Franz Volhard Lecture. Evolution of the medullipin concept of blood pressure control: a tribute to Eric Muirhead.

THE HYPOTHESIS: The medullipin system discovered by the late Eric E. Muirhead is a feedback blood-pressure control system operating from the renal medulla. In contrast to the renin-angiotensin system, which upregulates pressure, the medullipin system downregulates blood pressure. THE MECHANISM: A rise in arterial pressure has two important consequences. First, medullary blood flow increases, renal interstitial fluid pressure rises and there is a reduction in the medullary urea osmotic gradient. Second, secretion of medullipin I is increased, which circulates to the liver, where it is converted to the active hormone, medullipin II, by a P-450 cytochrome oxidase pathway. Both of these mechanisms work in parallel to reduce arterial pressure with an increase in the urinary excretion of sodium and water coupled with systemic arterial vasodilation by medullipin II.