Role of Secondary Hyperparathyroidism in the Genesis of Hypertriglyceridemia and VLDL Receptor Deficiency in Chronic Renal Failure

Recent studies have revealed marked down-regulation of hepatic lipase (HL), lipoprotein lipase (LPL) and very low density lipoprotein-receptor (VLDL-R) expressions in animals with chronic renal failure (CRF). Acquired deficiency of these proteins, which together play an important role in catabolism of triglyceride-rich lipoproteins, is involved in the pathogenesis of CRF hypertriglyceridemia. Down-regulation of HL and LPL expressions in CRF can be completely reversed by parathyroidectomy (PTx), suggesting the role of excess parathormone (PTH). However, the role of hyperparathyroidism in the pathogenesis of CRF-induced VLDL-R deficiency has not been investigated before, and was studied here. To this end, VLDL-R mRNA (Northern analysis) and VLDL-R protein (Western analysis) of the fat pad and soleus muscle were compared in CRF (5/6 nephrectomized) rats, CRF animals with PTx (CRF-PTx) and sham-operated control animals. The CRF animals exhibited marked hypertriglyceridemia coupled with significant reductions in skeletal muscle and adipose tissue VLDL-R mRNA abundance and protein mass. Parathyroidectomy resulted in a significant, but partial, amelioration of CRF hypertriglyceridemia. However, in contrast to its effect on HL and LPL expressions, PTx did not improve VLDL-R expression, suggesting a PTH-independent mechanism for the latter abnormality. The differential effect of PTx on HL and LPL on the one hand and VLDL-R on the other can, in part, account for partial as opposed to complete correction of the associated hypertriglyceridemia with PTx in the CRF animals.