Hypopituitarsim is associated with triglyceride enrichment of very low-density lipoprotein

The dyslipidemia associated with hypopituitarism may contribute to increase d vascular mortality. The atherogenic potential of lipoproteins is determin ed not only by concentration but also by their composition. We therefore st udied very low-density lipoprotein composition and apolipoprotein B kinetic s in 16 hypopituitary subjects and 16 controls. Hypopituitarism was associa ted with reduced high-density lipoprotein cholesterol (0.98[0.82-1.18] vs. 1.35[1.15-1.41] mmol/liter, P < 0.001) and increased triglyceride concentra tions (1.64[1.09-2.77] vs. 1.12[0.66-1.67] mmol/liter, P = 0.01). Total (P = 0.76) and low-density lipoprotein cholesterol (P = 0.56) concentrations w ere similar. Very low-density lipoprotein-triglyceride was significantly in creased (1.48[1.02-2.55] vs. 0.9[0.31-2.30] mmol/liter, P = 0.004), but ver y low-density lipoprotein cholesterol levels were similar (P = 0.93). The m olar ratios of very low-density lipoprotein-triglyceride:apolipoprotein B ( 6193[4283-9566] vs. 3599[3188-6854], P = 0.005) and very low-density lipopr otein-triglyceride:cholesterol (2.8[1.98-3.78] vs. 1.6[1.44-2.80], P < 0.00 3) were significantly increased; very low-density lipoprotein-cholesterol:a polipoprotein B molar ratios (P = 0.93) were similar. Very low-density lipo protein apolipoprotein B fractional synthetic rate (a measure of apolipopro tein B catabolism, P = 0.42) and pool size (P = 0.63) were similar. The ver y low-density lipoprotein apolipoprotein B absolute synthetic rate (a measu re of apolipoprotein B synthesis) tended to be higher in hypopituitarism (1 7.7[2.91-19.50] vs. 26.6[19.64-28.05] mg/kg per day, P = 0.24) but failed t o reach statistical significance. The absolute synthetic rate, and hence ve ry low-density lipoprotein production, correlated with very low-density lip oprotein triglyceride:apolipoprotein B ratio (P = 0.02, Rs = 0.63), suggest ing that triglyceride enrichment of very low-density lipoprotein is importa nt in the mechanism underlying very low-density lipoprotein overproduction in hypopituitarism. Because triglyceride-enriched lipoproteins are proather ogenic, this may contribute to the vascular mortality observed in hypopitui tarism. The reasons for these observations are unknown; GH deficiency or ro utine endocrine replacement may be important.