Catecholamine uptake, accumulation, and release in acute porphyria

Hypertension and tachycardia are well known features of acute porphyria and have been shown to be related to increased circulating catecholamines. The mechanism by which circulating catecholamines are increased was studied using the isolated perfused rat heart and human platelets as a model of adrenergic neuronal function. It was found that neither delta-aminolevulinate (ALA) nor porphobilinogen (PBG) blocked uptake or caused release in the isolated perfused rat heart. Platelets from six patients with acute prophyria, three in remission and three latent, with matching normal controls were studied with regard to their uptake of [(3)H]norepinephrine in the presence of ALA or PBG. It was found that ALA and PBG significantly reduced uptake and accumulation of [(3)H]-norepinephrine in patients with acute porphyria; however, no similar reduction in uptake and accumulation was observed in the platelets of normal controls. Therefore, it appears that there is a latent defect in the catecholamine uptake and (or) accumulation of platelets of patients with acute prophyria which only manifests itself in the presence of ALA or PBG. If platelet uptake serves as a model of adrenergic neuron uptake, this suggests that elevated circulating catecholamine levels during acute attacks of acute porphyria are caused at least partially by blockade of re-uptake into the sympathetic neurons.     

The friction of polymers under hydrostatic pressure

This paper reports data on the effect of hydrostatic gas pressure on the coefficient of sliding friction of several polymers. In general increasing the pressure causes a reduction in the observed coefficient of friction. Two simple friction models are used in an attempt to explain the data. Neither is completely satisfactory. However there appears to be a good empirical correlation between the observed friction and the low strain value of the dynamic loss modulus.     

Synthesis and mutagenicity of a series of nitrated carbazoles and hydroxycarbazoles

The effects of a component of an Oriental medicine and green tea plants utilized for the traditional beverage on the proliferation of mesangial cells were determined in terms of the 3H-thymidine uptake. When magnesium lithospermate B was added to the medium of the mesangial cell culture, it suppressed the proliferation of mesangial cells at a concentration of 50 micrograms/ml. The 3H-thymidine uptake began to display an inhibitory action from the 6.25 micrograms/ml (-)-epicatechin 3-O-gallate, (-)-epigallocatechin 3-O-gallate or green tea tannin mixture, showing a more conspicuous inhibition at 50 micrograms/ml that did the magnesium lithospermate B at the corresponding concentration. In particular, (-)-epigallocatechin 3-O-gallate, the predominant component of the green tea tannin mixture, exerted an inhibitory effect at a relatively low concentration.     

High power performance of asymmetric Fabry-Perot MQW modulators

We have demonstrated experimentally that a normally-on surface normal asymmetric Fabry-Perot modulator can still operate at high optical powers (equivalent to intensities of >20 kW/cm²). We have identified two distinct operating regimes: one thermally assisted regime where the maximum reflection change increases at high powers and peak values of 75% are achieved, and one nonthermal regime where reflection changes approaching 55% are achieved albeit at higher applied voltages