Archives internationales de physiologie, de biochimie et de biophysique最新文献

Experiments were performed in EGTA-skinned trabeculae from toad ventricle to explore the effects of the cAMP on calcium sensitivity of the contractile system. 10(-3) M of the cAMP derivative dibutyryl cAMP (dcAMP) failed to affect calcium sensitivity of chemically skinned ventricular trabeculae. 10(-5) M of the phosphodiesterase inhibitor isobutylmethylxantine (IBMX) produced a significant shift to the left of the tension-pCa relationship. The computed half maximally activating pCa (pCa50) were 6.32 +/- 0.03 and 6.40 +/- 0.01 in the absence and presence of IBMX respectively, (P < 0.05). Simultaneous perfusion of 10(-5) M IBMX and 10(-3) M dcAMP suppressed the leftward shift of the tension-pCa curve induced by IBMX (pCa50: 6.33 +/- 0.04 and 6.33 +/- 0.05 for control and IBMX respectively). Perfusion with the phosphodiesterase inhibitor milrinone (10(-5) M), did not produce any significant changes in the tension-pCa relationship. Simultaneous perfusion of 10(-5) M milrinone and 10(-3) M dcAMP significantly shifted to the right the tension-pCa curve. The computed pCa50 were 6.32 +/- 0.02 and 6.23 +/- 0.03 under control conditions and in the presence of dcAMP plus milrinone respectively (P < 0.05). In agreement with what has been described in mammalian heart, the results indicate that in amphibian ventricle, cAMP produced a decrease in the calcium sensitivity of the contractile proteins that is only evident in the presence of phosphodiesterase inhibitors. It is suggested that this decrease in myofilament sensitivity to calcium may be one of the mechanisms by which beta-agonists enhance myocardial relaxation in the amphibian heart.

The in vivo incorporation of acetate into nonsaponifiable lipids was studied in different tissues from 14-day-old chick. Total nonsaponifiable lipids (nmol/30 min/g tissue) were mainly synthesized in testicles and liver. The in vivo CO2 production from acetate by 1-day-old chick did not exhibit diurnal variations. However, in 14-day-old chick, a maximal value was observed in the middle of the light period, while a minimal value was found 9 h after the start of the dark period. No significant diurnal differences were detected in the in vivo acetate incorporation into nonsaponifiable lipids by liver and duodenal mucosa from 1-day-old chick. Nevertheless, a clear diurnal rhythm was found in liver and duodenal mucosa from 14-day-old chick, but not in brain and kidney from animals of the same age. Distribution of radioactivity from (1-14C)acetate among the different constituents of the nonsaponifiable fraction has been also studied at 3-h intervals. Cholesterol was the major sterol formed from acetate by chick liver at any time of day. In duodenal mucosa and kidney, maximal values in the percentage of cholesterol synthesized were observed during the light period.

To study some characteristics of calcium-activated potassium channels free from plasma membrane lipid perturbations, neonatal red blood cells were selected. To this end, cells not previously treated (ATP depletion and/or reversible lysis) were exposed to the ionophore A23187 in a NO3 medium with calcium. The net efflux of potassium from the cells was studied. Preincubation in a medium devoid of potassium induced a significant decrease only in the rate constant of potassium flux. The data suggest that, in the absence of plasma membrane lipid impairment, changes in internal sites reactivity with calcium ions of channel proteins would be involved in the refractoriness. This would be at variance with channel density modifications.

In view of the inhibitory influence of Mammillary Medial Nuclei, pars lateralis (MMN) on corticoadrenal activity, experiments were conducted in order to determine whether these nuclei are involved in the control of adrenal response to ether stress. In bilateral MMN lesioned rats, prestress plasma corticosterone concentration (C) is significantly higher than that in sham lesioned animals. Acute stress produced a significant C increase in both, sham and lesioned rats, being this increase lower in lesioned animals. After exposure to ether vapors. adrenal concentration of norepinephrine was similar in lesioned and control animals. Whereas, adrenal epinephrine concentration was significantly higher in lesioned rats than that found in the sham lesioned ones. This study demonstrates that the integrity of MMN is not essential for adrenal response to acute stress.

