Epinephrine synthesis by rat arteries

Cardiorenal epinephrine kinetics: evidence for neuronal release in the human heart

There are experimental data suggesting that epinephrine (Epi) may act as a cotransmitter in sympathetic nerves, stimulating presynaptic beta 2-receptors and enhancing norepinephrine (NE) release. To examine neuronal Epi release, patients with congestive heart failure and hypertension and healthy subjects were examined with the isotope-dilution method. At baseline, small cardiac and renal Epi spillovers were found in patients. During intense supine exercise, cardiac NE and Epi spillovers increased concomitantly with similar magnitude, whereas no renal Epi spillover could be detected. Blockade of neuronal uptake 1 caused a consistent decrease in both cardiac and renal fractional extractions of NE and Epi. The present study demonstrates baseline cardiorenal Epi release in patients with congestive heart failure and renal Epi release in hypertensive patients. Furthermore, Epi is removed by neuronal uptake in both the heart and kidney, and cardiac Epi spillover increases during exercise. This study, in contrast to other results, provides evidence for cardiac neuronal Epi release.

Glucocorticoid induction of epinephrine synthesizing enzyme in rat skeletal muscle and insulin resistance

Rat skeletal muscle contains two enzymes which can make epinephrine: phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase. We studied the time-course and mechanism by which the glucocorticoid dexamethasone increases muscle PNMT activity. We also examined the hypothesis that increased muscle E synthesis may contribute to glucocorticoid-induced insulin resistance. Dexamethasone (1 mg/kg s.c. for 12 d) increased muscle PNMT activity seven-fold but did not change NMT activity. Immunotitration with an anti-PNMT antibody indicated that the PNMT elevation was due to increased numbers of PNMT molecules. Dexamethasone rapidly increased PNMT activity and this elevation was largely maintained 6 d after glucocorticoid treatment stopped. Muscle epinephrine levels were transiently elevated by dexamethasone. Dexamethasone-treated rats had elevated insulin levels after a glucose load, and chronic administration of the PNMT inhibitor SKF 64139 reversed this increase. Chronic SKF 64139 improved glucose tolerance in normal rats. Dexamethasone induced muscle synthesis of the epinephrine-forming enzyme PNMT. A PNMT inhibitor lowered insulin levels in glucocorticoid-treated rats and glucose levels in untreated rats. These findings are compatible with antagonism of insulin-mediated glucose uptake by epinephrine synthesized in skeletal muscle.