Antihypertensive action of medullipin I given by mouth

Persistent Hypotension Associated with Hypermedullipinemia: A New Syndrome

A new syndrome is described in a patient with advanced renal insufficiency. This consists of severe and persistent hypotension causing weakness but associated with a clear mental status. Also present is evidence for decreased vascular reactivity. The hypotension was not orthostatic. The hypotension was associated with a circulating vasodepressor substance having the characteristics of medullipin 1. The medullipin appears to have been derived from the remaining right kidney. Hypotension existed despite the presence of major prohypertensive mechanisms, including an endstage kidney, hyperreninemia and hyperaldosteronemia. It is likely that hypotension due to hypermedullipinemia is an entity occurring in the human being.

Evidence for a renomedullary vasodepressor hormone

1. Recent physiological experiments have established that increasing the perfusion pressure of the kidney causes the release of vasodepressor substance from the renal medulla. 2. The substance is not a platelet activating factor, a prostaglandin or nitric oxide and the vasodepressor response to increased renal perfusion is not due simply to inhibition of renin release. 3. The mechanisms by which the renomedullary vasodepressor substance lowers arterial pressure remain to be determined. Sympathoinhibition may account for part of the response, but the hypotension still occurs in autonomic ganglion blocked animals. 4. The source of substance appears to be the renomedullary interstitial cells, though the control of the production and release of the substance remain to be determined. 5. The substance may be a lipid but it is yet to be fully isolated and identified. 6. The threshold for release of the substance appears to be close to normal resting arterial blood pressure. 7. Despite strong evidence that the renal medulla releases a vasodepressor hormone in response to increased renal perfusion pressure, much is still to be determined regarding the physiology of this hormone and its involvement in the aetiology of hypertension.

Pressure range for release of renomedullary depressor substance in rabbits

We investigated the relation between renal perfusion pressure and the release of a renal vasodepressor substance in vivo to determine whether this substance was released at physiological pressures. We perfused the left kidneys of anesthetized rabbits using an extracorporeal circuit that allowed renal perfusion pressures to be set at 65 mm Hg (control) and increased to 95, 125, 155, or 185 mm Hg for 30-minute experimental periods. Systemic blood pressure did not change significantly when renal perfusion pressure was maintained at 65 mm Hg throughout. When renal perfusion pressure was increased to 95, 125, 155, or 185 mm Hg, systemic blood pressure fell significantly at rates of 0.17 +/- 0.04, 0.79 +/- 0.31, 0.60 +/- 0.11, and 2.18 +/- 0.79 mm Hg/min, respectively (P < .05). Restoration of renal perfusion pressure to 65 mm Hg abruptly reversed the falls in systemic blood pressure in each group. There was a natriuresis and diuresis that were both pressure related and progressive in the face of each constant level of increased renal perfusion pressure. In summary, there was a continuum of arterial vasodepressor responses across a renal perfusion pressure range from resting pressure to 185 mm Hg. We suggest that the threshold level for the release of significant amounts of a renal medullary depressor substance, probably medullipin, is just above normal arterial blood pressure and that the rate of release increases with increasing arterial pressure.

Lipomedullipinoma: a source of hypermedullipinemia

Previously we reported a case of persistent hypotension associated with hypermedullipinemia (Blood Pressure 1992; 1:138-148). The hypermedullipinemia appeared to result from the autonomous secretion of medullipin I (Med I) by renomedullary interstitial cells (RIC's) in the patient's remaining endstage kidney. The patient subsequently died. At autopsy, the remaining kidney contained a yellow mass (1 x 1 x 0.5 cm) consisting of adipocytes and RIC's, termed a lipomedullipinoma. This mass was extracted and chromatographed by procedures known to yield Med I. Med I was identified following these procedures. Renal tissue outside the yellow mass failed to yield Med I. It appears that the hypermedullipinemia of this case resulted from autonomous, hypersecretion of Med I by the lipomedullipinoma.