The circulatory and renal sympathoinhibitory effects of gastric leptin are altered by a high fat diet and obesity.

Gastric leptin elicits its cardiovascular and splanchnic sympathoinhibitory responses via a vagal afferent mechanism, however the latter are blunted/abolished in animals fed a medium high fat diet (MHFD). In a diet-induced obesity model we sought to determine whether the renal sympathetic nerve discharge (RSND) and regional vasodilator responses to gastric leptin are also affected by diet and/or obesity. The diet induced obesity model was used in 2 separate studies. After 13 weeks on a MHFD the animals were classified as either obesity prone (OP) or obesity resistant (OR) depending on their weight gain. Control animals were fed a low fat diet for an equivalent period. Arterial pressure (AP) and heart rate (HR) were monitored in isoflurane-anaesthetised, artificially ventilated animals and RSND or regional vascular responses to leptin (15 μg/kg) administered close to the coeliac artery were evaluated. OP rats had higher baseline AP compared to control/OR rats (P<0.05). Close arterial leptin inhibited RSND in control animals but this response was abolished in OR and OP animals (P<0.01 for both). Leptin administration increased renal vascular conductance in control animals but this response was significantly attenuated only in OP animals (P<0.05). The vasodilator response in the superior mesenteric artery was not significantly different in any of the groups (P>0.05). Together these results suggest that, while the renal sympathoinhibitory responses to gastric leptin are affected by diet, the vasodilator responses to leptin in the renal vascular bed are only affected in OP animals. These changes may impact on cardiovascular homeostatic mechanisms in obesity.
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