Endocrine activity, histochemistry and ultrastructure of ovine corpora lutea

Summary

The progesterone concentration, histology, histochemistry and ultrastructure of the corpora lutea of six sheep hysterectomized early in the oestrous cycle were studied 137–146 days after ovulation. In one of these animals the corpus luteum had recently regressed to become a corpus albicans.

The progesterone concentrations in the luteal tissue were comparable with the values for active corpora lutea of the cycle. However in the peripheral blood of the hysterectomized sheep the concentration of progesterone was much lower than that in the luteal phase of the cycle.

The lutein cells of the hysterectomized sheep differed from those in the cycle in that the nucleoli were smaller, there were fewer free ribosomes and less granular and agranular endoplasmic reticulum; also the lipid droplets were larger, and cytoplasmic granules that stained with azocarmine were seen. Acid phosphatase activity was higher and there were large cytosomes of a type not seen in the cycle; these may be a morphological expression of the impaired hormone release. Karyorrhexis, a distinctive feature of regression at the end of the oestrous cycle, was only observed in the hysterectomized sheep with the corpus albicans.

In conclusion, luteal regression following hysterectomy appears to differ from regression at the end of the oestrous cycle in that the initial changes involve impaired hormone release from the gland rather than impaired synthesis.