In vivo and in vitro effects of beta-endorphin on glucose metabolism in the rat

The effects of beta-endorphin (beta-Ep) on plasma glucose levels in rats and on glucose metabolism in isolated rat liver cells were examined. Intravenous injection of beta-Ep (5 micrograms/100 g BW) into ether-anaesthetized rats resulted in prompt and sustained hyperglycaemia with increases in the plasma glucagon and somatostatin levels and decrease in the plasma insulin level. When liver cells isolated from fed rats were incubated in the presence of beta-Ep at concentrations of 6 X 10(-8) M to 6 X 10(-7) M, glucose release into the medium increased within 15 min in a dose-related manner. Time course experiments showed that beta-Ep increased the level of cyclic AMP within 3 min. Significant increase in gluconeogenesis in liver cells isolated from fasted rats was also observed on addition of 10(-7) M beta-Ep in the presence of 10 mM L-lactate. These results suggest that the hyperglycaemia induced by beta-Ep may be caused, at least in part, by the effects of beta-Ep on releases of pancreatic hormones and glucose production in liver cells.     

The effects of amylin on carbohydrate metabolism in skeletal muscle in vitro and in vivo.

1. The effects of synthetic human amylin on basal and insulin-stimulated (100 and 1000 microunits/ml) rates of lactate formation, glucose oxidation and glycogen synthesis were measured in the isolated rat soleus muscle preparation incubated in the presence of various concentrations of glucose (5, 11 and 22 mM). 2. The rate of glucose utilization was increased by about 2-fold by increasing the glucose concentration from 5 to 22 mM. 3. Synthetic human amylin (10 nM) significantly inhibited (by 46-56%) glycogen synthesis, irrespective of the concentration of insulin or glucose present in the incubation medium. 4. Amylin (10 nM) did not affect insulin-stimulated rates of 2-deoxy[3H]glucose transport and phosphorylation. 5. Intraperitoneal administration of insulin (100 micrograms/kg) to rats in vivo stimulated the rate of [U-14C]glucose incorporation into glycogen in the diaphragm by about 80-fold. This rate was decreased (by 28%) by co-administration of amylin (66 micrograms/kg).     

In vitro and in vivo metabolism of myristicin in the rat

Myristicin [5-allyl-1-methoxy-2,3-(methylenedioxy)benzene] is a flavoring plant constituent and has been known to produce significant psychopharmacological responses as well as insecticidal activity. From in vitro and in vivo metabolism of myristicin, the two metabolites 5-allyl-1-methoxy-2,3-dihydroxybenzene and 1′-hydroxymyristicin were identified using GC–MS after derivatization of sample matrices with a mixture of BSTFA–TMCS. Those metabolites from in vitro study were also confirmed in urine after an oral administration of myrisitcin to rats, and enzymatic hydrolysis of urine suggested that these metabolites were excreted as conjugated forms as well.     

In vitro effects of toxaphene on mitochondrial calcium ATPase and calcium uptake in selected rat tissues

$\text{In vitro}$ effects of toxaphene on Ca²⁺-ATPase activity and ⁴⁵Ca²⁺-uptake were studied in mitochondrial fractions of heart, kidney and liver tissues of rat. Mitochondrial fractions were prepared by the conventional centrifugation method. Ca²⁺-ATPase activity was determined by measuring the inorganic phosphate liberated during ATP hydrolysis. Toxaphene inhibited Ca²⁺-ATPase in a concentration dependent manner in all the three tissues. Substrate activation kinetics, with heart, kidney and liver tissue fractions, revealed that toxaphene inhibited Ca²⁺-ATPase activity non-competetively by decreasing the maximum velocity of the enzyme without affecting the enzyme-substrate affinity. Toxaphene also inhibited mitochondrial ⁴⁵Ca²⁺-uptake in the three selected tissues in a concentration dependent manner. These results indicate that toxaphene is an inhibitor of mitochondrial Ca²⁺-ATPase and calcium transport in heart, kidney and liver tissues of rat.     

