INTERACTIONS BETWEEN LARGE AND SMALL BOVINE LUTEAL CELLS IN A SEQUENTIAL PERIFUSION COCULTURE SYSTEM

The objectives of this experiment were to study large and small luteal cell interactions and examine the effect of arachidonic acid (AA) on progesterone production by separated bovine luteal cells. Corpora lute a collected from Holstein cows (n = 5) on d 12 of the estrous cycle we re dispersed, and small (SLC) and large (LLC) luteal cells were separa ted by unit gravity sedimentation and flow cytometry. Cells were incub ated at 37-degrees-C in separate perifusion chambers with a modified H am's F-12-HEPES medium and aerated with 95% O2:5% CO2. The flow rate o f medium was 100 muL/min, and fractions were collected at 30-min inter vals for 4 h. Luteal cells were arranged in tandem so that medium from the first cell type would pass through the chamber containing the sec ond cell type. Luteal cells were arranged so that medium flowed from 1 ) SLC to SLC, 2) LLC to LLC, 3) SLC to LLC, 4) LLC to SLC, 5) SLC to L LC, 6) LLC to SLC; medium for arrangements 5 and 6 contained 10 muM AA . Cells in arrangements 5 and 6 were perifused for 30 min before AA wa s added. Progesterone was measured with an enzymeimmunoassay. The LLC to LLC arrangement had a greater (P < .05) average progesterone secret ion rate than all other cell arrangements, and the SLC to SLC arrangem ent had the least progesterone secretion rate. The SLC and LLC interac tions produced three major findings: 1) secretion from SLC seemed to i nhibit progesterone production in LLC; 2) addition of AA to the LLC to SLC arrangement reduced progesterone secretion rate compared with the LLC to SLC arrangement alone; 3) addition of AA to the SLC to LLC arr angement prevented the reduction in progesterone secretion described f or the unsupplemented SLC to LLC arrangement. The results of this stud y indicate that SLC and LLC from midluteal phase corpora lutea interac t and regulate progesterone secretion and that AA seems to be involved in this interaction. Perhaps AA cascade products have an integral rol e in the regulation of luteal progesterone production.