The Hyperglycaemic Activity of Some Catecholamines and the Effect of α- and β-Adrenergic Blocking Compounds in the Mouse

In order to classify the receptors involved in the hyperglycaemic response to catecholamines in the mouse, the relative potency of noradrenaline, adrenaline and isoprenaline in the induction of hyperglycaemia has been tested by giving increasing doses from 10 μg/kg to 1 mg/kg of one of the amines intraperitoneally. Following catecholamine administration the maximal concentration of glucose in the blood occurred between 10 and 30 min. and amounted to about 300 mg%. The relative potency was: adrenaline > noradrenaline while isoprenaline was inactive. The antagonistic effect on adrenaline induced hyperglycaemia of the α-adrenergic blocking compounds: phenoxybenzamine HCl (dibenzyline®) and phentolamine (regitin®) and the β-adrenergic blocking compounds: 1-(isopropylamino)-3-(o-phenoxyphenoxy)-2-propanol (Ph QA 33) and propranolol were tested by giving 1 and 10 mg/kg intraperitoneally 30 min. before the administration of adrenaline. Only phentolamine at the highest dose level was capable of preventing the hyperglycaemic response to adrenaline. Phenoxybenzamine, Ph QA 33 and propranolol proved to be inactive. It is concluded that the mechanism of adrenaline induced hyperglycaemia in mice cannot be explained simply by an α- and/or β-receptor activation.     

Comparison between uptake2 and rOCT1: effects of catecholamines, metanephrines and corticosterone

Active and specialized transmembrane transport systems are responsible for the functional inactivation of catecholamines. Uptake₂, the classical extraneuronal uptake system, and rOCT1, a recently cloned organic cation transporter, share a number of properties. The present study was undertaken to investigate putative differences between these two transporters that might clarify their relative physiological roles. Uptake of [³H]MPP⁺ ([³H]1-methyl-4-phenylpyridi-nium) by Caki-1 cells (to study uptake₂) and by primary cultured rat hepatocytes (to study rOCT1) was kinetically and pharmacologically characterized. In both cell types, [³H]MPP⁺ was avidly taken up and accumulated. All compounds tested (catecholamines, metanephrines and corticosterone) inhibited [³H]MPP⁺ uptake, albeit with different potencies. In Caki-1 cells, the ranking order of inhibitory potency was: (–)isoprenaline > (–)adrenaline >> (–)noradrenaline > dopamine. Metanephrine and normetanephrine were equipotent. Corticosterone had an IC₅₀ of 102 nM. In cultured hepatocytes, the ranking order of inhibitory potency was: (–)isoprenaline > dopamine > (–)adrenaline >> (–)noradrenaline. Metanephrine was about seven times more potent than normetanephrine. Corticosterone had an IC₅₀ of 72 μM, being about 700-fold less potent in inhibiting rOCT1 than uptake₂. The results showed that uptake₂ and rOCT1 can be clearly distinguished on a functional basis. On the one hand, uptake₂ prefers adrenaline among the endogenous catecholamines, whereas rOCT1 has similar affinity for adrenaline and dopamine. On the other hand, corticosterone and normetanephrine are significantly more potent in inhibiting uptake₂ than rOCT1. The results are compatible with a possible physiological role of corticosteroids in the modulation of adrenaline effects in tissues equipped with uptake₂, without significant interference with the hepatic and renal excretion of catecholamines. Received: 2 October 1998 / Accepted: 23 December 1998     

Temperature dependence of catecholamine depletion by reserpine in the heat of the toad (Bufo marinus)

1. The catecholamines in toad ventricle were adrenaline (90%) and noradrenaline (10%); there was no dopamine.

2. Phenoxybenzamine and tyramine stimulated the isolated heart and reduced the catecholamine content.

3. Reserpine treatment of toads kept at 20° C did not affect the adrenaline but reduced the noradrenaline content of the ventricle.

4. At 37° C, reserpine caused depletion of both adrenaline and noradrenaline, and the stimulant actions of phenoxybenzamine and tyramine were lost.

