Showing papers on "Epinephrine published in 1972"

Cyclic AMP and Aclrenergic Receptor Control of Rat Liver Glycogen Metabolism

Abstract: We used the isolated perfused rat liver as a model system to study mechanisms by which catecholamines alter hepatic carbohydrate metabolism. Epinephrine, norepinephrine, phenylephrine and isoproterenol all cause activation of glycogen phosphorylase, and increase glucose output. The effects of all of these agents are blocked by the alpha blocker phentolamine, whereas the beta blocker propranolol only inhibits the effect of norepinephrine. Cyclic AMP levels rise in the liver and the perfusate following epinephrine. This rise is accentuated by phentolamine and blocked by propranolol. Isoproterenol causes a greater elevation of cyclic AMP than phenylephrine while the reverse is true with respect to phosphorylase. The above data leads us to conclude that there are two independent mechanisms whereby catecholamines may activate glycogenolysis: 1) a beta receptor—mediated effect resulting in a rise in cellular cyclic AMP levels, which by the wellknown cascade mechanism activates phosphorylase; and 2) an alpha rec...

Characterization and Tissue Localization of Catecholamine Synthesizing Enzymes

Abstract: 1 . Three enzymes involved in catecholamine biosynthesis, namely, aromatic-L-amino acid decarboxylase (AADC), dopamine-β-3-hydroxylase (DβH) and phenylethanolamine-N-methyl transferase (PNMT) were purified from bovine adrenal glands. The purified enzymes were used to induce the production of the corresponding immullologically pure antienzymes in rabbits. The latter were utilized for immunochemical studies as well as for localization of catecholamine synthesizing enzymes in peripheral tissue and brain by the indirect immunofluorescent method. 2. Immunochemical studies reveal heterogeneity of DβH and PNMT among different species. Bovine PNMT occurs in different molecular forms and differently charged isozymes were separated from the low molecular form of the enzyme. The PNMT charged isozymes are indistinguishable from each other on immunoelectrophoresis. The corticoid inducible PNMT is immunologically distinguishable from the uninducible form. 3. AADC was localized in all medullary cells and in all catecholamine and serotonin containing cell bodies of the peripheral and central nervous system. DβH was localized in adrenal medullary cells, peripheral and central norepinephrine cell bodies and transected peripheral and central norepinephrine nerve fibers. The primitive catecholamine cell system in the ganglia lacks specific DβH immunofluorescence and seems therefore to contain dopamine and not norepinephrine. PNMT was localized in the cytoplasm of most of the adrenal medulla glands in rats and mice and in all medullary cells in the guinea pig. By combining the immunofluorescence technique with the formaldehyde condensation technique it was possible to separate the norepinephrine containing cells from the epinephrine containing cells in the adrenal medulla of rats. 4. Serum DβH activity was assayed by a sensitive enzymatic procedure. The activity of this enzyme in serum depends on the rate of release of the enzyme from the sympathetic innervated tissues and on the rate of degradation in some sites not yet known. Evidence was presented that serum DβH levels are altered by changes in the sympathetic nervous system functions. Human serum DβH activity increases with age; infants under 1 year of age have extremely low enzyme activity levels. The enzyme activity was investigated in patients with various disorders. Extremely high values were found in some neuroblastoma patients and low values in some patients with familial dysautonomia. The latter finding implies the involvement of the parasympathetic system in the regulation of serum DβH levels. 5. The effects of hypophysectomy on catecholamine synthesizing enzymes was investigated. The increase in the turnover rate of cardiac norepinephrine after hypophysectomy is associated with an increase in circulatory DβH. Chronic treatment with ACTH restores the turnover rate of cardiac norepinephrine and the serum DβH levels to almost normal levels. PNMT activity as well as the PNMT-protein content is markedly reduced in the adrenals of hypophysectomized animals and histochemical studies reveal a marked reduction in number and/or size of medullary cells. Thus, atrophic changes in adrenal medulla may contribute to the decrease in the levels of catecholamine synthesizing enzymes after hypophysectomy.

