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Publisher Summary In vitro studies demonstrated that the enhanced synthesis of norepinephrine in peripheral nervous tissue, which occurs during nerve stimulation, is the result of increased activity of the enzyme tyrosine hydroxylase in the intact tissue. Because this effect can be prevented by the addition of norepinephrine to the medium that bathes the stimulated tissue, it was presumed that the activation of tyrosine hydroxylase is a consequence of reduced end-product feedback inhibition. Experiments suggest that the activation of tyrosine hydroxylase during nerve stimulation might be mediated by a different process, because the addition to the incubation medium of the synthetic pterin cofactor, 6,7-dimethyl-5,6,7,8-tetrahydropterin (Me2PtH4), which is able to antagonize competitively the inhibition of tyrosine hydroxylase by norepinephrine, does not eliminate the enhanced synthesis of norepinephrine associated with nerve stimulation of the isolated, intact vas deferens preparation. Results suggested that tyrosine hydroxylase is activated during nerve stimulation by a mechanism that is unrelated to an altered affinity for either norepinephrine or pterin cofactor.

This paper introduces an experimental technique and associated data analysis procedure for studying the shear dependent viscosity of oils containing polymers at shear rates up to 10 6 s −1 and temperatures up to 170°C, conditions which are typically experienced in operating engines. The experimental apparatus is a capillary viscometer with a controlled nitrogen gas pressure as the driving force and uses constant volume efflux bulbs to measure the oil flow rate. The main contribution of this work is the coupling of experimental calibration measurements and a theoretical analysis to develop a calibration procedure which can be used to extract accurate high-shear rate viscosity data from capillary viscometer measurements when the fluid viscosity is being influenced by temperature, pressure, and shear rate.

Publisher Summary This chapter focuses on studies on the mechanism of regulation of tyrosine hydroxylase (TH) activity during nerve stimulation. Most of the studies on the regulation of TH activity in adrenergic neurons have been performed with either mouse vas deferens preparations or the hypogastric nerve-vas deferens preparation of the guinea-pig. These tissues contain short adrenergic neurons and the entire cell body, axon and nerve terminals are present intact in the isolated preparations of these tissues. For this reason these tissues may represent a more appropriate model system of in vivo adrenergic neuronal metabolism and, in particular, they may provide a model for central adrenergic neurons, most of which are much shorter than the bulk of the neurons of the peripheral sympathetic nervous system. The properties of the enzymes of the mouse vas deferens preparation and the guinea-pig vas deferens preparation are very similar. Both enzymes have a higher affinity for tetrahydrobiopterin than for 6,7-dimethyltetrahydropterin. The guinea-pig vas deferens tissue is capable of converting both tyrosine and phenylalanine to catecholamines, although tyrosine is much the preferred substrate.