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M A Barrand

Publications and source records attributed to M A Barrand.

At least 37 records · Page 2Linked to original sources
PubMed1992

Differential recognition of mdr1a and mdr1b gene products in multidrug resistant mouse tumour cell lines by different monoclonal antibodies.

An immunocytochemical method was used to test the reactivity of the anti-P-glycoprotein antibodies, C219, MRK 16, JSB-1 and 265/F4 against multidrug resistant (MDR) variants derived from the human small cell lung carcinoma line, NCI-H69, the mouse fibrosarcoma line, RIF-1 and the mouse mammary tumour cell line, EMT6. C219 produced positive staining in MDR variants of both human and mouse tumour cell lines. MRK 16 and JSB-1 however recognised P-glycoprotein only in the human MDR cell lines and not in the mouse MDR cells. 265/F4 appeared the most selective of the monoclonal antibodies used, producing positive staining of MDR variants derived from the RIF-1 line, but not of MDR variants derived from the EMT6 line. Total RNA was prepared from the mouse cell lines and, following reverse transcription, cDNA sequences were amplified by the polymerase chain reaction with primers specific for either the murine mdr1a or the mdr1b genes. From this it was possible to show that only the mdr1a gene is overexpressed in the resistant EMT6 lines that do not stain with 265/F4 whereas both mdr1a and mdr1b are overexpressed in the positively staining resistant fibrosarcoma line, RIF/1.0. Low level expression of mdr1b was detected in the sensitive parent RIF-1 cells and increasing levels of expression correlated with increasing resistance in the lines, RIF/0.1, 0.2, 0.4 and 1.0. Expression of mdr1a was found only in the more resistant fibrosarcoma cell lines. It seems that 265/F4 recognises only the mdr1b P-glycoprotein. Western blotting confirmed that this antibody detects a 170 kDa protein only in membranes derived from the resistant fibrosarcoma cells. 265/F4 may thus be used to distinguish between the murine P-glycoprotein isoforms so revealing differences between tumour cell lines in cellular localisation and in the time of appearance of mdr1a and mdr1b P-glycoprotein following drug exposure.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

Evidence for regulatory control of iron uptake from ferric maltol across the small intestine of the rat.

1. 59Fe absorption from the novel iron compound, ferric maltol, was studied in rats pretreated twice daily for two weeks with non-radioactive ferric maltol in oral doses containing 7 mg elemental iron. Tissue accumulation of 59Fe 2 h after administration of radioactive ferric maltol into the stomach was significantly lower in iron pretreated animals than in saline-treated controls. 2. 59Fe uptake from ferric maltol into isolated fragments of ileum and of duodenum was of similar magnitude in control animals but in iron-treated animals, duodenal uptake was significantly lower than that of the ileum. 3. Absorption of 59Fe was also investigated in anaesthetized rats after intestinal perfusion with saline (controls) or with 5 mM chenodeoxycholate to render the intestines more permeable. 4. Changes in permeability of the small intestine were monitored by estimating the amount of [14C]-mannitol absorbed and fluid secreted with reference to the non-absorbable [3H]-inulin in the perfusate effluents. 5. Despite the increased permeability of the intestines after bile salt treatment, there was little difference from control in the tissue accumulation of 59Fe from ferric maltol 2 h after intraduodenal administration. However 59Fe absorption from ferrous sulphate was significantly increased after bile salt treatment. 6. Gel filtration profiles of plasma made 5 and 60 min after intraduodenal administration of [59Fe]-ferric [3H]-maltol demonstrated that metal and ligand do not enter the circulation as the complex even when intestinal permeability is increased. 7. Uptake of 59Fe was investigated in isolated fragments of rat small intestine after saline or bile salt perfusion. Although 59Fe uptake from ferric maltol was somewhat greater in the bile salt-treated intestinal fragments, saturable kinetics were still observed. By contrast, "Fe uptake from ferrous sulphate: ascorbate was greatly enhanced by bile salt pretreatment and a very large diffusional component of uptake was evident. 8. It is concluded that iron uptake from ferric maltol may well be under endogenous regulatory control even in damaged intestines, so it is unlikely that this novel iron compound can bring about iron overload when administered orally.

Animals↗
PubMed1991

Dissociation of a ferric maltol complex and its subsequent metabolism during absorption across the small intestine of the rat.