Adrenocortical Control of the Biosynthesis of Epinephrine and Proteins in the Adrenal Medulla

Abstract: The activity of phenylethanolamine-N-methyl transferase (PNMT) in the adrenal medulla declines markedly after hypophysectomy. Enzyme activity is restored if animals are treated with ACTH or very large doses of glucocorticoids, but not by "replacement" doses of glucocorticoids or by other pituitary or adrenal hormones. These observations indicate that basal levels of PNMT activity require that the medulla receive the very high concentrations of hydrocortisone or corticosterone that are available to it by virtue of its unique location within an envelope of adrenal cortex. The resotration by dexamethasone treatment of the PNMT activity in medullas of hypophysectomized animals is blocked by concurrent administration of actinomycin D or puromycin. Moreover, hypophysectomy is associated with decreases in the quantity of immunochemically assayable PNMT protein in the medulla and in the rate at which PNMT is synthesized from isotopically labeled amino acid precursors. These changes are also reversed by dexamethasone. Adrenomedullary polysomes are markedly disaggregated after hypophysectomy; however, polysome patterns revert to normal if animals are treated with ACTH or dexamethasone. These observations all suggest that glucocorticoids stimulate the synthesis not only of PNMT, but also of a wide variety of medullary proteins. The decrease in adrenal PNMT activity caused by hypophysectomy is associated with corresponding decreases in the mass of chromaffin cells and in the amounts of epinephrine stored in the adrenal medulla and secreted in response to physiological stimuli. After the induction of insulin hypoglycemia, adrenals of hypophysectomized dogs release considerably less epinephrine, and more norepinephrine, than those of control animals. Inasmuch as norepinephrine is far less potent than epinephrine in accelerating the breakdown of glycogen, the impairment in epinephrine synthesis caused by pituitary insufficiency may be related to the insulin sensitivity that often characterizes this disease.

Metabolic Regulation of Heme Catabolism and Bilirubin Production. I. HORMONAL CONTROL OF HEPATIC HEME OXYGENASE ACTIVITY

Abstract: Heme oxygenase (HO), the enzyme system catalyzing the conversion of heme to bilirubin, was studied in the liver and spleen of fed, fasted, and refed rats. Fasting up to 72 hr resulted in a threefold increase in hepatic HO activity, while starvation beyond this period led to a gradual decline in enzyme activity. Refeeding of rats fasted for 48 hr depressed hepatic HO activity to basal values within 24 hr. Splenic HO was unaffected by fasting and refeeding. Hypoglycemia induced by injections of insulin or mannose was a powerful stimulator of hepatic HO. Glucose given together with the insulin abolished the stimulatory effect of the latter. Parenteral treatment with glucagon led to a twofold, and with epinephrine to a fivefold, increase of hepatic HO activity; arginine, which releases endogenous glucagon, stimulated the enzyme fivefold. These stimulatory effects of glucagon and epinephrine could be duplicated by administration of cyclic adenosine monophosphate (AMP), while thyroxine and hydroxortisone were ineffective. Nicotinic acid, which inhibits lipolysis, failed to modify the stimulatory effect of epinephrine. None of these hormones altered HO activity in the spleen. These findings demonstrate that the enzymatic mechanism involved in the formation of bilirubin from heme in the liver is stimulated by fasting, hypoglycemia, epinephrine, glucagon, and cyclic AMP. They further suggest that the enzyme stimulation produced by fasting may be mediated by glucagon released in response to hypoglycemia. The possibility is considered that the enhanced HO activity in the liver may increase hepatic heme turnover and hence, bilirubin production, which may explain the rise of unconjugated serum bilirubin observed in fasting or hypoglycemic individuals.

Differences in Direct Effects of Adrenergic Stimuli on Coronary, Cutaneous, and Muscular Vessels

Abstract: Direct effects of adrenergic stimuli on coronary vessels in dogs were compared with effects on vessels to skin (hind paw) and skeletal muscle (gracilis muscle) after intravenous administration of practolol (2 mg/kg), a selective myocardial beta receptor blocker which minimized indirect effects of myocardial stimulation on coronary vascular resistance. The left circumflex coronary, cranial tibial, and gracilis arteries were perfused separately but simultaneously at constant flow. Perfusion pressures, left ventricular pressure and dP/dt. and heart rate were recorded. Changes in perfusion pressure to each bed reflected changes in vascular resistance. The direct constrictor effects of sympathetic nerve stimulation, norepinephrine and phenylephrine on coronary vessels were minimal compared with effects on cutaneous and muscular vessels. Subsequent blockade of vascular beta receptors did not augment the constrictor responses. Angiotensin, a nonadrenergic stimulus, produced striking coronary vasoconstriction which exceeded that in skin and approximated that in muscle. These results suggests that there is a paucity of alpha adrenergic receptors in coronary vessels compared to cutaneous and muscular vessels. Direct dilator responses to isoproterenol were similar in coronary and cutaneous vessels, but were greater in muscular vessels. Responses to glyceryl trinitrate, a nonadrenergic dilator, also were greater in skeletal muscle. Therefore, differences in effects of isoproterenol on the three beds may reflect differences in reactivity to dilator stimuli rather than differences in the density of beta receptors. In contrast to norepinephrine, the predominant direct effect of epinephrine on coronary vessels was dilatation mediated through activation of vascular beta receptors. A constrictor effect caused by stimulation of alpha receptors was unmasked by propranolol. Finally, the order of potency of agonists in stimulating coronary vascular beta receptors and the demonstration of selective beta receptor blockade with practolol suggest that beta receptors in coronary vessels resemble those in peripheral vessels more than those in myocardium.

