CHANGES IN UTERINE G-PROTEIN CONTENT DURING PREGNANCY IN THE GUINEA-PIG

G-protein content (G(i alpha), G(s alpha), G(q/11 alpha), G(o alpha) a nd beta subunits) has been measured in membranes prepared from guinea pig uterus at different stages of pregnancy using SDS-PAGE and immunob lotting. Quantification using HRP- or I-125-labelled IgG as second ant ibody showed a good correlation between added membrane protein and mea sured G-protein content. Gs alpha appears as two bands of 45 kDa and 5 2 kDa respectively, the content of both were comparatively high in the nonpregnant uterus and fell about 4-fold close to term (60-67 days). G(i alpha) showed the converse with low level in membranes from the no n-pregnant uterus with level approximately 6-fold higher by term. G(o alpha) exhibited changes similar to G(i alpha). The changes in the con tent of G(q/11 alpha) where biphasic, with comparatively high levels i n membranes from the non-pregnant uterus, a sharp fall early in pregna ncy followed by a 3-fold rise by near term. The uterine membrane conte nt of the common beta subunit exhibited changes comparable to that of G(i alpha) and G(o alpha) with a 6-fold rise in content between non- a nd late-pregnant. Measurement of the effect of GTP gamma S action on p hosphatidylinositol phospholipase C activity in uterine membranes with exogenous substrate showed pregnancy-dependent effects. In membranes from the non-pregnant uterus 0.1 mu M GTP gamma S caused a modest stim ulation of activity of 16 +/- 1.9%, whilst at 100 mu M it inhibited th e enzyme by 25 +/- 6.48 %. In membranes from the late-pregnant guinea pig uterus GTP gamma S at both concentrations caused stimulation of en zyme activity. The data demonstrate sharp changes in G-protein content in membranes of the guinea pig uterus during pregnancy and provide fu rther proof that inhibitory as well. as stimulatory GTP effects on IP3 production, which may change during pregnancy, are apparent.