     

Protection of cell proteins against free-radical attack by nootropic drugs: scavenger effect of pyritinol confirmed by electron spin resonance spectroscopy

The potency of nootropic drugs to protect cell proteins and lipids against free radical attack was studied. In an in vitro system, generating hydroxyl radicals by a Fenton-type reaction, the soluble proteins (bovine serum albumin and cytosol protein from brain) were quickly insolubilized and precipitated. Pyritinol (and tamitinol) exhibited the best protection against insolubilization of protein while centrophenoxine (meclophenoxate) and its dimethylaminoethanol moiety were less effective, piracetam (and oxiracetam) being without effect. The lipid peroxidation induced by free radicals from cyclic redox reactions of iron-ascorbate was not influenced by pyritinol, indicating the selectivity of its scavenger action. The efficient scavenging of hydroxyl radicals by pyritinol was confirmed by electron spin resonance spectroscopy measurement of hydroxyl radicals entrapped by spin trap. Millimolar concentrations of pyritinol competitively decreased the formation of spin adducts. The results suggest that the protective effect of pyritinol against free-radical induced derangement of cell proteins may be an important part of its antirheumatic, as well as nootropic, action.     

Plasma protein binding of catecholamines,prazosin and propranolol in diabetes mellitus

Summary In the present study equilibrium dialysis has been used to determine the degree of protein binding of the catecholamines adrenaline and noradrenalin and the adrenergic receptor blockers, prazosin and propranolol in diabetics. The binding of the catecholamines in plasma from Type I and II diabetic patients was not significantly different from that of healthy subjects. The ratio of the bound and free catecholamine concentrations was correlated with the level of albumin (HSA). Significantly reduced protein binding of prazosin was observed in Type I and II diabetic subjects compared to healthy volunteers. The binding of propranolol was significantly reduced in Type I patients. The ratios between the bound and unbound concentrations of prazosin and propranolol were significantly correlated with the levels of a,-acid glycoprotein (AAG). The results suggest that non-enzymatic glycosylation of plasma proteins may increase the unbound fraction of the adrenergic blockers prazosin and propranolol.     

The effects of acute and chronic administration of morphine on the turnover of brain and adrenal catecholamines in rats

Brain and adrenal catecholamine turnover in adult female rats treated with morphine was investigated. A different time course response of brain and adrenal catecholamines to -methyl-p-tyrosine methylester (AMT) administration in normal rats was observed; the catecholamine turnover rate in adrenal glands appeared to be much slower than in the brain. Acute morphine increased the turnover of brain dopamine and noradrenaline as well as of adrenal catecholamines, whereas chronic morphine treatment induced a decrease in the turnover of brain noradrenaline. Withdrawal induced by nalorphine produced an increase in the utilization of brain noradrenaline and adrenal catecholamines; this effect could be related to the withdrawal stress situation induced by the opiate antagonist. Although the mechanism of morphine action may implicate other neurotransmitters besides catecholamines, our results contribute to evidence that brain and adrenal catecholamines could be involved in the mechanism of morphine tolerance and/or dependence.     

Potentiation by β-Adrenoceptor Blocking Agents of the Inhibitory Effect of Adrenaline on Carrageenin-Induced Rat Paw Oedema

Abstract: The β-adrenoceptor blocking agents (±)-practolol, (±)-propranolol, (—)-propranolol and (±)-sotalol were found to reduce the adrenaline induced inhibition of carrageenin-induced rat paw oedema during the first hour of development and then potentiate adrenaline for at least 3 hours. Experiments carried out with (+)-propranolol indicated that both effects depended on the levoisomers of the substances and accordingly on some kind of β-blockade. It has previously been suggested that normal stores of endogenous catecholamines might be essential for the development of carrageenin-induced rat paw oedema (ARNTZEN & BRISEID 1973). Under the experimental conditions used in the present work (—)-propranolol did not counteract the increase in the catecholamine content of the spleen caused by adrenaline injection, more than (+)-propranolol. It is suggested that the marked potentiation of the oedema inhibition caused by adrenaline might be due to a combined effect of increased adrenaline stores and β-adrenoceptor blockade.     

