A study on the relationship between parity and differentiation of granulated metrial gland cells

Granulated metrial gland (GMG) cells are a feature consistently associated with rodent pregnancy. Little information is available, however, on the life history of GMG cells in pregnancies other than first pregnancy. To determine if the frequency of GMG cells in the mesometrial triangle of mice is altered by parity, a study of histological sections from pregnant uteri of several females of genotype C.B-17 scid/scid.bg/bg being retired from a breeding program was undertaken. Pregnancies in this study ranged from first to 13th; day 12.5 of gestation was used for all analyses. The frequency of GMG cells in a constant, measured area of the metrial gland on day 12.5 of pregnancy was not significantly altered between first and second pregnancies. A small but statistically significant decline in GMG cell frequency was observed in two females who had given birth to 10 or more litters. However, neither the size of individual day 12.5 GMG cells, nor their granularity changed with parity. The surface area of the placenta in sections was not altered by the decrease in GMG cells. These data suggest that the differentiation of GMG cells from their non-granulated progenitors is a tightly regulated process, that GMG cell progenitors may be fully mature in first pregnancy, and that depletion of GMG cell progenitors is not induced by advanced parity or age.