Synthesis, Binding, Release, and Metabolism of Norepinephrine in Normal and Transplanted Dog Hearts

Vasostatin-1 Stops Structural Remodeling and Improves Calcium Handling via the eNOS-NO-PKG Pathway in Rat Hearts Subjected to Chronic β-Adrenergic Receptor Activation

PURPOSE

Chronically elevated catecholamine levels activate cardiac β-adrenergic receptors, which play a vital role in the pathogenesis of heart failure. Evidence suggests that vasostatin-1 (VS-1) exerts anti-adrenergic effects on isolated and perfused hearts in vitro. Whether VS-1 ameliorates hypertrophy/remodeling by inducing the chronic activation of β-adrenergic receptors is unknown. The present study aims to test the efficacy of using VS-1 to treat the advanced hypertrophy/remodeling that result from chronic β-adrenergic receptor activation and to determine the cellular and molecular mechanisms that underlie this response.

METHODS AND RESULT

Rats were subjected to infusion with either isoprenaline (ISO, 5 mg/kg/d), ISO plus VS-1 (30 mg/kg/d) or placebo for 2 weeks. VS-1 suppressed chamber dilation, myocyte hypertrophy and fibrosis and improved in vivo heart function in the rats subjected to ISO infusion. VS-1 increased phosphorylated nitric oxide synthase levels and induced the activation of protein kinase G. VS-1 also deactivated multiple hypertrophy signaling pathways that were triggered by the chronic activation of β-adrenergic receptors, such as the phosphoinositide-3 kinase (PI3K)/Akt and Ca²⁺/calmodulin-dependent kinase (CaMK-II) pathways. Myocytes isolated from ISO + VS-1 hearts displayed higher Ca²⁺ transients, shorter Ca²⁺ decays, higher sarcoplasmic reticulum Ca²⁺ levels and higher L-type Ca²⁺ current densities than the ISO rat hearts. VS-1 treatment restored the protein expression of sarcoplasmic reticulum Ca²⁺ uptake ATPase, phospholamban and Cav1.2, indicating improved calcium handling.

CONCLUSIONS

Chronic VS-1 treatment inhibited the progression of hypertrophy, fibrosis, and chamber remodeling, and improved cardiac function in a rat model of ISO infusion. In addition, Ca²⁺ handling and its molecular modulation were also improved by VS-1. The beneficial effects of VS-1 on cardiac remodeling may be mediated by the enhanced activation of the eNOS-cGMP-PKG pathway.

Structure and function of the aromatic amino acid hydroxylases

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Nitric oxide synthase containing nerves in the atrioventricular node of the guinea pig heart

Immunoelectron microscopy was performed to localize immunoreactivity for nitric oxide synthase (NOS) in the guinea-pig atrioventricular node. Many small ganglia were found in the interatrial septum near the atrioventricular node. A small number of neurons in these ganglia were immunoreactive. NOS immunoreactive axons were observed in nerve bundles near or within the node. Very thick immunoreactive axons, 8-10 microns in diameter, were found between the conductive tissue and the ordinary cardiac muscles. Electron-microscopic examination confirmed that these axons were unmyelinated. Nerve bundles in this region contained both myelinated and unmyelinated axons; however, immunoreactivity was detected exclusively in unmyelinated axons. Fine NOS-immunoreactive nerve fibers with terminal varicosities were often seen in the atrioventricular node. Close contact between NOS-immunoreactive axon varicosity and specialized cardiac muscle cell was observed. Intranodal ganglia were observed among the specialized cardiac muscles. They were surrounded by numerous axons, some of them were immunoreactive. Direct axo-somatic synapses from NOS-immunoreactive terminals to the intranodal ganglion cells were observed. The present results indicate a possibility that nitric oxide plays a role in the neural control of the conductive tissue in the heart through direct neuromuscular contact.

Evidence for reduction of norepinephrine uptake sites in the failing human heart

OBJECTIVES

This study investigated the role of neuronal uptake of norepinephrine (uptake-1) in human heart failure as a local factor for altering concentrations of norepinephrine at the cardiac myocyte membranes.

BACKGROUND

Several beta-adrenergic neuroeffector defects occur in heart failure. Whether an alteration in norepinephrine uptake-1 occurs is still unresolved.

METHODS

The role of norepinephrine uptake-1 was studied in electrically stimulated (1 Hz, 37 degrees C) human ventricular cardiac preparations and isolated myocardial membranes.

