ITP pyrophosphohydrolase and IDP phosphohydrolase in rat tissue.

The existence of a nucleoside triphosphate pyrophosphohydrolase specific for ITP has been demonstrated in the cytosol fraction of a variety of rat tissues. The enzyme, stable to moderate heat treatment, was present in erythrocytes as well as brain, heart, kidney, liver, lung, muscle, ovaries, spleen, testes and thymus. The specific activity of the enzyme ranges from 26 to 150 mumoles/min/g protein. In addition, evidence is given for a heat labile nucleoside diphosphate (IDP) phosphohydrolase present in most rat tissues, and particularly high in the adrenal (137 mumoles/min/g protein). An "ITP-IMP cycle" is proposed as a rgulating mechanism for intracellular levels of ATP.     

Anserine and carnosine in chicks (Gallus gallus) rat pups (Rattus rattus) and ducklings (Anas platyrhynchos): comparative ontogenetic observations.

1. Muscle and brain from developing chick embryos, as well as from day-old chicks, rats, and ducks were analyzed for the histidine-containing dipeptides, anserine and carnosine. 2. Anserine was found in the brain of all species studied, whereas in muscle, anserine was found only in chicks. 3. At 15 days, the muscle of developing chick embryo contained 41 +/- 9 mumoles/100 g anserine while carnosine was present at a level of less than 3 mumoles/100 g. 4. In day-old chicks the anserine level in muscle was 100 +/- 35 mumoles/100 g while the carnosine level was 22.5 +/- 1 mumoles/100 g. 5. These findings cast doubt on earlier hypotheses relating anserine and carnosine to muscle activity.     

Effect of envenomation on enzymes of brain of albino rats

Effects of high doses of cobra venom, (150 micrograms/120 +/- 20 g body wt) and viper venom (300 micrograms/120 +/- 20 g body wt) on aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), acetylcholinesterase (ACh) and alkaline phosphatase (ALP) of brain of albino rats were studied. While AST, LDH, ACh and ALP activities increased in both viper and cobra venom treated rats, ALT decreased in both groups compared to control.     

Disruption of seminiferous epithelial function in the rat by ovarian protein

The granulosa cell produces an inhibitor of aromatase activity, which recently was purified to homogeneity (follicle-regulatory protein: FRP). Since extracts of testicular homogenates also contain factor(s) with biological properties similar to FRP, including inhibition of granulosa cell aromatase, we examined the effects of ovarian FRP on testicular function. Forty-five-day-old rats received daily FRP injections (100 micrograms or 300 micrograms). After 15, 30, 45, and 70 days of therapy, (n = 5 each group), trunk serum was measured for testosterone, androstenedione, estradiol, and FSH levels by established radioimmunoassays (RIA). One testis from each rat was homogenized, centrifuged, and evaluated for sperm head counts; the other testis was dissected by transillumination, and the length of seminiferous epithelial stages determined. After 15 (control: 4.8 +/- 0.2 mm; 100 micrograms: 6.0 +/- 0.3 mm; 300 micrograms: 6.6 +/- 0.3 mm) and 30 days (control: 4.6 +/- 0.2 mm; 100 micrograms: 6.3 +/- 0.2 mm; 300 micrograms: 5.9 +/- 0.2 mm) of treatment the length of the "strong" seminiferous tubule segment in FRP-treated rats was greater than in control rats (p less than 0.05). Serum levels of steroids and FSH were similar in all groups. After 30, 45, and 70 days of treatment, the sperm head counts for the 100-micrograms and 300-micrograms dosages were 26%, 29%, 30% and 20%, 34%, and 24% of control values, respectively. By 70 days of treatment, cycle Stage VII was markedly reduced or absent in FRP-treated rats, and their round spermatids contained ring chromatin; both conditions indicate degeneration. FRP (50 micrograms/ml) was added to rat Sertoli cell cultures for 4 days after which transferrin and androgen-binding protein (ABP) were measured. FRP enhanced Sertoli cell secretion of ABP (58 vs. 138 +/- 7 microliters eq/culture) and transferrin (2.1 vs. 4.7 +/- 0.6 microgram/culture). In conclusion, systemic injection of FRP alters seminiferous epithelial function by reducing maturation of mature sperm forms. Adding FRP to Sertoli cells in culture enhances secretion of transferrin and ABP; this suggests that maturation of the germinal elements may be linked to the secretory function of seminiferous tubules.     

