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

This paper shows the usefulness of polyacrylamide gel electrophoresis (PAGE) separation of a few well-characterized muscle proteins, the parvalbumins, in the systematic study of 13 cichlid species. The separation of the isoforms of these abundant, quite species-specific fish parvalbumins is fast, easy, and requires but small quantities of muscle material. Used alone, this technique suggests hypotheses for species classification. In conjunction with morphological analysis, it makes it possible to confirm or invalidate doubts about the determination.

Since the hypotensive and natriuretic properties of crude cardiac extracts were first demonstrated in 1981 in the rat, the effector molecule has been isolated, purified and synthesized. The hormonal factor is produced by atrial myocytes in mammals and stored as a prohormone. Secretion mainly results from a volemic stress inducing an atrial stretch. Secretion includes a maturation step. A peptide of 28 amino-acids (ANP) is then released into the bloodstream. ANP has a half-life of a few minutes. ANP binds to specific receptors expressed at the target cell surface. B-receptors mediate the biological actions of ANP by an increase in cGMP while C-receptors are involved in clearance of the peptide. The kidney as well as the cardiovascular and endocrine systems are the main target sites for ANP. The renal effects of ANP are expressed by an enhanced diuresis and natriuresis which may result from an increased glomerular filtration rate and/or a reduced tubular reabsorption of salt and water. Renal hemodynamics may also be modified due to a renal specific vasodilator effect of ANP. The reduction of systemic blood pressure may result from changes in cardiac output and/or in peripheral vascular resistance. Several neurohumoral interactions of ANP also contribute to sustain the cardiovascular and renal effects described above. In view of these properties, ANP is of particular interest in order to understand the homeostasis of salt and water under physiological as well as or physiopathological conditions. In this regard, therapeutic prospects are intensively investigated. Finally, evolutionary perspectives are actually considered from studies in lower vertebrates.

Testes of prepubertal, pubertal and adult Wistar rats were stimulated with low-intensity pulsed ultrasound for 20 min a day, for 7 days. No significant changes were found in the spermatogenic activity as well as in plasma LH and FSH levels following ultrasound treatment. The testicular androgenic activity, however, was significantly increased in prepubertal treated animals, in addition to a significant increase in seminal vesicle growth and secretory activity. In spite of normal androgenic levels, pubertal treated rats presented also an increase in the seminal vesicle secretory activity, thus suggesting a direct action of ultrasound on the gland.

The purpose of this study was to determine the effect of a higher than normal epinephrine content in skeletal muscles, on metabolic and hormonal adjustments during a subsequent exercise. Four groups of 10 rats were studied: two control groups, one at rest and one after an exercise leading to exhaustion on a treadmill (28 m.min-1, 8% grade) and two epinephrine-infused groups (EI), one at rest and one after the same type of exercise. Epinephrine-infused rats (EI) received an infusion of epinephrine (5 nM.kg.min-1, i.v.) for 20 minutes, and were rested 20 minutes before the start of the exercise or rest period. In the soleus muscle, epinephrine content was shown to be multiplied by 15 and 8 times the control values, respectively following 20 and 60 min after the end of the infusion. Control rats received a corresponding volume of sterile saline with the same schedule. The exercise lasted 49 +/- 14 vs 54 +/- 6 minutes respectively for EI and control rats (not significant). At rest, plasma concentrations of epinephrine, norepinephrine, plasma free fatty acids, glycerol, glucose and lactate as well as the glycogen content of the liver, the soleus, gastrocnemius lateralis and superficial vastus lateralis muscles were not different between saline and epinephrine-infused rats. Immediately after exercise, plasma lactate concentration was not increased after exercise in EI vs (2.26 +/- 0.39 vs 4.53 +/- 0.73 mM). One possible explanation of this observation is that re-released epinephrine might induce a vasodilation in the splanchnic or the skeletal muscle vascular beds and thus favors lactate clearance during exercise.

The gill epithelium which comprises several types of cell faces multiple functions (O2/CO2 transfer, acid-base balance and ionic regulation). Little is known of the respective cellular localization of these functions. TEM examination of the catfish gill shows, in pavement cells, cytoplasmic vesicles and apical pits, both ornamented with studs reminiscent of the proton pumps observed in H+ secretory epithelia. Ornamented apical pits are more frequently observed in acidotic fish. Taking together with our previous studies, this finding suggests that pavement cells play an important role, in addition to transfer of gas, by secreting protons. A new model of gill exchanges is proposed.

