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F Rivera

Publications and source records attributed to F Rivera.

At least 109 records · Page 6Linked to original sources
PubMed1995

Role of nitric oxide and prostacyclin in the control of renal perfusion in experimental cirrhosis.

Nitric oxide (NO) and prostacyclin (PGI2) are two important modulators of renal function under normal conditions; however, little is known on their contributory role in cirrhosis with ascites. In this study, mean arterial pressure, renal hemodynamics, and sodium excretion were measured in 15 rats with cirrhosis and ascites and 16 control rats. Animals were studied in normal conditions, after inhibiting the synthesis of NO (N omega-nitro-L-arginine, 50 micrograms.kg-1.min-1) or prostaglandins (lysin acetylsalicylate, 15 mg.kg-1).min-1 and following the concomitant inhibition of both systems. Cirrhotic rats showed increased systemic pressure sensitivity and blunted renal vasoconstrictor response to nitric oxide inhibition as compared with control rats. As a consequence, the glomerular filtration rate increased in cirrhotic rats but not in control rats. In both groups of animals, NO inhibition was associated with significant increased urinary sodium and fractional sodium excretion. The only significant effect observed after prostaglandin biosynthesis inhibition was a decrease in renal plasma flow in cirrhotic rats. The concomitant inhibition of both systems reduced renal plasma flow and did not change glomerular filtration rate, with no differences between control and cirrhotic rats. Prostaglandin inhibition did not prevent the natriuretic effect of the NO inhibitor in both groups of animals. These results indicate that in experimental cirrhosis both NO and PGI2 play an important role in the maintenance of renal perfusion within normal limits.

Animals↗
PubMed1995

Parathyroid hormone and platelet cytosolic calcium concentration in essential hypertension.

To investigate the possible relationships between blood pressure, parathyroid hormone (PTH) and platelet cytosolic Ca2+ concentration ([Ca2+]i) in patients with essential hypertension, we studied 17 patients with this disease aged 48 +/- 2 years and 17 normotensive controls aged 44 +/- 3 years. Platelet [Ca2+]i was measured by spectrofluorimetry using the dye Fura-2 acetoxymethylester. Patients with essential hypertension displayed lower levels of serum ionized Ca2+ (0.99 +/- 0.03 versus 1.1 +/- 0.01 mmol/l, P < 0.05) and higher serum intact PTH levels (37 +/- 3 versus 26 +/- pg/ml, (P < 0.01) than the normotensive controls. Although serum levels of intact PTH were significantly correlated with mean arterial pressure (MAP) in the combined group of subjects (r = 0.42, P < 0.05), there was no correlation when each group was considered separately. Resting platelet [Ca2+]i was also higher in patients than in controls (57 +/- 3 versus 48 +/- 2 nmol/l, P < 0.005). When platelets were stimulated in vitro with thrombin, the increment in [Ca2+]i was also greater in patients than in controls in the presence of extracellular Ca2+ (264 +/- 24 versus 194 +/- 19 nmol/l, P < 0.05) but not in its absence (123 +/- 12 versus 112 +/- 10 nmol/l). The thrombin-induced increment in [Ca2+]i was correlated with MAP in the hypertensive patients (r = 0.64, P < 0.01) and in the combined group of subjects (r = 0.42, P < 0.05). There was no relationship between resting or thrombin-induced [Ca2+]i and serum PTH in either group of patients or in the combined group of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Nitric oxide production in arterial vessels of cirrhotic rats.