RESULTS

The effectiveness of norepinephrine in increasing the force of contraction was decreased in relation to the degree of heart failure. In contrast, the potency of norepinephrine was increased in failing hearts (New York Heart Association functional class IV) in relation to the concentrations producing 50% of the maximal effect (EC50). The EC50 values for isoproterenol, which is not a substrate for norepinephrine uptake-1, were reduced in myocardium in functional classes II to III and IV compared with those in nonfailing myocardium. The uptake inhibitors cocaine and desipramine (3 mumol/liter) potentiated the positive inotropic effects of norepinephrine in nonfailing myocardium (p < 0.05) but not in functional class IV myocardium. Radioligand binding experiments using the uptake inhibitor hydrogen-3 mazindol revealed a significant decrease by approximately 30% in norepinephrine uptake-1 carrier density in functional classes II to III and IV myocardium versus nonfailing myocardium (p < 0.05).

CONCLUSIONS

In human heart failure, there is a presynaptic defect in the sympathetic nervous system, leading to reduced uptake-1 activity. This defect in the failing heart can be mimicked by the effects of uptake blocking agents, such as cocaine and desipramine, in the nonfailing heart only. Compromised norepinephrine uptake-1 in functional class IV cannot be further increased by cocaine and desipramine. The pathophysiologic consequences could be an increased synaptic concentration of norepinephrine predisposing to adenylyl cyclase desensitization.

Normalization of circulating atrial natriuretic peptides in cardiac transplant recipients

To assess whether heart transplantation (Htx) alters the marked elevation of circulating atrial natriuretic peptides usually found in patients with congestive heart failure (CHF), 14 subjects (nine with compensated and five with decompensated CHF), each with an ejection fraction < or = 28%, were evaluated. Immediately before and hourly for the first 12 hours after Htx, then daily for 21 days and every 1 to 4 weeks for 6 months, the circulating concentrations of the N-terminus (pro atrial natriuretic factor [ANF] 1-98), midportion of the N-terminus (pro ANF 31-67), and C-terminus (that is, ANF) of the 126 amino acid prohormone were measured. Increased (p < 0.001) levels of these peptides were found in superior vena cava, right atrial, and peripheral venous samples 1 hour after Htx in all subjects except one. The atrial natriuretic peptide levels correlated only with right atrial pressure (p < 0.01) in the first 24 hours. Circulating concentrations of these peptides returned to those of healthy adults between 5 and 12 days after Htx in 11 out of 14 Htx recipients. Thus successful Htx can restore the elevated circulating concentrations of atrial natriuretic peptides to those of healthy adults.

No reinnervation of hepatic sympathetic nerves after liver transplantation in human subjects

Transplantation of the liver results in surgical denervation of the organ. However, it is not known whether and to what extent sympathetic reinnervation occurs postoperatively in the transplanted human liver. Thirty-two liver biopsies (right lobe) were obtained from 13 liver-transplanted patients 1, 3, 6, 12 or 30 months after transplantation and 11 biopsies were obtained from 11 non-transplanted subjects with normal liver tests. The concentrations of the sympathetic neurotransmitter norepinephrine and of epinephrine were determined in liver tissue homogenates. The concentration of norepinephrine was 0.019 +/- 0.05 nmol. g wet liver tissue-1 (mean and SE, n = 32) in the transplanted patients, which was only 1% of the concentration in biopsies from control subjects (2.180 +/- 0.420 nmol.g wet liver tissue-1). The hepatic norepinephrine concentration did not increase significantly over time in liver-transplanted patients during the observation period (0.015 +/- 0.008 nmol.g wet wt-1 (1 month post) (n = 8) vs. 0.024 +/- 0.018 nmol.g wet wt-1 (12 months post) (n = 6) and 0.012 +/- 0.006 nmol.g wet wt-1 (30 months post) (n = 5)) (p < 0.05). The liver tissue concentration of epinephrine was markedly lower in liver-transplanted subjects (0.01 +/- 0.003 nmol.g wet tissue-1) than in control subjects (0.04 +/- 0.007 nmol.g-1) (p < 0.01). This study indicates that within the first years after transplantation, there is no evidence of sympathetic liver nerve reinnervation in liver-transplanted patients.

