In vitro effects of leptin on human adipocyte metabolism.
OBJECTIVE
Leptin receptors are expressed in adipocytes, suggesting potential autocrine/paracrine effects. Studies on the direct effects of leptin on adipose tissue metabolism in different species have yielded controversial data. To assess the in vitro effects of leptin on human adipocyte metabolism: lipolysis, the insulin-induced inhibition of lipolysis and lipogenesis were studied in adipocytes obtained from infants and adults.


METHODS
Lipolysis was studied by incubating adipocytes with increasing concentrations of leptin or isoprenaline. Glycerol in the incubation medium was measured as an indicator of lipolysis. For the lipogenesis and insulin-induced inhibition of lipolysis experiments, the cells were preincubated with 0, 25, or 250 ng/ml of leptin for 2 h.


RESULTS
Leptin did not stimulate lipolysis in human adipocytes, either in children or adults. Preincubation with leptin did not affect the insulin-induced inhibition of lipolysis, but decreased the insulin-induced lipogenesis (p < 0.05).


CONCLUSIONS
This study shows that leptin has no direct lipolytic effect in human adipocytes. The lack of effect on the insulin-induced inhibition of lipolysis and the negative effect on lipogenesis indicates that the effect of leptin is not at the proximal insulin-signalling pathway but further downstream.
Pediatric Endocrine Research Unit, Department of Pediatrics, Huddinge University Hospital, Karolinska Institute, Stockholm, Sweden.
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Elimam
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Kamel
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Marcus
D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000328:Adult; D002469:Cell Separation; D002675:Child, Preschool; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D007223:Infant; D007328:Insulin / Q000494:pharmacology; D020738:Leptin / Q000494:pharmacology*; D008055:Lipids / Q000096:biosynthesis; D008066:Lipolysis / Q000187:drug effects
D007004:Hypoglycemic Agents; D007328:Insulin; D020738:Leptin; D008055:Lipids; D005947:Glucose