Influence of nonselective ET(A)/ET(B) receptor blockade on renal function in conscious rats: effects of renal denervation.

The effects of nonselective ET(A)/ET(B) receptor blockade with intravenous bolus injection of bosentan (10 mg/kg) on renal excretory function and blood pressure were investigated in conscious, male, normotensive Wistar rats before and one week after bilateral renal denervation. Renal denervation was followed by an increase in urine flow rate from 4.54+/-0.38 to 5.72+/-0.36 microl/min x 100 g b.w. (p<0.05) and a decrease in urine osmolality from 855.5+/-44.6 to 707.4+/-47.5 mosm/kg H(2)O (p<0.05). Bosentan administration in sham-operated rats resulted in decrease in urine flow rate from 4.54+/-0.38 to 3.49+/-0.34 microl/min x 100 g b.w. (p<0.05), and increase in urine osmolality from 855.5+/-44.6 to 1075.0+/-76.1 mosm/kg H(2)O (p<0.05). Sodium excretion decreased from 226.9+/-20.0 to 155.1+/-11.0 nmol/min x 100 g b.w. (p<0.01). Bosentan administration in renal denervated rats did not produce any changes in renal water or electrolyte excrections. Blood pressure, heart rate, clearance of Inulin or clearance of paraaminohippuric acid (PAH) did not change in sham-operated or renal denervated rats during nonselective ET(A)/ET(B) receptor blockade. Bosentan did not alter the baroreflex sensitivity or sympatho-vagal balance in sham-operated or renal denervated rats. In conclusion, an interaction between renal nerves and endothelins appears to be involved in the regulation of the renal excretory function.     

Impaired parathyroid hormone action on urinary phosphorus excretion in isolated perfused kidney of streptozotocin-induced diabetic rats.

To study the effects of diabetes on the renal actions of parathyroid hormone (PTH), we observed urinary excretion of cyclic adenosine monophosphate (cAMP) and phosphorus in isolated perfused rat kidney. Diabetic rats were kept for 7 days after an intraperitoneal injection of 70 mg/kg streptozotocin (STZ). STZ-induced diabetic rats were treated with a daily injection of 20 U/kg lente-type insulin for 7 days. Plasma albumin, calcium, phosphorus, and PTH levels were not different among normal control, diabetic and insulin-treated diabetic groups. In the control rat kidney, the addition of PTH increased urinary cAMP excretion from 8 +/- 3 to 190 +/- 49 pmol/5 min and urinary phosphorus excretion from 11.3 +/- 4.4 to 33.6 +/- 10.8 microg/5 min. In the STZ-diabetic rat kidney, basal urinary cAMP was impaired, and PTH altered neither urinary cAMP nor phosphorus excretion (from below 0.7 to below 0.7 pmol/5 min, and from 15.5 +/-4.5 to 13.6 +/- 8.1 microg/5 min, respectively). Insulin treatment completely recovered the PTH actions. These results show that insulinopenic diabetes induces PTH resistance in the kidney.     

Effect of Cassia fistula Linn. leaf extract on diethylnitrosamine induced hepatic injury in rats

The hepatoprotective and antioxidant effect of Cassia fistula Linn. leaf extract on liver injury induced by diethylnitrosamine (DEN) was investigated. Wistar rats weighing 200+/-10g were administered a single dose of DEN (200mg/kg b.w., i.p.) and left for 30 days. For hepatoprotective studies, ethanolic leaf extract (ELE) of C. fistula Linn. (500mg/kg b.w., p.o.) was administered daily for 30 days. AST, ALT, ALP, LDH, gamma-GT and bilirubin were estimated in serum and liver tissue. Lipid peroxidation (LPO), SOD and CAT were also estimated in liver tissue as markers of oxidative stress. DEN induced hepatotoxicity in all the treated animals were evident by elevated serum ALT, AST, ALP and bilirubin levels and a simultaneous fall in their levels in the liver tissue after 30 days. Induction of oxidative stress in the liver was evidenced by increased LPO and fall in the activities of SOD and CAT. ELE administration for 30 days prevented the DEN induced hepatic injury and oxidative stress. In conclusion, it was observed that ELE of C. fistula Linn. protects the liver against DEN induced hepatic injury in rats.     