Catecholaminergic and peptidergic nerve components of intramural ganglia in the rat heart. An immunohistochemical study

Immunohistochemical properties of the terminal nerve network in the rat heart were assessed by use of the elution-restaining method. The colocalization of the enzymes involved in catecholamine synthesis (tyrosine hydroxylase--TH. dopamine-beta-hydroxylase--DBH) as well as the respective distributions of the neuropeptides associated with the adrenergic nervous system (neuropeptide tyrosine--NPY, C-terminal flanking peptide of neuropeptide Y--C-PON) were studied in series of serial sections throughout the interatrial septum and the atrioventricular junction. Our data suggest that ganglion cells of sulcus terminalis as well as the epicardial ganglia enclosed between the superior vena cava and ascending aorta are VIP- and TH-negative, but neuropeptide Y- and DBH-immunoreactive. They give rise to three intraseptal nerves directed towards the specialised structures of the atrioventricular junction. These nerve fascicles contain abundant, thick TH-immunoreactive nerve fibres and scarce, thin NPY- and DBH-immunoreactive fibres. The cell bodies of the intramural ganglion cells localized between the right and left branches of the bundle of His (Moravec and Moravec 1984) are strongly TH- and DBH-immunoreactive. They are innervated by thick nerve fibres having the same immunohistochemical properties (NPY- and DBH-immunoreactivities) as those of a subpopulation of the epicardial ganglion cells and seem to supply some of the TH-immunoreactive nerve fibres directed via the intraseptal nerves to the epicardial ganglia. The existence of a multicomponent nerve network, characterized by a reciprocal innervation of the sinus node and atrioventricular node areas, is suggested by our immunohistochemical data.

Adrenergic neurons and short proprioceptive feedback loops involved in the integration of cardiac function in the rat

Serial cryostat and paraffin-embedded sections through the atrioventricular junction of the rat heart were studied at the light-microscopic level after indirect immunohistochemical staining (tyrosine hydroxylase, neuropeptide Y, C-terminal flanking peptide of neuropeptide Y immunoreactivities) or silver impregnation. The distribution of these immunoreactivities in the Hissian ganglion (Moravec and Moravec 1984) as well as the relationships of the Hissian ganglion cells with the surrounding structures have been studied to assess its function. The results suggest that the Hissian ganglion is composed of large multipolar neurons displaying both tyrosine hydroxylase (TH) and related peptide (neuropeptide Y. C-terminal flanking peptide of neuropeptide Y) immunoreactivities. The dendritic projections of these adrenergic cells penetrate the reticular portion of the atrioventricular node and the upper segments of the interventricular septum where they constitute sensory-like corpuscles. The hypothesis that the adrenergic neurons of the atrioventricular junction are involved in short proprioceptive feedback loops necessary for beat-to-beat modulation of cardiac excitability and intracardiac conduction can thus be suggested.

Decreased adrenergic neuronal uptake activity in experimental right heart failure. A chamber-specific contributor to beta-adrenoceptor downregulation

The reduction of myocardial beta-adrenoceptor density in congestive heart failure has been thought to be caused by agonist-induced homologous desensitization. However, recent evidence suggests that excessive adrenergic stimulation may not produce myocardial beta-receptor downregulation unless there is an additional defect in the local norepinephrine (NE) uptake mechanism. To investigate the association between beta-adrenoceptor regulation and NE uptake activity, we carried out studies in 30 dogs with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary artery constriction and 23 sham-operated control dogs. We determined NE uptake activity by measuring accumulation of [3H]NE in tissue slices, NE uptake-1 carrier density by [3H]mazindol binding and beta-adrenoceptor density by [3H]dihydroalprenolol binding. Compared with sham-operated dogs, RHF dogs showed a 26% decrease in beta-adrenoceptor density, a 51% reduction in NE uptake activity, and a 57% decrease in NE uptake-1 carrier density in their right ventricles. In addition, right ventricle beta-receptor density correlated significantly with NE uptake activity and NE uptake-1 carrier density. In contrast, neither NE uptake activity nor beta-receptor density in the left ventricle and renal cortex was affected by RHF. Thus, the failing myocardium is associated with an organ- and chamber-specific subnormal neuronal NE uptake. This chamber-specific loss of NE uptake-1 carrier could effectively reduce local NE clearance, and represent a local factor that predisposes the failing ventricle to beta-adrenoceptor downregulation.

