Insulin-induced up-regulation of lipoprotein lipase messenger ribonucleic acid and activity in mammary gland

The effects of insulin on lipoprotein lipase (LPL) messenger RNA (mRNA) wer e studied in mammary glands from virgin and late-pregnant rats. Virgin and pregnant rats (at 17 days of gestation) were subjected to a continuous infu sion (35 ml/day) with 50% glucose for 72 h to produce a prolonged hyperinsu linemic-euglycemic condition. Gestation causes a 4-fold increase in LPL mRN A accompanied by a 3- to 4-fold increase in total LPL activity. Experimenta l hyperinsulinemia, generated by the 50% glucose infusion, had a similar ef fect in both pregnant and virgin rats, by enhancing (2- to 3-fold) both the ir LPL activity and LPL mRNA. Thus, total LPL activity and LPL mRNA signifi cantly correlated with plasma insulin (r = 0.789, P < 0.001; and r = 0.772, P < 0.001, respectively). Furthermore, total LPL activity was correlated w ith LPL mRNA (r = 0.765, P = 0.001). In conclusion, the present study shows that insulin participates in the control of LPL expression in mammary glan ds, revealing its role as a modulator of the enzyme at a mRNA level.