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

This experiment was designed to study the effects of cell-to-cell contact, arachidonic acid (10 microM; AA), oxytocin (10 microM), 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 degrees C in 5% CO2 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 pretreatment 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.(ABSTRACT TRUNCATED AT 250 WORDS)