Precipitates were obtained by 6 N HCl hydrolysis of human erythrocytes and subsequent extractions with ethanol-ether 1:1 and with tetrahydrofuran. The mean quantity of these precipitates (n = 16) was 16.60 +/- 1.60 (standard deviation) mg/ml, (15.09 +/- 1.45 mg/g) and from saline washed erythrocyte samples (n = 8) 16.65 +/- 0.73 mg/ml, (15.14 +/- 0.67 mg/g). A large part of these precipitates (about 74%) is associated with haemoglobin (in average 12.34 mg/ml). Melanins account for the difference (16.60-12.34) = 4.26 mg/ml, approximately 8.7% of haemoglobin-free erythrocyte solids. Precipitates from red cells, and from haemoglobin produced similar UV-VIS and IR spectra. The precipitates from haemoglobin are mainly derivatives of haeme (about 97%); the remaining approximately 3% are melanins from globin. The total melanins are about 1.3% of haeme-free solids of erythrocytes. Precipitation from the erythrocytes with 6 N HCl was also achieved in practically complete argon atmosphere, and similar quantities were obtained as those in air with the same UV-VIS and IR spectra. Since granules or solid particles are not found in the cytoplasm of normal human erythrocytes, we conclude that soluble melanins are present. Small amounts of melanins can be present in the membranes as well, since the precursors of melanins: norepinephrine, epinephrine are present in these membranes.

The purpose of this study is to present a simple kinetic model for the study of the lactate metabolism. This model based on pharmacokinetic theory, does not require labelled molecules and yields a finer approach to lactate metabolism than does a simple observation of blood lactate concentration. The variations in parameter values have been studied in six male subjects after intensive exercise (385 W, 110 rpm and 1 min) (IE) followed by three different recovery periods: passive recovery (RE), moderate exercise (ME) and heavy exercise (HE). Blood lactate concentration was measured prior to IE and during the first hour of recovery. After mathematical treatment, the results show that the apparent clearance increases 2.83 +/- 0.76 fold from RE to ME and 1.96 +/- 0.61 fold from RE to HE. The steady state blood lactate concentration induced by the intensity of recovery (La(ss)) increases slightly (1.53 +/- 0.37 fold) from RE (1.40 +/- 0.36 mmol.l-1) to ME (2.04 +/- 0.32 mmol.l-1). Then La(ss) increases markedly (3.78 +/- 0.91 mmol.l-1) during HE (2.81 +/- 0.78 fold the La(ss) value at RE). The ratio between the apparent rates of lactate production (F"K0) during RE, ME and HE was calculated. F"K0 increases in a linear way versus intensity of exercise recovery. It was concluded that in the human: 1) the blood lactate concentration is not an accurate indicator of lactate production, 2) in our experiment, the apparent lactate production is a linear function of exercise intensity and 3) the abruptly increasing blood lactate concentration at a high level of exercise intensity is due to a decrease in apparent clearance.

This work was aimed at elucidating the effect of thyroid function on the physiology and biochemistry of the islet-cell population within the endocrine pancreas. To this end, we performed a comparative study of the physiochemical properties of islet-cell membranes and of the dynamics of glucose-induced insulin secretion in isolated pancreatic islets prepared from euthyroid i.e. control (C), hypothyroid (H), and thyroxin-supplemented hypothyroid (HT) rats. H rats were obtained by injecting normal rats with 131iodine, while HT rats consisted of H rats treated with thyroxin (T4). Insulin secretion was studied in isolated islets perifused with 3.3 and 16.6 mM glucose. Physicochemical properties of the partially purified islet plasma membranes were assessed by measurements of fluorescence polarization with the fluorophore 1,6-diphenyl-1,3,5-hexatriene (DPH) as a lipidic molecular probe. Insulin output during either the first or second phase of insulin secretion in H islets was significantly lower than in C islets. The slope of the curve in the second phase of insulin secretion was also lesser in H than in C islets, suggesting an additional defect in their velocity of hormone release. T4 administration of H rats reversed the decrease in insulin output to the range found in C islets but was incapable of correcting the defect in the hormone-secretion velocity. Several changes were found in the physicochemical properties of the membranes obtained from H islets as compared to C islets.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginase (L-arginine-ureidohydrolase, EC 3.5.3.1) catalyses the hydrolysis of arginine to ornithine and urea. Its primary metabolic role is to remove the excess of ammonia through synthesis of urea. Ornithine, as a product of arginase reaction can be used for synthesis of polyamines. Rapid tissue growth after partial hepatectomy is accompanied by an increase in biosynthesis of polyamines. The aim of this study was to examine the importance of arginase in regenerating liver after partial hepatectomy and to investigate the influence of folic acid and methotrexate on arginase activity on this model of compensatory growth. It was established that arginase activity was significantly reduced in regenerating rat liver tissue at different time intervals after partial hepatectomy. Administration of folic acid to hepatectomized rats led to inhibition of arginase activity. Administration of methotrexate after hepatectomy increased the arginase activity.

Human neonatal red cells (placental blood) incubated in hypertonic sucrose media showed a significative lytic process in a relatively short time interval. The addition of sodium chloride into the sucrose media reduced the extent of hemolysis. In contrast, the addition of calcium chloride enhanced the hemolysis in these red cells. Calcium-membrane components complex formation that destabilize membrane's bilayer structure would explain the calcium effect above mentioned (on account of the low ionic strength media used and exposed fixed negative charges) This study intends to clarify, in neonatal red cells, the relation between surface charges and cellular stability.