1. The fate and disposition of [59Fe]-ferric [3H]-maltol after intravenous administration were investigated in anaesthetized rats. Immediate dissociation of ferric iron from maltol took place in the circulation even with high doses of ferric maltol (containing 1 mg elemental iron). In plasma samples withdrawn within 1 min of injection and subjected to gel filtration, 59Fe eluted with the high molecular weight proteins whilst the tritium was associated with low molecular weight material. 2. The rates of elimination of 59Fe and of tritium from the plasma and their ultimate fate were very different. The half life for 59Fe in the plasma was around 70 min and 59Fe appeared mainly in the bone marrow and liver. There was an initial rapid exit of tritium from the plasma with a half life of around 12 min. This was followed either by a plateau or by a rise in tritium levels, involving entry of maltol metabolites into the circulation. These metabolites could be recovered in the urine. 3. Entry of 59Fe and of tritium into the blood plasma after intraduodenal administration of [59Fe]-ferric [3H]-maltol was also very different. At low doses of ferric maltol (containing 100 micrograms elemental iron), the tritium appeared in the plasma in highest amounts within seconds and then decreased whilst there was a slow rise in 59Fe levels. At higher doses of ferric maltol (containing 7 mg elemental iron), levels of 59Fe in the plasma were highest at 5 min and then fell whereas tritium levels rose steadily. Mucosal processing of 59Fe prevented further entry of iron at high dose into the circulation. 4. Initial rates of uptake of [3H]-maltol into isolatcd intestinal fragments were measured over a range of concentrations and revealed that maltol alone could diffuse freely into the tissues whereas maltol complexed to iron showed saturable uptake kinetics similar to those seen with the iron itself. 5. After intestinal uptake, 59Fe and tritium were associated with different subcellular fractions, maltol itself being metabolized to the glucuronide conjugate within the intestinal mucosa. 6. It is concluded that dissociation of metal and ligand takes place before entry into the intestinal mucosa. Iron is then taken up on the endogenous carrier and processed in the normal way whilst maltol enters by diffusion, its rate of entry being limited by the degree of dissociation. It is subsequently metabolized by conjugation and eliminated rapidly from the body in the urine.

Animals↗
PubMed1990

Lipid peroxidation effects of a novel iron compound, ferric maltol. A comparison with ferrous sulphate.

Lipid peroxidation effects of ferric maltol have been compared with those of ferrous sulphate both in lecithin liposomes and in brush border and mitochondrial membranes prepared from rat small intestine. Ferrous sulphate, but not ferric maltol, initiated peroxidation in liposomes as measured by conjugated diene production, but, with 500 microM ascorbic acid present, both caused intense peroxidation which was inhibitable by N2, tocopherol, maltol and ferrous chelators, but not by OH or H2O2 scavengers. The rate of peroxidation increased with ferrous sulphate concentration up to 100 microM but was independent of ferric maltol concentration between 5-500 microM. Material eluted from rat small intestine contained a reducing factor, similar in size to ascorbic acid, capable of generating ferrous ions from ferric maltol and initiating peroxidation. Peroxidation in mitochondrial membranes appeared unaffected by addition of iron whilst that in brush border membranes was detectable only in the presence of iron. At iron concentrations of 100 microM and above ferric maltol produced less liposomal peroxidation than ferrous sulphate. Maltol itself may delay recycling of Fe3+ to Fe2+. Thus ferric maltol could provide a less toxic alternative to ferrous salts in the oral treatment of iron-deficiency.

Animals↗
PubMed1990

The importance of reductive mechanisms for intestinal uptake of iron from ferric maltol and ferric nitrilotriacetic acid (NTA).

Intestinal iron absorption is thought to proceed with iron mainly in the ferrous form, yet the novel iron complex, ferric maltol is an effective oral preparation. Although possessing a high oil: water partition coefficient, ferric maltol does not diffuse across the intestine but donates its iron to the endogenous uptake system. Reduction of the ferric iron in the gut lumen appears to precede iron uptake both from ferric maltol and from ferric nitrilotriacetic acid (NTA) which is a non-penetrating iron ligand. Uptake of radiolabelled iron (59Fe) into isolated fragments of rat small intestine was inhibited by the ferrous chelator, bathophenanthroline sulphonate (BPS) and enhanced at low concentrations by the reducing agent ascorbic acid. Spectrophotometric evidence was obtained that ferrous ions are generated from these ferric complexes in the presence of ascorbic acid and other reducing agents. The rate of ferrous ion formation was independent of ferric maltol concentration at low ascorbic acid levels and decreased with increasing ferric maltol concentration at higher levels of ascorbate. Maltol has a high affinity for ferric ions and may delay reduction at higher concentrations. By contrast, a higher rate of ferrous ion generation was seen with ferric NTA and this increased with iron ligand concentration. Washings from the intestinal lumen also brought about ferrous ion formation from these ferric ligands. Gel filtration revealed these reducing factors to be of low molecular weight. The washings, however, interfered with 59Fe uptake into the isolated fragments, but when reducing fractions only from the filtered washings were used, enhanced iron uptake was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1989

In-vivo effects of (E)-2-(3',4'-dimethoxyphenyl)-3-fluoroallylamine (MDL 72145) on amine oxidase activities in the rat. Selective inhibition of semicarbazide-sensitive amine oxidase in vascular and brown adipose tissues.

