In-situ mechanical characteristics of the tongue are not altered in the obese zucker rat

Study Objectives: Obese Zucker rats have more collapsible isolated upper airways, compared with their lean counterparts. The functional characteristics of the tongue as a potential mechanism for the enhanced upper airway collapsibility in the obese Zucker rat are unknown. This study measured the functional characteristics of the tongue muscle in lean and obese Zucker rats. Design: In-situ tongue force (twitch and peak) and fatigability were measured in anesthetized obese and lean Zucker rats. Setting: Animal housing facility at the University of Buffalo. Subjects: Eight lean and eight obese Zucker rats. Intervention: Tongue force and fatigability were measured before, during, and following cocontraction of the tongue protrudor and retractor muscles via direct stimulation of the common hypoglossal nerve. Measurements and Results: Obese rats were significantly heavier than their lean counterparts (718 ± 101 gm vs. 545 ± 32, P < 0.05). Total force production at all stimulation frequencies was not different between lean and obese Zucker rats before or after fatigue (P = 0.436). Forces were significantly reduced at the end of the 5-minute stimulation period (P < 0.001) and returned to baseline within 1 minute after fatigue in both lean and obese rats. At the end of the fatigue protocol, tongue force averaged 63.3% ± 13.8% and 72.3% ± 17.8% of the initial force in obese and lean rats respectively (P = 0.85). Conclusion: Obesity does not alter the in-situ force production of the tongue muscle. Thus, increases in collapsibility of the isolated upper airway previously noted in obese Zucker rats cannot be ascribed to upper airway muscle dysfunction or enhanced fatigability.