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al. 2000 ). Those animals presented a leptin resistance to their anorexigenic effect ( Passos et al. 2004 ). During lactation, in rats, malnutrition causes hypoprolactinemia ( Lisboa et al. 2006 ), explaining the failure in milk synthesis

tissue does not generate an appropriate regulatory response – the so-called phenomenon of ‘leptin resistance’. Many small mammals inhabiting temperate and arctic regions exhibit annual cycles in body mass and adiposity (e.g. Heldmaier

transcription. The JAK2/STAT3 pathway stimulates suppressor of cytokine signaling 3 ( SOCS3 ) transcription, a leptin-inducible inhibitor of leptin signaling ( Vaisse et al . 1996 ). In obesity, leptin resistance has been associated with changes in the JAK2

of hepatic insulin resistance and non-alcoholic steatohepatitis ( Sahai et al . 2004 ). It is possible that activation of Ob-Ra may be responsible for leptin-induced up-regulation of 11β-HSD1 expression in hepatocytes (which lack Ob-Rb; Liu et al

loss of leptin control on hypotha-lamic pathways regulating appetite and energy expenditure ( Spiegelman & Flier 2001 ). In fact, diet-induced obesity is now regarded as a status of leptin resistance ( Sahu 2004 ). Numerous studies suggest that leptin

polymorphism increases not only insatiability but also lipogenic activity ( Morales et al . 2002 ), contributing to thrifty genotype and obesity in a similar way to the syndrome of leptin resistance described in humans. The exposure of pregnant Iberian sows to

additional dysfunctions such as higher central adiposity, hyperleptinemia, IR and leptin resistance, and secondary hypothyroidism ( Oliveira et al . 2009 , de Oliveira et al . 2010 ). Maternal smoking increases catecholamine levels in the amniotic fluid

). pSTAT3 induces the transcription of several genes, including suppressor of cytokine signalling 3 (SOCS3), which inhibits JAK2–STAT3 signalling, leading to central leptin resistance ( Bjørbaek et al . 1999 , Flier 2004 , Howard et al . 2004 , Donato

. Such lack of sensitivity to leptin inspired the notion of leptin resistance ( Frederich et al. 1995 ). Leptin resistance has been described in several conditions (from obese individuals to pregnant females and seasonal animals) and encompasses

The aim of our work was to compare the degree of leptin resistance in diet-induced obesity-prone and resistant rats, both in terms of reduction of feeding and of endocrine effects on somatotroph and thyroid axes. We concluded that both groups of