Considerations on the Cause of Disappearance of the Adrenergic Transmitter in Uterine Nerves during Pregnancy

Sjöberg, N.-O. Considerations on the cause of disappearance of the adrenergic transmitter in uterine nerves during pregnancy. Acta physiol. scand. 1968. 72. 510–517. With a combination of fluorescence histochemical and fluorimetric techniques it has been demonstrated that the smooth muscle coats of the guinea-pig uterus have a fairly rich supply of short adrenergic neurons, i.e. neurons arising in the vicinity of the organ, emitting a green fluorescence owing to their noradrenaline content. During the last period of pregnancy the neuronal fluorescence as well as the uterine noradrenaline disappears. Using animals with unilateral pregnancy it has been possible to establish that despite a marked difference in weight and distention between the two horns there is no difference in the reaction of the adrenergic nerves during the period of pregnancy studied (32–63 days of gestation). Hence, it seems probable that the marked changes in transmitter content found during the latter part of pregnancy are due to a humoral rather than to a mechanical factor.