In vivo metabolism of calcitriol in the pregnant rabbit doe

The production rate, the disappearance rate and the half life of calcitriol in gravid rabbit does at 24 days of gestation were compared, under unstressed steady state conditions, to those of nonpregnant animals. The contribution of the fetoplacental unit to the circulating levels of fetal calcitriol was also assessed. The calcitriol levels (139.6 +/- 19.9 vs 55.3 +/- 8.8 pmol/l and production rates (113.9 +/- 8.8 vs 59.2 +/- 9.2 pmol/min/Kg) were higher in pregnant than in nonpregnant animals (P less than 0.01). However, clearance rates (1.07 +/- 0.18 vs 1.12 +/- 0.20 ml/min/Kg and circulating half life (442 +/- 49 vs 368 +/- 35 min; NS) were similar in both groups of animals. Fetal levels (62.3 +/- 1.6 pmol/l) and specific activity (11166 +/- 864 dpm/pmol) of calcitriol were lower than those of the respective mothers (P less than 0.005). Taken together these data suggest that, calcitriol is transported through the placenta; and that the fetoplacental unit contributes to the fetal and perhaps to the maternal calcitriol levels.     

In vitro study of microwave effects on calcium efflux in rat brain tissue

In this study we investigated the prospect of microwave-induced alteration of ⁴⁵Ca²⁺ efflux from rat neural tissue at low pulse repetition frequencies and low power densities under in vitro conditions. Rat cerebral tissue, preloaded with ⁴⁵Ca²⁺, was exposed to pulsed-microwave radiation (1-GHz carrier frequency) according to one of several PRF-power density exposure schemes: 16 Hz at 0.5, 1.0, 2.0, or 15 mW/cm², or 32 Hz at 1.0 or 2.0 mW/cm² average power density. Measurements of radioactivity in the efflux medium and in the tissue sample were used to calculate an efflux value for each sample. The results indicate that the radiation conditions used did not alter calcium efflux in rat brain tissue.     

In vivo and in vitro effects of aluminum treatment on rat liver mitochondrial function

This study examines the effect on mitochondrial respiration and permeability of in vivo and in vitro aluminium (Al) exposure. Rats were treated intraperitoneally with AlCl₃ to achieve serum and liver Al concentrations comparable to those seen in Al-related disorders. Mitochondria isolated from Al-treated rats had higher (p<0.01) Al concentration, lower (p<0.05) state 3 respiration, respiratory control (RCR), and ADP/O ratio (succinate substrate), and greater passive swelling in 100 mM KCl or 200 mM NH₄NO₃ than controls. The in vitro addition of Al (0–180 μM) to mitochondria from normal rats also decreased (p<0.01) state 3 respiration, RCR, and ADP/O and stimulated passive swelling in KCl and NH₄NO₃ at 42–180 μM Al. These studies show that Al depresses mitochondrial energy metabolism and increases membrane permeability. The toxicity associated with Al may be related to its effect on mitochondria.     

In vivo and in vitro hormonal effects on the metabolism of immature oocytes of Xenopus laevis.

The rate of in vitro amino acid uptake by Xenopus laevis ovarian follicles from hormonally (HCG) stimulated females was compared to that of ovarian follicles from nonstimulated females. An increased rate of uptake was found in HCG-stimulated ovarian follicles. Evidence is presented that indicates that oocytes from HCG-stimulated females have higher protein synthetic rates relative to oocytes from nonstimulated females. When ovarian follicles from unstimulated females were treated with HCG in vitro, it was found that the response obtained mimics the in vivo stimulation both in terms of its effect on amino acid uptake by the ovarian follicles and on the metabolism of the oocyte itself as indicated by increased protein synthetic rates and changes in ribosome metabolism. In order to demonstrate these HCG-mediated changes in oocyte metabolism in vitro, the presence of the entire ovarian follicle was required.     

