[Physiological and pharmacological studies of umbilical cord flow in man]

The results of investigations on physiology and pharmacology of the smooth muscle umbilical cord arteries are presented. In the first part of the investigations it has been found that there is a close dependence between the blood flow and perfusion pressure in the arterial bed of the cord. The pressure flow relationship is linear. The blood vessels of the umbilical cord influence actively the perfusion pressure changes. On the basis of the presented investigations, the possibility of existence of autoregulation in the umbilical cord circulation has been found which testifies to an active but not passive role of the vessels in the circulation between the foetus and placenta. It has been stated that the umbilical cord vessels show a spontaneous contractile activity which may play an important role in the regulation of the umbilical flow. In the case of lack of the smooth muscle spontaneous contractile activity, this could be induced by using active pharmacological substances, as for instance noradrenaline. The reaction of another important pharmacological substance bradykinin (BRS), has been closely associated with oxygen saturation of the perfusion solution. Changes in the sensitivity of the umbilical cord blood vessels to BRS, depending on the saturation with oxygen, have been emphasised, and the role and participation of kinins in closing up umbilical cord blood vessels immediately following labour have been discussed.