Activation of the anti-cancer drug ifosphamide by rat liver microsomal P450 enzymes

The NADPH-dependent metabolism of ifosphamide catalyzed by rat liver microsomes was investigated in order to identify individual P450 enzymes that activate this anti-cancer drug and to ascertain their relationship to the P450 enzymes that activate the isomeric drug cyclophosphamide. Pretreatment of rats with phenobarbital or clofibrate increased by up to 8-fold the activation of both ifosphamide and cyclophosphamide catalyzed by isolated liver microsomes. Studies using P450 form-selective inhibitory antibodies demonstrated that constitutively expressed P450s belonging to subfamily 2C (forms 2C11/2C6) make significant contributions to the activation of both oxazaphosphorines in uninduced male rat liver microsomes, while the phenobarbital-inducible P450 2B1 was shown to be a major catalyst of these activations in phenobarbital-induced microsomes. Pretreatment of rats with dexamethasone increased liver microsomal activation of ifosphamide approximately 6-fold without a corresponding effect on cyclophosphamide activation rates. Ifosphamide activation catalyzed by dexamethasone-induced liver microsomes was minimally inhibited by anti-P450 2B or anti-P450 2C antibodies, but was selectively inhibited by anti-P450 3A antibodies. Selective inhibition of liver microsomal ifosphamide activation was also effected by the macrolide antibiotic triacetyloleandomycin, an inhibitor of several dexamethasone-inducible 3A P450s. These studies establish that a dexamethasone-inducible family 3A P450 can make an important contribution to rat liver microsomal ifosphamide activation, and suggest that dexamethasone pretreatment might provide a useful approach for modulation of ifosphamide metabolism in order to improve its therapeutic efficacy in cancer patients.     

Role of cholesterol in regulating apolipoprotein B secretion by the liver

The review examines the evidence that the supply of cholesterol available for incorporation into nascent lipoprotein particles exerts a regulatory influence on apolipoprotein (apo) B secretion by the liver. Support for this hypothesis comes both from in vitro experiments and from recent observations in normal subjects and patients with dyslipidemia associated with familial hypercholesterolemia, obesity, noninsulin dependent diabetes mellitus, growth hormone deficiency and cholesteryl ester storage disease. The findings do not negate a role for triglyceride synthesis in determining apoB secretion in very low density lipoprotein, but the inhibitory effects on the latter process of pharmacological blockade of cholesterol synthesis or esterification suggest that it is conditional upon an adequate supply of cholesteryl ester.     

Homologous and heterologous desensitisation of somatostatin-induced increases in intracellular Ca2+ and inositol 1,4,5-trisphosphate in CHO-K1 cells expressing human recombinant somatostatin sst5 receptors

The mechanisms responsible for somatostatin (SRIF)-induced increases in intracellular Ca2+ concentration ([Ca2+]i) and subsequent desensitisation were studied in CHO-K1 cells expressing human sst5 receptors (CHOsst5 cells). To study the nature of the desensitisation, interactions with uridine triphosphate (UTP) were examined. SRIF (pEC50 7.10) and UTP (pEC50) 5.14) caused concentration-dependent increases in [Ca2+]i but the SRIF maximum was about 40% of that to UTP. SRIF-, but not UTP-, induced increases in [Ca2+]i were transient and abolished by pertussis toxin. SRIF and UTP caused sustained increases in Ins(1,4,5)P3 but the SRIF maximum was about 30% of that to UTP. Removal of [Ca2+]e attenuated the SRIF-induced peak rise in [Ca2+]i but had no effect on the peak increases in Ins(1,4,5)P3. UTP-induced increases in [Ca2+]i and Ins(1,4,5)P3 were attenuated in the absence of [Ca2+]e. Following pre-exposure to SRIF (1 microM) or UTP (100 microM) for 5 min, subsequent SRIF responses were desensitised. Similar results were obtained in the absence of [Ca2+]e. Pre-exposure to SRIF had no effect on subsequent responses to UTP but in the absence of [Ca2+]e, responses to UTP were attenuated. The results suggest that SRIF but not UTP-induced increases in [Ca2+]i in CHOsst5 cells are mediated by pertussis toxin sensitive G proteins and are caused by an entry of extracellular Ca2+ and release from an Ins(1,4,5)P3 sensitive Ca2+ store. Homologous or heterologous desensitisation of agonist-induced increases in [Ca2+]i could be demonstrated in the presence or absence of extracellular Ca2+ respectively, and the latter appeared to involve depletion of a common intracellular Ca2+ store.     

