A radiometric assay for phenylethanolamine N-methyltransferase and catechol O-methyltransferase in a single tissue sample: application to rat hypothalamic nuclei, pineal gland, and heart.

A simple and highly sensitive method for simultaneous assay of phenylethanolamine N-methyltransferase (PNMT) and catechol O-methyltransferase (COMT) is described. These enzymes are determined in a single tissue homogenate using S-[methyl-3H] adenosyl-L-methionine as methyl donor and sequentially incubating with the substrates phenylethanolamine and epinephrine. The radioactive products of the enzymatic reactions, N-methylphenylethanolamine and metanephrine, are extracted and then separated by thin-layer chromatography. The identity of the reaction products has been established chromatographically and the conditions for both enzymatic reactions in the assay procedure have been defined. Measurement of PNMT activity in the rat pineal gland or in minute fragments of other tissues (e.g., brain nuclei) has not been possible using previously described methods. Activities of PNMT and COMT in the rat pineal gland, various hypothalamic nuclei, and the auricular and ventricular myocardia are herein reported.

Hemodynamic and plasma catecholamine responses to hyperthermic cancer therapy in humans.

Cancer patients, treated with hyperthermia (to 41.5 degrees C) under thiopental and fentanyl anesthesia, had smaller increases in heart rate and cardiac index and lesser decreases in mean arterial pressure than those reported in normal volunteers. At basal body temperature anesthesia did not alter catecholamine levels. Increasing body temperature to 39.5 degrees C and 41.5 degrees C resulted in parallel increases in heart rate and cardiac index that were directly related to the increases in plasma norepinephrine levels. At basal temperature cutaneous venous plasma norepinephrine levels exceeded those of arterial; mixed-venous plasma levels were intermediate. At 39.5 degrees C and 41.5 degrees C there were sequential increases in plasma norepinephrine. The increases in mixed-venous and arterial norepinephrine were significantly greater than in cutaneous venous blood. The differential increases in norepinephrine levels in cutaneous venous, mixed-venous, and arterial blood indicate that during hyperthermia sympathetic nerve activity in skin is decreased while that in other areas is increased, suggesting that alterations in sympathetic activity modulate the hemodynamic changes that attend hyperthermia in man.