Radioimmunoassay of 5-methoxy tryptophol in sheep plasma and pineal glands

No 5-methoxytryptophol (ML) could be detected in sheep plasma using a specific, sensitive radioimmunoassay developed for the purpose. Blood samples were collected from sheep during darkness and daylight and during various stages of the estrous cycle, but in no sample was the ML content above the detection limit of the method. Addition of 1 mM pargyline and neostigmine to blood immediately after collection to block metabolism did not result in a detectable ML concentration. The failure to detect ML was not due to degradation since added ML was not degraded by blood enzymes even after 16 hours incubation at 37 degrees C. Injection of 100 microgram and 1 mg ML sc in sheep resulted in a rapid rise of ML to 95-130pg/ml and 560-1000pg/ml respectively and disappearing with a half life of approximately 15-20 minutes. Sheep pineal glands collected during the light phase contained ML (51 +/- 5pg/mg tissue. X +/- SE, n = 7) which represents less than 6% of the melatonin content. It is concluded that if ML is present in sheep blood it is present at very low levels. It is thus unlikely to be a major circulating pineal hormone in this species, however, its role within the CNS as a local hormone cannot be excluded.