Distribution and function of beta-adrenoceptors in different chambers of the canine heart

1 An improved binding assay involving (-)-[(3)H]-dihydroalprenolol (DHA) and KCl-washed cardiac membranes was developed to study beta-adrenoceptors in the canine heart quantitatively.2 Receptor numbers varied from 3.8 to 7.1 pmol/g fresh tissue, showing a steady increase from left atrium --> right atrium --> right ventricle --> interventricular septum --> left ventricle. With one minor exception, the same pattern was found for adenylate cyclase activity and Na(+), K(+)-activated ATPase activity.3 The binding of DHA was inhibited in the expected manner by beta-adrenoceptor agonists and antagonists, and was stereospecific, in confirmation of previous studies. Dissociation constants determined from Scatchard analyses included DHA: 2.5 nM; (-)adrenaline: 230 nM; (-)noradrenaline: 1167 nM. Kinetic analyses of the binding of DHA yielded a K(D) of about 4 nM.4 The distribution of beta-receptors is closely related to that of blood flow and the arrival plus retention of a circulating catecholamine, but is markedly different from that of endogenous noradrenaline, and thus adrenergic nerve terminals. Most receptors thus appear not at synapses but diffusely localized where they can react with circulating adrenaline.5 Evidence is discussed that beta-receptors at synapses respond primarily to neural noradrenaline, less to circulating adrenaline, and hardly at all to circulating noradrenaline; responses mediate increased cardiac output during exercise. In contrast most cardiac beta-receptors appear to respond only to adrenaline, and to be used, except at times of severe circulatory stress, during psychological stress.

Morphology of cardiac nerves in experimental infarction of rat hearts. II. Electron microscopical findings

Alterations of cardiac nerves in myocardial infarction were investigated by electron microscopy after differing intervals in 28 rats. During the first 4 h there are, in non-myelinated nerves within the myocardium, a swelling of the axoplasm with the occurrence of 'pale' axons and swelling of axonal mitochondria and neurosecretory granules. After bursting of the axolemma, these are spilled into the adjacent interstitial space. After 4 h first myelin figures are observed, and in some axons an accumulation of neurofilaments takes place. During the second to seventh day an extensive vesicular disintegration of axonal structures develops. Because of regressive changes, axons cannot be identified with certainty within the necrosis. After two or three weeks nerves with lamellar enfoldings of cytoplasmic processes corresponding to Büngner bands can be seen at the infarction border. These nerves may contain only a few residual axons. Myelinated nerves show a mainly vesicular disintegration. The results are discussed with regard to their functional significance and the special conditions of the animal model, in which ligature of the coronary artery may not only produce ischemia, but may also, by simultaneous ligature of the adjacent cardiac nerves, induce Wallerian degeneration.

A thin-layer chromatographic procedure for the assay of labelled noradrenaline and its metabolites in tissues and in incubation medium

A method for the extraction, separation and quantitative determination of [3H]noradrenaline [3H-NA] and its five major metabolites has been devised using thin layer chromatography. This procedure was used to study the pattern of 3H-NA and its metabolites in the total radioactivity of the tissues and that released spontaneously from the rat isolated vas deferens. Whereas in tissues 3H-NA represented almost all of the total radioactivity (94-8+/-0.47%), in the samples of spontaneous outflow it represented only 16-8+/-2.1%. The rest was mostly accounted for by the five metabolites, primarily 3H-DOPEG and 3H-MOPEG. These findings show that in the rat vas deferens 3H-NA is preferentially metabolized via the two glycol derivatives, i.e. 3H-DOPEG and 3H-MOPEG.

Effect of the activation of alpha-adrenoreceptors on the synthesis and release of noradrenaline by peripheral adrenergic nerves in vivo

The synthesis and release of noradrenaline (NA) in the heart and submaxillary glands were studied in the rat following s.c. injections of oxymetazoline (50 mug/kg) or noradrenaline (500 mug/kg). NA release was evaluated from the decline in tissular specific radioactivity after administration of 3H-NA and NA synthesis by the estimation of the amounts of 3H-NA synthesized from 3H-tyrosine (TY) or 3H-Dopa, 30 min after the injection. Oxymetazoline treatment delayed the release of NA, the NA biological half-lives rising from 12 up to 36 hours in the heart and from 5.9 up to 21 hours in sub-maxillary glands. This inhibitory effect on NA release was interpreted as the consequence of the stimulation of alpha-adrenoreceptors. Thirty minutes after its injection, oxymetazoline increased both NA endogenous levels and 3H-NA amounts formed from 3H-TY: 3H-NA specific activities were not significantly altered. NA treatment led to an acceleration of NA release in the heart (NA biological half-life decreasing from 12 to 2.2 hours) but not in sub-maxillary glands. After injection of 3H-TY, the amounts of 3H-NA found in the heart and sub-maxillary glands were strongly reduced. Similar results were observed in the heart using 3H-Dopa as a precursor. These data are interpreted as the consequence of the removal of the newly synthesized 3H-NA by exogenous NA. The results obtained with oxymetazoline point out a dissociation between the NA release which is reduced and the NA synthesis which is unaltered. This indicates that NA synthesis rate by sympathetic nerve terminals is not immediately regulated by its release intensity. These data do not support the end-product feedback inhibition hypothesis according to which tyrosine hydroxylase is regulated by the intraneuronal NA concentration.

