Ockner R K, Burnett D A, Lysenko N, Manning J A
J Clin Invest. 1979 Jul;64(1):172-81. doi: 10.1172/JCI109437.
Female sex and estrogen administration are associated with increased hepatic production of triglyceride-rich lipoproteins; the basis for this has not been fully elucidated. Inasmuch as hepatic lipoprotein production is also influenced by FFA availability and triglyceride biosynthesis, we investigated sex differences in FFA utilization in rat hepatocyte suspensions and in the components of the triglyceride biosynthetic pathway. Isolated adult rat hepatocyte suspensions were incubated with albumin-bound [(14)C]oleate for up to 15 min. At physiological and low oleate concentrations, cells from females incorporated significantly more (14)C into glycerolipids, especially triglycerides, and into oxidation products than did male cells, per milligram cell protein. At 0.44 mM oleate, incorporation into triglycerides in female cells was approximately twice that in male cells. Comparable sex differences were observed in cells from fasted animals and when [(14)C]-glycerol incorporation was measured. At higher oleate concentrations, i.e., fatty acid:albumin mole ratios in excess of 2:1, these sex differences were no longer demonstrable, suggesting that maximal rates of fatty acid esterification and oxidation were similar in female and male cells. In female and male hepatic microsomes, specific activities of long chain acyl coenzyme A synthetase, phosphatidate phosphohydrolase, and diglyceride acyltransferase were similar, but glycerol-3-phosphate acyltransferase activity was slightly greater in females at certain substrate concentrations. Microsomal incorporation of [(14)C]oleate into total glycerolipids was not significantly greater in females. In further contrast to intact cells, microsomal incorporation of [(14)C]oleate into triglycerides, although significantly greater in female microsomes, accounted for only a small fraction of the fatty acid esterified.The binding affinity and stoichiometry of partially purified female hepatic fatty acid binding protein (FABP) were similar to those of male FABP. In contrast, the concentration of FABP, per milligram cytosolic protein, was 44% greater in female liver than in male, as indicated by measurement of [(14)C]oleate binding and of 280 nm OD in the FABP fraction of 105,000 g supernate after gel filtration chromatography. These experiments demonstrate profound sex differences in hepatocyte utilization of long chain fatty acids at concentrations within and below the physiological range, and suggest that these are attributable at least in part to corresponding differences in cytosolic FABP concentration. At higher FFA concentrations, sex differences in hepatocyte FFA utilization are virtually eliminated, suggesting that under these conditions, differences in FABP concentration are not rate determining. Sex differences in hepatic lipoprotein production may largely reflect these important differences in the initial stages of hepatocyte FFA utilization.
女性性别和雌激素给药与富含甘油三酯的脂蛋白肝脏生成增加有关；其基础尚未完全阐明。鉴于肝脏脂蛋白生成也受游离脂肪酸（FFA）可用性和甘油三酯生物合成的影响，我们研究了大鼠肝细胞悬液中FFA利用以及甘油三酯生物合成途径各组分中的性别差异。将分离的成年大鼠肝细胞悬液与白蛋白结合的[(14)C]油酸孵育长达15分钟。在生理和低油酸浓度下，每毫克细胞蛋白中，雌性细胞比雄性细胞将显著更多的(14)C掺入甘油脂质，尤其是甘油三酯以及氧化产物中。在0.44 mM油酸浓度下，雌性细胞中甘油三酯的掺入量约为雄性细胞的两倍。在禁食动物的细胞中以及在测量[(14)C]-甘油掺入时观察到了类似的性别差异。在较高油酸浓度下，即脂肪酸：白蛋白摩尔比超过2:1时，这些性别差异不再明显，这表明雌性和雄性细胞中脂肪酸酯化和氧化的最大速率相似。在雌性和雄性肝脏微粒体中，长链酰基辅酶A合成酶、磷脂酸磷酸水解酶和甘油二酯酰基转移酶的比活性相似，但在某些底物浓度下，雌性的甘油-3-磷酸酰基转移酶活性略高。[(14)C]油酸掺入雌性微粒体中总甘油脂质的量并无显著增加。与完整细胞形成进一步对比的是，[(14)C]油酸掺入微粒体甘油三酯中，尽管在雌性微粒体中显著更高，但仅占酯化脂肪酸的一小部分。部分纯化的雌性肝脏脂肪酸结合蛋白（FABP）的结合亲和力和化学计量与雄性FABP相似。相反，通过凝胶过滤色谱后在105,000 g上清液的FABP组分中测量[(14)C]油酸结合和280 nm光密度表明，每毫克胞质蛋白中FABP的浓度在雌性肝脏中比雄性高44%。这些实验证明，在生理范围内及以下浓度时，肝细胞对长链脂肪酸的利用存在显著的性别差异，并表明这些差异至少部分归因于胞质FABP浓度的相应差异。在较高FFA浓度下，肝细胞FFA利用的性别差异几乎消除，这表明在这些条件下，FABP浓度差异不是速率决定因素。肝脏脂蛋白生成中的性别差异可能在很大程度上反映了肝细胞FFA利用初始阶段的这些重要差异。