Indirect evidence exists implicating vascular nitric oxide in the pathogenesis of arterial vasodilation in cirrhosis. In the current study, a coincubation assay to estimate the vascular nitric oxide production was developed and the nitric oxide production by arterial segments of cirrhotic and control rats was assessed. In the assay, measurement of reporter monolayer cell-associated cGMP levels allows the influence of nitric oxide released by arterial segments to be determined. RFL-6 cells served as reporter cells. Nitric oxide production was determined in thoracic aorta and mesenteric arteries of 22 control rats, 10 cirrhotic rats without ascites, and 12 cirrhotic rats with ascites. Basal and bradykinin-stimulated (10(-6) mol/L) intracellular content of nitric oxide-dependent cGMP was significantly higher in RFL-6 cells coincubated with aortic segments of cirrhotic rats with (21.3 +/- 3.6 pmol/10(5) cells, P < .05 and 44.7 +/- 7.0 pmol/10(5) cells, P < .025) and without ascites (15.3 +/- 3.0 pmol/10(5) cells, P < .05 and 43.2 +/- 7.6 pmol/10(5) cells, P < .05) than in those incubated with aortic segments of control rats (9.7 +/- 1.3 and 19.5 +/- 2.5 pmol/10(5) cells). RFL-6 cells exposed to bradykinin-stimulated mesenteric arterial segments of cirrhotic rats also showed increased cGMP content (ascitic: 2.73 +/- 0.31 pmol/10(5) cells, P < .005; nonascitic: 2.58 +/- 0.51 pmol/10(5) cells, P < .025) compared with cells exposed to control mesenteric arterial segments (1.28 +/- 0.15 pmol/10(5) cells). No differences between cirrhotic and control vessels were observed after endothelium denudation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Thyroid testing using the Cobas Core immunoassay system. A multicentre study.

The random access immunoanalyzer Cobas Core and the Cobas Core Thyroid Assays were assessed as to their clinical usefulness in the analysis of different thyroid diseases. Four centres participated in this study measuring the following five thyroid tests per sample on the instrument: thyrotropin, free thyroxine, thyroxine, triiodothyronine and free triiodothyronine. The assessment was based on studies of precision and clinical samples. Within- and between-series precisions showed a mean CV over all assays of 4.3 and 6.1%, respectively. Comparison of the test results with clinical data demonstrated that the Cobas Core results are in accordance with diagnosed thyroid diseases. A good discrimination between normal and disease status and between untreated and treated status was found. Furthermore, 370 sera measured with Technicon Immuno-1 TSH and FT4 assays were compared to the respective Cobas Core EIAs). A good correlation between the assays was demonstrated.

Evaluation Studies as Topic↗
PubMed1994

Leiomyosarcoma of the soft tissues in a patient with nevoid basal-cell carcinoma syndrome.

A 57-year-old man was admitted with complaints of progressive anorexia, weight loss and right flank pain. He had been treated for basal-cell carcinoma of the skin 19 years before. On physical examination, eight moles in the face, back and left thigh were found along with palmar pits. In addition, a painful induration in his right thigh was evident. Biopsy proved that six moles were basal-cell carcinomas and the thigh mass a high-grade leiomyosarcoma. Computed tomographs revealed multiple metastases in the lungs and the liver. The patient was treated with epirubicin, with partial response, and subsequently with ifosfamide. He died 17 months after diagnosis. Whereas the world literature records several cases of soft tissue tumors in patients with nevoid basal-cell carcinoma syndrome, this is the first report of a simultaneous occurrence of leiomyosarcoma and nevoid basal-cell carcinoma syndrome.

Basal Cell Nevus Syndrome↗
PubMed1994

Circadian variations of portal pressure and variceal hemorrhage in patients with cirrhosis.

This study was aimed at investigating whether portal pressure, which is usually measured in the morning, is subject to circadian variations in patients with cirrhosis. Furthermore, a possible circadian variation for the occurrence of variceal bleeding was also investigated. Ten patients with alcoholic cirrhosis and portal hypertension had serial measurements of portal pressure, evaluated by the hepatic venous pressure gradient (the difference between wedged and free hepatic venous pressures), during a 24-hr period. In addition, a survey of the hour of occurrence of variceal hemorrhage was performed in 101 consecutive cirrhotic patients with hematemesis, in whom the precise moment of onset of bleeding could be determined, and the origin of bleeding was confirmed by emergency endoscopy. Statistical evaluation with the population-mean cosinor method allowed detection of a circadian variation in portal pressure. Portal pressure progressively declined during the afternoon and evening (from 17.9 +/- 5.3 mm Hg at 12 PM to a nadir of 16.8 +/- 4.9 mm Hg at 7 PM (p < 0.05). Thereafter, portal pressure increased during the night, returning to baseline values at 9 AM (18.1 +/- 5.1 mm Hg). The acrophase was at 8:32 AM (+/- 100 min) with an amplitude of 3.45 +/- 1.1 (% of mean +/- S.E.) (rhythm detection: p < 0.03). Similarly, the analysis of the time of occurrence of variceal hemorrhage with the use of a multiple-components rhythmometry test disclosed two peaks in the prevalence of esophageal bleeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Renal effects of natriuretic peptide receptor blockade in cirrhotic rats with ascites.

