HISTOLOGICAL AND BIOCHEMICAL STUDIES ON THE OVARY AND OF PROGESTERONE LEVELS IN THE SYSTEMIC BLOOD OF THE GREEN ACOUCHI ( <i>MYOPROCTA PRATTI</i> )

Abstract

Summary. Combined histological and biochemical studies have been made in a small series of pregnant and non-pregnant acouchis. All pregnant animals had twin foetuses and their ovaries contained two to five large corpora lutea (cl) of ovulation and variable numbers of accessory cl which were very much smaller in size and bore evidence of having arisen from un-ovulated follicles. Normal Graafian follicles were also present, together with many small atretic follicles. The true corpora reached maximum size by the end of the 2nd week of pregnancy and had regressed before parturition. The occurrence of maximum secretory activity in early pregnancy, as indicated from estimates of the mean size of luteal cells, was confirmed by assays of luteal progesterone concentration. The accessory cl tended to increase in number as pregnancy advanced. The luteal cells, though slightly smaller, were otherwise indistinguishable from those of the true corpora and, depending on the stage of pregnancy, contributed 25 to 100% of the total amount of progesterone secreted by the ovary. In early pregnancy, plasma progesterone concentration increased rapidly to a level that was four times as great as that found in non-pregnant acouchis, and which thereafter declined. The rate of growth and decline of the cl of pregnancy, their secretory activity and the levels of progesterone in the systemic blood are compared with those reported in some other hystricomorph rodents.