Subcellular localization of prolactin in the anterior pituitary cells of the female Japanese house bat, Pipistrellus abramus.

We investigated the subcellular localization of PRL and GH in the pituitary gland of the female Japanese house bat by the double immunolabeling procedure using the protein A-gold method combined with electron microscopy and demonstrated a seasonal alteration in the distribution of PRL within the cells. The seasonal changes were related to the different phases of the bats' reproductive cycles. Mammosomatotrophs (MS cells) containing both PRL and GH were constantly present throughout the reproductive cycles of the female bats and they were remarkably hypertrophied during pregnancy. The distribution pattern of PRL and GH within the MS cells was extremely variable owing to the different phases of reproductive cycles of the bats. We divided MS cells into the following four types: the cell containing 1) only mixed granules containing both PRL and GH, 2) both mixed and PRL granules, 3) mixed, PRL and GH granules, 4) both mixed and GH granules. While pure PRL-containing cells were observed in pregnant and lactating bats, they were not observed in bats obtained during prehibernation, midhibernation, and arousal periods. These results suggest that MS cells in the female bats hypertrophy during pregnancy and that some of them may be transformed into PRL-producing cells.