Regulatory roles of high-density and low-density lipoproteins in cellular proliferation and secretion of progesterone and insulin-like growth factor I by enriched cultures of bovine small and large luteal cells.
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We tested the hypotheses that bovine high-density (HDL) and low-density (LDL) lipoproteins differentially influence cellular proliferation and progesterone and IGF-I production by bovine small and large luteal cells. Unit gravity sedimentation was used to produce enriched cultures of small (> 95% pure) and large (75 to 90% pure) luteal cells from corpora lutea (CL) on d 4 and 10 of the estrous cycle. Addition of LDL, HDL, or both resulted in the maintenance of higher (P < .05) numbers of 3beta-hydroxysteroid dehydrogenase (HSD)-positive small and large cells in culture and produced a marked proliferation of 3beta-HSD-negative small luteal cells compared to control medium. Low-density lipoprotein and HDL each stimulated greater (P < .01) progesterone secretion in enriched large cell cultures on both days of the cycle, and by small luteal cells on d 10, compared to the control. Together, LDL and HDL maximized this response. Lipoproteins markedly stimulated (P < .01) the secretion of IGF-I by bovine large luteal cells, and secretion was greater (P < .05) by cells from d 10 CL compared to d 4 CL. Results suggest that the actions of lipoproteins in bovine luteal cells extend beyond their widely recognized roles in steroidogenesis and include remarkable effects on cellular proliferation and IGF-I secretion. Type of lipoprotein (LDL vs HDL) did not have differential effects on any of the variables measured.