SITE OF CATECHOLAMINE MODULATION OF FETOMATERNAL ELECTRIC-POTENTIAL DIFFERENCE IN THE PIG

Feto-maternal vascular (PDF-M) and amniotic-maternal (PDA-M) potential differences were measured simultaneously on seven occasions in six co nscious pigs of 100-106 days gestation. Resting values of PDF-M and PD A-M were not significantly different although the range was wide. Feta l intravascular injection of 20 mu g adrenaline, but not of saline, wa s associated with a prompt reversible change, of equal magnitude, in b oth PDF-M and PDA-M. In some experiments polarity was reversed. Fete-a mniotic potential difference did not change. There was no change in fe tal plasma K+ and Na+ concentrations. Because of the simultaneous and equal alterations in PDF-M and PDA-M following adrenaline and the anat omical configuration of the pig conceptus, we conclude that the catech olamine modifiable component of PDF-M is generated by electrogenesis i n the pig placenta, probably by its chorionic (trophoblastic) cell lay er.