The Corpus Luteum of the Sheep: Relationships Between Morphology and Function During the Oestrous Cycle

Abstract

Certain structural and functional aspects of the regression of the corpus luteum in the sheep were studied using biochemical, histological, electron microscopic and histochemical techniques. Alterations in the size and density of mitochondria in the lutein cells on Day 12 or 13 of the oestrous cycle were the first sign of luteal regression seen. This was followed by the appearance of cytoplasmic lipid droplets on Day 13 or 14, in the large, definitive lutein cells. The rapid decline in the secretory activity of the corpus luteum on Day 15 was associated with a reduction in Δ5-3β-hydroxysteroid dehydrogenase and diaphorase activities, as well as with shrinkage of the lutein cells and pyknosis of their nuclei. Despite a general correlation between all the above regressive changes, however, there was in a few instances a lack of complete concordance between the parameters studied. It is therefore not possible to state that any one criterion gives a consistently reliable indication of the functional state of the corpus luteum. A good correlation was found between the progesterone concentration in the ovarian venous blood and that in the luteal tissue during the regression of the corpus luteum. The occurrence of some regressive changes on Day 12 may be related to the fact that this is the time when the ovine corpus luteum must be stimulated by an embryo in the uterus to survive.

Proceedings of the Australian Society for Reproductive Biology

“…In structural terms, they may reflect variations in sialic acid content or perhaps different combinations of the subunits reported by Gospodarowicz (1972) and Papkoff (1974) (Deane et al, 1966). On the basis of this finding and the data reported we postulate that the ability of the uterus to effect luteolysis is dependent on prior exposure to a finite amount of progesterone.…”

Effects of PMSG and the prostaglandin F-2 analogue, cloprostenol, on superovulation, fertilization and egg transport in the ewe

“…The administration of Cloprostenol in an attempt to control the timing of luteal regression and hence of oestrus and the ovulatory stimulus did not reduce the variation in ovulation rate or in the incidence of large (>6 mm diameter) follicles. Cloprostenol was injected at a time when cytological regression and perhaps also functional regression of the CL would have begun in many of the ewes (Deane, Hay, Moor, Rowson & Short, 1966;Bjersing, Hay, Moor, Short & Deane, 1970). Since, however, a single injection of Cloprostenol at the dosage used in this experiment is sufficient to induce luteolysis followed by ovulation when administered at mid-cycle (Trounson et al, 1976), this treatment was expected to have an overriding influence on luteal regression irrespective of the secretion of endogenous prostaglandin F-2a.…”

The Sheep Ovary: Regulation of Steroidogenic, Haemodynamic and Structural Changes in the Largest Follicle and Adjacent Tissue Before Ovulation

“…The CL regresses rapidly 48-72hr before ovulation (Deane et al, 1966) and at this stage the ovaries contain one or two large (4-5 mm diameter) activated follicles. The theca interna of these follicles contains many elongated fibroblastlike cells interspersed with large epithelioid cells that have ultrastructural characteristics typical of steroid-secreting cells.…”