Protection against epinephrine-induced myocardial necrosis by drugs that inhibit platelet aggregation.

Abstract: To investigate the possibility that the myocardial necrosis seen after epinephrine infusion is related to the platelet aggregating effects of epinephrine, 10 dogs pretreated with aspirin, 10 dogs pretreated with dipyridamole and 10 dogs not pretreated were infused with epinephrine, 4 μg/kg per min; their hearts were studied histologically after sacrifice 1 week later. All of the control animals had necrosis, 6 with 3+, 2 with 2+, and 2 with 1+ necrosis. Seven of the 10 dogs pretreated with aspirin and 7 of the 10 pretreated with dipyridamole had no evidence of myocardial necrosis. Three dogs pretreated with aspirin had 1+ necrosis; 3 pretreated with dipyridamole had 2+, 1+ and trace degrees of necrosis, respectively. This demonstration of a protective effect of antiplatelet aggregating agents suggests that intravascular platelet aggregation plays a role in catecholamine-induced myocardial necrosis. Clinical acute myocardial infarction seen after prolonged stress (during which catecholamine secretion is increased) may be related to similar intravascular platelet thrombosis induced by catecholamines occluding a coronary artery previously narrowed by atherosclerosis.

Epinephrine-induced hypokalemia: relation to liver and skeletal muscle

Abstract: Experiments were performed in anesthetized dogs to find the site of potassium uptake underlying the reduction of plasma [K] during the continuous infusion of epinephrine. In two groups of dogs, epinephrine (2 µg/kg/min) was infused i.v. Plasma [K] was measured 1) in a systemic artery and a femoral vein and 2) in a systemic artery and a hepatic vein. In both groups, arterial [K] increased, then fell below control by minute 10 of the infusion. In time first group, arterial [K] exceeded femoral venous [K] during time hyperkalemia and during the development of hypokalemia, indicating uptake of potassiunm by skeletal muscle. Propranolol reversed the hypokalemia. In the second group, hepatic venous [K] exceeded arterial [K] during the hyperkalemia, indicating loss of potassium by the liver, but was less than arterial [K] during the development of hypokalemia, indicating uptake of potassium by the liver at that time. In a third group, epinephrine (0.2 µg/kg/min) was infused locally into one femoral artery and plasma [K] was measured in the other femoral artery and both femoral veins. Venous [K] from the infused leg was reduced sooner and significantly more than was that from time opposite leg. These data suggest that epinephrine acts directly to increase the uptake of potassium by both liver and skeletal muscle and that the effects are mediated through adrenergic beta receptors.

Colchicine inhibits adrenal medullary secretion evoked by acetylcholine without affecting that evoked by potassium.

Abstract: In perfused rabbit adrenal glands, colchicine (500 μM) inhibited the catecholamine secretion evoked by acetylcholine (20 μg/ml) but not that evoked by excess potassium (60 mM). Since both stimuli are believed to release catecholamines ultimately by the same secretory process, exocytosis, it is concluded that these inhibitory effects of colchicine exerted against acetylcholine result from an action early in the process of stimulus-secretion coupling, possibly at the level of the acetylcholine receptor, and that it is inappropriate to use such inhibitory effects to support the view that secretion proper (exocytosis) in chromaffin cells involves colchicine-sensitive elements such as microtubules.

