Effects of high density lipoprotein containing high or low beta-carotene concentrations on progesterone production and beta-carotene uptake and depletion by bovine luteal cells

Luteal cells were isolated from mid-luteal heifer ovaries by collagenase di gestion. Cells were cultured with DMEM/Ham's F12 medium in serum pre-treate d plastic culture dishes for periods of up to 11 days. As beta-carotene is almost completely insoluble in all polar solvents, it was added to cultures in either dimethyl sulphoxide (DMSO), tetrahydrofuran (THF) or as high-den sity lipoprotein (HDL) containing high or low beta-carotene concentrations. Medium was replaced after 24 h, thereafter medium was changed every 48 h, Treatment of cells with DMSO alone or with beta-carotene (5 mu mol/l) in DM SO both resulted in significant (P < 0.01) stimulation of progesterone prod uction. beta-Carotene (5 mu mol/l) in THF did not alter progesterone produc tion but 50 mu mol/l beta-carotene in TNF resulted in significant inhibitio n (P < 0.02) of progesterone production on days 3 and 7, Cultures were also supplemented with bovine HDL preparations containing equal concentrations of cholesterol (25 mu g/ml) but high or low beta-carotene (12.4 or 0.44 mu g/mg of cholesterol). Both HDL preparations significantly stimulated proges terone production (P < 0.001) but the high beta-carotene HDL was significan tly (P < 0.02) more effective than the low beta-carotene HDL. However, when given together with bovine luteinizing hormone (bLH) or dibutyryl cAMP (db cAMP), the high beta-carotene HDL stimulated progesterone production less t han did the low NDL (P < 0.01). Uptake and depletion of beta-carotene by lu teal cells were also examined in culture, beta-carotene supplementation inc reased luteal cell beta-carotene from an initial level of 373 ng per 10(6) cells to 2,030 ng per 10(6) cells by day 6. In contrast, the levels in cont rol cells decreased to 14% of starting values during the same period. Cells treated with HDL containing high p-carotene on day 1 or days 1 and 3 were then incubated with or without bLH or dbcAMP for a further 2 days to invest igate the effect of bLH and dbcAMP on depletion of beta-carotene by luteal cells, beta-Carotene depletion in the luteal cells was significantly higher (P < 0.05) in LH- and dbcAMP-treated cells than in the control cells in bo th groups. These results indicate that the use of solvents such as DMSO or THF may have undesirable effects due to alteration of cell membrane permeab ility. Supplementation with bLH or dbcAMP may increase the metabolism of be ta-carotene in luteal cells, bLH or dbcAMP together with high beta-carotene WDL may, when combined with the effect of increased beta-carotene metaboli sm, give less stimulation than with low beta-carotene HDL. (C) 2000 Elsevie r Science B.V. All rights reserved.