Early metabolic effects of platelet-derived growth factor and transforming growth factor-beta in rat liver in vivo

The short term metabolic effects of the in vivo administration of platelet-derived growth factor have been examined in the liver of the rat. Meal-fed male Wistar rats weighing between 150-180 g received an intraperitoneal injection of platelet-derived growth factor (17 units/100 g weight), transforming growth factor-beta (185 ng/100 g weight), or saline. At 5 min after injection, the livers were freeze-clamped. Samples of the tissue were subsequently assayed for metabolite content and enzyme activities. Platelet-derived growth factor injection caused an elevation in the liver content of pyruvate from 0.14 +/- 0.012 to 0.19 +/- 0.009 mumol/g wet weight liver (p less than or equal to 0.01) and an increase in the cytosolic phosphorylation potential [sigma ATP]/[sigma ADP][sigma Pi] from 6670 +/- 540 to 8970 +/- 750 (p less than or equal to 0.01). In addition an increase in the hepatic content of the hexose monophosphate pathway metabolites, 6-phosphogluconate (0.027 +/- 0.004 to 0.037 +/- 0.005 mumol/g wet weight) (p less than or equal to 0.05), ribulose 5-phosphate (0.013 +/- 0.001 to 0.017 +/- 0.001 mumol/g wet weight) (p less than or equal to 0.05) and combined sedoheptulose 7-phosphate and ribose 5-phosphate (0.052 +/- 0.007 to 0.062 +/- 0.004 mumol/g wet weight) (p less than or equal to 0.05) was observed. The elevation in the hexose monophosphate pathway metabolites resulted from a 1.3-fold elevation in the activity of glucose-6-phosphate dehydrogenase [EC 1.1.1.49] when measured in a crude homogenate. Kinetic analysis performed on partially purified glucose-6-phosphate dehydrogenase demonstrated no significant change in the Km of the enzyme for either NADP+ or glucose 6-phosphate, while a 2.4-fold increase in the Vmax was observed. In view of the rapidity of the change in total measured enzyme activity and increase in the Vmax of glucose-6-phosphate dehydrogenase, it is postulated that platelet-derived growth factor causes a covalent modification of the existing enzyme. Transforming growth factor-beta caused no change in the hepatic metabolite content in the treated animals when compared to saline treated controls.     

Effects of ethinyl estradiol on isoproterenol-induced death in ventricular fibrillation in DOCA-salt pretreated male and female rats

To assess the effects of ethinyl estradiol on the incidence of death in ventricular fibrillation induced by isoproterenol in DOCA-salt pretreated rats we implanted male and female rats simultaneously with a 20 mg DOCA pellet and pellets containing either ethinyl estradiol or vehicle (wax). Rats drank saline after implantation. After 6 days rats were challenged with a single, sc dose of 150 micrograms of isoproterenol. The average daily dose of estradiol per rat was estimated on the basis of the quantity of pellet lost during 6 days. In male rats the average daily dose of 61.2 +/- 20.2 micrograms/rat of ethinyl estradiol decreased the incidence of mortality by 80%, from 73.3% (11/15) in vehicle treated to 13.3% (2/15) in estradiol treated rats. Death occurred within 19.2 +/- 8.0 minutes from the injection of isoproterenol and was due to ventricular fibrillation. Serum levels of magnesium and potassium were comparable in the two groups both before and after isoproterenol. Isoproterenol induced death in 9 of 11 DOCA-salt pretreated, ovariectomized rats within 22.3 +/- 9.8 minutes. Only 3 of 11 DOCA-salt ovariectomized rats receiving the average daily dose of 28.4 +/- 12.1 micrograms/rat of ethinyl estradiol died. None of 10 ovariectomized untreated rats died from isoproterenol challenge. Serum levels of magnesium and potassium were comparable in the estradiol and vehicle treated groups. The average daily dose of 2.8 +/- 0.42 micrograms/rat of ethinyl estradiol elicited uterine growth but did not influence the incidence of mortality, since 9 out of 16 and 10 out of 16 rats died following isoproterenol in vehicle and estradiol treated DOCA-salt ovariectomized rats. We conclude that only pharmacological doses of estradiol exert protective effects against DOCA-salt induced myocardial sensitization to isoproterenol and that this protection is not associated with relevant changes in serum potassium or magnesium.     

