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Insulin induces rapid changes of plasma leptin in lean but not in genetically obese (fa/fa) rats
C Pagano1, P Englaro, M Granzotto
1Endocrine-metabolic laboratory, University of Padova, Italy.
Objectives:
To evaluate the plasma leptin concentration in lean and genetically obese fa/fa rats and to assess the response to 2 h hyperinsulinaemia.
Background:
The recently discovered peptide leptin is a putative link between the size of the adipose mass and the hypothalamic centres controlling feeding behaviour. Several genetic models of animal obesity have been characterized as carriers of mutations of either the ob gene or leptin receptor.
Experimental Design:
Lean (+/?) and obese (fa/fa) Zucker rats were studied under pentobarbital anaesthesia and underwent a 2 h euglycaemic hyperinsulinaemic clamp. Plasma leptin was measured in basal condition and at the end of the clamp study. Glucose rate of disappearance was evaluated by means of the isotope dilution technique using 3-3H-glucose as tracer.
Results:
fa/fa rats showed a 40 fold higher leptin concentration compared to lean littermates (0.47 +/- 0.10 vs 19.55 +/- 1.50 ng/ml, P < 0.0001). Euglycaemic hyperinsulinaemia increased plasma leptin in lean but not in genetically obese rats.
Conclusions:
Our results suggest that insulin may be a regulator of in vivo leptin secretion by adipose tissue of lean rates whereas it is ineffective in increasing plasma leptin in obese Zucker rats.