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Biomedical subjects

T R Hall

Publications and source records attributed to T R Hall.

At least 109 records · Page 6Linked to original sources
PubMed1982

Effects of monoaminergic and cholinergic drugs on release of follicle stimulating hormone from co-incubated pituitary glands and hypothalami.

1. Male rat pituitary glands and hypothalami were incubated with agonists and antagonists of various neurotransmitters, and release of follicle stimulating hormone (FSH) measured. 2. Noradrenaline and cholinergic agonists stimulated release of FSH, responses blocked by the alpha antagonist, phentolamine, and by atropine respectively. 3. Dopamine did not affect basal, but inhibited noradrenaline-stimulated, release of FSH. The dopamine antagonist, pimozide, stimulated release of FSH. 4. Neither serotonin nor its antagonist, methysergide, affected release of FSH. 5. None of these drugs acted directly on the pituitary gland, suggesting that they act by altering secretion of the gonadotrophin releasing hormone.

Animals↗
PubMed1982

Failure of exogenous serotonin to inhibit the release of 3H-serotonin induced by electrical field stimulation in superfused goldfish brain slices.

1. Goldfish brain slices preloaded with 3H-serotonin were superfused with a solution of Krebs-Ringer phosphate at 30 degrees C in the presence of 1 microM fluoxetine, a serotonin uptake blocker. 2. The effects of exogenous serotonin, Ca2+ absence and Ca2+ chelation on basal and electrically-evoked tritium overflow were investigated. 3. Exogenous 1 or 10 microM serotonin did not alter the stimulated tritium overflow, but this was reduced to 44% and to 31% of the control value when the superfusion was performed in Ca2+-free and in Ca2+-free-EGTA conditions. 4. Neither Ca2+ absence, Ca2+ chelation or 1 microM exogenous serotonin altered basal tritium efflux; however, the latter was significantly increased when the superfusion was performed in the presence of 10 microM serotonin.

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PubMed1982

Characteristics of monoamine oxidase activity in brain and other organs of the adult bullfrog, Rana catesbeiana.

1. Monoamine oxidase (MAO) activity was measured in brain, liver, kidney and intestine of the adult bullfrog by a fluorometric method. 2. All tissues contained both type A and type B MAO, on the basis of responses to specific inhibitors, but with different ratios in each tissue. 3. MAO activity was optimum at 30 degrees C. However, MAO type B showed greater activity changes related to incubation temperature than did type A. 4. The Michaelis constant (Km) of MAO also varied with temperature, with a nadir around 20 degrees C. The functional significance of this is not clear. 5. Arrhenius plots showed that the activation energy for MAO B was higher than for MAO A.

Animals↗
PubMed1982

Monoamine oxidase types A and B in the vertebrate brain.

1. Monoamine oxidase (MAO) activity was measured in brains of teleosts, amphibians a reptile, birds and mammals. Selective inhibitors were used to determine the relative proportion of MAO type A and MAO type B. 2. Brain homogenates of all tetrapods showed double sigmoid inhibition curves, indicating the presence of both forms of MAO. 3. Brain homogenates of all teleosts showed single sigmoid inhibition curves, with greater sensitivity to type A inhibitors. 4. These results indicate that tetrapod brains contain both type A and type B MAO activity, whereas teleost brains contain only a type A-like enzyme. 5. It is possible that the presence of two forms of MAO in brain may confer an advantage to a terrestrial lifestyle.

Animals↗
PubMed1982

Effects of inhibitors on monoamine oxidase activity in perch (Perca flavescens) brain in vitro.

1. Perch brain homogenates were incubated in vitro and monoamine oxidase (MAO) activity was determined fluorometrically, using a kynuramine substrate. 2. Clorgyline, harmaline and deprenyl inhibited MAO activity in a concentration-related manner, with single sigmoid inhibition curves, and the type A inhibitors harmaline and clorgyline were more effective than the type B inhibitor deprenyl. 3. Two types of inhibition were recognized in vitro; a fast-onsetting inhibition, similar to that produced by a reversible inhibitor, and a slow-onsetting inhibition, which is time- and concentration-dependent and presumably represents inactivation of the enzyme.