The aim of this study was to assess the effect of HS-142-1, a recently discovered specific antagonist of endogenous natriuretic peptides, on systemic hemodynamics, renal function, and the renin-aldosterone system in rats with cirrhosis and ascites. The study consisted of three protocols, each including 10 conscious control rats and 10 conscious rats with carbon-tetrachloride-induced cirrhosis with ascites. In protocol 1, HS-142-1 administration (by intravenous bolus of 20 mg.kg-1.body weight in all protocols) was not associated with significant changes in mean arterial pressure, heart rate, cardiac output or total peripheral resistance in the two groups of animals. In protocol 2, HS-142-1 induced a significant reduction in glomerular filtration rate (from 4.2 +/- 0.5 to 2.6 +/- 0.3 ml/min, p < 0.025) in control animals. A decrease in renal plasma flow and an increase in renal vascular resistance also occurred, but these changes were not statistically significant. In cirrhotic rats, HS-142-1 resulted in a significant decrease in renal plasma flow (from 10.9 +/- 0.7 to 4.3 +/- 0.6 ml/min, p < 0.001) and a significant increase in renal vascular resistance (from 6.0 +/- 0.6 to 16.3 +/- 2.7 mm Hg.min.ml-1, p < 0.025). Glomerular filtration rate decreased more in cirrhotic rats with ascites than in control rats (from 3.8 +/- 0.3 to 1.3 +/- 0.2 ml/min, p < 0.001). Changes in urine flow rate and urinary sodium excretion rate paralleled those of glomerular filtration rate in both groups of animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1994

Increased nitric oxide-dependent vasorelaxation in aortic rings of cirrhotic rats with ascites.

To assess whether aortic vessels of rats with cirrhosis and ascites possess an enhanced vascular response to endothelium-derived, nitric oxide-dependent vasodilators, we performed relaxation studies in isolated aortic rings of 21 control rats and 24 rats with carbon tetrachloride-induced cirrhosis and ascites. We carried out studies after contracting the vessels with norepinephrine. We measured endothelium-dependent vasodilator response by administering increasing concentrations of acetylcholine (10(-6) to 10(-2) mol/L) and ADP (10(-7) to 10(-4) mol/L). We evaluated endothelium-independent response by giving increased concentration of sodium nitrite (10(-5) to 10(-2) mol/L). The maximal absolute tension developed in response to norepinephrine was significantly decreased in cirrhotic rings (816 +/- 72 mg, p < 0.025) compared with control (1,425 +/- 75 mg) rings. Dose-response curves for endothelium-dependent vasodilators were shifted to the left in aortic rings of cirrhotic rats, and EC50 for acetylcholine and ADP were significantly decreased in cirrhotic (0.8 +/- 0.15 mmol/L and 0.42 +/- 0.16 mumol/L, p < 0.025 and p < 0.01, respectively) than in control rings (1.91 +/- 0.33 mmol/L and 3.09 +/- 0.82 mumol/L). In both acetylcholine- and ADP-stimulated vessels, differences between cirrhotic and control rings disappeared after nitric oxide synthesis inhibition with N omega-nitro-L-arginine (10(-4) mol/L). No difference in the relaxing effect of sodium nitrite was observed between cirrhotic and control rings. These results therefore demonstrate for the first time enhanced in vitro vascular responsiveness to nitric oxide-dependent vasodilators in rats with cirrhosis and ascites, giving further support to the concept that nitric oxide activity is increased in cirrhosis.

