Bovine luteal cell activity in culture. Maintenance of steroidogenesis by high density lipoprotein containing high or low beta-carotene concentrations

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Beta-carotene is transported in bovine blood in association with high density lipoprotein (HDL) and is also found in high concentrations within the bovine corpus luteum. We have examined the effect of HDL, containing high or low β-carotene concentrations, upon cyclic AMP-stimulated luteal cell steroidogenesis in culture. Cells were cultured in defined medium containing a low (1%) supplement of lipoprotein-deficient serum. In all experiments, addition of HDL (200 μg cholesterol/ml), irrespective of β-carotene concentration, markedly enhanced luteal progesterone synthesis and in most experiments maintained luteal cell steroidogenesis for at least 2 weeks in culture. In approximately 50% of experiments, β-carotene significantly enhanced progesterone synthesis, although no effect was seen in the other experiments. This inconsistency may be due to variations between cells from different corpora lutea since the same HDL samples had different effects on four cultures prepared from individual corpora lutea. These data show (1) that trophic-stimulated luteal cell steroidogenesis can be maintained at a high level in culture if sufficient substrate is provided and (2) that β-carotene can enhance luteal steroidogenesis although the effect is variable in vitro.