The gill calcium transport cycle in rainbow trout is correlated with plasma levels of bioactive, not immunoreactive, stanniocalcin

The aims of this study were to determine the most appropriate duration for the measurement of the maximal accumulated O2 deficit (MAOD), which is analogous to the anaerobic capacity, to ascertain the effects of mass, fat free mass (FFM), leg volume (Vleg) and lower body volume (V1b) on anaerobic test performance, to examine the reproducibility for peak power output (Wpeak) or maximal anaerobic power using an air-braked cycle ergometer and to produce approximations for the percentages of aerobic and anaerobic metabolism during exercise of short duration but high intensity. A group of 12 endurance trained cyclists [mean age 25.1 (SD 4.6) years; mean body mass 73.43 (SD 7.12) kg; mean maximal oxygen consumption 5.12 (SD 0.35) l.min-1; mean body fat 12.5 (SD 4.1) %] accordingly performed four counterbalanced treatments of 45, 60, 75 and 90 s of maximal cycling on an air-braked ergometer. The mean O2 deficit of 3.52 l for the 45-s treatment was significantly less (P < 0.01) than those for the 60 (3.75 l), 75 (3.80 l) and 90-s (3.75 l) treatments. These data therefore indicate that in predominantly aerobically trained subjects the O2 deficit attains a plateau after 60 s of maximal cycling on an air-braked ergometer. Statistically significant interclass correlation coefficients (P < 0.05) between the anthropometric variables (mass, FFM, Vleg and Vlb) and Wpeak or maximal anaerobic power (0.624-0.748) and MAOD (ml) or anaerobic capacity (0.666-0.772) furthermore would suggest the relevance of taking into account muscle mass during anaerobic tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neocortical ectopias in BXSB mice: effects upon reference and working memory systems

BXSB mice have an approximately 40-60% incidence of neocortical ectopias in layer I of the prefrontal/motor cortex. Prior studies have found major behavioral differences between those with ectopias and their non-ectopic littermates. Some of these findings indicate that the two groups differ with respect to spatial reference and working memory. The purpose of this study was to measure reference and working memory in the same animals to test the hypothesis that the ectopics would have better reference memory but less effective working memory. The Lashley III maze has cul-de-sacs which must be eliminated, and T-choices where the animal has to decide whether to go left or right. Ectopic and non-ectopic mice were equally able to learn the maze and did not differ on cul-entry or T-choice errors. Then the maze was inverted and the animals were retested. Turning the maze upside down did not change the relative status of the blind alleys. Therefore, the reference memory knowledge from the prior week's training could be used to avoid entering the culs. However, inverting the maze caused a left-right mirror image reversal of the T-choices. Therefore, prior reference memory information would interfere with learning the new path through the maze, whereas working memory would enable the mouse to eliminate T-choice errors. Ectopic mice made less cul-entry errors and more T-choice errors than their non-ectopic littermates, as predicted.     

Differential c-fos expression in the nucleus of the solitary tract and spinal cord following noxious gastric distention in the rat

c-Fos has been used as a marker for activity in the spinal cord following noxious somatic or visceral stimulation. Although the viscera receive dual afferent innervation, distention of hollow organs (i.e. esophagus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract and lumbosacral spinal cord, which receive parasympathetic afferent input (vagus, pelvic nerves), than the thoracolumbar spinal cord, which receives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasympathetic afferent input to c-Fos expression in the nucleus of the solitary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric distention to 80 mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distension/80 induced c-Fos throughout the nucleus of the solitary tract, with the densest labeling observed within 300 microns of the rostral pole of the area postrema. This area was analysed quantitatively following several manipulations. Gastric distension/80 induced a mean of 724 c-Fos-immunoreactive nuclei per section. Following subdiaphragmatic vagotomy plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and vagotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/section), but spinal transection/80 induced 200 nuclei per section. Repetitive bolus injections of norepinephrine produced transient pressor responses mimicking the pressor response produced by gastric distension/80. This manipulation induced minimal c-Fos in the nucleus of the solitary tract and none in the spinal cord. It is concluded that noxious visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute to gastric distention-induced c-Fos in the nucleus of the solitary tract. The induction of c-Fos in the nucleus of the solitary tract is significantly greater than in the viscerotopic segments of the spinal cord, which is partially under tonic descending inhibition, but is not subject to modulation by vagal gastric afferents. Distention pressures produced by noxious gastric distention are much greater than those produced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physiological mechanisms of feeding and satiety. The large vagal nerve-mediated induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain.     

Thoracoscopic pleural tent

Lung volume reduction has been performed in patients with advanced emphysema to relieve dyspnea and improve exercise tolerance. Median sternotomy and video-assisted thoracoscopy have been proposed as equally adequate approaches; however, prolonged postoperative air leakage is the most prevalent complication in all series. For this reason, on the basis of the experience achieved with the median sternotomy approach, buttressing of the suture line with different materials and techniques for space reduction have been proposed. We describe a technique to create a pleural tent after thoracoscopic volume reduction. The thoracoscopic creation of a pleural tent is feasible and results in a duration of postoperative air leaks and hospital stays similar to that achieved with stapler line buttressing.     

Congenital chylothorax in siblings

We describe two cases of congenital chylothorax in siblings with important differences from previously described familial cases. Our findings support the likelihood of an autosomal recessive inheritance in some cases of this condition, rather than X-linked recessive inheritance, which has also been suggested. Autopsy findings from one of these cases and others previously described suggest that the pathophysiological mechanisms involved may be variable.