Inactive hepatic lipase in rat plasma.

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Hepatic lipase (HL) activity is found in the liver, adrenal glands, ovaries, and plasma.
• Understanding HL's different forms and locations is crucial for metabolic research.

Purpose of the Study:

• To compare the subunit size and activity of hepatic lipase in rat liver, adrenal glands, and plasma.
• To investigate the origin and characteristics of different HL forms in plasma.

Main Methods:

• Subunit size analysis of HL in liver, adrenal glands, and plasma using SDS-PAGE.
• Measurement of HL activity and activity/mass ratio.
• In vivo heparin administration and analysis of postheparin plasma.
• Peptide-N-glycosidase F digestion to assess glycosylation differences.
• Co-elution studies with preparative polyacrylamide gel electrophoresis.
• Association studies with lipoproteins (HDL, LDL, VLDL).

Main Results:

• HL in liver and adrenal glands appeared as a 55 kDa band, while plasma HL showed 57 kDa and 59 kDa bands.
• Activity/mass ratios were similar for liver and adrenal HL but lower in plasma.
• Heparin administration increased plasma HL activity ~100-fold, introducing a 55 kDa band.
• The 55 kDa band in postheparin plasma co-eluted with activity and persisted after PNGase F digestion.
• Larger plasma HL forms (57/59 kDa) increased as the 55 kDa form decreased, suggesting transformation.
• Both HL forms in plasma were associated with HDL.

Conclusions:

• Rat plasma contains a larger, inactive form of hepatic lipase.
• This larger plasma HL form likely originates from the smaller HL form found in the liver and adrenal glands.
• Heparin administration facilitates the conversion and release of active HL into circulation, associated with HDL.