[The effect of potential beta-adrenolytic agents on oxidation and phosphorylation processes in myocardial muscle mitochondria in vitro].
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Concentrations ranging from 1-9 x 10(-7) mol.dm-3 were employed for in vitro studies. Under the selected experimental conditions, both agents markedly decreased the stimulated consumption of oxygen by the cardiac muscle mitochondria in the condition S3, the rate of the formation of energy by mitochondria as well as the respiratory control index. The coefficient of oxidative phosphorylation was not markedly changed due to the effect of the added agents. The results of the present paper suggest possible integration of the cardiac muscle mitochondria in the oxidative metabolism of the potential beta-adrenolytic agents FA33 and FP33, which requires further in vivo studies.Keywords:
BETA (programming language)
Cardiac muscle
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Respiration and oxidative phosphorylation of hepatocytes were studied as affected by low temperatures and cryoprotectors. Fast freezing of these cells down to -196 degrees C with the presence of mentioned substances causes considerable destruction of their structures. The intensity of the oxygen endogenic uptake lowers significantly, respiration and oxidative phosphorylation become uncoupled. Two-stage freezing down to -196 degrees C also causes a complete uncoupling of the oxidation and phosphorylation processes in the hepatocyte mitochondria. When freezing hepatocytes down to -196 degrees C by the multistage programme with the presence of cryoprotectors in a 10% concentration, the mitochondria retain 20, 30 and 40% of their functional properties, respectively.
Cellular respiration
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The techniques of hyperglycemic and euglycemic clamps previously used in human investigation have been adapted to small rodents to measure in vivo peripheral (muscle, adipose tissues) glucose metabolism and in vivo hepatic glucose production, in lean and genetically obese (fa>/fa) rats. The aim of the study was 1) to assess the in vivo relevance of previously described in vitro abnormalities of muscle and adipose tissues producing insulin resistance in genetically obese (fa/fa) rats; 2) to decide whether livers of obese rats were insulin resistant. It was observed that during either hyperglycemic or euglycemic clamps, peripheral glucose metabolism by muscle and adipose tissue of obese rats was similar to that of lean controls but at the cost, for the obese rats, of plasma insulin levels that were 3.5 times higher than control. This indicated that peripheral tissues of obese rats were indeed insulin resistant when tested in vivo. It was also observed hat raising plasma insulin levels in lean rats inhibited the in vivo hepatic glucose production. In contrast, in obese rats, hepatic glucose production was high in spite of a marked increase in basal insulinemia. Furthermore, hepatic glucose production of obese rats failed to be inhibited by further increasing their hyperinsulinemia. This is the first demonstration of a hepatic insulin resistance in genetically obese fa/fa rats.
Hyperinsulinemia
Carbohydrate Metabolism
Glucose clamp technique
Basal (medicine)
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The effect of different temperatures on the biochemical activity and morphology of insect flight muscle mitochondria was examined. It was found that respiration and phosphorylation have the same thermal response at temperatures of 25 degrees C. and below. The energy of activation for both systems is approximately 12,300 calories. Oxidation and phosphorylation can be uncoupled effectively by temperature, for at temperatures above 25 degrees C. there is more rapid heat inactivation of phosphorylation. This is evident from reduced P/O values as well as from morphological deterioration in the mitochondrial population. The thermal response of both this sarcosomal enzyme system and the respiration in the living fly are quantitatively similar.
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Stimulation of mitochondrial respiration by physiological concentrations of Ca2+ was studied to determine which components of oxidative phosphorylation are affected by Ca2+. The kinetic dependence of the respiratory chain, phosphorylation subsystem and proton leak on the mitochondrial membrane potential in isolated rat heart mitochondria respiring on 2-oxoglutarate or succinate was measured at two different concentrations of external free Ca2+. The results show that proton leak is not directly affected by Ca2+, but that both the respiratory and phosphorylation systems can be directly stimulated by Ca2+ depending on conditions. Although Ca2+ directly stimulates the phosphorylation system, this has relatively little effect on respiration rate with 2-oxoglutarate in States 3 and 4 because the subsystem has little control over respiration. However, in intermediate states, the phosphorylation system has greater control and Ca2+ stimulation of this system contributes substantially to the stimulation of respiration and phosphorylation. In the case of succinate oxidation neither the respiratory subsystem nor the phosphorylation system is stimulated by Ca2+.