The effect of isolation on myocardial properties

Denervation deprives the heart of its normal adrenergic and cholinergic control via the sympathetic and parasympathetic pathways. In a heart which is blood supplied by a donor animal of the same species, normal contractility is maintained, probably by blood borne catecholamines or possibly by unknown inotropic agents of the donor. A heart receiving blood oxygenated by isolated lungs is in a state of failure. Substitution of blood by a cell and protein free solution diminishes oxygen availability in cardiac muscle, both in the perfused and bathed preparation. In the unphysiological environment, myocardial cells lose K+ and gain Na+. Under best possible conditions of oxygen supply but in a later stage of perfusion, contractility during rhythmical stimulation is depressed more at lower than at higher rates. Frequency potentiation and the inotropic effectiveness of noradrenaline is more pronounced in vitro than in situ. In excised papillary muscles and ventricular and atrial strips, the disarrangement and a more or less severe lesion of individual fibres accelerates the decay in mechanical performance. The role of endogenous catecholamines for the maintenance of normal contractility in situ and in vitro is still a matter of discussion.

Myocardial sensitivity to catecholamines following exposure of rats to irregular, signalled footshock

Emotional stress is associated with an increased activity of both the pituitary-adrenal cortical system and the sympathetic-adrenal medullary systems resulting in raised plasma levels of glucocorticoids and catecholamines. There is evidence to suggest that prolonged stress induced adrenergic hyperactivity initiated myocardial pathogenesis and that this may relate to a corticosteroid catecholamine interaction. In the present study driven atrial strips removed from stressed male CSF rats were found to exhibit an enhanced sensitivity to both norepinephrine and epinephrine. These animals had previously been subjected to irregular foot shock associated with a warning signal; a situation producing a high plasma steroid level. The enhanced myocardial sensitivity to both catecholamines was observed in naive animals subjected to a single period, and persisted unchanged in animals stressed daily over a 28 day period. The hypersensitivity of the myocardium observed immediately after stress was maintained for at least 24 hr, whereas the circulating steroid level had returned to control values within 3 hr. In animals subjected to regular stress without a warning signal, a situation producing a much lower steroid level, no enhanced myocardial sensitivity was observed. While the aetiology of the phenomenon of enhanced myocardial sensitivity to catecholamines is not entirely understood, the evidence presented suggests that it may be related to the extreme elevation of circulating glucocorticoids. The sensitivity of the vas deferens however, was unaltered even though the animals were subjected to the stressor producing a high plasma steroid level. This apparent specifcity of the stress induced sensitivity change is discussed on the basis of receptor differences.

Effects of myocardial infarction on adrenergic nerves of the rat heart muscle, a histochemical study

The anterior branch of the left coronary artery of the rat heart was ligated and the effects of anoxia on adrenergic nerves were studied histochemically using formaldehyde-induced fluorescence for localization of norepinephrine. Greenish catecholamine fluorescence was associated in the normal or infarcted myocardium only with adrenergic nerves. Constant but not prominent changes were seen in adrenergic nerve fibers 2 or 4 h after ligation of the coronary artery; the number of dilicate adrenergic fibers was reduced and some diffusion of the histochemical reaction was seen in small areas of the infarcted myocardium. Strong effects of anoxia were seen 8 h or more after ligation of the coronary artery. These were characterized by a prominent diffusion of the histochemical reaction and gradual disappearance of adrenergic structures in 2 to 4 days of anoxia. During the healing phase the appearance of numerous adrenergic nerve fibers was closely connected with the ingrowth of a new vascular bed into the infarction area. The observations indicate that adrenergic nervous structures of the myocardium resist the effects of anoxia, which may indicate the viability of sympathetic nerves in the infarcted area during long periods of anoxia.