In vitro and in vivo effects of some benzodiazepine drugs on human and rabbit erythrocyte carbonic anhydrase enzymes

Carbonic anhydrase inhibitors (CAIs) are a class of pharmaceuticals used as antiglaucoma agents, diuretics and antiepileptics. Thus, discovery of novel CAIs has become of great importance in the recent years. In the current study, in vitro and in vivo inhibition effects of benzodiazepine drugs, diazepam and midazolam, on human erythrocytes carbonic anhydrase I and II isozymes were investigated. After purification of the isoenzymes, in vitro inhibition assays were performed and K(i) values were determined to be of 141.5 μM and 40.7 μM for hCA I and of 5.11 μM and 0.58 μM against hCA II by the esterase activity assay, respectively. The drugs showed strong inhibitory effects on hCA II, in the same range as the clinically used sulphonamide acetazolamide. For in vivo studies, five adult male New Zealand White rabbits (3-4.2 kg) were selected for intravenous administrations of the drugs (2 mg/kg and 0.2 mg/kg body weight, respectively). The enzyme was significantly inhibited by 2 mg/kg diazepam (p < 0.05), and 0.2 mg/kg midazolam (p < 0.05) for up to 30 min following intravenous administration.     

In vitro and in vivo effects of some benzodiazepine drugs on human and rabbit erythrocyte carbonic anhydrase enzymes

Carbonic anhydrase inhibitors (CAIs) are a class of pharmaceuticals used as antiglaucoma agents, diuretics and antiepileptics. Thus, discovery of novel CAIs has become of great importance in the recent years. In the current study, in vitro and in vivo inhibition effects of benzodiazepine drugs, diazepam and midazolam, on human erythrocytes carbonic anhydrase I and II isozymes were investigated. After purification of the isoenzymes, in vitro inhibition assays were performed and K_i values were determined to be of 141.5 μM and 40.7 μM for hCA I and of 5.11 μM and 0.58 μM against hCA II by the esterase activity assay, respectively. The drugs showed strong inhibitory effects on hCA II, in the same range as the clinically used sulphonamide acetazolamide. For in vivo studies, five adult male New Zealand White rabbits (3–4.2?kg) were selected for intravenous administrations of the drugs (2?mg/kg and 0.2?mg/kg body weight, respectively). The enzyme was significantly inhibited by 2?mg/kg diazepam (p?<?0.05), and 0.2?mg/kg midazolam (p?<?0.05) for up to 30?min following intravenous administration.     

Lithium's effects on rat liver glucose metabolism in vivo

Oral administration of lithium carbonate to fed-healthy rats strongly decreased liver glycogen content, despite the simultaneous activation of glycogen synthase and the inactivation of glycogen phosphorylase. The effect seemed to be related to a decrease in glucose 6-phosphate concentration and to a decrease in glucokinase activity. Moreover, in these animals lithium markedly decreased liver fructose 2,6-bisphosphate, which could be a consequence of the fall in glucose 6-phosphate and of the inactivation of 6-phosphofructo-2-kinase. Liver pyruvate kinase activity and blood insulin also decreased after lithium administration. Lower doses of lithium carbonate had less intense effects. Lithium administration to starved-healthy and fed-streptozotocin-diabetic rats caused a slight increase in blood insulin, which was simultaneous with increases in liver glycogen, glucose 6-phosphate, and fructose 2, 6-phosphate. Glucokinase, 6-phosphofructo-2-kinase, and pyruvate kinase activities also increased after lithium administration in starved-healthy and fed-diabetic rats. Lithium treatment activated glycogen synthase and inactivated glycogen phosphorylase in a manner similar to that observed in fed-healthy rats. Glycemia was not modified in any group of animals. These results indicate that lithium acts on liver glycogen metabolism in vivo in at least two different ways: one related to changes in insulinemia, and the other related to the direct action of lithium on the activity of some key enzymes of liver glucose metabolism.     