Animals↗
PubMed1982

Monoamine oxidase activity in several tissues of the goldfish. Carassius auratus.

1. Monoamine oxidase (MAO) was determined fluorometrically in male goldfish tissues, and the effects of specific inhibitors determined. 2. MAO activity in kidney greater than intestine greater than pancreas greater than brain approximately liver greater than testis. Apparent Michaelis constant (Km) was higher in the first three and lower in the last three tissues. 3. Specific MAO type A inhibitors (harmaline, clorgyline) were much more effective than a type B inhibitor (deprenyl) in reducing MAO activity. 4. Apparently goldfish tissues contain only a single type A-like MAO.

Animals↗
PubMed1982

Some characteristics of monoamine oxidase activity in tissues of the adult female grassfrog (Rana pipiens).

1. Monoamine oxidase (MAO) activity was measured fluorometrically in tissues of the grass-frog, Rana pipiens. 2. Incubation with specific inhibitors revealed the presence of two forms of MAO, type A and type B, in all tissues examined, though the ratios were different in each tissue. 3. Liver contained the greatest, and oviduct and skeletal muscle the lowest amounts of MAO activity, and brain also contained relatively high MAO levels. 4. The apparent Michaelis constant (Km) was similar in most tissues but was higher in pancreas, muscle and oviduct. Values of Km were lower than those reported for mammalian tissues.

Animals↗
PubMed1982

In vivo and in vitro effects of temperature on monoamine oxidase activity in brain and other tissues of the goldfish. Carassius auratus L.

1. The maximum velocity (Vmax) and apparent Michaelis constant (Km) of brain and liver monoamine oxidase (MAO) in goldfish were different in fish acclimated to 22 degrees C and to 7 degrees C ambient temperature. 2. In brain, Vmax and Km were dependent upon incubation temperature, but both parameters were lower in 7 degrees C, adapted fish over most of the incubation temperature range. 3. The values obtained for Km showed a plateau at incubation temperatures at and below 25 degrees C for warm water fish, and at and below 20 degrees C for cold water fish. The activation energy of brain MAO was lower in fish adapted to the colder water. 4. These results show that goldfish MAO displays changes in functional activity in response to a change in environmental temperature. Apparently the purpose of this adaptation is to compensate for a reduction in enzyme concentration.

Animals↗
PubMed1982

Neurotransmitter effects on release of prolactin and growth hormone in vitro from pituitary glands of the pigeon, Columba livia.

Single pigeon anterior pituitary glands were incubated with or without a hypothalamus in media containing various drugs. Release of prolactin and growth hormone was quantified by an electrophoretic-densitometric method. The hypothalamus stimulated release of both prolactin and growth hormone from the pituitary gland. Dopamine did not affect hormone release from pituitary glands incubated alone, but inhibited hypothalamus-stimulated release of prolactin and augmented hypothalamus-stimulated release of growth hormone in a dose-related manner. The effects of dopamine were reversed by its antagonist, pimozide. Serotonin stimulated release of prolactin and inhibited release of growth hormone from pituitary-hypothalamus co-incubations, and these effects were blocked by its antagonist, methysergide. Thyrotrophin releasing hormone (TRH) stimulated release of both hormones directly from pituitary glands incubated alone. Dopamine now inhibited TRH-stimulated release of prolactin, without affecting TRH-stimulated release of growth hormone. These results indicate that the neurotransmitters, dopamine and serotonin, affect the in-vitro release of factors from the hypothalamus which control the secretion of prolactin and growth hormone. In addition, dopamine may inhibit release of prolactin directly from the pituitary gland, but only when secretion of prolactin is high initially.

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