INTERACTIONS BETWEEN LARGE AND SMALL LUTEAL CELLS COLLECTED DURING THE MID-LUTEAL OR LATE-LUTEAL STAGES OF THE BOVINE ESTROUS-CYCLE

The effects of contact between large and small bovine luteal cells tog ether with those of luteinizing hormone (LH) or arachidonic acid (AA) on progesterone production during the oestrous cycle were investigated . Corpora lutea were collected during the mid-luteal stage (Days 10-12 ; n = 4) and late-luteal stage (Days 17-18; n = 4) of the oestrous cyc le. Large and small luteal cells were dispersed and separated and then incubated together or separately. Mid-luteal stage cells were treated with LH (0 or 5 ng) whereas late-luteal stage cells were treated with LH (0 or 5 ng) or AA (0 or 10 mu M). Culture medium was collected and replaced 1, 3 and 6 h after starting treatments. Progesterone product ion decreased (P < 0.0001) with increased incubation time irrespective of cell arrangement, the stage of the oestrous cycle or treatment. Du ring the 18 h before treatment, cells in the contact arrangement produ ced more progesterone (P < 0.003) than cells without contact in both m id- and late-luteal stages of the oestrous cycle; progesterone product ion within cell arrangements between prospective treatment groups was similar. After initiating treatments, mid-luteal stage cells in the co ntrol group without contact produced more progesterone (P < 0.01) than cells with contact. Mid-luteal stage cells treated with LH produced m ore (P < 0.0001) than control cells; progesterone production between c ell arrangements within the LH treatment group was similar. In the lat e-luteal stage cells, both LH and AA increased (P < 0.001) progesteron e production by comparison with control cells; LH and AA treatment gro ups produced similar results. Cells in the control group without conta ct produced more (P < 0.01) progesterone than cells with contact, wher eas LH- and AA-treated cells in contact produced more (P < 0.03) proge sterone than cells without contact. These data show that, during the f irst 18 h of incubation, contact between small and large luteal cells stimulates progesterone production; however, after 18 h, contact in un treated cells appears to inhibit progesterone unless the cells are sti mulated with LH or AA.