Relation between the amount of smooth muscle of venous tissue and the degree of supersensitivity to isoprenaline caused by inhibition of catechol-O-methyl transferase

The relation between the smooth muscle cell mass of dog saphenous vein strips and the degree of supersensitivity to isoprenaline caused by U-0521 (3,4-dihydroxy-2-methyl propiophenone), an inhibitor of the catechol-O-methyl transferase (COMT), was studied. For the quantitative determination of smooth muscle mass, the thickness of the muscle layer as determined by light microscopy and the maximal shortening induced by supramaximal concentration of phenylephrine were used. After the strips had been contracted by 3x10-6M phenylephrine, a concentration which was able to produce an about 90% maximal contraction, dose-response curves to the relaxant effect of isoprenaline were determined in the absence and in the presence of U-0521 (10-4M). It was observed that U-0521 caused marked supersensitivity to the relaxant effect of isoprenaline (varying between 3 and 81 times), as well as an increase of the maximal relaxation caused by this amine (varying between 7 and 120%). The correlation between these data and the smooth muscle cell mass shows that there was a direct proportionality between these parameters. Oxytetracycline (10-4M), an inhibitor of binding of catecholamines to collagen, did not produce any enhancement of the effects of isoprenaline. It is concluded that COMT is related to smooth muscle cells in this tissue.

Effect of pretreatment with 6-hydroxydopamine on the uptake and metabolism of catecholamines by the isolated perfused rat heart

1. Isolated rat hearts from control and 6-hydroxydopamine pretreated animals were perfused with (3)H-noradrenaline or (3)H-dopamine, either at a low perfusion concentration (1.50 x 10(-10) mol/ml (3)H-dopamine; 1.18 x 10(-10) mol/ml (3)H-noradrenaline) or a high perfusion concentration (296.69 x 10(-10) mol/ml (3)H-noradrenaline, 327.45 x 10(-10) mol/ml (3)H-dopamine) for 8 minutes.2. At the low perfusion concentration, the total activity, the radioactivity in the alumina eluates (sum of (3)H-dopamine, (3)H-noradrenaline and deaminated catechol metabolites) and the concentration of (3)H-dopamine. (3)H-noradrenaline and the deaminated catechol metabolites were decreased in the hearts of the pretreated rats as compared with the controls. The O-methylated amine metabolites were increased. The deaminated O-methylated metabolites were increased in the experiments with (3)H-noradrenaline and decreased in the (3)H-dopamine experiments.3. Uptake of (3)H-dopamine and (3)H-noradrenaline by the hearts of 6-hydroxydopamine pretreated rats was decreased to a much smaller extent when perfused with the high concentration than with the low concentration.4. At the high perfusion concentration there was a significant difference between control and pretreated animals with regard to the total radioactivity and the radioactivity in the alumina eluates only. The absolute and relative amounts of metabolites were not significantly changed by pretreatment with the exception of the deaminated catechol metabolites in the (3)H-dopamine experiments.5. It is concluded that neuronal Uptake 1 is greatly impaired in the hearts from rats pretreated with 6-hydroxydopamine, but extraneuronal Uptake 2 remains intact.

The metabolism of (3H)noradrenaline released by electrical stimulation from the isolated nictitating membrane of the cat and from the vas deferens of the rat

1. The noradrenaline (NA) stores of the isolated medial muscle of the cat's nictitating membrane were labelled with [(3)H]NA and the tissue was set up in an isolated organ bath for field stimulation. The tritiated NA and its metabolites released spontaneously and by field stimulation were determined by scintillation counting following chromatographic separation.2. NA represented 11.8 +/- 1.0% of the total radioactivity of the spontaneously released tritiated compounds. The rest was accounted for by NA metabolites: (a) normetanephrine (NMN), 35%; (b) 4-hydroxy-3-methoxymandelic acid (VMA), 20%; (c) 3,4-dihydroxyphenylglycol (DOPEG), 10%; (d) 3,4-dihydroxymandelic acid (DOMA), 10%; (e) 4-hydroxy-3-methoxyphenylglycol (MOPEG), 14%.3. Field stimulation at 25 shocks/sec with supramaximal stimuli of 1 msec duration increased the outflow of NA six to eightfold and that of NMN, DOPEG and VMA two to threefold. The increase in outflow of DOMA and MOPEG was small. NA represented 35.8 +/- 4.1% of the total increase in radioactivity.4. After pargyline pretreatment field stimulation increased the outflow of NA and NMN. Stimulation in the presence of pyrogallol raised the release of NA, DOMA and DOPEG. Neither pargyline nor pyrogallol affected the total release induced by stimulation.5. Cocaine 0.3 mug/ml. increased the release due to stimulation at 4 shocks/sec but not at 25 shocks/sec. Cocaine did not affect the metabolism of the released transmitter.6. Phenoxybenzamine (10 mug/ml.) increased release by stimulation at 4 and 25 shocks/sec. Metabolism of the released transmitter was prevented in the presence of phenoxybenzamine.7. Phentolamine (3 mug/ml.), like phenoxybenzamine, blocked responses to field stimulation, but failed to modify release and subsequent metabolism of NA liberated by field stimulation.8. The main NA metabolites in the rat vas deferens were DOPEG, DOMA and MOPEG. Stimulation at 4 shocks/sec resulted in an increased outflow of NA and of DOPEG. Fifty per cent of the total increase of radioactive compounds was accounted for by NA metabolites.9. These experiments show that for the calculation of the actual output of transmitter it is important to include the metabolites and not to rely on the determination of [(3)H]NA alone.

