Lack of epinine formation in adrenal medulla and brain of rats during cold exposure and inhibition of dopamine beta-hydroxylase

Studies on the mechanism of the positive inotropic action evoked by epinine on the rabbit isolated papillary muscle at different rates of beating

1. Effects of epinine on cyclic AMP and contractility were investigated in rabbit papillary muscles driven at a rate of 0.5 or 2.0 Hz. 2. When the frequency of stimulation was increased from 0.5 to 2.0 Hz, the log dose-response curve for the positive inotropic effect of epinine was displaced to the left, whereas the maximum of the developed tension was not changed. 3. At both frequencies phentolamine (1 mumol/l) shifted the lower part of the log dose-response curve for epinine to the right, whereas pindolol (30 nmol/l) affected mainly the upper part. In the presence of both alpha- and beta-adrenoceptor antagonists, the whole curve was shifted to the right in a parallel manner. However, cocaine (30 mumol/l) did not significantly influence the log dose-response curve of epinine. 4. At 0.5 Hz a submaximal effective concentration of epinine (100 mumol/l) led to an approximately 100% increase of the cyclic AMP level after 60s; the same increase of the cyclic AMP level was induced at 2.0 Hz by one-third the concentration of epinine (30 mumol/l). 5. Phentolamine (1 mumol/l) did not affect the increase of the cyclic AMP level evoked by epinine, whereas pindolol (30 nmol/l) completely depressed it. 6. The present results indicate that epinine produces its positive inotropic effect through direct stimulation of myocardial alpha-adrenoceptors as well as beta-adrenoceptors, depending upon the concentration: in lower concentrations it acts mainly on alpha-adrenoceptors, whereas in higher concentrations it acts predominantly on beta-adrenoceptors. The positive inotropic effect through beta-adrenoceptor stimulation is mediated by cyclic AMP, while that through alpha-adrenoceptors is not.

Metabolism of 3, 4-dihydroxyphenylalanine, its metabolites and analogues in vivo in the rat: urinary excretion pattern

The metabolism and interrelationships of orally and intraperitoneally administered L-dopa, related amino acids and their metabolites have been studied 2. Amino acids were decarboxylated. N-Methyldopa formed dopamine but not epinine. D-Dopa was absorbed from the intestine and metabolized by a series of reactions which resulted in greater decarboxylation than was observed after L-dopa. Transamination was a minor pathway. 3. m-Hydroxylated phenylpyruvic acids were poorly reduced, but vanilpyruvic acid was reduced fairly readily. Lactic acids were largely unchanged. Lactic and pyruvic acids formed phenylethylamines and their metabolites. Small amounts of phenylpyruvic acids may be decarboxylated to phenylacetic acids. 4. Glycine conjugates were formed from phenylacetic acids, a partially reversible change 3,4-Dihydroxyphenylacetic acid was metabolized to homovanillic and m-hydroxyphenylacetic acids, especially when given orally. Little 3-hydroxy-4-methoxyphenylacetic acid was oxidized to 3,4-dihydroxyphenylacetic acid but some increase in m-hydroxyphenylacetic acid excretion was observed. 5. 2-Phenylethanol analogues were largely converted to the corresponding acids. 3,4-Dihydroxyphenylethanol was partially m-O-methylated before oxidation. 6. beta-Phenylethylamine analogues were oxidized mainly to phenylacetic acids. but a variable amount of analogous phenylethanol was also formed, especially from m-tyramine. Dopamine was O-methylated, a process not readily reversible. It was also p-dehydroxylated following oral and intraperitoneal administration but not after oral neomycin; biliary excretion of amines may be involved in this sequence of events. N-Methylated amines were oxidized less readily than the parent amine. 7. Differences in route of administration resulted in quantitative changes in degradation pathways, an effect deriving, to some extent, from p-dehydroxylation and O-methylation in the gut.