Synergistic Cardioprotective Effects of Combined Chromium Picolinate and Atorvastatin Treatment in Triton X-100-Induced Hyperlipidemia in Rats: Impact on Some Biochemical Markers

Hyperlipidemia is one of the major risk factors for atherosclerosis and ischemic heart disease. Chromium (Cr) mineral is playing a crucial role in glucose and lipid homeostasis. The aim of this study was to evaluate the protective effects of combined chromium picolinate (CrPic) and atorvastatin treatment against hyperlipidemia-induced cardiac injury. Seventy-five male albino rats were divided into five groups (15 rats each). Hyperlipidemia was induced by intraperitoneal injection of a single dose of Triton X-100 (300 mg/kg body weight (b.w) (group ??). Treatment of hyperlipidemic rats was induced by daily administration of CrPic at a dose of 200 μg/kg b.w/day (group ???), atorvastatin at a dose of 10?mg/kg/day (group IV), and combined treatment with both (group V) by gavage for 7 days. At the end of experiment, serum and heart tissues were obtained. Hyperlipidemia was confirmed by histopathology of heart tissues, marked serum dyslipidemia, increased atherogenic indices, and values of ischemia-modified albumin. In addition to increased values of proprotein convertase subtilisin/kexin type 9, activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase enzyme and high relative expression levels of pentraxin-3 were observed. However, paraoxonase-1 activity was markedly decreased in the hyperlipidemic group. Significant improvement in all assessed parameters was observed in the rat group treated with both CrPic and atorvastatin. It can be concluded that combined CrPic and atorvastatin treatments had synergistic cardioprotective effects against hyperlipidemia which may be through modulating atherosclerosis as well as cardiac and aortic damage and/or activation of anti-inflammatory and anti-oxidant pathways, thus reversing endothelial dysfunction.     

Fecal corticosterone assessment in the epaulette shark,Hemiscyllium ocellatum

The present study examined the feasibility of measuring the steroid hormone corticosterone in fecal extracts of epaulette sharks, Hemiscyllium ocellatum. Six immature, captive-raised epaulette sharks (four females and two males) were obtained from two different zoos and were maintained in a closed-system, 530-liter aquarium. After a one-month adaptation, fecal samples were collected daily from each animal for 33 days. Five-day sets of samples were pooled within animals to insure sufficient material for analysis. Fecal hormone extraction was achieved using repeated cycles of dichloromethane and aqueous washes. The levels of corticosterone were measured by reverse-phase high-performance liquid chromatography (HPLC). Corticosterone presence in HPLC eluent peaks from fecal extracts was determined by comparison of the elution pattern of corticosterone standard with the elution patterns of fecal extracts with and without the addition of tritiated corticosterone or exogenous, unlabeled corticosterone. Exclusive presence of corticosterone in HPLC eluent peaks presumed to be corticosterone was determined by nuclear magnetic resonance mass spectrometry. Corticosterone levels, calculated from a 10-point standard curve, ranged from 1.2 to 20.9 ng/g feces across all sharks, with 92.3% of values being < or =13.5 ng/g. Within individuals, the lowest average for corticosterone levels across 33 days was 2.6+/-0.4 ng/g feces, and the highest average was 8.4+/-2.2 ng/g feces. This study demonstrated that corticosterone was extractable from and reliably measurable in fecal extracts of epaulette sharks. This is the first evidence of this hormone in epaulette sharks and the first report of fecal corticosterone in elasmobranchs.     

Hepatoprotective and antioxidant properties of Suaeda maritima (L.) dumort ethanolic extract on concanavalin-A induced hepatotoxicity in rats

Hepatoprotective and antioxidant properties of Suaeda maritima (L.) Dumort on concanavalin-A induced stress in Wistar albino rats have been reported. Rats were administered with ethanolic extract of Suaeda maritimna at the concentration of 75, 150 and 300 mg/kg of body wt. for 9 days and concanavalin-A was administrated (iv) 12 mg/kg on 9th day. Rats in concanavalin-A administered group showed elevated levels of AST, ALT, ALP and bilurubin. Pretreatment of rats with ethanolic extract (300 mg/kg) significantly reduced these serum parameters compared to concavalin-A administered group. Histopathological examination of liver sections showed that, normal liver architecture was disturbed by hepatotoxin intoxication. The extract treated group and silymarin treated group retained the normal cell architecture, although less visible changes were observed. Preliminary phytochemical analysis showed the presence of triterpenioids and may be responsible for the hepatoprotective activity. The LD50 was calculated as 3 g/kg of the body weight. IC50 values of hydroxyl (52.21+/-1.32 microg/ml) and nitric oxide radicals (09.14+/-0.94 microg/ml) scavenging results showed comparable activity with vitamin-C. Results of this study may be useful for the development of herbal medicine from Suaeda maritima for the treatment of hepatitis.     

