An important function of the tubuloglomerular feedback (TGF) system is regulation of the load of sodium entering the distal tubule, a physiological variable that influences urinary sodium excretion. Results will be discussed of simulation studies of the potential impact of the emergence of limit cycle oscillations (LCO) in the TGF system on its regulatory efficacy. When TGF feedback gain magnitude is below the critical value where the system bifurcates and LCO appear, TGF regulatory ability in response to infinitesimal perturbations increases with the magnitude of the feedback gain in accordance with linear system theory. However, the emergence of LCO at larger gain values reduces the ability of TGF to compensate for both infinitesimal and finite perturbations in nephron filtration rate. These effects arise from nonlinear elements in the TGF system. Further, the model predicts that maximal regulatory ability will occur at the bifurcation boundary. Hence, these studies suggest that the emergence of LCO in the TGF system may enhance renal sodium excretion.
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