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

We have studied the effects of in vivo administration of different T3 doses to thyroidectomized rats on electrophysiological properties, measured in vitro, of papillary muscle fibers. The treatment with increasing T3 doses was associated with a significant reduction of the action potential duration up to a dose as large as 25 micrograms/100 g body weight every second day. The treatment with larger doses of T3 tended to restore the values of the action potential duration present in animals treated with physiological doses (5 micrograms/100 g body weight every second day). Action potential duration is frequency dependent. As the stimulation rate was increased from 1 to 5 Hz, this duration increased in all groups. However the difference between the rat groups remained significant. The cardiac frequency measured in unanaesthetized rats increased as the T3 doses. Furthermore the intrinsic frequency showed a similar increase, indicating a direct effect of T3 on the pacemaker cells in all thyroid states. The mechanism of this action of the thyroid hormone is not, however clear.

The aim of the investigation was to assess whether endogenous triacylglycerol contributes to the maintenance of the atrial functions. To attain this information, the atria from fed and fasted rats were treated with oxfenicine which is a cardioselective inhibitor of carnitine palmitoyltransferase I. In the presence of glucose, oxfenicine suppressed lipolysis without affecting the pacemaker and contractile activities. When exposed to 2-deoxyglucose in a substrate-free medium, the atria displayed a progressive fall of the contractile strength and pacemaker rate. The dysfunctions appeared faster in the atria from fed rats coinciding with a smaller triacylglycerol mobilization. Under this condition, oxfenicine abolished the triacylglycerol breakdown, increased the fall in the peak tension, elicited a rise in the resting tension and accelerated the decline of the pacemaker rate, leading in a significant number of atria to a complete cessation of the spontaneous contractions. These effects proceeded faster in the fed rats atria. Present data suggest that glucose oxidation is sufficient to meet the atrial energy demand when the fatty acid catabolism is impeded. The noxious effects of oxfenicine, attained after the glucose metabolism was eliminated, lend direct evidence to the notion that endogenous triacylglycerol supports, at least partly, the atrial functions.

The serum thyroid hormone levels [total (TT3) and free (FT3) triiodothyronine] and the heart rates were determined in neonatal rats of different ages (1-5-10 days). Thyroid hormone levels increase gradually in the first 10 days of age. The heart rate, tested at a body temperature of 37 degrees C, also increases during the same period. As the increase in heart rate in this phase of rat life is not due to the catecholamines, it is suggested that such an increase might depend on the increased thyroid hormone activity. On the other hand in congenitally hypothyroid rats the levels of both hormones and heart rates are lower than in normal animals of the same age. The electrophysiological properties of ventricular muscle fibres include a longer action potential, irrespective of stimulation frequency, in younger, naturally hypothyroid animals. The duration of action potential is greater in the congenitally hypothyroid animals, at all ages. These data demonstrate that, as in young and adult rats, the age-related modifications in heart rate, found in neonatal rats, might be due to thyroid dependent modifications of cardiac electrophysiology.

Liver microsomal glucuronidation of acetaminophen, chloramphenicol, salicylic acid, lorazepam, p-nitrophenol and morphine were measured in 8 days bile duct ligated rats. Compared to normals, cholestatic rats showed a decrease of 31% for p-nitrophenol glucuronidation; salicylic acid glucuronidation increased 281%; acetaminophen glucuronidation increased 38% while morphine, chloramphenicol and lorazepam values were similar to controls. We concluded that cholestasis produces non predictable changes on liver drug glucuronidation pathways.

In anaesthetized rats, intraperitoneal injection of pilocarpine (0.1 to 1 mg.Kg-1) induced a dose-dependent flow of saliva. During salivation by pilocarpine (0.5 mg.Kg-1), the blood content of submaxillary glands was not significantly increased but the blood volume of the animals was reduced. The salivary flow rate induced by pilocarpine was similar in normal and kininogen-deficient rats. L-NG-nitro-arginine (L-NOARG, 35 mg.Kg-1), a nitric oxide synthesis inhibitor, increased the salivary flow elicited by pilocarpine (0.5 mg.Kg-1). L-NOARG did not modify the blood volume loss but decreased the blood content of the submaxillary glands. The volume of salivary secretion induced by isoproterenol (250 mg.Kg-1) was lower in kininogen-deficient rats than in normal rats. It was significantly reduced by HOE 140 (2 mg.Kg-1), a bradykinin antagonist. L-NOARG increased the salivary flow induced by isoproterenol during the ten first minutes of collection but suppressed it thereafter. We concluded that kinins are not involved in the stimulating effect of pilocarpine on rat salivary glands but these peptides would participate to the development of the salivation induced by isoproterenol in rats. Nitric oxide contributes to the control of the vascular tone in rat salivary glands. The influence of L-NOARG on salivation would be explained by its effects on blood pressure and vascular resistances.

We determined whether regional myocardial work efficiency (segment work/regional O2 consumption) would be elevated by surgically-augmented inflow. In 10 anesthetized open-chest dogs, shunt between the ascending aorta and the superior vena cava was used to increase cardiac output. Hetastarch (15 ml/kg) was infused before opening the shunt to maintain coronary perfusion pressure. Regional myocardial segment work and O2 consumption (MVO2) were measured, during control and two levels of elevated flow. Regional segment work (g.mm/min) was calculated as the integrated products of force (g - miniature transducer) and segment shortening (mm - ultrasonic dimension gauge) during an averaged beat expressed per minute. Local MVO2 (ml O2/min/100g) was calculated from regional blood flow (microspheres) and O2 saturations (microspectrophotometry). It was found that regional myocardial segment work increased significantly (P < 0.05) from 926 +/- 94 to 1656 +/- 220 to 1479 +/- 309 (g.mm/min) for closed, half-open, and open shunt. This increase was primarily associated with increased segment shortening (from 147 +/- 14.1 to 204.4 +/- 20.1 to 232 +/- 26.1 mm/min). Both force development and regional MVO2 were unchanged during the experiment. Regional myocardial efficiency was significantly elevated during shunt function (from 95 +/- 12 to 187 +/- 31 to 213 +/- 57 g.mm/ml O2/100g). Systolic ejection stiffness (defined as the slope of the force-length relationship during the period of ejection) decreased from 8.0 +/- 0.9 to 4.7 +/- 0.4 to 4.5 +/- 0.9 g/mm during elevated inflow. It is concluded that when cardiac work is augmented primarily by segment shortening, regional myocardial efficiency is improved. This improvement is associated with decreased resistance to shortening (stiffness).