In vitro and ex vivo effects of antidepressants on rat brain membrane-bound phosphatidylinositol synthetase activity

The in vitro and ex vivo effects of antidepressant drugs on membrane-bound phosphatidylinositol (PI) synthetase and PI: myo-inositol exchange enzyme activities were examined. In rat brain subcellular fractions, PI synthetase occurred exclusively in the microsomes. In comparison, the activity of CDP-diglyceride independent PI: myo-inositol exchange enzyme was low (3%). Of the various CDP-diglycerides tested for the activation of PI synthetase, CDP-dipalmitin was the most active. Addition of 1 mM of desipramine, amitriptyline, imipramine, iprindole, clomipramine and mianserin in vitro significantly inhibited (30–60%) PI synthetase activity, whereas the same concentration of zimelidine and fluoxetine had no effect. At low liponucleotide concentrations, PI synthetase activity was significantly enhanced by imipramine (1 mM), whereas the enzyme activity was inhibited at higher liponucleotide concentrations (>0.3 mM). In contrast, imipramine had no effect on the PI: myo-inositol exchange enzyme activity. No significant alteration in the PI synthetase activity was found following either acute (2 h) or chronic (21 d) treatment of rats with imipramine. The above results indicate that the de novo synthesis of PI is inhibited in vitro but not ex vivo by some antidepressant drugs. However, in view of the high concentration of the drugs required, the pharmacological significance of this inhibitory action with respect to their therapeutic effects is doubtful.     

In vivo and in vitro effects of oestradiol-17β on lipid metabolism in Notemigonus crysoleucas

The effects of oestradiol-17β on the gonosornatic index, liver size, hepatic and body lipid levels in the cyprinid teleost, Notemigonus crysoleucas , were investigated. Administration of oestradiol to female TV. crysoleucas during the gonadal preparatory and prespawning seasons stimulates increases in ovarian size. During the early spawning season oestradiol therapy results in a reduction of ovarian gonosomatic index. Oestrogen treatment of males causes a suppression of testicular growth. In female fish exposed to long (15-5L/8-5D) or intermediate (12L/12D) photoperiods oestradiol increases body fat reserves. At short photoperiods (9L/15D) oestrogen treatment of females results in body fat store depletion Low doses deplete and high doses of oestradiol increase body lipid reserves in male fish. The hepatosomic index increases in both male and female fish following oestrogen treatment. Oestradiol therapy during the gonadal preparatory season, but not during the prespawning season, increases total liver lipids. The in vitro effects of oestradiol on liver lipid and carbohydrate metabolism were also examined. Under the conditions used in these experiments, lipid depletion was observed in liver slices incubated with or without oestradiol. Pretreatment of fish with oestradiol before liver tissue was removed drastically reduced in vitro lipid depletion. Oestradiol retards the gluconeogenesis and glycogenesis seen in liver slices incubated in a hormone-free medium.     

In vivo effects of chronic contamination with depleted uranium on vitamin D3 metabolism in rat

The extensive use of depleted uranium (DU) in today's society results in the increase of the number of human population exposed to this radionuclide. The aim of this work was to investigate in vivo the effects of a chronic exposure to DU on vitamin D(3) metabolism, a hormone essential in mineral and bone homeostasis. The experiments were carried out in rats after a chronic contamination for 9 months by DU through drinking water at 40 mg/L (1 mg/rat/day). This dose corresponds to the double of highest concentration found naturally in Finland. In DU-exposed rats, the active vitamin D (1,25(OH)(2)D(3)) plasma level was significantly decreased. In kidney, a decreased gene expression was observed for cyp24a1, as well as for vdr and rxralpha, the principal regulators of CYP24A1. Similarly, mRNA levels of vitamin D target genes ecac1, cabp-d28k and ncx-1, involved in renal calcium transport were decreased in kidney. In the brain lower levels of messengers were observed for cyp27a1 as well as for lxrbeta, involved in its regulation. In conclusion, this study showed for the first time that DU affects both the vitamin D active form (1,25(OH)(2)D(3)) level and the vitamin D receptor expression, and consequently could modulate the expression of cyp24a1 and vitamin D target genes involved in calcium homeostasis.