Ascending myogenic autoregulation: Interactions between tubuloglomerular feedback and myogenic mechanisms

A mathematical model of the renal vascular and tubular systems was used to examine the possibility that synergistic interactions might occur between the tubuloglomerular feedback (TGF) and myogenic autoregulatory mechanisms in the kidney. To simulate the myogenic mechanism, the renal vasculature was modelled with a resistance network where the total preglomerular resistance varies with intravascular pressure. In addition, a steady-state model of glomerular filtration, proximal and Henle's loop reabsorption, and TGF-modulation of afferent arteriolar resistance was derived. The results show that, if TGF acts on the distal portion of the preglomerular vasculature, then any TGF-induced vasoconstriction should raise upstream intravascular pressure and, thereby, trigger a myogenic response in the more proximal vascular segments, a phenomenon referred to as an ascending myogenic (AMYO) response. The model further predicts that the magnitude of the AMYO response can be similar in magnitude to the TGF-induced increment in afferent resistance. Hence, the effects of TGF excitation on whole kidney hemodynamics may be much greater than pedicted from measurements in single nephrons. Moreover, a significant fraction of the intrinsic myogenic autoregulatory response to increased renal perfusion pressure may result from a synergistic interaction between the TGF and myogenic mechanisms.