Search PubMed⌕ Search

Biomedical subjects

B A Callingham

Publications and source records attributed to B A Callingham.

At least 55 records · Page 3Linked to original sources
PubMed1985

The interaction of hydralazine with a semicarbazide-sensitive amine oxidase in brown adipose tissue of the rat. Its use as a radioactive ligand for the enzyme.

Hydralazine is a potent irreversible inhibitor of the semicarbazide-sensitive amine oxidase (SSAO) found in brown fat. Initially it may act on the enzyme as a competitive inhibitor, but irreversible inhibition occurs rapidly in a concentration- and temperature-dependent manner. The presence of primary amines known to be substrates for the enzyme, but not of secondary amines, which are not metabolized by SSAO, diminishes this rate of inactivation, whereas removal of O2 is without effect. The kinetic pattern of inactivation of SSAO by hydralazine is consistent with an active-site-directed site-saturable binding followed by the development of an irreversible enzyme-inhibitor complex. [3H]Hydralazine, used as an affinity label for SSAO, shows saturable binding to brown-fat membranes. This binding is inhibited by other inhibitors of SSAO. The rate of binding to membrane pellets containing SSAO is not affected by substrates for the enzyme. However, if solubilized partially purified SSAO preparations are used instead, the rate of binding is lowered in the presence of the SSAO substrate benzylamine. 3H-labelled material solubilized from [3H]hydralazine-treated membrane pellets by Triton X-100 at that detergent/protein ratio which releases SSAO from membranes shows the same gel-filtration characteristics as SSAO and appears by lentil lectin-agarose affinity chromatography to contain similar carbohydrate moieties. 3H-labelled material, partially purified by gel filtration and affinity chromatography, produces predominantly a single band of radioactivity on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The position of this band corresponds to an Mr of about 94 000, almost exactly half the Mr already estimated for the functional unit of SSAO. Radiolabelled hydralazine may thus be used as a label for purified SSAO, but it is not specific enough to be suitable as a ligand in vivo.

Adipose Tissue, Brown↗
PubMed1984

Solubilization and some properties of a semicarbazide-sensitive amine oxidase in brown adipose tissue of the rat.

A semicarbazide-sensitive clorgyline-resistant amine oxidase (SSAO) was solubilized from membrane fractions of rat brown adipose tissue by the non-ionic detergent, Triton X-100. Alteration of ionic strength or addition of chelating agents alone failed to release the enzyme from its membrane. Lipid-depletion led to loss of enzyme activity and alteration of substrate affinity. Over 80% of the activity of the solubilized enzyme was found in gel filtration fractions corresponding to an Mr of between 160 000 and 180 000. The glycoprotein nature of SSAO was established from affinity chromatography with either immobilized concanavalin A or Lens culinaris lectin. Elution of over 50% SSAO activity from the lentil lectin was achieved with 0.25M-alpha-methyl D-mannoside to give 80-90-fold purification of the enzyme. Irradiation inactivation gave a value for Mr of around 183 000 for both soluble and membrane-bound SSAO. Substrate affinity and inhibitor sensitivity of the enzyme were unaltered by solubilization. The copper-chelating agent, diethyldithiocarbamate, did not affect the enzyme, shedding doubt on the suggestion that SSAO is a copper-requiring enzyme. The significance of these findings in relation to the nature of SSAO and to its disposition within the cell membrane is discussed.

Adipose Tissue, Brown↗
PubMed1984

Effects of natriuretic fractions of human urine on the isolated anococcygeus muscle of the rat.

Freeze-dried samples of human urine were reconstituted and chromatographed on Sephadex G-25 columns. Fractions possessing natriuretic activity were eluted after the salts. Application of aliquots of these fractions, after further freeze drying and reconstitution, to the isolated anococcygeus muscle of the rat produced dose-dependent contractions of this smooth muscle. The potency of these samples in causing contractions was positively correlated with their ability to cause natriuresis in water-loaded conscious rats. Use of selective antagonists of possible agonistic agents showed that the ability of the samples to contract smooth muscle was not due to catecholamines, acetylcholine, 5-hydroxytryptamine, prostaglandin E and angiotensin II.