Streptozotocin-induced diabetes influences the activity of ecto-nucleoside triphosphate diphosphohydrolase 1 of rat osseous plate membranes

We report the kinetic characterization of an ecto-nucleosidetriphosphate diphosphohydrolase 1 from rat osseous plate membranes in streptozotocin-induced diabetic rats, which arises during ectopic mineralization twenty days after a subcutaneous implantation of demineralized bone matrix, Insulin deficiency decreased the ecto-nucleoside triphosphate diphosphohydrolase activity from 1293.1 +/- 39.8 (control rats) to 556.0 +/- 8.2 nmol Pi/(min mg). Two families of ATP hydrolyzing sites showed cooperative effects with specific activities of 256.2 +/- 7.7 nmol Pi/(min mg) and 299.8 +/- 8.9 nmol Pi/(min mg), and studies on the stimulation of the enzyme by magnesium and calcium ions showed that the decrease in enzyme activity results from changes in the affinity of the enzyme for these ions. To our knowledge this is the first study associating the effects of type I diabetes with an ecto-nucleoside triphosphate diphosphohydrolase activity from rat osseous plate membranes.     

Calcitonin secretion during postnatal development in the rat: beta-adrenergic agents and vitamin D3 metabolites

The possible contribution of catecholamines and vitamin D3 metabolites to the high plasma calcitonin (CT) levels in suckling baby rats is unknown. So, in vivo and in vitro (using a perifusion system) effects of beta-adrenergic agents and vitamin D3 metabolites on CT release were studied in the rat during the postnatal development. In 13-day-old rats, the increase in plasma CT levels induced by isoproterenol injection (0.1 micrograms/kg b.w.) was inhibited by a previous administration of propranolol. A significant decrease in plasma CT levels was observed after propranolol injection in baby rats (0.68 +/- 0.05 ng/ml vs. 0.93 +/- 0.01 ng/ml). A daily injection of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3; 25 pmoles/rat/day during 4 days) induced a marked rise in plasma calcium (16.1 +/- 0.2 mg/dl), and a great decrease in thyroidal CT contents (approximately 70% of control values) in 13-day-old rats while no change was noted with 24,25-dihydroxycholecalciferol (24,25-(OH)2D3). A negative correlation between plasma calcium and thyroidal CT stores was found in suckling and in weaning rats treated with different doses of 1,25-(OH)2D3, suggesting an indirect effect of 1,25-(OH)2D3 on CT secretion. The mobilization of the thyroidal CT content was greater in weaning than in suckling rats in response to a given hypercalcemia. In vitro, 5 X 10(-5) M isoproterenol induced a rapid increase in CT secretion rate while 1,25-(OH)2D3 inhibited the rise in CT release induced by 3.0 mM calcium.(ABSTRACT TRUNCATED AT 250 WORDS)     

A role for membrane transport in modulation of intramuscular free glutamine turnover in streptozotocin diabetic rats.

