Pre- 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 cephalic vein of newborn dogs. For the sake of comparison, some experiments were also carried out on the veins of adult animals. 2. 5-HT reduced, in a concentration-dependent manner the overflow of tritium evoked by electrical stimulation of tissues previously loaded with 3H-noradrenaline for the same range of concentrations (0.01-1 microM 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 adults, respectively. 3. Postjunctionally, 5-HT caused concentration-dependent contractions of vessels from both neonates and adults and its EC50 values were not significantly different at the two ages. The maximal 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 antagonized 5-HT effects while ketanserin was ineffective, both pre- and postjunctionally, in newborn and adult dogs. 5. It is concluded that there are 5-HT receptors at pre- and postjunctional level at birth and that these receptors probably belong to the 5-HT1 type.
Paiva
M Q
MQ
Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal.
Santos
M J
MJ
Guimarães
S
S
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008719:Methiothepin / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D014661:Vasoconstriction; D014680:Veins / Q000187:drug effects* / Q000378:metabolism
D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D008719:Methiothepin; D009638:Norepinephrine