Animals↗
PubMed1983

Inhibitory actions of hydralazine upon monoamine oxidizing enzymes in the rat.

The inhibition by hydralazine of the clorgyline-resistant amine oxidase (CRAO) and monoamine oxidase (MAO) activities in various rat tissues has been studied. Hydralazine was a potent, time-dependent inhibitor of rat heart CRAO activity in vitro. The inhibition was not reversed by dialysis for 18 hr at 4 degrees, and only partially reversed by dialysis at 37 degrees. Dialysis at 4 degrees in the presence of pyridoxal phosphate (10(-4) M) also did not reverse the inhibition. Ex vivo inhibition of CRAO was found in heart and aorta homogenates in a dose-dependent manner after administration of hydralazine (1-40 mg/kg i.p.) to rats. In contrast, MAO-A activity was unaffected or, in some cases, significantly increased in these tissue homogenates from drug-treated animals. However, in vitro inhibition by hydralazine of both MAO-A and B activities of rat liver mitochondrial fractions was found, and these effects were fully reversible by dialysis for 18 hr at 4 degrees. Inhibition of MAO-A was competitive (Ki of 2.5 X 10(-6) M), while inhibition of MAO-B showed complex mixed non-competitive kinetics. These results indicate that hydralazine possesses different inhibitory properties towards the various amine oxidases in rat tissues, and these actions are discussed in relation to the clinical use of the drug as an anti-hypertensive agent.

Animals↗
PubMed1982

Altered hypothalamic and sympathetic responses to hypoglycaemia in familial obesity.

The responses of pituitary hormones and venous catecholamine concentrations to insulin hypoglycaemia were studied in 12 formerly obese women with familial obesity who had lost about 30 kg by dieting. These responses were compared with those of 10 lean women. The post-obese women showed an exaggerated response in cortisol output but an impaired release of growth hormone. 6 of the post-obese women had in addition both an impairment in prolactin output and a failure to increase their venous noradrenaline concentrations during hypoglycaemia. These results suggest that an alteration in hypothalamic control, displayed by limited responses in pituitary hormone secretion and by reduced sympathetic activity, may be an innate feature of people with familial obesity

Body Weight↗
PubMed1982

In vitro and in vivo inhibition by benserazide of clorgyline-resistant amine oxidases in rat cardiovascular tissues.

Bernserazide (D,L-serine 2-[2,3,4-trihydroxybenzyl]-hydrazide) as been shown to inhibit the clorgyline-resistant amine oxidase (CRAO) activities which metabolize benzylamine in homogenates of rat aorta, heart and brown adipose tissue. In vitro studies showed a concentration- and time-dependent inhibition of CRAO in heart and aorta which was reversed by dialysis for 18hr. At high concentrations (10(-4)-10(-3)M) benserazide appeared to increase enzyme activity towards and occasionally above control value. These increases became more prominent after long periods of preincubation (especially in the presence of saturating benzylamine concentrations) and remained after dialysis of those homogenates preincubated with benserazide. The administration of benserazide for one or seven days in daily doses of 5-150 mg/kg also inhibited CRAO activity in vivo in a dose-dependent manner, with greater inhibition after seven days treatment. Reversal of inhibition, by dialysis of tissue homogenates from benserazide-treated rats, was much slower than was found with homogenates incubated in vitro with the drug. After benserazide administration to rats, MAO-A activity towards 5-hydroxytryptamine was generally not inhibited, and in fact was significantly increased in some cases. The administration of L-DOPA (250 mg/kg) together with benserazide (40 mg/kg) resulted in a similar degree of CRAO inhibition in aorta and heart to that seen after benserazide alone. These findings are discussed with regard to the use of these drugs in the therapy of Parkinson's Disease, although the paucity of information about the physiological function of CRAO makes the significance of its inhibition by benserazide unclear.

Amine Oxidase (Copper-Containing)↗
PubMed1982

Plasma catecholamines and autonomic responsiveness in obesity.