Acetylcholine↗
PubMed1994

Magnetic resonance imaging of the normal and chronically injured adult rat spinal cord in vivo.

We assessed the capacity of MRI to show and characterise the spinal cord (SC) in vivo in normal and chronically injured adult rats. In the chronically injured animals the SC was studied by MRI and histological examination. MRI was performed at 1.5 T, using gradient-echo and spin-echo (SE) sequences, the latter with and without gadolinium-DTPA (Gd-DTPA). Several positions were tried for good alignment and to diminish interference by respiratory movements. Images of the SC were obtained in sagittal, coronal, and axial planes. Normal SC was observed as a continuous intensity in both sequences, although contrast resolution was better using SE; it was not possible to differentiate the grey and white matter. Low signal was seen in the damaged area in chronically injured rats, which corresponded to cysts, trabeculae, mononuclear infiltrate, and fibroglial wall on histological examination. Gd-DTPA failed to enhance the SC in normal or chronically injured rats. It did, however, cause enhancement of the lesion after acute SC injury.

Animals↗
PubMed1994

nm23-H1 expression and disease recurrence after surgical resection of small hepatocellular carcinoma.

BACKGROUND/AIMS: The nm23-H1 gene is thought to act as a metastasis-suppressor gene. This study investigates the relationship between nm23-H1 messenger RNA (mRNA) expression and intrahepatic tumor recurrence after surgical resection of small hepatocellular carcinoma. METHODS: Seventeen cirrhotic patients with solitary hepatocellular carcinoma < 5 cm underwent surgical resection. In 7 patients, the neoplasm recurred after a 12-month median follow-up, whereas the other 10 patients were free of disease after a 30-month median follow-up. Both groups were similar according to age, sex, etiology, status of the underlying liver, tumor size, and other pathological characteristics of the neoplasm. nm23-H1 mRNA levels were assessed in matched tumor and surrounding cirrhotic liver samples by Northern blot hybridization using a 900-base pair probe, which is a BamHI fragment of pnm23-H1 recombinant complementary DNA clone encoding the nm23-H1 human gene. RESULTS: Eight of the 10 patients without disease recurrence during follow-up showed nm23-H1 overexpression with an increase ranging between three- and 45-fold when compared with the nontumoral surrounding liver. Only 1 of the 7 patients with tumor recurrence showed higher nm23-H1 mRNA levels in the tumor than in the nonneoplastic sample (P = 0.013). CONCLUSIONS: nm23 mRNA overexpression in small solitary hepatocellular carcinoma is associated with a lower recurrence rate after surgical resection, suggesting that this gene may participate in the metastatic dissemination of this neoplasm.

Aged↗
PubMed1994

Blunted natriuretic response to human urine extracts with Na+,K(+)-ATPase inhibiting activity in experimental cirrhosis.

Human urine and plasma extracts contain a material that inhibits the enzyme Na+,K(+)-ATPase (the endogenous sodium pump) and produces natriuresis in the bioassay animal. This endogenous sodium pump inhibitor(s), also known as digitalis-like factor, is thought to be involved in sodium and extracellular fluid volume homeostasis. Increased urine and plasma sodium pump inhibiting activity have been reported in patients with cirrhosis and sodium retention. The aim of the study was to assess the renal response to i.v. administration (0.2 ml/min per kg bw for 10 min) of a human urine extract containing sodium pump inhibiting activity (28.5 nmol equivalent ouabain/ml) in eight conscious rats with cirrhosis and ascites and eight control rats. Baseline urinary excretion of Na+,K(+)-ATPase inhibiting activity was significantly higher in cirrhotic rats with ascites than in control rats (235 +/- 40 vs 91 +/- 16; p < 0.01). Human urine extract induced a significant (p < 0.05) increase in glomerular filtration rate in control (3.2 +/- 0.4 to 4.2 +/- 0.5 ml/min) and cirrhotic rats (3.0 +/- 0.3 to 4.0 +/- 0.5 ml/min). In control rats it also increased urinary sodium excretion (1.47 +/- 0.22 to 2.43 +/- 0.5 microEq/min, p < 0.01) and fractional sodium excretion (0.29 +/- 0.01 to 0.43 +/- 0.04%, p < 0.025). In contrast, in cirrhotic rats with ascites neither sodium excretion nor fractional sodium excretion was significantly affected. No changes were observed in plasma aldosterone and atrial natriuretic peptide concentrations in either group. These data suggest that in cirrhosis there is a renal resistance to the natriuretic effect of endogenous sodium pump inhibitor(s).

