Neuroeffector maturity of portal veins from newborn rats, rabbits, cats and guinea pigs.

Isolated portal veins from newborn and adult rats, rabbits, cats and guinea pigs were studied isometrically. Spontaneous activity and induced responses to transmural nerve stimulation (NS), noradrenaline, tyramine, acetylcholine and BaCl2 were quantitated. In agreement with our previous observations the portal veins of the newborn rat was found to lack spontaneous activity and responsiveness to applied stimuli whereas the newborn rabbit's portal vein showed inconsistent and weak responses. In the neonatal cat and guinea pig portal veins the pattern of the spontaneous activity and induced responses resembled those found in vessels from adult animals. It is concluded that the portal vein maturity at birth in several respects dramatic neuroeffector development of the portal vein during the postnatal period in the rat corresponds to prenatal events in cats and guinea pigs which are more highly developed at birth. Consequently, the lack of responsiveness of the portal vein during the first week of life does not seem to be secondary to the hormonal and hemodynamic adjustments during the neonatal period. Rather, the postnatal development of the rat portal vein occurs according to a genetically predetermined schedule, possible in parallel with the ontogenesis of vascular control in general.