Dissociation of potentiation of isoprenaline by cocaine from inhibition of uptake in cat spleen

1. Cocaine hydrochloride, 10 mug/ml, potentiated isoprenaline and noradrenaline in isolated spleen strips from normal cats and from cats treated with reserpine 24 h previously.2. Isoprenaline was taken up almost as well as noradrenaline by spleen strips from cats treated with reserpine.3. Cocaine blocked uptake of noradrenaline but did not reduce uptake of isoprenaline. Drug concentrations used in these studies were the same as in potentiation experiments.4. It is concluded that inhibition of uptake is not the mechanism by which cocaine potentiates the effect of isoprenaline on the spleen and might be only a contributory factor in the case of noradrenaline potentiation.

Uptake and metabolism of catecholamines in the perfused hearts of different species

1. The uptake of (+/-)-(3)H-noradrenaline was studied in isolated perfused hearts of rat, mouse, guinea-pig, pigeon and toad (Bufo marinus), and the IC50 (concentration causing 50% inhibition) values for inhibition of uptake of (+/-)-(3)H-noradrenaline by (-)-noradrenaline were calculated. IC50 values ranging from 0.28 muM (rat heart) to 2.34 muM (toad heart) were found.2. In all species except the toad, (-)-noradrenaline showed a higher affinity than (-)-adrenaline for the uptake process, but the reverse was found for the toad heart.3. Mouse and pigeon hearts contained increasing amounts of metabolites of noradrenaline with increasing perfusion concentrations of noradrenaline, but the guinea-pig and toad hearts did not. The in vitro activities of noradrenaline catabolizing enzymes in heart homogenates were measured but did not explain the differences in the pattern of catabolism of noradrenaline found in the intact hearts of the different species.4. In all hearts except the toad, cocaine was an effective blocking agent for the uptake of (+/-)-(3)H-noradrenaline and led to an increase in (3)H-normetanephrine in these hearts. In the pigeon heart, cocaine plus phenoxybenzamine in the perfusate resulted in an inhibition of both (3)H-noradrenaline uptake and (3)H-normetanephrine formation.5. In guinea-pig and pigeon perfused hearts, the uptake of (3)H-noradrenaline into atria and ventricles reflected the relative concentrations of endogenous catecholamines in these regions, but this was not found for rat, mouse and toad hearts.6. It was concluded that species differences exist for both the accumulation and metabolism of catecholamines in isolated perfused hearts.

The extraneuronal uptake and localization of noradrenaline in the cat spleen and the effect on this of some drugs, of cold and of denervation

1. Extraneuronal uptake of noradrenaline (NA) was examined in the cat spleen first by perfusing with NA for 10 min, followed by a 2-min wash to clear the extracellular fluid, then measuring the amount retained, its subcellular distribution and the tissue components involved as revealed by the development of the characteristic fluorescence. Secondly, thin spleen slices were exposed to NA in vitro and the development of fluorescence in various structures, particularly arterial smooth muscle, measured.2. The cat spleen accumulated large quantities of NA and this, like the development of fluorescence, was concentration-dependent. After particle separation most of the retained amine appeared in the high-speed supernatant, with a lesser amount in the coarse granule fraction. There was little amine in either the mitochondrial or microsomal fraction. The microsomal fraction from unperfused spleens was rich in NA, presumably from storage granules from the adrenergic nerves. On an intermittent sucrose density gradient the NA-rich particles sedimented between 1.0 and 1.5 M sucrose, corresponding to the recently described dense granules from bovine splenic nerves.3. Fluorescence histochemistry revealed several tissues accumulating NA. At an NA concentration of 10(-5) g/ml., arterial smooth muscle and endothelium showed intracellular fluorescence; at 10(-4) g/ml., collagen, the perimeter of the smooth muscle cells of the capsule-trabecula-vein system and the reticular cells forming the framework of the spleen developed fluorescence. In the reticular cells the fluorescence was intracellular. The fluorescence pattern on the perimeter of non-arterial smooth muscle corresponded to the pattern of basement membrane as shown by PAS staining. The red pulp, lymphoid tissue and the phagocytic cells of the ellipsoids did not fluoresce.4. Cooling the tissue to 15 degrees C or less, phenoxybenzamine in a concentration of 5 x 10(-5) g/ml. or normetanephrine in a concentration of 10(-4) g/ml. prevented both uptake and loss of NA in arterial smooth muscle but had no effect on collagen.5. Chronic post-ganglionic denervation or reserpine had no effect on the development of fluorescence in any extraneuronal tissue.