Animals↗
PubMed1994

Intracellular calcium concentration in vascular smooth muscle cells of rats with cirrhosis.

A decreased pressor response to endogenous vasoconstrictors, such as angiotensin II and vasopressin, is a characteristic finding in cirrhosis with ascites; this has been considered as partially responsible for the arteriolar vasodilation present in this disease. Previous investigations suggested that this abnormality is due to a post-receptor defect leading to altered intracellular Ca2+ mobilization. To assess this hypothesis, vascular responsiveness to angiotensin II (3.10(-8) M) and intracellular Ca2+ concentration in basal conditions and following angiotensin II (1-100 nM) and vasopressin stimulation (100 nM) were measured in aortic rings and in primary cultured aortic vascular smooth muscle cells, respectively. The study was carried out in 43 control rats and 40 rats with CCl4-induced cirrhosis and ascites. Cells were grown to confluence on glass cover slips and then loaded with Fura-2, a fluorescent intracellular Ca2+ indicator, for continuous monitoring of intracellular Ca2+ concentration. A decreased constrictor response to angiotensin II was detected in cirrhotic aortic rings in comparison to control rings (increase in tension: 31 +/- 5 vs 79 +/- 14 mg, p < 0.005). No differences in intracellular Ca2+ concentration between cirrhotic and control cells were observed in basal conditions (104 +/- 6 and 100 +/- 3 nM, respectively). Angiotensin II administration to cirrhotic vascular smooth muscle cells had a dose-dependent biphasic effect consisting of a rapid increase, followed by return to a sustained level significantly higher than the basal value. This response was identical to that observed in control vascular smooth muscle cells. Similar findings were obtained following vasopressin stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1994

Intracellular calcium concentration and activation of the Na+/H+ exchanger in essential hypertension.

To investigate the relationship between changes in intracellular calcium concentration ([Ca2+]i) and agonist-induced activation of the Na+/H+ exchanger in essential hypertension (EH), platelet [Ca2+]i and pHi were measured in 24 patients with EH (14 males) aged 48 +/- 2 years and 23 matched normotensive controls (NT) (12 males) aged 45 +/- 3 years. Measurements were done with spectrofluorimetry using the dyes Fura-2 for [Ca2+]i and BCECF for pHi. [Ca2+]i and pHi were measured in the resting condition and after stimulation in vitro with 0.1 U/ml human thrombin. The thrombin-induced rise in pHi was Na+ dependent and amiloride sensitive, indicating that it was mediated by the Na+/H+ exchanger. Unstimulated [Ca2+]i was higher in patients with EH than in NT (60 +/- 3 vs. 48 +/- 1 nmol/liter, P < 0.005), but there were no differences in resting pHi between both groups (7.16 +/- 0.01 vs. 7.16 +/- 0.008). In the presence of 1 mmol/liter external calcium (Ca2+o), thrombin-induced increment in [Ca2+]i was significantly greater in patients with EH than in NT (281 +/- 21 vs. 206 +/- 19; P < 0.05) as was the pHi increment (EH: 0.137 +/- 0.01; NT: 0.095 +/- 0.01; P < 0.05). Both agonist-induced increments in [Ca2+]i and in pHi were correlated with mean arterial pressure (MAP) only in the EH group (r = 0.58, P < 0.005 and r = 0.59, P < 0.005, respectively). The agonist-induced rise in pHi was positively correlated with the rise in [Ca2+]i both in the EH group (r = 0.65, P < 0.001) and in the NT (r = 0.55, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗
PubMed1994

Ovarian and extragonadal malignant germ-cell tumors in females: a single-institution experience with 43 patients.

