1. Allogenic transplants of cultured renomedullary interstitial cells exert a powerful anti-hypertensive action. The blood pressure of hypertensive animals usually drops slowly over 8–12 h whereas the pulse is unchanged or reduced.
2. Lipids derived from the cultured cells exert a similar anti-hypertensive action.
3. The anti-hypertensive action of transplanted cultured cells almost certainly results from the secretion of a substance(s) that acts in the manner of a hormone. The tissue culture lipid is a prime candidate hormone.
4. The relationship of the kidney to the hypertensive state is considered to entail pro- and antihypertensive actions. The pro-hypertensive actions include (a) activation of the renal pressor system (mainly renin—angiotensin), (b) failure to prevent sodium and fluid overloading because of either an injured or absent kidney or the excessive action of mineralocorticoids (mainly aldosterone). The antihypertensive actions of the kidney include (a) the relief of sodium and fluid overloading through diuresis—natriuresis and (b) the action of the renomedullary interstitial cell hormone (the antihypertensive renomedullary hormone).