The oxidation of adrenaline and noradrenaline by the two forms of monoamine oxidase from human and rat brain.

The selective monoamine oxidase inhibitors clorgyline and (?)-deprenyl were used to study the distribution of monoamine oxidase-A and -B (MAO-A, MAO-B) activities towards (?)-noradrenaline and (+),(?)-adrenaline in homogenates from seven different regions of human brain. The activities towards 5-hydroxytryptamine and 2-phenethylamine, which are essentially specific substrates for the A- and B-forms, respectively, under the conditions used in this work, were also determined. Noradreanline and adrenaline were substrates for both forms of the enzyme in all regions studied. The total MAO activity was found to be highest in the hypothalamus and lowest in the cerebellar cortex. Use of the selective MAO inhibitors clorgyline and (?)-deprenyl also showed adrenaline and noradrenaline to be substrates for both forms of the enzyme in rat brain. In human cerebral cortex and rat brain the two forms were found to have similar K(m)-values and maximum velocities towards adrenaline. These values for the two forms were also found to be similar in human cerebral cortex when noradrenaline was used as the substrate. In contrast MAO-A showed a significantly lower K(m) and a higher maximum velocity towards noradrenaline in rat brain. These results suggest that the rat may not provide a close model of the human for studies on the effects of MAO inhibitors on brain noradrenaline metabolism.

Molecular size of the high-affinity glutamate-binding site on synaptic membranes from rat brain.

We have used radiation inactivation as a means of determining the molecular size of the high-affinity glutamate-binding site on rat brain synaptic membranes. The molecular size was 75,000 +/- 15,000 in the absence of glutamate and 263,000 +/- 34,000 in the presence of glutamate. These data may be interpreted as suggesting that the high-affinity glutamate-binding site is comprised of a number of subunits. The minimum sub-unit size detected by this method was 75,000 +/- 15,000.

Isolation of mycoplasma spp. from racing pigeons (Columba livia).

Live and dead racing pigeons (Columba livia) from five lofts in Norfolk and Suffolk were examined clinically and cultured for Mycoplasma spp. Both clinically healthy birds and those showing signs of mild respiratory disease were included. The oropharynx was the culture site for 130 live birds, the nasal sinuses and other tissues for 58 carcases. Mycoplasma columbinum, M. columborale and M. columbinasale were isolated from the oropharynges and nasal sinuses; M. columbinum and M. columbinasale from the brain and M. columbinum and M. columborale from lungs and air sacs. One or more of these three Mycoplasma spp. was isolated at necropsy from 28% of 58 pigeons. Only 11% of 37 pigeons reacted sero-logically by the metabolism inhibition test to M. columbinum and none to M. columborale. Twenty-five birds examined for M. gallisepticum antibody by the haemagglutination-inhibition test were negative. No sex or age predilection to infection with Mycoplasma was apparent. About 10% of pigeons in all five lofts showed clinical signs of the respiratory disease sometimes described as 'mycoplasmosis catarrh', but most dead birds from which Mycoplasma spp. were isolated also had concomitant infections of various kinds. Although suggestive, the results of these investigations provide no clear evidence that Mycoplasma spp. are aetiologically involved in natural respiratory disease of pigeons. No conclusive satisfactory treatment was found for the elimination of mycoplasmas.

Metabolism of monoamines in malignant hyperthermia-susceptible pigs.

A comparison of monoamine oxidase activities in the hypothalamus and striatum between malignant hyperthermia-susceptible (Pietrain) and malignant hyperthermia-resistant (Landrace/Large White) pigs showed no significant difference between the two breeds. The concentrations of noradrenaline, dopamine and their non-O-methylated metabolites did not reflect the low activities of monoamine oxidase type A differentially. The malignant hyperthermia-susceptible pigs had significantly greater concentrations of 3,4-dihydroxyphenyl glycol in the striatum, and of 3,4-dihydroxymandelic acid in the hypothalamus. Consequently, in the brain, low monoamine oxidase type A activity does not appear to be involved in susceptibility to malignant hyperthermia. In addition, monoamine oxidase activities in the heart, liver, kidney and intestinal mucosa and catechol-O-methyl transferase activities in the kidney were the same in the susceptible and resistant pigs.

Oxaloacetate- and acetoacetate-induced calcium efflux from mitochondria occurs by reversal of the uptake pathway.

1. Addition of oxaloacetate or acetoacetate to isolated rat liver mitochondria results in an efflux of Ca2+. Concomitant with this efflux is an immediate oxidation of endogenous nicotinamide nucleotides, a fall in the mitochondrial membrane potential and an increase in the rate of respiration. The primary effect in this sequence may be either (a) physiologically important stimulation of a Ca2+-efflux carrier, followed by Ca2+ re-uptake, a fall in membrane potential and increased respiration, or (b) physiologically unimportant damage to mitochondrial integrity, followed by a fall in membrane potential, increased respiration and Ca2+ efflux. 2. Ruthenium Red and EGTA will restore the increased respiratory rate to one approximating to the control rate of respiration. However, addition of lanthanide, at a concentration which inhibits the uptake but not the normal efflux of Ca2+, inhibits the rate of Ca2+ efflux induced by oxaloacetate or acetoacetate. Therefore the observed efflux is occurring by a reversal of the uptake pathway (uniporter) and thus follows the fall in membrane potential. 3. From these results we conclude that the decrease in membrane potential and increase in the rate of respiration seen during oxaloacetate- or acetoacetate-induced Ca2+ efflux cannot be accounted for by rapid Ca2+ cycling, but are due to damage to mitochondrial integrity.