Validity of Retrograde Corpora Lutea of Pregnancy As an Index of Past Gestation in Sika Deer, Cervus nippon

Abstract

Corpora lutea of the sika deer (Cervus nippon, Cervidae) were histologically examined in order to elucidate their retrograding processes after parturition. They showed a remarkable regression within one month as luteal cells decreased in number and, by nine months after parturition, turned into masses of blood vessels containing many arterioles with a diameter of 30μm or less. In retrograde corpora lutea (RCL), older than 1.5 years after parturition, arterioles of these dimensions decreased markedly, while those measuring 50μm or more became dominant. These findings indicate that an examination of RCL can distinguish females less than nine months after parturition from those mote than 1.5 years after parturition. Based on the findings of RCL from the ovaries of a 10.5-year-old female, it is suggested that RCL remain in the ovaries for at least 8.5 years after parturition. It was, however, difficult to distinguish RCL of pregnancy from retrograde accessory corpora lutea (RACL). In order to arrive at a complete count of RCL, the ovaries should be examined at thicknesses of 0.5 mm. To check the presence/absence of RCL of pregnancy within nine months or less after parturition, sectioning at thicknesses of 2 mm is sufficient.