Effect of isoprenaline on the output of melatonin from fetal and newborn lamb pineals glands in vitro

We have measured the output of melatonin in vitro from the pineal glands of lambs in late gestation (135-143 days) and the early newborn period (4-8 days). The basal output of melatonin/mg pineal tissue was significantly lower in the fetal group (16.3 ± 3.9 pg melatonin · (30 min)^-1 · mg^-1) than in the newborn group (148.1 ± 43.6 pg melatonin · (30 min)^-1 · mg^-1). Addition of the β-adrenergic agonist, isoprenaline (10⁵ mol/l) significantly stimulated melatonin output from both the fetal (to 24.9 + 3.9 pg melatonin · (30 min)^-1 · mg^-1) and newborn pineals (to 247.7 plus minus 67.3 pg melatonin · (30 min)^-1 · mg^-1). Pineals from newborn lambs produced 9-10-fold more melatonin than the fetal pineal glands, before, during and after addition of isoprenaline. These results show that functional β-adrenergic receptors are present before birth on the sheep pinealocyte and that there is a marked increase in the melatonin synthetic capacity of the pineal in the newborn period.