REGULATION OF CHOLESTERYL ESTER TRANSFER ACTIVITY IN ADIPOSE-TISSUE -COMPARISON BETWEEN HAMSTER AND RAT-SPECIES

The present study demonstrates cholesteryl ester transfer activity (CE TA) in cultured hamster and rat adipose tissue. Cultured hamster and r at adipose tissue fragments released CETA into the conditioned medium, and this was associated with a reciprocal decrease in adipose tissue CETA. Regional variations in adipose CETA were observed. The levels of CETA released from cultured hamster and rat adipocytes were higher th an those from adipose tissue fragments. In hamsters but not in rats, t he secretion of CETA from cultured adipose tissue was increased by ins ulin and inhibited by EDTA in a dose-dependent fashion. Monoclonal ant ibodies against human cholesteryl ester transfer protein inhibited the CETA secreted from hamster adipose tissue but not that from rat adipo se tissue. Fasting for 24 h and a high-cholesterol saturated fat-rich diet increased adipose CETA in hamsters and rats, and this was associa ted with an elevation of plasma CETA only in hamsters. This supports t he view that, in hamsters, adipose CETA has in situ and intravascular functions, whereas in rats the role of adipose CETA is restricted to t issue-specific functions. Hamster cholesteryl ester transfer protein m ay differ from rat adipose-associated CETA in the structure of the act ive site and the regulatory mechanism for its secretion.