We wished to examine the effects of diabetes on muscle glutamine kinetics. Accordingly, female Wistar rats (200 g) were made diabetic by a single injection of streptozotocin (85 mg/kg) and studied 4 days later; control rats received saline. In diabetic rats, glutamine concentration of gastrocnemius muscle was 33% less than in control rats: 2.60 +/- 0.06 mumol/g vs. 3.84 +/- 0.13 mumol/g (P < 0.001). In gastrocnemius muscle, glutamine synthetase activity (Vmax) was unaltered by diabetes (approx. 235 nmol/min per g) but glutaminase Vmax increased from 146 +/- 29 to 401 +/- 94 nmol/min per g; substrate Km values of neither enzyme were affected by diabetes. Net glutamine efflux (A-V concentration difference x blood flow) from hindlimbs of diabetic rats in vivo was greater than control values (-30.0 +/- 3.2 vs. -1.9 +/- 2.6 nmol/min per g (P < 0.001)) and hindlimb NH3 uptake was concomitantly greater (about 27 nmol/min per g). The glutamine transport capacity (Vmax) of the Na-dependent System Nm in perfused hindlimb muscle was 29% lower in diabetic rats than in controls (820 +/- 50 vs. 1160 +/- 80 nmol/min per g (P < 0.01)), but transporter Km was the same in both groups (9.2 +/- 0.5 mM). The difference between inward and net glutamine fluxes indicated that glutamine efflux in perfused hindlimbs was stimulated in diabetes at physiological perfusate glutamine (0.5 mM); ammonia (1 mM in perfusate) had little effect on net glutamine flux in control and diabetic muscles. Intramuscular Na+ was 26% greater in diabetic (13.2 mumol/g) than control muscle, but muscle K+ (100 mumol/g) was similar. The accelerated rate of glutamine release from skeletal muscle and the lower muscle free glutamine concentration observed in diabetes may result from a combination of: (i), a diminished Na+ electrochemical gradient (i.e., the net driving force for glutamine accrual in muscle falls); (ii), a faster turnover of glutamine in muscle and (iii), an increased Vmax/Km for sarcolemmal glutamine efflux.     

Effect of glibenclamide on thyroid hormone metabolism in rats

This study was undertaken to elucidate the effect of glibenclamide, one of sulfonylurea drugs, on thyroid hormone metabolism in vivo and on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat liver and kidney. Glibenclamide (0.2 mg/kg body weight) was intraperitoneally administered to normal and streptozotocin-induced (50 mg/kg) diabetic rats for 14 days. The liver and kidney of normal rats were perfused for 30 minutes with a synthetic medium containing 20 micrograms/dl T4 and glibenclamide (200 or 400 ng/ml), and production of T3 in the tissues was measured by radioimmunoassay. Serum T4 and T3 levels in control and streptozotocin-induced diabetic rats were not changed by daily intraperitoneal glibenclamide administration. The production of T3 (111 +/- 40 and 95 +/- 16 ng/g/30 min, mean +/- SD) and the conversion rate of T4 to T3 (11.1 +/- 2.9 and 10.2 +/- 2.3%) in the liver perfused with glibenclamide (200 and 400 ng/ml) were not significantly different from those in controls (109 +/- 41 ng/g/30 min and 12.8 +/- 5.4%). And those (120 +/- 33 and 99 +/- 19 ng/g/30 min, and 3.5 +/- 0.6 and 2.5 +/- 0.4%) in the kidney perfused with glibenclamide (200 and 400 ng/ml) were similar to those in controls (98 +/- 33 ng/g/30 min and 3.0 +/- 1.5%).     

Comparative analysis of tryptophan oxygenase activity and glucocorticoid receptor under the influence of insulin

This investigation addresses the interaction of insulin (INS) and glucocorticoid (GC) signaling in the hepatic regulation of tryptophan oxygenase (TO) enzyme activity in the rat. Male Wistar rats (200-250 g b.w) received an injection of the different doses of INS (10, 25, 50, 70 and 100 microg/200 g b.w., i.p.) and were used for experiments 3 h and 18 h after INS administration. This study shows that maximum of TO activity was found at dose of 50 microg of INS with peak increases observed at 3 h and 18 h after injection of INS, while INS had no effect on TO activity in adrenalectomized rats. The analysis of INS effects on glucocorticoid receptor-complex (GC/GR complex) stability shows that complexes from INS-treated rats are less stable than those from control animals. In addition, INS-stimulated stability of glucocorticoid receptor (GR) protein was significantly increased from the controls. Furthermore, the results show that GC/GR complexes from INS-treated rats could be activated and accumulated at higher rate in cell nuclei of control animals. These data support the involvement of INS in modulation of GC signaling pathway which mediates, in part, the activity of TO.     

The effect of phenobarbitone on cytoplasmic NADP-linked dehydrogenase activities in rat liver

Phenobarbitone administered in drinking water (0.5 g/l) or by daily intraperitoneal injection (100 mg/kg body weight) consistently caused an elevation of hepatic NADP-linked malic enzyme in rats maintained on a pellet diet. Three to four days appeared to be required for maximum response. The effect was also observed in animals maintained on a protein rich diet, in which the basic hepatic malic enzyme activity was low, but not in animals maintained on a sucrose rich diet, in which the basic enzyme activity was almost twice normal. Methyl cholanthrene, administered by daily intraperitoneal injection (40 mg/kg body weight), resulted in elevated hepatic levels not only of malic enzyme but also of the pentose phosphate pathway dehydrogenases. The timing of the "starve-refeed" response of the hepatic NADP-linked dehydrogenases in phenobarbitone-treated rats was similar to that in controls, and similar maximum enzyme activities were reached. The role of cytoplasmic NADP-linked dehydrogenases in the provision of reducing equivalent is discussed, particularly in relation to hepatic microsomal drug metabolism.     

