Responsiveness of porcine large and small luteal cells to luteotropic or luteolytic hormones and cell morphologic changes during the estrous cycle and pregnancy.

Isolated porcine luteal cells from d 10 and 15 of the estrous cycle (estrus = d 0) were incubated with or without combinations of FSH (0, 10, 10(2), 10(3) ng), LH (0, 10, 10(3) ng), oxytocin, or prostaglandin F2 alpha (PGF2 alpha) (each at 0, 10, 10(3), and 10(5) pg). Progesterone (P4) content was determined after overnight incubation (0 h) then at 2 and 24 h of incubation. The basal (0 h) P4 production of large cells (LC) from d 10 corpora lutea (CL) was 31-fold higher than that by small cells (SC) at 0 h. The LC and SC from d 10 but not those from d 15, were stimulated to a small extent by LH (P < .05). The FSH inhibited P4 production (P < .05) by SC at 24 h on d 10 and by LC after 2 or 24 h of incubation on d 15. There was no interaction between LH and FSH on P4 production. Oxytocin and PGF2 alpha decreased P4 production by d 15 LC at 2 h of incubation (P < .05) and by d 15 SC after 2 or 24 h of incubation (P < .05 and P < .01). The morphology of cells from CL of the cycle or early or mid pregnancy were examined using scanning and transmission electron microscopy (EM). Freshly isolated LC (using scanning EM) from d 10 contained many microvilli arranged in apparent networks on their membranes, but SC had smooth surfaces and contained only a few microvilli. Internally, LC had more small mitochondria than did SC and a different organization of smooth endoplasmic reticulum (SER). The SC from CL of pregnant (d 30 to 60) gilts contained more mitochondria than SC from CL of cyclic gilts. The results indicate that FSH, oxytocin, and PGF2 alpha can have a direct cellular luteolytic effect in the late luteal phase in pigs. The FSH influenced LC, whereas oxytocin and PGF2 alpha effected a more pronounced decrease in P4 from SC. The lower amount of P4 produced overall by SC may be associated with fewer microvilli, mitochondria, and SER in SC.