Variations in the activity of catechol-O-methyltransferase (COMT) in peripheral organs and in the brain of rat and rabbit fetus during development have been studied. The pattern of changes in COMT activity in rat fetus differed to a great extent according to the respective organs studied. In kidney and liver sharp declines occurred between days 18 and 20 and days 16 and 18 of fetal life respectively, followed by progressive increases up to onset of birth. Brain COMT of rat fetus declined progressively from day 16 of fetal life up to 0 hours after birth, while COMT activity in adrenal and heart showed its maximum value at the 20th day of fetal life and at 0 hours after birth respectively. In the contrary, the developmental changes in activity of rabbit fetus were very similar in all the organs except in the adrenals, since it decreased between day 24 to 8 hours after birth in heart, liver, brain and kidney. In the adrenals an important increase could be seen between the 24th and 28th days of fetal life. Rat COMT activity during 4 and 8 hours of postnatal life in heart, liver and kidney declined from 0-hour value but it increased in the brain and adrenals. COMT in rabbit increased after birth in all the organs studied. The results suggest that metabolic degradation of catecholamines by 3-O-methylation in rat and rabbit fetus may have different developmental patterns to some extent according to the physiological status of the organ concerned. These species related differences for monoamine inactivation during fetal development may suggest a physiological role for COMT as a marker of the maturation of the autonomic nervous system. © 1979 Springer-Verlag.
