Intercellular communication within the rat anterior pituitary gland: IV. Changes in cell-to-cell communications during pregnancy.

Cell-to-cell communication by gap junctions was investigated in the female rat anterior pituitary gland from 9 through 21 days of pregnancy and subsequently on days 2 and 20 of the lactational period. Compared with intact estrus females, the major morphological characteristics of the pituitary gland during pregnancy were remarkably developed prolactin cells and gonadotrophs. A close relationship of both cell types was clearly evident. Gap junctions were present at each of the time intervals studied; however, they were noted only between adjacent folliculo-stellate cells. No remarkable changes were noted in the number of gap junctions during the middle stage of pregnancy (day 9 through day 15), with the relative number resembling that found in intact, 90-day-old controls during estrus (0.47 +/- .01 junctions/follicle-control vs. 0.50 +/- 0.08--day 15 of pregnancy). In the later stages of pregnancy (day 17 through day 21), a demonstrable increase was observed (0.64 +/- 0.10--day 17, 0.79 +/- 0.11--day 19 and 0.72 +/- 0.12--day 21), whereas during the lactation, this pattern returned to that seen at midpregnancy. Since both prolactin and the gonadal steroid hormones dramatically fluctuate during pregnancy and lactation, it is postulated that they may have an active role in gap junction formation during these two phases of reproductive life.