Neonatal hormone treatment and maturation of the pineal noradrenergic system: hydrocortisone and thyroxine.
The circadian release of norepinephrine from nerve terminals in the pineal gland drives acetyl-CoA:serotonin N-acetyltransferase (NAT; EC 2.3.1.5) activity in the adult pineal from a daytime low to a nighttime high. In the newborn, enzyme activity is intermediate between the adult's daily extremes and has only a small circadian fluctuation. With age, these fluctuations increase in amplitude until the adult pattern is attained at about days 10-12. Treatment of neonates with thyroxine for the first 3 days of life accelerated, whereas administration of hydrocortisone acetate at birth retarded the developmental decline in daytime serotonin-N-acetyltransferase activity. Maximal differences in daytime enzyme activity of controls and thyroxine-treated animals were seen at day 4 and between controls and steroid-treated pups at day 8. Desipramine treatment increase NAT activity in 8-day-old animals; hydrocortisone-treated animals were least affected. Freshly cultured pineals from steroid-treated animals were more responsive to low, and less responsive to high, concentrations of norepinephrine than glands from thyroxine-treated or control animals. They were also less responsive to isoproterenol both in acute and 48-h organ culture. Pineals from hydrocortisone-treated animals in culture accumulated less exogeneous norepinephrine than glands from controls but released a greater fraction of their content on transfer to fresh medium. Normal and steroid-treated animals released the same fraction of their norepinephrine contents into the medium when reuptake was blocked by desipramine (DMI).
D000123:Acetyltransferases / Q000378:metabolism*; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002940:Circadian Rhythm / Q000187:drug effects*; D006854:Hydrocortisone / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D009924:Organ Culture Techniques; D010870:Pineal Gland / Q000187:drug effects / Q000254:growth & development*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000494:pharmacology*
D000123:Acetyltransferases; D001191:Arylamine N-Acetyltransferase; D013974:Thyroxine; D011188:Potassium; D006854:Hydrocortisone; D009638:Norepinephrine