From 1978 to 1992, 276 patients (pts) with MGCT were treated in our institution. Forty-three of the pts were female (15.5%). Median age at diagnosis was 20 years (newborn-70). Histology was dysgerminoma (D) in 14 pts (including 2 anaplastic D), endodermal sinus tumor (EST) in 9 pts, immature teratoma in 10 pts and mixed tumors in 10 pts. Primary locations were as follows: ovary (O) 33 pts and extragonadal (EG) 10 pts (pineal in 4 cases, mediastinum in 3, sacrum in 2 and pharynx in 1). Stage: I in 20 (16 O, 4 EG), II in 7 (5 O, 2 EG), III in 12 (10 O, 2 EG) and IV in 4 (2 O, 2 EG). Serum AFP was elevated in 20/22 non-dysgerminoma pts, HCG in only 5 pts and LDH in 15/36 pts. TREATMENT RESULTS: Ovarian tumors: all but one pt (biopsy only) underwent surgery: unilateral oophorectomy was performed in 15 pts and bilateral oophorectomy (+/- hysterectomy, +/- others) in 17 pts. Fourteen pts were rendered disease-free, 8 pts had residual tumor (RT) < 2 cm and 11 RT > 2 cm. Chemotherapy (PVB or BEP) was given to 28 pts, radiotherapy to 2 pts and no additional treatment to 3. Finally, 30 pts achieved complete response (CR) and none have relapsed at a median follow-up of 43 months. EG tumors: None of the pts underwent radical surgery. Radiotherapy was applied to 4 pineal tumors and BEP or PVB were given to all 10 pts. To date 6 pts are disease-free, 1 is alive with mature teratoma, 2 are alive with disease and 1 died of toxic effects. The projected overall survival of the series as a whole is 89% at 10 years, and it is significantly higher for pts without EST (p < 0.02) and for pts with AFP < 1000 (P < 0.01) and age < 22 years at diagnosis (p < 0.01). The projected event-free survival at 10 years is 80.4% (87.7% for ovarian tumors vs. 54% for extragonadal, p = 0.05). No events were recorded after 28 months. CONCLUSIONS: The present results reflect the dramatic effectiveness of cisplatin-based chemotherapy for ovarian MGCT and confirm that unilateral oophorectomy can preserve fertility without compromising cure. Age > 22 years, histology (EST) and serum AFP > 1000 ng/ml are possible prognostic factors (univariate analysis) to be tested in an independent body of data on cisplatin-treated patients.

Adolescent↗
PubMed1994

Effect of antihypertensive treatment on intracellular calcium concentration and intracellular pH in essential hypertension.

The platelet intracellular calcium concentration ([Ca2+]i) and intracellular pH (pHi) were measured by spectrofluorimetry with the dyes Fura-2 and BCECF, respectively, in 19 patients with essential hypertension (10 males), aged 48 +/- 2 years, before and after 12 weeks of antihypertensive treatment and in 19 normotensive controls (11 males), aged 46 +/- 3 years. [Ca2+]i and pHi were measured in the resting state and after stimulation in vitro with 0.1 U/ml human thrombin. In patients with essential hypertension, both resting [Ca2+]i (61 +/- 4 nmol/l) and thrombin-induced maximal increase in [Ca2]i (291 +/- 26 nmol/l) were significantly (P < 0.01) greater than in the normotensive controls (resting 49 +/- 2 nmol/l and thrombin-induced 199 +/- 21 nmol/l). With respect to pHi, no difference in resting pHi between both groups was found (7.16 +/- 0.01 vs. 7.16 +/- 0.01). However, pHi increment at 300 seconds in response to thrombin was higher in the patients with essential hypertension than in the controls (0.131 +/- 0.02 vs. 0.083 +/- 0.01 pH units, P < 0.05). The increment in pHi was blunted by the amiloride derivative EIPA, indicating that it was mediated by the Na+/H+ exchanger. After antihypertensive therapy in the essential hypertensive patients, basal [Ca2+]i was significantly reduced (52 +/- 2 nmol/l, P < 0.01) and was not statistically different to the value found in the normotensive controls. Resting pHi suffered no significant modification after treatment (7.17 +/- 0.01, P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Intracellular calcium mobilization and activation of the Na+/H+ exchanger in platelets.