A tetra-polar electrical impedance device has been constructed to permit study of gastric emptying using a microcomputer. An alternative current of 100 kHz, 4 mM peak-to-peak, is injected through a pair of surface electrodes on the upper abdomen. The voltage variations picked up across the second pair of electrodes correspond to the variations of epigastric impedance in response to the applied current. The low frequency voltage corresponding to gastric emptying and recording noise is then conditioned and digitised at a sampling frequency of 1 Hz. A parallel 8-bit signal is finally converted to standard serial form and sent, in real time, to a microcomputer via a serial port. In a process of off-line analysis, the emptying trace was extracted from measured traces by taking successive Fast Fourier Transform (FFT) of length 64 points and was then fit by three mathematical models: linear, exponential and Weibull. The rate of emptying was calculated in terms of the time needed to achieve 50% emptying (T 1/2) from the best fit model. A clinical experiment was done in 20 healthy volunteers to investigate the reproducibility of the method and compared to a scintigraphic method. Successive measurements on the same subject gave statistically similar results and were statistically independent. No correlation has been observed between impedance and scintigraphic methods.

In pregnant female rats, concentrations of tri-iodo-L-thyronine in maternal serum, amniotic fluid and placental tissue after 15, 18 and 20 days of gestation were measured by homologous radioimmune-analysis. The three experimental groups of pregnant rats were: 1) euthyroid (or control), 2) hypothyroid, provoked by iodine-deficient diet for two months before conception and during gestation, 3) hyperthyroid, provoked by subcutaneous injections of L-thyroxine during gestation. Maternal serum L-T3 was measured in order to check the thyroid state. Significant decreases in L-T3 concentrations were found at all stages of gestation in the amniotic fluid of hypothyroid group. The hormonal concentrations in the placental tissues were correlated with the different treatments (decreased in hypothyroid state and increased in hyperthyroid state). This could suggest that the transfer of maternal iodothyronines to the foetus influences its foetal thyroid development.

A heuristic model of the relation between blood lactate (L) and VO2 during exercise was used to assess the comparative merits of two methods of reference threshold determination: the habitual linear interpolation method (LT), and a new method using inverse parabolic (second degree) interpolation (PT); the new method capitalizes on the demonstrated curvilinear relation between blood lactate and O2 uptake. Both types of interpolated thresholds were computed, and their error evaluated against the "true" 4-mmol lactate threshold. A combined parametric and Monte Carlo investigation showed that parabolic thresholds are generally superior, being less biased and more precise than their linear counterpart.

Rat tissue blood flows and heart output were determined in adult Wistar rats under up to two hours of cold (4 degrees C) exposure, using radioactive 46Sc microspheres. Circulating glucose, lactate and triacylglycerol levels were also determined. Glucose concentrations increased with cold exposure in spite of the drainage of substrates induced by the activation of thermogenesis. Plasma triacylglycerol levels agree with a high involvement of fats in the sustenance of heat production. Cold-exposure had an immediate effect decreasing skin circulation, but increased that of muscle and brown adipose tissue. Kidney and intestine blood flows were maintained. In liver, blood flow increased progressively with cold-exposure. White adipose tissue showed--at first--low blood flow, but increased in parallel to that of liver. The data presented show a distribution of the blood in the body of the cold-exposed rat in which thermogenic responsibilities and supply of blood are evenly distributed throughout. The importance of haemodynamic changes in brown adipose tissue was considerable but the increased share of muscle blood flow suggests that it may have a global role in maintaining thermal homeostasis.

The aim of this work was to determine the possible rapid modulatory effect of glucose on the activity of pancreatic islet lysosomal enzymes. For this purpose, beta-N-acetylglucosaminidase and beta-galactosidase activities were measured in homogenates of isolated rat islets after a 5, 15, 30 or 60-min exposure to either 3.3 or 16.6 mM glucose. The enzyme activities were determined spectrofluorometrically by means of their respective 4-methylumbelliferyl derivatives as substrates. beta-N-acetylglucosaminidase activity measured in freshly isolated non-incubated islets was 5.482 +/- 0.281 mumol/mg protein/h at 37 degrees C. In islets incubated with 3.3 mM glucose, this activity dropped significantly after 5 min and remained almost constant until the end of the incubation period. In islets incubated with 16.6 mM glucose, beta-N-acetylglucosaminidase activity also decreased significantly at 5 min, and attained its lowest value after 15 min of incubation. After this interval, the activity began to recover and thereafter gained a value close to that measured in non-incubated islets by 60 minutes' time. Despite this ultimate recovery, the enzyme activities measured were significantly lower than those found in islets incubated with 3.3 mM glucose. beta-galactose activity in freshly isolated non-incubated islets was 0.515 +/- 0.094 mumol/mg protein/h at 37 degrees C. This value remained almost unchanged throughout the incubation period in the presence of either 3.3 or 16.6 mM glucose. These results show that beta-N-acetylglucosaminidase activity, a lysosomal hydrolase of pancreatic rat islets,--and only this enzyme--is modulated by glucose.(ABSTRACT TRUNCATED AT 250 WORDS)