Effect of cyclodextrin-encapsulated β-carotene on progesterone production by bovine luteal cells

Experiments were conducted to examine the effect of cyclodextrin-encapsulated beta -carotene on basal or cholesterol (cyclodextrin-encapsulated), LH and dibutyryl cyclic AMP (dbcAMP)stimulated progesterone production by bovine corpus luteum cells isolated from mid-luteal heifer ovaries by collagenase digestion. Cells were cultured with serum-free DMEM/Ham's F12 medium in serum pre-treated plastic culture dishes for periods of up to 11 days. Medium was replaced after 24h and thereafter every 48h. beta -carotene was added to cultures in a carrier molecule, dimethyl-beta -cyclodextrin, to facilitate dissolution. All treatments were started on day 3 of culture. Treatment of cells with 1 or 2 mu mol/l beta -carotene resulted in sharp inhibition of progesterone production. On the contrary, treatment of cells with 0.1 mu mol/l beta -carotene resulted in significant stimulation (P < 0.05) of both basal and cholesterol-stimulated progesterone secretion. The effect of <beta>-carotene on LH or dbcAMP-stimulated progesterone production was also examined. Treatment of cells with LH or dbcAMP always resulted in stimulation of progesterone secretion (P < 0.001). However, cells treated with LH plus <beta>-carotene or dbcAMP plus beta -carotene both produced significantly (P < 0.01) less progesterone relative to those cells treated with LH or dbcAMP alone on days 7, 9 and 11 of culture. These results indicate that <beta>-carotene can enhance luteal steroidogenesis when present at low concentrations but is inhibitory at higher concentrations and that encapsulation of beta -carotene in cyclodextrin is an effective method of supplying it to cells in culture. (C) 2000 Elsevier Science B.V. All rights reserved.