ONTOGENY OF HYDROXYINDOLE-O-METHYLTRANSFERASE GENE-EXPRESSION AND ACTIVITY IN THE RAT PINEAL-GLAND

Postnatal development of hydroxyindole-O-methyltransferase (HIOMT) mRN A expression, HIOMT activity and melatonin content was investigated in the rat pineal gland from birth to adulthood (62-day old). For each a ge, animals were sacrificed at two different time-points: midday and m idnight. HIOMT mRNA was first detectable one day after birth and maxim al diurnal levels were reached at the end of the first week. A 2-fold nocturnal increase appeared significantly 11 days after birth. HIOMT a ctivity was detectable from 5 days of life and significant day/night v ariations did not appear before 21 days after birth. Appearance of mel atonin synthesis and rhythm followed that of HIOMT mRNA. The 10-day de lay observed between the appearance of the nocturnal increase in HIOMT activity and expression is discussed in term of differential regulati on of both HIOMT mRNA expression and HIOMT activity. (C) 1998 Elsevier Science B.V. All rights reserved.