Glycerol kinase activities in muscles from vertebrates and invertebrates

1. Glycerol kinase (EC 2.7.1.30) activity was measured in crude extracts of skeletal muscles by a radiochemical method. The properties of the enzyme from a number of different muscles are very similar to those of the enzyme from rat liver. Glycerol kinase from locust flight muscle was inhibited competitively by l-3-glycerophosphate with a K(i) of 4.0x10(-4)m. 2. The activity of glycerol kinase was measured in a variety of muscles from vertebrates and invertebrates in an attempt to explain the large variation in the activity of this enzyme in different muscles. 3. In vertebrates glycerol kinase activities were generally higher in red muscle than in white muscle; the highest activities (approx. 0.2mumole/min./g. fresh wt.) were found in the red breast muscle of some birds (e.g. pigeon, duck, blue tit) whereas the activities in the white breast muscle of the pheasant and domestic fowl were very low (approx. 0.02mumole/min./g.). 4. On the basis of glycerol kinase activities, muscles from insects can be classified into three groups: muscles that have a low enzyme activity, i.e. <0.3mumole/min./g. (leg muscles of all insects studied and the flight muscles of cockroaches and the tsetse fly); muscles that have an intermediate enzyme activity, i.e. 0.3-1.5mumoles/min./g. (e.g. locusts, cockchafers, moths, water-bugs); and muscles that have a high enzyme activity, i.e. >1.5mumoles/min./g. (e.g. bees, wasps, some blowflies). 5. The function of glycerol kinase in vertebrate and insect muscles that possess a low or intermediate activity is considered to be the removal of glycerol that is produced from lipolysis of triglyceride or diglyceride by the muscle. Therefore in these muscles the activity of glycerol kinase is related to the metabolism of fat, which is used to support sustained muscular activity. A possible regulatory role of glycerol kinase in the initiation of triglyceride or diglyceride lipolysis is discussed. 6. The function of glycerol kinase in the insect muscles that possess a high activity of the enzyme is considered to be related to the high rates of glycolysis that these muscles can perform. The oxidation of extramitochondrial NADH, and therefore the maintenance of glycolysis, is dependent on the functioning of the glycerophosphate cycle; if at any stage of flight (e.g. at the start) the rate of mitochondrial oxidation of l-3-glycerophosphate was less than the activity of the extramitochondrial glycerophosphate dehydrogenase, this compound would accumulate, inhibit the latter enzyme and inhibit glycolysis. It is suggested that such excessive accumulation of l-3-glycerophosphate is prevented by hydrolysis of this compound to glycerol; the latter would have to be removed from the muscle when the accumulation of l-3-glycerophosphate had stopped, and this would explain the presence of glycerol kinase in these muscles and its inhibition by l-3-glycerophosphate.     

The effects of starving and refeeding on the intra-acinar distribution pattern of alcohol-dehydrogenase activity in rat liver

Microquantitative determinations of ADH activity were carried out on the livers of male and female rats. The animals were either starved for 84 h, or starved and then refed with a carbohydrate-rich diet for 6 nights. When the enzyme activity is expressed in mumoles/min/g dry weight, fasting does not appear to alter liver ADH activity, while in starved and subsequently refed rats it is diminished by 20%. Microquantitative measurements of ADH activity in 50-150 ng lyophilized tissue samples, microdissected the whole way along the sinusoidal length, made the computer-aided plotting of intra-acinar distribution patterns possible. The results showed that, under the feeding conditions selected, only minor changes in the ADH activity profiles occur in the liver acinus. These are within the range of the standard deviations of the normal mean values. From these results it can be deduced that fasting and refeeding do not lead to specific inhibition or induction of liver ADH activity. - The decrease of ADH activity of total liver (mumol/min) per total body weight in starved rats is obviously the result of a loss of protein which affects the liver cells of all acinar zones almost equally.