PubMed · 8769903
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R Sahelian. 1996. Melatonin.. https://doi.org/10.1001/archfami.5.4.196b
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The Goodwin model is a negative feedback oscillator which describes rather closely the putative molecular mechanism of the circadian clock of Neurospora and Drosophila. An essential feature is that one or two clock proteins are synthesized and degraded in a rhythmic fashion. When protein synthesis in N. crassa (wild-type frq+and long-period mutant frq7) was inhibited by continuous incubation with increasing concentrations of cycloheximide (CHX) the period of the circadian sporulation rhythmicity is only slightly increased. The explanation of this effect may be seen in the inhibition of protein synthesis and protein degradation. In the model, increasing inhibition of both processes led to very similar results with respect to period length. That protein degradation is, in fact, inhibited by CHX is shown by determining protein degradation in N. crassa by means of pulse chase experiments. Phase response curves (PRCs) of the N. crassa sporulation rhythm toward CHX which were reported in the literature and investigated in this paper revealed significant differences between frq+and the long period mutants frq7and csp -1 frq7. These PRCs were also convincingly simulated by the model, if a transient inhibition of protein degradation by CHX is assumed as well as a lower constitutive degradation rate of FRQ-protein in the frq7/ csp -1 frq7mutants. The lower sensitivities of frq7and csp -1 frq7towards CHX may thus be explained by a lower degradation rate of clock protein FRQ7. The phase shifting by moderate temperature pulses (from 25 to 30 degrees C) can also be simulated by the Goodwin model and shows large phase advances at about CT 16-20 as observed in experiments. In case of higher temperature pulses (from 35 to 42 or 45 degrees C=heat shock) the phase position and form of the PRC changes as protein synthesis is increasingly inhibited. It is known from earlier experiments that heat shock not only inhibits the synthesis of many proteins but also inhibits protein degradation. Taking this into account, the Goodwin model also simulates the PRCs of high temperature (heat shock) pulses.
Niacin is the oldest and most versatile agent in use for the treatment of dyslipidemia. It has beneficial effects on low-density lipoprotein cholesterol; high-density lipoprotein cholesterol; the apolipoproteins B and A-I constituting these fractions; triglyceride; and lipoprotein(a). Together, these benefits lead to a diminished incidence of coronary artery disease among niacin users. The chief constraints against niacin use have been flushing, gastrointestinal discomfort, and metabolic effects including hepatotoxicity. Time-release niacin has been developed in part to limit flushing, and now a nighttime formulation (Niaspan) has been developed that assists in containing this untoward effect. In a pivotal metabolic study, bed-time administration of 1.5 g time-release niacin was shown to have the same beneficial effects as 1.5 g plain niacin in 3 divided doses and to be well tolerated. Previous studies suggest that bedtime niacin administration diminishes lipolysis and release of free fatty acids to the liver; this, in turn, leads to an abolition of the usual diurnal increase in plasma triglyceride, which may result in diminished formation and secretion of triglyceride in the very-low-density lipoprotein fraction.
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