CIRCADIAN SECRETION PATTERNS OF MELATONIN AFTER MAJOR SURGERY

Biorhythms, such as regular variation in core body temperature and the pattern of the secretion of melatonin, are thought to be mediated by the same biological clock. Core body temperature is affected by the in flammatory response to major surgery. Apart from the well-known inhibi tory effect of bright light on its secretion, melatonin is an exceedin gly good marker of one of the central generating systems of circadian rhythms. We sequentially measured the plasma melatonin concentration p attern in patients who had undergone esophagectomy with thoracotomy to elucidate the circadian rhythm after major surgery. From seven patien ts who had received esophagectomy with thoracotomy for esophageal canc er, plasma concentrations of melatonin were measured using an RIA meth od. Blood samples were collected via each patient's arterial line at 0 0.00, 02.00, 04.00, 06.00, 08.00, 12.00, 16.00, 20.00, and 24.00 hr on the first postoperative day for six of the patients, and, far one pat ient, every 2 hr until the third postoperative day and every 4 hr ther eafter until the sixth postoperative day. Four patients out of seven h ad melatonin concentrations of over 30 pg/ml (mean 34 pg/ml) at 24.00 hr on the first postoperative day. Five patients showed circadian secr etion patterns of melatonin during the first postoperative day. One pa tient whose melatonin concentrations were measured consecutively for 6 days showed a regular circadian secretion pattern through the 6 days of the study. Even the stress caused by extremely invasive surgery did not significantly disturb the melatonin secretion pattern.