Cellular respiration
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S ummary Brain swelling was produced by exposing the cerebral cortex to air (rat) and by epidural compression (cat). The isolated mitochondria from swollen brains were investigated with regard to some basic properties relevant to their functional state, such as respiration, phosphorylation, respiratory control and ATPase activity. The biochemical findings correlated with clinical and electroencephalographic findings. In the moderate cases, the isolated mitochondria revealed a loosely coupled state of the oxidative phosphorylation, characterized by a decrease of respiration in the presence of a phosphate acceptor, with an essentially normal phosphorylative efficiency. The ATPase activity of the mitochondria was only slightly stimulated by 2,4‐dinitro‐phenol. On the other hand, the mitochondria of severe cases showed loss of phosphorylation, but in some cases, the improvement of phosphorylation was observed when serum albumin was added or the mitochondrial preparation was kept at 0 for two hours. The possible mechanism of the development of brain swelling was discussed from the viewpoint of the biochemical change in the mitochondria.
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A (nearly) linear dependence of the respiration rate on a given parameter value was proposed as the criterion for considering this parameter to be an efficient regulator of respiration in mitochondria. A number of possible candidates was tested using the dynamic model of oxidative phosphorylation developed previously, among others ADP, the ATP/ADP ratio, external phosphorylation potential and Atkinson's adenylate energy charge. Only the external phosphorylation potential log(ATP/ADP*P(i)) was found to fulfil the above-mentioned criterion and thus it was proposed to be the parameter which 'actually' regulates oxidative phosphorylation in mitochondria.
Energy charge
Cellular respiration
Bioenergetics
Respiration rate
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The effect of the 44-amino-acid peptide human pancreatic GH releasing factor (hpGRF-44) upon the secretion of GH was studied in control and hypothyroid adult male rats. In animals rendered hypothyroid by ingestion of propylthiouracil (PTU), basal and hpGRF-44-stimulated secretion of GH was depressed in vivo. Administration of T4 together with PTU prevented the decline in basal and hpGRF-provoked GH secretion in vivo. HpGRF-44-stimulated release of rat GH was also impaired in vitro, an effect partially reversed by administration of low doses of T4 in vivo. The depressed in vitro secretion of GH could not be restored in hypothyroidism pituitaries by incubation of the glands with T3. Thus, hypothyroidism blunts hpGRF-44-stimulated secretion of GH in vivo and in vitro in the hypothyroid adult male rat.
Propylthiouracil
Somatropin
Basal (medicine)
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Female rats were ovariectomized and either sham-pinealectomized or pinealectomized on day 24 of age and exposed to a photoperiod of 12 h light: 12 h dark. In vivo and in vitro measures of adrenocortical function were made at 6,7, and 8 weeks of age (18, 25, and 32 days post-pinealectomy, respectively). Pinealectomy diminished the postcastration rise in adrenal 5α-reductase activity in all age groups (P < .05). The proportionate secretion of corticosterone (compared with the total steroid output) by adrenal slices was likewise enhanced (P < .05) although the secretion and production of corticosterone in vitro was not altered. Pinealectomy substantially diminished (P < .05) the in vivo secretion rates of reduced metabolites of corticosterone (dihydrocorticosterone and tetrahydrocorticosterone) without altering corticosterone secretion. Consequently, proportionate secretion of corticosterone in vivo was also enhanced (P < .05). These findings are consistent with the notion that in ovariectomized rats removal of the pineal gland diminishes adrenal 5α-reductase activity without affecting ACTH secretion. However, in rats with ovaries intact, estrogen modified the effects of pinealectomy. Not only was the infra-adrenal metabolism of corticosterone diminished (higher proportionate output), but also resting levels of plasma corticosterone (P < .01), corticosterone production in vitro (P < .05), and total adrenal steroidogenesis in vitro (P < .01) were increased. Thus, ACTH secretion may be enhanced following pineal removal in the presence of estrogen. The data suggest that the pineal gland, together with the ovaries, plays a role in the modulation of adrenal steroidogenesis. (Endocrinology98: 20, 1976)
Pinealectomy
Corticosterone
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The effect of p-chloromercuribenzoate (pCMB) on oxidative phosphorylation and palmitate-stimulated respiration of liver mitochondria has been studied. pCMB (1 microM) does not affect oxidative phosphorylation but reduces the inhibiting effect of ATP on this process. Used at the same concentration, pCMB eliminates the inhibiting effect of ADP and ATP on mitochondrial respiration in the presence of 10 and 20 microM palmitate. pCMB has no effect on inhibition of oxidative phosphorylation by carboxyatractyloside or on palmitate-stimulated respiration of mitochondria. It is concluded that the SH-groups of mitochondria localized in the hydrophilic region outside the inner mitochondrial membrane participate in regulation of oxidative phosphorylation by ATP and in regulation of palmitate-stimulated respiration by ADP + ATP.
Uncoupling Agents
Cellular respiration
Adenosine triphosphate
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