Influence of lipolysis on the mobilization of 2,4,5,2′4′,5′‐hexachlorobiphenyl from adipocytes in vitro

Abstract

Epididymal adipocytes, isolated from rats pretreated with [ ¹⁴ C]‐2,4,5,2’,4’,5'‐hexa‐chlorobiphenyl (6‐CB), were utilized to examine the relationship between the mobilization of lipid and 6‐CB and to determine whether 6‐CB was differentially associated with subcellular organelles over time as has been demonstrated for newly synthesized lipid. Lipolysis, induced by the presence of 8 × 70 ⁻⁷ M isoproterenol (ISO) for 50 min, depleted approximately 7% of total cellular triacylglycerols (TG) regardless of time from treatment with 6‐CB. The percentage of cellular 6‐CB released from adipocytes to incubation buffer infranatants was not correlated with the magnitude of lipolysis produced over the 50‐min incubation period; nor was the percentage of 6‐CB released to the buffers correlated with the length of the incubation period, regardless of the presence of ISO. Although adipocytes responded similarly to lipolytic stimuli independent of time (days) since 6‐CB treatment, significant decreases were found in the percentage of 6‐CB released from adipocytes over time. The in vitro labeling of this newly synthesized TG in fat cells with [U‐ ¹⁴ C]glucose or [7‐ ¹⁴ C]palmitate demonstrated that TG was differentially distributed among adipocyte organelles. Newly synthesized TG was also the first to be mobilized under lipolytic stimulus. 6‐CB was not released in a similar fashion, since radioactivity associated with the chemical levels of [ ¹⁴ C]‐6‐CB and glucose‐derived ¹⁴ C in buffers were not correlated over time. 6‐CB was found to redistribute to all available lipid pools during the subcellular fractionation procedure and thus did not resemble TG. However, it is possible that 6‐CB may exist in equilibrium among organelle fractions and that it becomes sequestered within the nonsoluble lipid compartment with time, thus decreasing its appearance in the soluble buffer infranatants over the experimental time course.