One hour after MDL 72145 ((E)-2-(3',4'-dimethoxyphenyl)-3-fluoroallylamine) (2.5 mg kg-1) was given by intraperitoneal injection, the semicarbazide-sensitive amine oxidase (SSAO) activity of rat aorta and brown adipose tissue measured in-vitro was reduced by more than 95% of its control value, whereas the monoamine oxidase (MAO-A) activity remained virtually unaffected. The action of this drug on amine oxidases in the liver at this dose was less selective. The in-vitro effect of MDL 72145 on the soluble enzyme diamine oxidase from rat intestine was 100 fold less potent than that of semicarbazide but about equipotent with semicarbazide on sheep plasma amine oxidase. Overall MDL 72145 was selectively more active against membrane bound SSAO enzymes that deaminate primary monoamines. Although MDL 72145 does inhibit MAO-B activity these results suggest that this compound may be used to study the effect of selective inhibition of SSAO activity on the pharmacological responses of appropriate preparations in-vitro.

Adipose Tissue, Brown↗
PubMed1988

Characteristics of iron(III) uptake by isolated fragments of rat small intestine in the presence of the hydroxypyrones, maltol and ethyl maltol.

Accumulation of radioactive iron (59Fe) into isolated fragments of rat small intestine in the presence of two hydroxypyrones, maltol and ethyl maltol, was compared with that in the presence of another chelator of iron(III), nitrilotriacetic acid (NTA). The characteristics of uptake were similar with all three ligands. Between 10(-6) and 10(-4) M, iron uptake showed saturable kinetics. The uptake was partially inhibited by metabolic inhibitors. Above 10(-4) M a non-saturable uptake, unaffected by metabolic inhibitors became evident in the presence of the pyrones. The distribution of 59Fe after uptake was determined by gel filtration. At low iron concentrations (10(-6) M), 35-40% of absorbed iron was associated with proteins of molecular weights similar to those of ferritin and transferrin. At high concentrations (10(-3) M), the majority of 59Fe was found in a low molecular weight fraction. At each concentration, a small amount of 59Fe was bound to a membrane fraction. 5% Polyethylene glycol, which reduces glycocalyx viscosity enhanced uptake at low iron concentrations (10(-6) M) but did not affect the non-saturable diffusion seen at higher concentrations (10(-3) M). The iron(II) chelator, bathophenanthroline sulphonate (10(-3) M), decreased uptake at low iron concentrations but did not affect the non-saturable uptake. It is suggested that conversion of iron(III) to iron(II) may take place at the mucosal cell surface before uptake via the saturable system. Apparent Km values for iron uptake via the saturable system were higher in the presence of maltol and ethyl maltol than in the presence of NTA, presumably since the iron binds more avidly to the hydroxypyrones and so is less readily donated. Excess ligand, either pyrone or NTA, reduced the rate at which 59Fe was donated to the uptake system. The Vmax value for uptake from the pyrones was greater than from NTA. It is concluded that maltol, ethyl maltol and NTA can hold iron(III) in solution and donate it to an endogenous uptake system. But, the hydroxypyrones may be more suitable ligands for the oral administration of iron since, when complexed with iron, they lack the toxic effects associated with iron(III)-NTA and with iron(II) preparations.

Animals↗
PubMed1987

Some properties of semicarbazide-sensitive amine oxidases.

The semicarbazide-sensitive amine oxidases (SSAOs) comprise a substantial but diffuse group of enzymes separable from classical monoamine oxidase in several respects. Differences in cofactor requirement, molecular weight and subcellular distribution are crucial for such a separation. Differential sensitivity to enzyme inhibitors, characterized by resistance to inhibition by acetylenic MAO inhibitors coupled with sensitivity to semicarbazide and some related compounds are characteristic of these enzymes. SSAO enzymes have been found in the plasma of man, ox, pig and horse, for example as well as in the solid tissues of many species. Extensive studies have so far failed to produce any conclusive evidence to indicate what the precise functions of many of these enzymes may be. Indeed in most cases there is no clear idea as to the nature of the preferred physiological substrate, although many amines with pharmacological activity have been shown to be substrates. The actions of these amines may be potentiated following inhibition of SSAO, but as yet little is known whether or not these actions can be important in vivo. An attempt is made in this review to bring together some of the evidence to see if there are indications for future endeavours.

Amine Oxidase (Copper-Containing)↗
PubMed1987

Effects of the pyrones, maltol and ethyl maltol, on iron absorption from the rat small intestine.