The autonomic responsiveness of lean women to standing, passsive vertical tilting, noradrenaline infusion and the valsalva manoeuvre has been compared with that of obese women and a group of formerly obese women (post-obese). Upon standing, the lean and obese groups had comparable cardiovascular responses with similar rises in plasma noradrenaline. With passive 85 degrees head-up tilting at an ambient temperature of 26 degrees C the obese and post-obese subjects had a greater rise in plasma noradrenaline than the lean group who were less able to withstand the test. Noradrenaline infusions (at 26 degrees C) in the lean and post-obese subjects led to similar increases in plasma noradrenaline, systolic and diastolic pressures and plasma free fatty acids but the post-obese showed a greater bradycardia. The response to the valsalva manoeuvre was normal in lean and obese patients and was unaltered after a reduced energy intake in the obese. On energy restriction for two weeks 10 obese subjects showed a fall in pulse rate, in systolic and diastolic pressures and in plasma noradrenaline while the subjects remained supine. On standing there was less of a rise in plasma noradrenaline than when energy intake was high. The response in noradrenaline was restored to that seen on high energy intakes by giving L-dopa. Seasonal changes in venous noradrenaline concentrations were apparent in obese and post-obese patients but not in lean subjects. These differences may relate to altered responses to environmental temperature or to an altered food intake in the two obese groups. There appears to be no generalised in the autonomic system in obese women either before or after weight loss but the process of slimming does lead to a reduction in plasma noradrenaline levels.

Autonomic Nervous System↗
PubMed1981

Postprandial thermogenesis in obesity.

1. The thermogenic response and changes in plasma substrates and hormones were tested after a liquid meal in lean, obese and formerly obese women. 2. Subjects with a family history of obesity tested either while obese or after slimming to a normal weight had a thermogenic response, which was only half that of the lean group. 3. The immediate response in plasma glucose and insulin was greater in the lean subjects, but the sustained changes in circulating substrates did not differ in the three groups. Thyroidal hormone concentrations did not alter postprandially: venous noradrenaline levels rose in the obese groups only. 4. The differences in postprandial thermogenesis at rest would reduce the energy requirements of subjects with familial obesity, but they still had a metabolic rate estimated to be nearly 1MJ (240 kcal)/day in excess of the lean group so additional thermogenic defects must exist for familial obesity to be explained solely on a metabolic basis.

Adult↗
PubMed1981

Caffeine: its effect on catecholamines and metabolism in lean and obese humans.

1. The metabolic response of lean and obese women to caffeine was studied to see if caffeine could be used to demonstrate the subnormal thermogenesis in obesity previously shown after standard meals or intravenous infusions of noradrenaline. 2. The rise in resting metabolic rate with caffeine was similar in the lean and obese groups and beta-adrenoceptor blockade did not reduce the increment in metabolic rate in either group. These responses did not, therefore, correspond with the other subnormal thermogenic responses of the constitutionally obese. 3. In a post-obese group, i.e. previously obese women who were now of normal weight, there was a reduced response of the resting metabolic rate to caffeine. 4. Monitoring plasma substrate concentrations showed that the change in oxygen uptake corresponded to changes in plasma free fatty acids, so that in adults the metabolic effects of caffeine seem to be mediated by increases in adipocyte lipolysis. This effect seems to be mainly independent of the adrenergic system.

Adult↗
PubMed1981

The effect of DSP-4 (N-[2-chloroethyl]-N-ethyl-2-bromobenzylamine) on monoamine oxidase activities in tissues of the rat.

The in vitro inhibition of monoamine oxidase (MAO) in rat liver, and of the clorgyline-resistant amine oxidase (CRAO) in rat heart and aorta, by DSP-4 (N-[2-chloroethyl]-N-ethyl-2-bromobenzylamine) has been studied. Inhibition of each enzyme activity was independent of prolonged preincubation, was reversed by dialysis, and also Ackermann-Potter plots were consistent with reversible inhibition. Simple linear competitive inhibition of MAO-A and MAO-B was observed, with Ki values of 6 x 10(-6) and 8 x 10(-5) M, respectively. CRAO was inhibited in a mixed, non-competitive manner (Ki of 3.2 x 10(-5) and 7.8 x 10(-6) M in heart and aorta, respectively) which conformed to a kinetic model in which the binding of DSP-4 to CRAO increased the affinity of substrate binding, but prevented product formation. The possible significance of these results for the in vivo actions of the drug is discussed.

Amines↗