-1 x 10(3)) from 6.49 +/- 0.35 to 8.61 +/- 0.74 (P less than 0.05). Neither the maximal rate nor the overflow of tritium induced by stimulation of sympathetic nerve terminals was changed by the compound. The increase in basal tritium outflow produced by Bay K 8644 was calcium-dependent. However, it could not be antagonized by nitrendipine. The overflow of tritium induced by Bay K 8644 consisted mainly of 3,4-dihydroxyphenylglycol ([3H]-DOPEG), indicating that the compound produces a leakage from the storage vesicles of sympathetic nerve terminals of the isolated rat atria.

Inward movement of Ca2+ in K(+)-depolarized rat vascular smooth muscle.

The kinetics of the Ca2+ (45Ca2+) uptake in segments of rat aorta and its relationship with tension development in the presence of K+ concentrations ([K+]o) ranging from 3.5 to 100 mM was investigated. It was found that: 1) The curve relating 45Ca2+ uptake and time was virtually linear during the first 3 min. Therefore, the influx calculated as uptake in 3 min/3 min was not significantly different from that calculated as the slope of the uptake curve. The actual uptake of the cation during the loading period would be underestimated by about 30 percent if the loss of Ca2+ from that compartment during a 2 h clearing of the extracellular space in La3+ medium, is ignored. 3) 45Ca2+ activity remaining in the tissue after a 3 min labelling period followed by a 2 h washout can reliably be corrected to calculate Ca2+ influx. 4) The K(+)-induced tension development showed no significant correlation with the total exchangeable Ca2+ while it appeared as a steep function of Ca2+ influx between 15 and 80 mM [K+]o. 5) In [K+]o = 100 mM Ca2+ influx was 5 to 6 times larger than in normal [K+]o (5.3 mM). The estimated Ca2+ permeability (PCa) increased linearly as a function of [K+]o (5.3 to 100 mM). In [K+]o = 100 mM, PCa was estimated to be about 17-fold that in [K+]o = 5.3 mM. Similarly, the increased in Ca2+ conductance (GCa) for the same change in [K+]o was estimated to be 14-fold.

The Na+/H+ exchanger role in the intracellular pH regulation of human platelets.

The intracellular pH of human platelets was measured with a fluorescent intracellular probe. When platelets were in basal conditions (pHo 7.4, [Na+]o 140 mM) the pHi was 6.98 +/- 0.04. Five minutes after the addition of EIPA 60 microM, an inhibitor of Na+/H+ exchange, the pHi fell in 0.075 +/- 0.022 pH units (P less than 0.05). Preincubation in a sodium free, acid medium (pHo 6.3) induced a cell acidification to pH 6.61 +/- 0.03 (P less than 0.01). Preacidified platelets showed a recovery in sodium-containing solution that is a function of [Na+]o. The initial rate of recovery depends on [Na+]o in a Michaelis-Menten fashion, showing a Km of 35.6 mM and a Vmax of 0.213 pH units/min. These results show that the pHi is maintained in human platelets by a Na+/H+ exchange that is active even in basal conditions. The properties of the Na+/H+ exchanger in human platelets and in the less accessible smooth vascular cells are similar; generalized pathological alterations, like hypertension, could be reflected by both tissues.

Positive chronotropic effect of Bay K 8644: participation of endogenous norepinephrine.

The chronotropic effect of Bay K 8644, a dihydropyridine known to increase the slow inward current, was studied in spontaneously beating rat atria. Increases in atrial rate were concentration-dependent and the maximal increase (106 +/- 10 beats/min) was obtained at 3 x 10(-6) mol/l. Reserpine pretreatment, or propranolol 3 x 10(-7) mol/l, or propranolol plus prazosin 10(-6) mol/l decreased the maximum chronotropic effect of Bay K 8644 by about 60%. Blockade of the removal mechanisms of catecholamines (hydrocortisone 3 x 10(-5) mol/l plus cocaine 10(-5) mol/l) did not prevent the chronotropic effect of the compound. Exposure to Bay K 8644 increased the spontaneous outflow of tritium from atria preloaded with [3H]-norepinephrine by 30%. The results indicate that Bay K 8644 produces positive chronotropic effects through two mechanisms: a direct one and an indirect mechanism that involves the participation of norepinephrine released from sympathetic nerve endings.