Monoamine oxidase activities in tissues of thiamine-deficient rats

The oxidation of monoamine by homogenates of tissues of thiamine-deficient rats was measured with noradrenaline as substrate. Monoamine oxidase activities were depressed in tissues in which the catecholamine content had previously been found raised during thiamine deficiency, with the exception in the cerebral cortex. The impaired enzyme activities were restored to the control level by repeated thiamine injections. An accumulation of pyruvic acid did not inhibit monoamine oxidase activity and thiamine pyrophosphate is not implicated as a co-factor in the oxidation of monoamine substrate.

Effects of reserpine on the disposition of sympathomimetic amines in vascular tissue

1. The effects of reserpine pretreatment on the intrinsic inactivation of low concentrations of phenylephrine and noradrenaline in strips of rabbit thoracic aorta were assessed by measuring the rates of relaxation, after oil immersion to prevent loss of active amine by diffusion into the surrounding medium.2. Reserpine pretreatment considerably augmented the amplitude of responses to low concentrations of phenylephrine, noradrenaline and nordefrine (Cobefrine).3. Reserpine pretreatment did not reduce the overall rate of inactivation of either phenylephrine or noradrenaline, but it did appear to decrease the contribution of uptake and storage, measured as an increased effect of enzyme inhibition and a decreased effect of cocaine on the rate of inactivation.4. The role of catechol-O-methyl transferase (COMT), but not that of monoamine oxidase (MAO), in terminating the action of noradrenaline was increased in strips from animals pretreated with reserpine. Thus it appears that interference with intraneuronal storage diverts active amine to inactivation by COMT in vascular tissue, rather than by MAO as has been previously suggested.5. As in preparations not treated with reserpine, inhibition of MAO alone had little effect on the rate of inactivation of noradrenaline, and this enzyme appears to function predominantly as an alternate pathway of little importance as long as COMT activity is unimpaired. Enzymatic processes accounted for about 85 and 70% of the inactivation of a low concentration of noradrenaline in reserpine pretreated and untreated preparations, respectively.6. Cocaine potentiated responses to noradrenaline and phenylephrine as effectively in reserpine pretreated as in untreated preparations, and inhibition of the pathways of enzymatic inactivation did not appreciably decrease the potentiation produced by this agent.7. The present results cannot be explained by the hypothesis that interference with amine inactivation by nerve uptake and storage is responsible for the potentiation of responses to noradrenaline or phenylephrine by either reserpine or cocaine, and emphasize the unrealiability of potentiation as an index of interference with mechanisms involved in terminating the action of sympathomimetic amines.

Action of cocaine and chronic sympathetic denervation on vagal escape

1. The effect of cocaine has been studied on vagal escape and on the tachycardia due to vagal stimulation in the atropinized dog. All the dogs were submitted to acute cervical section of the spinal cord and acute or chronic sympathetic denervation.2. Cocaine, 5 mg/kg or 40 mug/kg/min, I.V., induces a significant enhancement of the ventricular escape. The effects of a continuous infusion of cocaine are more reproducible than those of a single injection of the drug.3. Cocaine, 40 mug/kg/min, I.V., potentiates the tachycardia due to vagal stimulation in the atropinized dog.4. Chronic thoracic sympathectomy markedly retards the recovery of the ventricular rate from the inhibitory action of the vagus. Under this condition, the infusion of cocaine does not significantly enhance the ventricular escape.5. These findings suggest that an adrenergic mechanism located at the sympathetic nerves supplying the heart is substantially involved in the phenomenon of vagal escape.