title: The humorally mediated antihypertensive system of the rat kidney: a physiological depressor mechanism?
abstract: The humoral renomedullary antihypertensive system, described by Muirhead [1], is known to be strongly activated upon unclipping renal hypertensive rats. The present study was designed to determine whether this system is tonically active in normotensive rat kidneys at normotensive pressure levels. Anaesthetized normotensive donor rats (NDR) were used to perfuse an isolated age-matched normotensive recipient (NRR) kidney, via an extracorporal circuit, set at different perfusion pressures, while the NDR mean arterial pressure and heart rate were measured continuously. The results showed non-significant alterations in the NDR heart rate and mean arterial pressure at 80 mmHg NRR kidney perfusion pressure, while at 100 and 150 mmHg there were significant, dose-dependent and gradual reductions in both the heart rate and mean arterial pressure in NDR. We conclude that the renal humoral antihypertensive system is active in normotensive kidneys already in the normotensive pressure range, but becomes further engaged in a dose-dependent way when renal perfusion pressure is raised.
mesh_terms: D000818:Animals; D001794:Blood Pressure; D006339:Heart Rate; D007679:Kidney Medulla / Q000502:physiology*; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains