Bioscientifica Proceedings

Summary. Data on the structure, quantitation, origins and functions of the large luteal (LL) and small luteal (SL) cells of sheep, goats and cattle are reviewed. Both LL and SL cells show ultrastructural features consistent with a steroidogenic function. However, in addition to differences in size and shape, LL cells differ from SL cells primarily in possessing large numbers of secretory granules, suggesting an additional protein/polypeptide synthetic and secretory function. In sheep, morphometric estimates show that the corpus luteum (CL) contains ≃ 10 × 10⁶ LL cells and ≃50–60 × 10⁶ SL cells: individual LL cells are ≃ × 6 greater in volume than SL cells. During formation of the CL, granulosa and theca cells are incorporated, and evidence suggests that granulosa cells give rise to LL cells and theca cells to SL cells. However, SL cells, or cells of thecal origin, may also give rise to some LL cells. Both LL and SL cells produce progesterone in vitro. On a per cell basis, LL cells produce more progesterone than do SL cells, but SL cells show a much greater progesterone-secretory response to LH. Oxytocin is synthesized, and secreted in granule form, only by the LL cells, and relaxin, whose presence has been demonstrated convincingly only in cattle, also appears to be produced only by LL cells. The two types of luteal cell in ruminants therefore show major differences in function: the occurrence of any significant functional interaction remains to be established.

© 1987 Journals of Reproduction & Fertility Ltd