The concentration of radioactivity from labeled epinephrine and its precursors in the dog adrenal medulla.

Abstract

Summary Twenty-six dogs were injected with 14C labeled epinephrine and its precursors and two different phenylethylamines. One dog was given an 125I labeled phenylethylamine. Blood samples were withdrawn at frequent intervals for the first 6 hours, the urine collected and the dog sacrificed at 6 or 24 hours. Tissue samples were obtained from 16 organs of each dog and the concentration of radioactivity determined and expressed as counts per minute per milligram of tissue. The average adrenal medulla:plasma ratio at 6 hours rose from 20 after 3,4-dihydroxyphenylalanine (dopa) to 740 after 3,4-dihydroxyphenylethylamine (dopamine) and then fell to 128 after norepinephrine and 126 after epinephrine. Similar ratios at 24 hours could not be obtained because of low plasma activity. However, activity concentrations in the adrenal medulla (cpm/mg) were tyrosine 34, dopa 110, dopamine 422, norepinephrine 401, and epinephrine 243. Activity concentrations in the adrenal medulla 6 hours after the administration of 14C labeled p-tyramine and phenylethylamine were low. Rapid deiodination of p-iodophenylethylamine 125I precluded any distribution studies. After dopamine the average adrenal medulla:kidney ratios were 72 and 170 after 6 and 24 hours, respectively. Similarly, adrenal medulla:liver ratios were 90 and 112. The plasma concentration of 14C radioactivity from dopamine fell more rapidly and to lower levels after the first hour than after any other compounds, a more rapid urinary excretion being also found. The concentration of radioactivity from labeled dopamine in the adrenal medulla is higher than the concentrations of 131I in metastases from thyroid cancer. These data suggest that similar studies after administration of labeled dopamine or similar compounds in patients with chromaffin tumors would be of interest.