Plasma indolethylamine-n-methyltransferase activity and growth hormone level during sleep: a pilot study

Polygraphic recordings and sequential growth hormone (GH) samplings were performed in eight healthy adult males. In the plasma samples from seven of the subjects, indolethylamine-N-methyltransferase (INMT) activity was also determined. Five of eight subjects showed significant fluctuation in plasma GH level, and six of seven subjects showed significant fluctuation in plasma INMT activity level. There were also significant positive correlations between plasma GH and INMT activity level during the second episode of NREM sleep stage 1 and during the third episode of NREM sleep stage 2. A significant negative correlation between plasma GH and INMT activity level during the seventh episode of sleep stage 2 and during the fifth episode of post sleep-onset wake was found. In view of a previous finding that INMT activity in the serum of psychiatric patients is positively correlated with severity of delusions, the observation that NREM sleep is associated with mental activity characterized by repetitive thoughts, and the result that GH level in plasma is increased in NREM sleep early at night, our present findings suggest the hypotheses that increased plasma INMT activity during sleep is indicative of both increased INMT activity in the central nervous system (CNS) and the activation or maintenance of NREM mental activity during sleep. Additional research will be needed in order to validate our observations and test these hypotheses.