PREJUNCTIONAL AND POSTJUNCTIONAL EFFECTS OF 5-HYDROXYTRYPTAMINE IN DOG CEPHALIC VEINS OF NEONATES

1. This investigation was undertaken to determine the existence of pre - and postjunctional effects of 5-hydroxytryptamine (5-HT) in the ceph alic vein of newborn dogs. For the sake of comparison, some experiment s were also carried out on the veins of adult animals. 2. 5-HT reduced , in a concentration-dependent manner the overflow of tritium evoked b y electrical stimulation of tissues previously loaded with H-3-noradre naline for the same range of concentrations (0.01-1 mu M 5-HT) in both neonates and adults. The maximal reduction of tritium overflow caused by 5-HT was 36 +/- 6% and 77 +/- 5% (n=4; P<0.001) in neonates and ad ults, respectively. 3. Postjunctionally, 5-HT caused concentration-dep endent contractions of vessels from bo th neonates and adults and its EC(50) values were not significantly different at the two ages. The ma ximal effect of 5-HT was smaller in newborn (0.69 +/- 0.03 g/mg) than in adult (1.16 +/- 0.06 g/mg) animals (n=9; P<0.01).4. Metitepin antag onized 5-HT effects while ketanserin was ineffective, both pre- and po stjunctionally, in newborn and adult dogs. 5. It is concluded that the re are 5-HT receptors at pre- and postjunctional level at birth and th at these receptors probably belong to the 5-HT1 type.