There is a high incidence of bony pathology in race horses. Thus, plasma GH, IGF-1, osteocalcin (OC), calcium (Ca) and inorganic phosphorus (P) concentrations were measured in 12 healthy Selle Français foals and their dams during the first five months after birth. Plasma IGF-1 and OC concentrations were higher in foals than in mares (336 +/- 25 vs 230 +/- 18 ng/ml, P < 0.05; 52.5 +/- 3.2 vs 4.9 +/- 0.1 ng/mg, P < 0.01, respectively). A significant positive linear relationship could be established between these two parameters in foals (IGF-1 = 19 + 0.619 OC; P < 0.05). Another striking evidence was the increase in plasma IGF-1, OC and P concentrations observed during the first week of postnatal life. IGF-1, OC, P and Ca concentrations remained elevated during the experimental period, indicating an intense skeletal growth (confirmed by growth curve) in these animals.

During exposure of normal rats to an ambient temperature of 36 degrees C or 40 degrees C, body temperature increases; thermolytic processes are set up and saliva is spread on the skin. In Wistar rats, thermolytic salivation started when body temperature was above 39 degrees C. This water loss was associated with a loss of body weight. A 10% reduction of plasma volume was observed in animals exposed to 40 degrees C but no change was observed in those exposed to 36 degrees C. Body weight loss was reduced by hexamethonium, atropine, prazosin, HOE 140, a bradykinin-antagonist, and NG-nitro-L-arginine (NOARG), a NO synthase inhibitor. The weight and blood content of the submaxillary glands, which are the main effectors of the thermolytic processes, increased as a function of the ambient temperature. The increase of blood content was enhanced by hexamethonium but reduced by atropine and NOARG. The weight increase was inhibited by hexamethonium, prazosin, HOE 140 and NOARG. At an ambient temperature of 40 degrees C, a large swelling developed around the submaxillary glands, resulting in a distention of the surrounding soft tissues. This local oedema fluid contained low levels of endogenous proteins but accumulated exogenous labelled albumin. This swelling was enhanced by atropine but decreased by hexamethonium, trasylol, HOE 140, NOARG, ketoprofen, a cyclooxygenase inhibitor, and prazosin. In kininogen deficient rats, the blood content of submaxillary glands increased as a function of ambient temperature. No increase in glandular weight and no swelling of the of the soft tissues were observed. After atropine, the weight of the glands increased and a swelling of the soft tissues appeared.(ABSTRACT TRUNCATED AT 250 WORDS)

In rats, thymic relative weight increased after birth reaching maximum values between days 15-30 and then decreased markedly in a similar way in both sexes, while the organ's absolute weight continued to increase until days 80-90 and declined slowly with apparent sex differences from day 30 onward. Scatchard analysis revealed that the [3H] dexamethasone (Dexa) receptor sites concentration showed a pattern comparable to that found in relative thymic weight, with no change in the apparent KD. The reduction of lymphocytes mitotic activity resulting in reduction of immature thymocytes production must be accompanied by a fall of the number of glycocorticoid receptors in ageing thymuses. Despite the profound decrease in the glucocorticoid receptor sites levels, the thymus sensitivity to Dexa remained unchanged during development. Indeed, in prepuberal and adult rats, the steroid administration was followed 4 days after by a transient thymic weight loss of about 70-80% which was mainly linked to the reduction in the cortical area. In contrast, the density of [3H] Dexa binding sites was reduced unexpectedly by 25% only after steroid treatment. These findings provided evidence that Dexa receptor-positive population cells in thymus was formed in a large part by relatively glucocorticoid resistant cells.

The effects of a restricted-diet (50% of the normal intake during 25 d) on the isometric developed tension (IDT), the metabolism of labelled glucose, and the levels of glycogen, of uteri isolated from ovariectomized (25 d) and non-ovariectomized rats were explored. The restriction of food intake produced a fall in the contractile activity of normal, non-ovariectomized, rats in permanent diestrous compared to normally fed rats in diestrous. On the contrary, in castrated rats, the IDT of isolated uterus from underfed rats, was significantly higher than its normal-fed controls. In normal rats the formation of 14CO2 from U 14C-glucose was significantly lower in uterine preparations from restricted-diet animals than the control one. On the other hand, in castrated rats, the formation of 14CO2 increased as a result of underfeeding. The post-incubation levels of glycogen in uteri from normal-fed animals diminished significantly in comparison to 0 time values. In uteri from rats subjected to a dietary restriction, the initial glycogen values were lower than in normal-fed controls, but they did not decline further after incubation in KRB medium. On the contrary, even when the levels of glycogen were significantly lower at 0 time than in diestrous animals, they diminished in ovariectomized rats after incubation, no matter the diet. The above results indicate that the effects of restricted-diet on contractile activity, levels of glycogen and glucose metabolism were not observed in ovariectomized rats. Further researches are needed to clarify that point.