High Fat Feeding in Rats Alters Respiratory Parameters by a Mechanism That Is Unlikely to Be Mediated by Carotid Body Type I Cells.

The carotid bodies (CB) respond to changes in blood gases with neurotransmitter release, thereby increasing carotid sinus nerve firing frequency and ultimately correcting the pattern of breathing. It has previously been demonstrated that acute application of the adipokine leptin augments the hypoxic sensory response of the intact in-vitro CB (Pye RL, Roy A, Wilson RJ, Wyatt CN. FASEB J 30(1 Supplement):983.1, 2016) and isolated CB type I cell (Pye RL, Dunn EJ, Ricker EM, Jurcsisn JG, Barr BL, Wyatt CN. Arterial chemoreceptors in physiology and pathophysiology. Advances in experimental medicine and biology. Springer, Cham, 2015). This study's aim was to examine, in-vivo, if elevated leptin modulated CB function and breathing.Rats were fed high fat or control chow for 16-weeks. High fat fed (HFF) animals gained significantly more weight compared to control fed (CF) animals and had significantly higher serum leptin levels compared to CF. Utilizing whole-body plethysmography, HFF animals demonstrated significantly depressed breathing compared to CF at rest and during hypoxia. However, amplitudes in the change in breathing from rest to hypoxia were not significantly different between groups. CB type I cells were isolated and intracellular calcium levels recorded. Averaged and peak cellular hypoxic responses were not significantly different.Despite a small but significant rise in leptin, differences in breathing caused by high fat feeding are unlikely caused by an effect of leptin on CB type I cells. However, the possibility remains that leptin may have in-vivo postsynaptic effects on the carotid sinus nerve; this remains to be investigated.