Epinephrine Binding to the Catecholamine Receptor and Activation of the Adenylate Cyclase in Erythrocyte Membranes

Abstract: Turkey erythrocyte membranes showed specific binding of [3H]epinephrine. The concentration of hormone required for half-maximal binding (30 μM) was the same as that required for half-maximal activation of the adenylate cyclase located in the same membrane preparation. The binding reaction at 37°C reached completion during the first minute of incubation, which agrees well with the known rapidity of the biological response to catecholamines. Specific binding was abolished by heating the membranes 1 min at 100°C. Chromatography of the bound 3H, after its extraction from the membranes, indicated that the hormone had fully retained its chemical structure. Epinephrine binding was inhibited by the β-adrenergic blocking agent propranolol, which also inhibited the activation of adenylate cyclase by the hormone. The specificity of phenethylamine derivatives in displacing [3H]epinephrine from the binding sites showed that a typical catecholamine receptor was responsible for the binding. Displacement of the bound hormone by analogs lacking the catechol group was more extensive at 37°C than at 0°C. Some of the analogs that displaced epinephrine from the binding site caused only a feeble activation of the adenylate cyclase, but were able to inhibit the activation of the enzyme by epinephrine. Thus, binding to a catecholamine receptor on a membrane preparation is an essential, but insufficient, condition to elicit a response.

Catecholamine induced increase of cyclic adenosine 3',5'-monophosphate in rat brain in vivo.

Abstract: — Four catecholamines injected into the cerebral ventricles increased the content of cyclic adenosine 3′,5′-monophosphate (cAMP) in vivo in the whole brain of rats. The highest rise (2.6-fold) was measured 2 min after an injection of 100 μg epinephrine. Isoproterenol and norepinephrine were less active and dopamine hardly increased the cAMP level. These results are compatible with the view that physiological actions of catecholamines in the nervous system may be mediated by an increase of CAMP.

Long-term effects of postnatal 6-hydroxydopamine treatment on tissue catecholamine levels

Abstract: Littermate albino rats were injected with doses of 6-hydroxydopamine hydrobromide (6-OHDA) intracisternally (i.c.) (0, 50, 100 or 200µg) or i.p. (0, 2.5, 5.0 or 10.0 mg/kg) at birth, and again 48 hours later. The animals were killed at 3, 12, 24 or 60 days of age and brain norepinephrine (NE) and dopamine, adrenal NE and epinephrine, and cardiac and splenic NE were determined. The i.c. administration of 6-OHDA produced doserelated decreases in the catecholamine contents of brain, heart and spleen, whereas the i.p. treatment decreased NE only in the heart and spleen. The highest i.c. dose reduced adrenal NE content in animals autopsied at 24 days of age and decreased epinephrine content in those animals sacrificed at 60 days of age; lower i.c. doses and all i.p. doses were ineffective. Brain NE was more depressed by i.c. 6-OHDA than was brain dopamine and showed less recovery to normal levels. Cardiac and splenic NE levels recovered partially from the effects of 6-OHDA administered via either route. Intracisternal 6-OHDA severely impaired growth; hence, the effect of the drug on catecholamine levels in the brain and in sympathetic neurons may result from both a toxic action on the nerve terminals and from the malnourished state of the animal. Other rats received i.c. 6-OHDA at birth, or at 12 or 24 days of age and again 48 hours later. The brain contents of both NE and dopamine were maximally depressed when treatment was begun at birth; a clear, age-related trend was observed which suggests increasing resistance to the effects of 6-OHDA.

Effects of adrenergic agonists and antagonists on adenylate cyclase activity of dog heart and liver.

Abstract: The purpose of this investigation was to differentiate cardiac and hepatic adrenergic receptors iim terms of the response of adenylate cyclase to catecholamines and beta antagonists added to particulate preparations of the enzyme. Dissociation constants (KB) for the heart preparation were 0.051 µM for propranolol and 56, 73 and 73 µM for butoxamine, isopropylmethoxamine and methoxamine, respectively. The KB for an antagonist did not differ with each of the three catecholamine agonists used (isoproterenol, epinephrine and norepinephrine). The affinities for the liver enzyme preparations were much higher, KB = 0.001 to 0.01 µM for propranolol and 1.7 to 4.0 µM for butoxamine, but these values varied with the agonist that was used. These data suggest a different type of beta receptor for these compounds in liver and heart. The higher potency of butoxamine in inhibiting adrenergic stimulation of liver adenylate cyclase provides an explanation for the observations made in vivo by other investigators, that methoxamine congeners blocked hepatic receptors more easily than the inotropic and biochemical responses of heart. The activation constants of catecholamines for cardiac adenylate cyclase were 275 to 660 times greater than the EC5O reported in time literature for these agents in stimulating cardiac contraction in vivo or in vitro . This discrepancy may reflect artifacts in the enzyme assay system, loss of sensitivity to stimulation after homogenization, or lack of dependence of augmentation of cardiac contraction on time activation of adenylate cyclase.