Long term treatment of moderate hypertension with penbutolol (hoe 893d). II. Effect on the response of plasma catecholamines and plasma renin activity to insulin-induced hypoglycemia

Summary The effect of insulin-induced hypoglycemia on the blood levels of catecholamines and renin activity has been studied in five patients with moderate hypertension before and after treatment for 3 – 8 months with penbutolol (PEN) 20 – 30 mg twice daily. Penbutolol caused no change in fasting blood glucose level. Insulin 0.1 IU per kg body weight i.v. reduced blood glucose concentration by approximately 50 per cent after 30 – 45 min, both before and during treatment with penbutolol. Hypoglycemia prior to medication was accompanied by a marked increase in the production of adrenaline and a minor increase of noradrenaline in all five patients. During treatment the response of adrenaline to hypoglycemia was reduced in four patients and the data was inconclusive in one. Basal renin activity was rather low in three patients, within the normal range in one and relatively high in one. Before penbutolol the hypoglycemia-induced increase in catecholamine production caused no change in plasma renin activity in the three patients with low basal levels, whereas a marked increase was observed in the other two. During medication plasma renin activity remained unchanged on induction of hypoglycemia regardless of the catecholamine response. Despite the marked increase in plasma adrenaline following insulin-induced hypoglycemia, no statistically significant increase in pulse rate was recorded.     

Effects of theophylline and propranolol on acetylcholine-induced release of adrenal medullary catecholamines

The effect of theophylline and propranolol on acetylcholine-induced catecholamine release was studied in isolated bovine adrenals perfused in vitro. The catecholamine release induced by half maximum dose of acetylcholine, 10^?4 M, was potentiated about 140 per cent by the presence of 1 mM theophylline in the perfusion medium. Theophylline enhanced the release of adrenaline but had little effect on the release of noradrenaline. The augmentary effect of theophylline on the adrenaline release was partially reduced by 10^?7 M atropine and by 10^?6 M propranolol. Propranolol by itself at a concentration of 10^?7 M, at which it had no membrane-stabilizing effect, reduced the acetylcholine induced secretion about 20 per cent. Propranolol had a greater inhibitory effect on the release of adrenaline than on noradrenaline. It is concluded that theophylline affected the release of adrenaline by mobilization of intracellular calcium stores and by preventing breakdown of cyclic AMP synthesized in response to stimulation of a β-adrenergic receptor located in the adrenalinestoring cells. A possible action of theophylline on cyclic GMP synthesized in response to stimulation of the muscarinic receptor is discussed.     

In vivo release of catecholamines in the locus coeruleus

To investigate the release of endogenous dopamine, noradrenaline and adrenaline in the locus coeruleus, this brain area was superfused with artificial cerebrospinal fluid (CSF) through push-pull cannulae and the release of catecholamines was determined in the superfusate radioenzymatically.Collection of superfusates in time periods of 10 min revealed that release rates of the three catecholamines fluctuated, thus pointing to the existence of ultradian rhythms with following mean periods (minutes per cycle): noradrenaline 52±4, dopamine 37±2, adrenaline 36±2. The rhythm frequency of noradrenaline was significantly lower than the frequencies of dopamine and adrenaline.When the locus coeruleus was superfused with neuroactive drugs, superfusates were collected in time periods of 3 min. Superfusion with tetrodotoxin (1 mol 1^–1) for 12 min elicited a prompt and sustained decrease (–70%) in the release rates of dopamine and adrenaline. The release rate of noradrenaline was also reduced, although to a lesser extent (–40%). Superfusion with veratridine (50 mol 1^–1) led to an immediate and very pronounced enhancement in the release rates of dopamine, noradrenaline and adrenaline. The veratridine-induced increase in catecholamine outflow was decreased strongly by simultaneous superfusion with tetrodotoxin.The findings suggest that the release of endogenous catecholamines in the locus coeruleus fluctuates according to ultradian rhythms. Changes in the release on superfusion with veratridine and tetrodotoxin demonstrate the neuronal origin of the three catecholamines. The observed differences in the release characteristics between noradrenaline on the one hand and dopamine and adrenaline on the other might indicate that noradrenaline is partly released from somatodendritic sites of the noradrenergic cell bodies in the locus coeruleus.This work was supported by the Fonds zur Förderung der wissenschaftlichen Forschung Correspondence to: N. Singewald at the above address     