The pyrones, 3-hydroxy-2-methyl-4-pyrone (maltol) and 3-hydroxy-2-ethyl-4-pyrone (ethyl maltol) chelate iron with a high affinity and selectivity. The resulting 1:3 (metal-ligand) complexes, being neutral, are able to partition readily across cell membranes and thus may facilitate iron transport across the intestinal wall. Absorption of radioactive iron (59Fe) in the presence of these pyrones was investigated in male rats 1, 2, 4 and 6 h after intraduodenal administration of a 7 micrograms dose and compared with that of 59Fe given as the sulphate, gluconate, fumarate or complexed to EDTA. Total body absorption and distribution were calculated from the 59Fe content of various tissue samples. With all the iron preparations used, blood levels of 59Fe were highest 1 h after injection whilst the 59Fe content at the major site of deposition, i.e. the bone marrow, increased up to 6 h. No 59Fe was found in the urine. Total body absorption of 59Fe was significantly higher from the pyrones than from the other four preparations. Over the dose range 0.7-700 micrograms, the proportion of 59Fe absorbed from both iron maltol and iron sulphate decreased with increasing dose. Enhanced 59Fe uptake from maltol was evident at 0.7-70 micrograms but not at 700 micrograms suggesting that use of these pyrones will not result in iron overload. Absorption of 59Fe given into the stomach was slower in onset but was sustained longer presumably via a steady delivery of iron to the duodenum from the gastric reservoir.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
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

Amine oxidase activities in brown adipose tissue of the rat: identification of semicarbazide-sensitive (clorgyline-resistant) activity at the fat cell membrane.

Amine oxidase activity, previously described in homogenates of brown adipose tissue of the rat, has now been investigated in preparations of isolated fat cells. It was found that the specific activities of both monoamine oxidase A (MAO) and of the semicarbazide-sensitive clorgyline-resistant amine oxidase (SSAO) were higher in isolated fat cells than in the original whole tissue. Brown adipocytes therefore represent a major source of both these enzymes. In plasma membranes prepared from these isolated brown fat cells by borate extraction there was a similar enrichment of activity of SSAO and of the plasma membrane marker enzyme, phosphodiesterase I. However in preparations of cell membranes made by binding the cells to polycation-coated beads, enrichment of phosphodiesterase I activity was much greater than that of SSAO. It is suggested that the disposition of the enzyme within the cell membrane may account for the discrepancy in these results, i.e. the sidedness of the membrane may be important. Histochemical visualization of enzyme activity in whole tissue at the ultrastructural level was undertaken. Positive staining of mitochondria was achieved in the presence of the MAO substrate, tryptamine. Staining around the edges of the brown fat cells was observed with the SSAO substrates, tyramine and benzylamine. Staining was largely absent when substrate was omitted or after pretreatment with the irreversible SSAO inhibitor, hydralazine and the slowly reversible inhibitor, semicarbazide. It is not definitely proven that this staining represents sites of enzyme activity but the results are consistent with evidence from other studies indicating that SSAO in brown adipose tissue of the rat may be found predominantly at the fat cell surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗
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

Changes in plasma noradrenaline and adrenaline associated with central and peripheral thermal stimuli in the pig.

1. The role of catecholamines in thermogenesis has been investigated in trained young pigs in various situations which increases heat production. Plasma noradrenaline and adrenaline concentrations were estimated by radioenzymic assay of samples taken from an indwelling jugular catheter to prevent disturbance and stress. 2. During 3 hr at ambient temperatures of between 25 and -5 degrees C, there was curvilinear increase in noradrenaline concentrations as temperature decreased, but adrenaline did not change. After 1-3 days at 5 or 1 degrees C, the concentrations of both amines were similar to those found at thermal neutrality. 3. Cooling the cervical region of the spinal cord resulted in a large increase in plasma noradrenaline whereas local cooling of the hypothalamus was associated with a small increase in the hormone. When cooling either region of the central nervous system, plasma adrenaline concentrations did not change. 4. During exposure to 45 degrees C, rectal temperature increased to 43 degrees C. Concentrations of catecholamines remained low or declined until the rectal temperature was above 41.5 degrees C when the concentrations increased in most animals. 5. Induced physical activity lasting 40 min was associated with an increase in both noradrenaline and adrenaline concentrations. 6. Blood samples from the inferior vena cava, just cephalad to the outlet of the adrenal veins, had much higher concentrations of noradrenaline during cold exposure than those taken simultaneously from the jugular vein. Therefore, at least part of the increase in noradrenaline concentrations reported above may have been due to release of the hormone from the adrenal medulla. 7. It is concluded that during short-term exposure to cold, and in exercise, there is a rapid catecholamine response, producing concentrations in the blood which could be high enough to stimulate thermogenesis. During longer-term cold exposure, catecholamine output is low and other factors must be of greater importance in maintaining thermogenic processes. Further, catecholamine output may result from thermal stimuli not only from outside the external surface of the animal but also from within the central nervous system.

Animals↗