The aim of the present study was to evaluate the regulatory relationship between the cytosolic free calcium concentration ([Ca2+]i and cytosolic pH (pHi). [Ca2+]i and pHi were measured using the fluorescent dyes fura-2 and BCECF [2',7'-bis-(carboxyethyl)-5,6-carboxyfluorescein] respectively. In a medium with 1 mmol/l extracellular calcium, thrombin (2.5 units/ml) induced an increment in [Ca2+]i of 638 +/- 31 nmol/l (n = 5) and an intracellular alkalinization of 0.14 +/- 0.01 pH units (n = 8). Both responses were dependent on the concentration of thrombin, displaying a sigmoidal dose-response pattern. The intracellular alkalinization was dependent upon extracellular Na+ and was amiloride-sensitive, indicating that it was mediated by activation of the Na+/H+ exchanger. When extracellular calcium was chelated with EGTA prior to the addition of thrombin, the intracellular alkalinization was not affected (0.15 +/- 0.02 at 2.5 units/ml thrombin, n = 8). Under these circumstances, the [Ca2+]i increment represents mobilization from internal stores, reaching 157 +/- 42 nmol/l at 2.5 units/ml thrombin. When platelets were preloaded with the intracellular calcium chelator MAPTAM (1,2-bis-5-methylaminophenoxylethane-NNN'-tetraacetoxymethyl acetate) to block the increase in [Ca2+]i induced by thrombin, no increment in pHi was observed. Moreover, MAPTAM-loaded calcium-depleted platelets had a basal pHi that was more acidic than in the presence of 1 mmol/l extracellular calcium (6.93 +/- 0.09 versus 7.14 +/- 0.01, n = 26, P < 0.001). Ionomycin induced an elevation of [Ca2+]i that was accompanied by a concomitant increase in pHi, which was Na(+)-dependent and amiloride-sensitive. [Ca2+]i and pHi increases induced by ionomycin were both dependent on the concentration of ionomycin. In conclusion, an increase in [Ca2+]i is necessary for the agonist-induced activation of the Na+/H+ exchanger in platelets. Non-agonist-induced increases in [Ca2+]i seems to prompt activation of the exchanger. In addition, Ca(2+)-depleted platelets have a more acidic basal pHi, indicating that the basal level of [Ca2+]i is also important for maintaining the basal pHi.

Blood Platelets↗
PubMed1993

Pathogenic and free-living amoebae isolated from swimming pools and physiotherapy tubs in Mexico.

A protozoological survey was done to isolate free-living amoebae from swimming pools and physiotherapy tubs in Mexico City. Amoebae were isolated by culture in nonnutritive agar medium combined with Escherichia coli. Identification of the isolates was done by morphology using specialized taxonomic keys and by isoelectric focusing of total proteins and isoenzymes in agarose. Pathogenicity of the isolates was determined in 3-week-old mice by intracerebral and intranasal inoculations. Statistical tools were used to determine the existence of significant differences on the incidence and diversity of the isolates in relation to the two types of water bodies analyzed. Water and environmental temperatures, pH, and chloride concentrations were determined at each sampling site. Twenty-nine amoebic strains from eight genera were isolated. Most frequently found were specimens of the genera (Acanthamoeba (with four pathogenic strains), Vahlkampfia, Hartmannella, and Naegleria. Amoebae were isolated more frequently in spring and summer, and could not be recovered from pools with chloride levels of 5.31 mg/ml or more. This survey demonstrates that chloride concentrations commonly used in recreative pools and therapy tubs are not sufficient to eliminate viable cysts of most free-living amoebae. Significantly higher numbers of isolates were retrieved from the pools than from the tubs.

Amebiasis↗