Release of 2-Thiobarbituric Acid Reactive Products from Glutamate,Deoxyuridine or DNA during Autoxidation of Dopamine in the Presence of Copper Ions

Abstract: Cytotoxic effects of catecholamine are thought to be caused by the formation of 0-semiquinone and superoxide radicals. Dopamine in the presence of copper ions releases aldehydic products from glutamate, deoxyuridine or DNA capablae of reacting with 2-thiobarbituric acid (TBA). The formation of TBA reactive products (TBAR) was concentration dependent of both dopamine and copper ion. Complete inhibition of formation of TBAR from glutamate, deoxyuridine or DNA was observed in the presence of thiourea and catalase. Mannitol, albumin and superoxide dismutase offered substantial protection. The present data indicate that dopamine in the presence of copper ions can lead to the formation of reactive hydroxyl radicals which can release aldehydic products from glutamate, deoxyuridine or DNA capable of reacting with TBA.     

The action of volatile anaesthetics on stimulus-secretion coupling in bovine adrenal chromaffin cells.

1. The action of four volatile anaesthetics, ethrane, halothane, isoflurane and methoxyflurane on stimulus-secretion coupling has been studied in isolated bovine adrenal medullary cells. All four agents inhibited the secretion of adrenaline and noradrenaline evoked by 500 microM carbachol at concentrations within the anaesthetic range. Total catecholamine secretion induced by stimulation with 77 mM potassium was also inhibited but at higher concentrations. All four agents inhibited the 45Ca influx evoked by stimulation with 500 microM carbachol and the 45Ca influx in response to K+-depolarization. 2. When total catecholamine secretion in response to potassium or carbachol was modulated by varying extracellular calcium or by adding halothane or methoxyflurane to the incubation medium, the amount of catecholamine secretion for a given Ca2+ entry was the same. 3. The action of methoxyflurane on the relationship between intracellular free Ca and exocytosis was examined using electropermeabilised cells, which were suspended in solutions containing a range of concentrations of ionised calcium between 10(-8) and 10(-4)M. The anaesthetic had no effect on the activation of exocytosis by intracellular free calcium. 4. Halothane and methoxyflurane inhibited the carbachol-induced secretion of catecholamines in a non-competitive manner. 5. Halothane and methoxyflurane inhibited the increase in 22Na influx evoked by carbachol. For halothane and methoxyflurane this inhibition of Na influx appears to be sufficient to account for the inhibition of the evoked catecholamine secretion. 6. We conclude that the volatile anaesthetics ethrane, halothane, isoflurane and methoxyflurane inhibit the secretion of adrenaline and noradrenaline induced by carbachol at concentrations that lie within the range encountered during general anaesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Catecholamine release during anaphylactic shock in guinea pigs

Summary In the acute anaphylactic as well as histamine shock of guinea pigs an increase of the serum catecholamines was found. Mepyramine doses high enough to abolish the anaphylactic bronchospasm did not prevent the catecholamine release, but reduced it. When the anaphylactic bronchoconstriction was inhibited by mepyramine, mean serum adrenaline concentrations 20 min after antigen were as high as in acute anaphylactic shock without administration of antihistamines; 120 min after antigen no increases was seen. In animals which died in the so-called protracted anaphylactic shock the serum adrenaline concentrations were the highest found at all. The results are discussed in view of the role of catecholamines in anaphylaxis.Supported by the Deutsche Forschungsgemeinschaft.     

Protective effect of boldine on dopamine-induced membrane permeability transition in brain mitochondria and viability loss in PC12 cells

