This study examined the effects of tumour necrosis factor-alpha (TNF alpha) on basal and stimulated progesterone secretion, as well as prostaglandin F2 alpha production, by small, large and mixed porcine luteal cells and assessed the action of TNF alpha in the presence and absence of indomethacin. Corpora lutea were isolated from gilts on days 8-9 of the oestrous cycle and enzymatically dissociated. Luteal cells were either subjected to elutriation to isolate small and large cells or were separated from erythrocytes by a polysucrose gradient to serve as the mixed luteal cell group. Then 24-well culture plates were seeded with 150,000 small, 30,000 large and mixed (30,000 large+100,000-250,000 small) luteal cells suspended in 1 ml medium 199 media supplemented with 5 micrograms insulin/ml, 40 ng cortisol/ml and 50 micrograms low-density lipoproteins/ml. Cells were cultured for up to 24 h in a humidified incubator at 37 degrees C with 5% CO2 in air. TNF alpha time- and dose-dependently suppressed (P < 0.05) LH-induced, but not basal, progesterone secretion by small luteal cells. Moreover, TNF alpha inhibited (P < 0.05) forskolin-mediated, but not cyclic AMP-mediated, progesterone secretion by small luteal cells. The LH-stimulated progesterone secretion by small luteal cells was not affected by TNF alpha in the presence of indomethacin. Progesterone secretion by large and mixed luteal cells was not affected by TNF alpha. Prostaglandin F2 alpha production by small and mixed, but not large, luteal cells was enhanced (P < 0.05) by TNF alpha.(ABSTRACT TRUNCATED AT 250 WORDS)