Sustained Depressor Effect of Renal Medullary Extract in the Normotensive Rat

Crude homogenates of rabbit, medulla produced a sustained depression of blood pressure when injected intravenously into the normotensive, anesthetized, pentolinium-treated rat. Similar activity was present in rat medulla, but not in extracts of renin-free cortex or certain nonrenal tissues. The sustained depressor activity of medulary extract possessed different physiological and chemical characteristics from the shortacting nucleotide depressor activity which is present in both cortical and medullary extracts. In addition, prolonged medullary depressor activity was separable from medullary nucleotide activity by column chromatography. The activity responsible for sustained depressor activity was a dialyzable, ethanol soluble, low molecular weight(<4500 mol wt) substance(s) which was resistant to a mixture of peptide hydrolases and destroyed by heating for one hour at 100°C.