Boldine ([S]-2,9-dihydroxy-1,10-dimethoxyaporphine) has been shown to exert antioxidant and anti-inflammatory effects. The present study elucidated the protective effect of boldine on catecholamine-induced membrane permeability transition in brain mitochondria and viability loss in PC12 cells. Dopamine (200 microM) and 6-hydroxydopamine (6-OHDA, 100 microM) attenuated Ca(2+) and succinate-induced mitochondrial swelling and membrane potential formation. Boldine (10-100 microM) and 10 microg/mL of superoxide dismutase (SOD) or catalase reduced the effect of catecholamine oxidation on brain mitochondria. Boldine, SOD, and catalase decreased catecholamine-induced mitochondrial cytochrome c release. Antioxidant enzymes attenuated the depressant effect of catecholamines on mitochondrial electron flow, whereas boldine did not reduce it. Boldine inhibited the catecholamine-induced decrease in thioredoxin reductase activity and the increase in thiol oxidation in mitochondria. It also showed a scavenging action on hydrogen peroxide and hydroxyl radicals and decreased the formation of melanin from dopamine. Boldine and antioxidant enzymes decreased the dopamine-induced cell death, including apoptosis, in PC12 cells. The results suggest that boldine may attenuate the catecholamine oxidation-induced brain mitochondrial dysfunction and decrease the dopamine-induced death of PC12 cells through a scavenging action on reactive oxygen species and inhibition of melanin formation and thiol oxidation.     

Rilmenidine (S 3341) and the sympathoadrenal system: adrenoreceptors,plasma and adrenal catecholamines in dogs

1 The effects of rilmenidine, a new alpha₂-adrenoreceptor agonist with antihypertensive properties, were investigated on plasma catecholamines, blood cell adrenoreceptors and adrenal medullary function. 2 In conscious sino-aortic denervated (SAD) dogs, rilmenidine (1 mg kg^?1 orally for 2 weeks) significantly reduced both blood pressure and heart rate when compared with placebo treatment. The drug decreased plasma noradrenaline and adrenaline levels and corrected the decrease in leucocyte beta-adrenoreceptors observed in placebo-treated SAD dogs. There was no change in platelet alpha₂-adrenoreceptors. 3 In anaesthetized normotensive dogs, rilmenidine (0.1 and 0.3 mg kg^?1 i.v.) induced a dose-dependent decrease in both cardiovascular parameters (blood pressure and heart rate) and catecholamine release from the adrenal medulla. 4 The present study shows that rilmenidine decreases sympathetic tone mainly by an action on the adrenal medulla. In addition, its ability to lower blood pressure in SAD dogs, i.e. a model of hypertension in which high sympathetic tone is present, indicates that rilmenidine may also depress other parts of the sympathetic nervous system.     

Central interleukin-10 attenuated lipopolysaccharide-induced changes in core temperature and hypothalamic glutamate, hydroxyl radicals and prostaglandin-E(2)

It has been documented that intravenous lipopolysaccharide (LPS) in rabbits causes fever accompanied by increased levels of extracellular glutamate, hydroxyl radicals, and prostaglandin E₂ (PGE₂) in the hypothalamus and circulating tumor necrosis factor-alpha (TNF-α). This investigation was to determine whether central interleukin-10 (IL-10) exerted its antipyresis by reducing changes in circulating TNF-α and extracellular glutamate, hydroxyl radicals and PGE₂ in the hypothalamus. The microdialysis probes were stereotaxically and chronically implanted into the preoptic anterior hypothalamus of rabbit brain for determinating extracellular glutamate, hydroxyl radicals, and PGE₂ in situ. It was found that systemically injected LPS (2 μg/kg, intravenously) increased the levels of core temperature, and extracellular glutamate, hydroxyl radicals, and PGE₂ in the hypothalamus accompanied by increased plasma levels of TNF-α. Pretreatment with IL-10 (10–100 ng, intracerebroventricularly) 1 h before intravenous LPS significantly reduced the LPS-induced changes in extracellular glutamate, hydroxyl radicals, and PGE₂ in the hypothalamus and fever, but not the increased levels of TNF-α in rabbits. These findings suggested that directly injected IL-10 into the lateral cerebral ventricle 1 h before intravenous LPS exerted its antipyresis by inhibiting the changes in extracellular glutamate, hydroxyl radicals and PGE₂ in the hypothalamus during LPS fever in rabbits.     

