Interaction of H2-receptor antagonists, cimetidine and ranitidine with microsomal drug metabolizing and other systems in liver.

Cimetidine has been demonstrated to impair microsomal oxidative drug metabolizing and other enzyme systems in mouse liver. The inhibition is rapid, occurring after a single administration and also found to be dose-dependent. It is more significant after daily administration for 15 days. Enzyme inhibition by ranitidine, another H2-receptor antagonist was comparatively less at all the concentrations of the drug tested. An increased activity of alkaline phosphatase, glutamate-pyruvate and glutamate-oxaloacetate transaminase was observed in liver with cimetidine administration, whereas that of lactate and succinate dehydrogenase was inhibited only after administration of 2000 mg cimetidine per kg body weight. Except alkaline phosphatase other enzymes were unaffected after ranitidine administration. Analysis of lipid classes in liver showed that phospholipid, triglycerides and free fatty acid contents were significantly decreased in drug administration while cholesterol level showed very little or no change. Microsomal and soluble protein contents were significantly increased which probably indicate that the inhibition in the enzyme activity by histamine H2-receptor antagonists may be a lipid mediated process and not resulted from the reduced availability of the enzyme protein.     

An emerging role for Cullin-3 mediated ubiquitination in sleep and circadian rhythm

Although the neurophysiological correlates of sleep have been thoroughly described, genetic mechanisms that control sleep architecture, long surmised from ethological studies, family histories and clinical observations, have only been investigated during the past decade. Key contributions to the molecular understanding of sleep have come from studies in Drosophila, benefitting from a strong history of circadian rhythm research. For instance, a number of recent papers have highlighted the role of the E3 ubiquitin ligase Cullin-3 in the regulation of circadian rhythm and sleep. We propose that different Cullin-3 substrate adaptors may affect specific molecular pathways and diverse aspects of circadian rhythm and sleep. We have previously shown that mutations in BTBD9, a risk factor for Restless Legs Syndrome (RLS) encoding a Cullin-3 substrate adaptor, lead to reduced dopamine, increased locomotion and sleep fragmentation. Here, we propose that Cullin-3 acts together with BTBD9 to limit the accumulation of iron regulatory proteins in conditions of iron deficiency. Our model is consistent with clinical observations implicating iron homeostasis in the pathophysiology of RLS and predicts that lack of BTBD9 leads to misregulation of cellular iron storage, inactivating the critical biosynthetic enzyme Tyrosine Hydroxylase in dopaminergic neurons, with consequent phenotypic effects on sleep.     

Continuous culture of the postimplantation rat conceptus

A procedure for continuous culture of rat conceptuses during organogenesis with a number of advantages over existing methods has been established. In this method, rat conceptuses of pregnancy Day 10 (embryonic age 9.5 days; Witschi Stage 13) with embryos at pre- or early somite neurula stage were cultured for 96 h in roller bottles fitted with New Brunswick swivel caps. These caps have 5 inlets which permit continuous gassing of culture bottles and withdrawal of samples or supply of growth medium. The culture medium used in this study was immediately centrifuged, heat-inactivated fresh male rat serum. Continuous gassing of roller bottles with humidified gas mixtures of 5% CO2 and increasing O2 concentrations (5, 20, 40 and 95%), and balanced N2 provided optimal progressive conceptus development and differentiation. The average pO2 of the medium rose from 73.4 to 427.3 mm Hg, while the pCO2 and pH remained relatively stable. During the 96-h culture period, growth and differentiation of conceptuses were considerable, reaching Witschi Stage 27/28. Cultured embryos developed 48-52 somites with extensive differentiation of various organs: brain and sensory organs, heart and circulatory system, limb bud and hepatic prominence, and numerous internal visceral organs. Embryonic DNA and protein contents increased 100- to 200-fold from the initial values. Therefore, this improved procedure with periodic progressive increases in pO2 and stable low pCO2 and physiologic pH in the medium permits growth and differentiation of rat conceptuses in vitro over a prolonged period of time.