Contact-associated interactions between large and small bovine luteal cells during the estrous cycle

Abstract

This experiment was designed to study the effects of cell-to-cell contact, arachidonic acid (10 μM; AA), oxytocin (10 μM), and luteinizing hormone (5 ng; LH) on bovine luteal cell function. Corpora lutea collected from Holstein cows between Days 10 and 12 (n = 4; midluteal stage) or 17 and 18 (n = 4; late-luteal stage) of the estrous cycle (Day 0 = estrus) were dispersed, and small and large cells were separated by unit gravity sedimentation and flow cytometry. Large and small luteal cells were either incubated together, allowing intercellular contact, or separately, without intercellular contact, with culture well inserts. Cells were incubated in a modified Ham's F-12- N-hydroxyethylpiperazine- N′-2-ethanesulfonic acid medium. After an 18-hr preincubation period, treatments were introduced and cells were incubated for 240 hr. Media samples were collected and treatments were replaced at 48-hr intervals. Incubations were maintained at 37° C in 5% CO 2 in humidified air. Overall, progesterone secretion decreased with increased incubation time (P < 0.0001), regardless of treatment, stage of the cycle, or cell arrangement. During the 18-hr pre-treatment period, large and small luteal cells with contact secreted more progesterone than did luteal cells without contact during both the mid- (P < 0.0001) and late-luteal stages (P < 0.06) of the estrous cycle. After treatments were initiated, both mid- and late-stage luteal cells treated with LH secreted more (P < 0.0001) progesterone than occurred with any other treatment; oxytocin, AA, and control treatments were similar. A significant treatment × incubation time × intercellular contact interaction showed that: 1) after 48 hr of treatment, luteal cells without contact in the control and AA treatment groups secreted more progesterone (P < 0.01) than did luteal cells with contact; no other differences were found between the two cell arrangements within these treatment groups; 2) progesterone secretion by luteal cells with contact after treatment with LH for 48 hr was greater (P < 0.001) than that by luteal cells without contact; no other differences were found between the two cell arrangements within this treatment group; 3) no differences were found between the two cell arrangements throughout the incubation treatment period in the oxytocin-treated cells. These data suggest that large and small bovine luteal cells interact to regulate progesterone production during mid- and late-luteal stages of the estrous cycle and that this interaction is modified by endogenous compounds present at the level of the corpus luteum.