On the mechanisms of phenothiazine-induced mitochondrial permeability transition: Thiol oxidation, strict Ca dependence, and cyt c release

Phenothiazines (PTZ) are drugs widely used in the treatment of schizophrenia. Trifluoperazine, a piperazinic PTZ derivative, has been described as inhibitor of the mitochondrial permeability transition (MPT). We reported previously the antioxidant activity of thioridazine at relatively low concentrations associated to the inhibition of the MPT (Brit. J. Pharmacol., 2002;136:136-142). In this study, it was investigated the induction of MPT by PTZ derivatives at concentrations higher than 10 μM focusing on the molecular mechanism involved. PTZ promoted a dose-response mitochondrial swelling accompanied by mitochondrial transmembrane potential dissipation and calcium release, being thioridazine the most potent derivative. PTZ-induced MPT was partially inhibited by CsA or Mg²⁺ and completely abolished by the abstraction of calcium. The oxidation of reduced thiol group of mitochondrial membrane proteins by PTZ was upstream the PTP opening and it was not sufficient to promote the opening of PTP that only occurred when calcium was present in the mitochondrial matrix. EPR experiments using DMPO as spin trapping excluded the participation of reactive oxygen species on the PTZ-induced MPT. Since PTZ give rise to cation radicals chemically by the action of peroxidases and cyanide inhibited the PTZ-induced swelling, we propose that PTZ bury in the inner mitochondrial membrane and the chemically generated PTZ cation radicals modify specific thiol groups that in the presence of Ca²⁺ result in MPT associated to cytochrome c release. These findings contribute for the understanding of mechanisms of MPT induction and may have implications for the cell death induced by PTZ.     

Effect of treatment by clonidine on the synthesis of catecholamines in the heart, submaxillary and adrenal glands in the rat

The synthesis of catecholamines has been studied in the heart, sub-maxillary glands and adrenal of the rat by intravenous injection of [³H]tyrosine and evaluation, 30 min later, of the newly formed [³H]catecholamines. The synthesis rates of catecholamines have been estimated by calculation of the ratio: amount of [³H]catecholamine/ specific activity of [³H]tyrosine in the tissue. Clonidine (50 $\text{μg}\text{kg}$ i.p.) was administered 1 hr before the injection of [3H]tyrosine. Such treatment did not change significantly the endogenous levels of tyrosine or catecholamines in the organs studied. In clonidine treated rats, the synthesis rate of noradrenaline was reduced by 38 per cent in the heart and by 40 per cent in the sub-maxillary glands. In the adrenal, a 45 per cent reduction of the dopamine synthesis and a 60 per cent reduction of the adrenaline + noradrenaline synthesis were observed after clonidine treatment. The mechanisms by which clonidine reduces catecholamines synthesis are discussed.     

Ionophore mediated catecholamine release from chromaffin granules: Comparison of X-537 A and X-14547 A effects

The carboxylic ionophore X-14547 A induces release of catecholamines from bovine chromaffin granules. This release is rapid and depends upon the ratio of ionophore to granule protein. When compared to X-537 A (lasolacid) which is known to mediate catecholamine release from the same preparation, X-14547 A is about 10 times more potent on a molar basis. Catecholamine release by X-14547 A is not accompanied by release of other components (ATP, protein or dopamine β-hydroxylase) of the granule matrix and therefore is not caused by lysis of the granule as previously proposed for X-537 A. X-14547 A also differs from X-537 A by its lack of specificity, both adrenaline and noradrenaline being equally released by this ionophore. These differences might reflect different release mechanisms. The absence of noradrenaline transport across a chloroform phase by X-14547 A suggests that its action might not involve direct translocation of the catecholamine cation across the granule membrane.     

Release of 2-thiobarbituric acid reactive products from glutamate, deoxyuridine or DNA during autoxidation of dopamine in the presence of copper ions.

Cytotoxic effects of catecholamine are thought to be caused by the formation of 0-semiquinone and superoxide radicals. Dopamine in the presence of copper ions releases aldehydic products from glutamate, deoxyuridine or DNA capable of reacting with 2-thiobarbituric acid (TBA). The formation of TBA reactive products (TBAR) was concentration dependent of both dopamine and copper ion. Complete inhibition of formation of TBAR from glutamate, deoxyuridine or DNA was observed in the presence of thiourea and catalase. Mannitol, albumin and superoxide dismutase offered substantial protection. The present data indicate that dopamine in the presence of copper ions can lead to the formation of reactive hydroxyl radicals which can release aldehydic products from glutamate, deoxyuridine or DNA capable of reacting with TBA.