Time of Appearance and Duration of Pregnancy Cell Types in Hypophysis of the Rat. ∗

Abstract

Numerous observers have reported the presence of peculiar cell types ('pregnancy cells') in the pars anterior of the hypophysis during pregnancy. Despite their rather distinctive appearance little is known regarding their allocation with respect to the reproductive cycle. Data are lacking on the time of their appearance following copulation, their persistence, and the effect of parturition and lactation upon their survival.

To determine these points, a large number of carefully selected female rats, with no previous reproductive history, was utilized. The procedure consisted in obtaining material from (1) a series of timed pregnancies, dated from actual copulation or from the discovery of a vaginal plug; (2) a series of postpartum animals sacrificed at definite intervals throughout the period of lactation; (3) a series of daily stages following premature withdrawal of litters; and (4) a series of stages throughout pseudopregnancy.

Pituitaries, ovaries, and uteri of all stages were fixed with Zenker-formol-osmic fixative for histological study. Pituitaries were sectioned at 3 microns, other tissues at 5 and 7 microns. The mounted tissues were stained with Delafield's haematoxylin and eosin or with Mallory's triple connective tissue stain.

Time of appearance and duration post coitus. Material from animals of 5 hour, 12 hour, 1 day, and daily stages thereafter throughout the gestational period (22 days) was studied in this series, from 3 to 5 animals being used for each stage in the preliminary work. In the pituitaries of these animals pregnancy cells became discernible on the 3rd day following copulation. The large ovoid cells, with an eccentrically located vesicular nucleus and with a clear, homogeneous cytoplasm, stained deeply with eosin. These cell types were readily apparent by the 4th day. An increase in number and to some degree in size followed until the 12th day, after which time the pregnancy pituitary appeared to undergo no further change.