Up-regulation in late pregnancy of both Go1 alpha and Go2 alpha isoforms in human myometrium

The nature of the 39 kDa pertussis toxin substrate previously detected in human pregnant myometrium was investigated. Comparison of membranes from non-pregnant and from 39-40 week pregnant myometrium revealed a higher level at 39 kDa of pertussis toxin ADP-ribosylation and Go alpha immunoreactivity in late pregnancy. Furthermore, quantification of both Go alpha isoforms with specific anti-alpha o1- and alpha o2-antibodies revealed an increase in their expression in late pregnancy. At the same time, only limited changes in the levels of Gi1,2, Gi3 and Gq were observed. In rat myometrial membranes, neither pertussis toxin substrate nor Go alpha immunoreactivity could be detected at the 39 kDa level. These results demonstrate that, in the human myometrium in late pregnancy, there is an increase in the expression of both isoforms of the Go alpha subunits, suggesting a role for these proteins throughout gestation and/or near term for parturition.