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Biomedical subjects

D A BROWN

Publications and source records attributed to D A BROWN.

12 recordsLinked to original sources
PubMed1964

WATER PERMEABILITY OF THE FETAL ERYTHROCYTE.

The rate constant for the diffusion of tritiated water across the fetal erythrocyte membrane has been measured as 0.056 +/- SD 0.013 msec.(-1) The equivalent pore radius calculated by the method of Paganelli and Solomon for the fetal erythrocyte is 3.9 A. The effect of a normal distribution of channel sizes within the erythrocyte membrane is discussed and the theoretical effect of variation of the distribution on the diffusion to bulk flow ratio is evaluated. Since membrane channels of 4 A characterize a variety of membranes, it is suggested that permeability differences may be associated with slight variations in the statistical distribution of the channel sizes within the membrane. The limits of +/-0.5 A standard deviation that qualitative experiments place on the expected variability of channel size will not account for the lower rate of water diffusion in the fetal cell.

Diffusion↗
PubMed1964

OBSERVATIONS ON THE MODE OF ACTION OF SOME CENTRAL DEPRESSANT DRUGS ON TRANSMISSION THROUGH THE CAT SUPERIOR CERVICAL GANGLION.

Methylpentynol, paraldehyde, amylobarbitone and procainamide blocked transmission through the cat superior cervical ganglion, and antagonized the ganglion-stimulating actions of acetylcholine and carbachol injected intra-arterially to the ganglion. Comparison with the effects of tetraethylammonium indicated that the impaired response to acetylcholine could not wholly account for the failure of transmission, which suggested that an impaired release of transmitter substance was a contributory factor. Methylpentynol, paraldehyde and procainamide also blocked the ganglion-stimulating action of potassium chloride. In contrast, amylobarbitone and pentobarbitone did not block the stimulating action of potassium chloride, but antagonized specifically the actions of acetylcholine and carbachol. The anti-acetylcholine activities of the two barbiturate drugs at this site accord with their relative ganglion-blocking activities. It is concluded that the ganglion-blocking action of methylpentynol, paraldehyde and procainamide arises from a nonspecific depression of both presynaptic and postsynaptic elements in the ganglion, but that barbiturate compounds act more specifically on the acetylcholine receptor.

Acetylcholine↗
PubMed1962

An eserine-like action of chloral hydrate.

The intra-arterial injection of chloral hydrate potentiated the transmission of nerve impulses through the cat superior cervical ganglion, antagonized the ganglionblocking action of hexamethonium, and greatly enhanced the ganglion-stimulant action of acetylcholine. Effects on the ganglion-stimulant actions of carbachol, nicotine, tetramethylammonium and potassium chloride were slight or absent. Chloral hydrate itself usually had no direct stimulant action. The neuromuscular-blocking action of tubocurarine on the isolated rat diaphragm preparation was completely and rapidly reversed by chloral hydrate. This reversal was prevented by previoustreatment of the muscle with neostigmine. Chloral hydrate potentiated the actions of acetylcholine and nicotine on the isolated rabbit duodenum, and, in concentrations exceeding 1 mg/ml., produced a spasm which was abolished by hyoscine but not by mepyramine. It was concluded that these eserine-like effects were manifestations of an anticholinesterase action of chloral hydrate. Neither chloralose nor trichlorethanol showed evidence of this property.

Acetylcholine↗
PubMed1959

Some pharmacological properties of the alpha-toxin of staphylococcus pyogenes.

The alpha-toxin of Staphylococcus pyogenes produced a slowly developing contracture of isolated preparations of rabbit jejunum and of guinea-pig ileum which persisted after thorough washing and left the gut unresponsive to further doses of alpha-toxin or of acetylcholine. After incubation with antitoxin, the alpha-toxin no longer produced a contracture. Antitoxin only prevented the alpha-toxin response if added to the bath fluid before but not after the alpha-toxin. Certain drugs reduced the alpha-toxin contracture when added to the bath fluid before or after the alpha-toxin, but the contracture reappeared on washing. Papaverine abolished the contracture and pethidine was only slightly less active. Mepyramine, amyl nitrite, caffeine, aminophylline, adrenaline and ephedrine partly reduced the contracture. Hexamethonium, cocaine, tubocurarine and gallamine had no effect. The effect of atropine was only small. The gut-stimulant activity/haemolytic unit of two alpha-toxin samples differed greatly; this difference did not appear to be due to activity of impurities. The implications of these observations are discussed.

Acetylcholine↗