Hormonal regulation of lipoprotein lipase activity from 5-day-old rat hepatocytes.
Lipoprotein lipase (LPL) activity is known to be synthesized, active and functional in the 1-day-old rat liver: it peaks just at birth triggered by parturition. During suckling LPL mRNA, LPL synthesis and LPL activity are still high at 5 days and then fade reaching adult values at weaning. How LPL expression is gradually extinguished is not known. Therefore we studied the effect of different doses of several hormones on LPL activity released by incubated hepatocytes from 5-day-old rats. In the presence of heparin the release of LPL activity in the medium was linear until 3 h and was always significantly increased vs. without heparin. At 3 h in the presence of heparin the main hormonal effects were: dose-dependent increase (30-60%) with dexamethasone; dose-dependent increase (20-60%) with glucagon; dose-independent decrease (50-60%) with ethinylestradiol, testosterone, progesterone and prolactin; no effect with insulin; 20-40% increase with adrenaline < 1 mM but 40-50% decrease with noradrenaline < 10 microM. Increase of LPL release by glucagon and adrenaline agrees with the increased LPL expression we previously found in an undifferentiated hepatoma cell line when the adenylate cyclase/protein kinase A pathway was activated. The effect of glucagon is concordant with our previous observations that fasting increases liver LPL activity in neonatal rats. The high estradiol levels known to be present in male and female 9-19-day-old rats might contribute to liver LPL extinction during suckling.
Julve
J
J
Departament de Bioquimica i Biologia Molecular, Universitat de Barcelona, Spain.
Robert
M Q
MQ
Llobera
M
M
Peinado-Onsurbe
J
J
D000818:Animals; D000833:Animals, Suckling; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005934:Glucagon / Q000008:administration & dosage / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology*; D066298:In Vitro Techniques; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008099:Liver / Q000187:drug effects* / Q000201:enzymology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar
D006728:Hormones; D003907:Dexamethasone; D006493:Heparin; D005934:Glucagon; D008071:Lipoprotein Lipase