Interaction of Vasopressins and Linear N‐Terminal ACTH Fragments in the Induction of Natriuresis

Abstract.Because a) a mixture of alpha‐melanotropin (MSH) and corticotropin (1–13)‐tridecapeptide (1–13 ACTH) has apparently been isolated from natriuretic fractions of posterior pituitary which also contained arginine‐vasopressin, and b) the natriuretic activity of the isolated fraction was greater than that of any of the above three peptides (synthetic) given separately, possible interaction was studied with model substances in the chloralosed cat preparation. It was found that with both alpha‐MSH and lysine‐vasopressin, extracted samples were more natriuretic than synthetic samples despite an equivalence of pressor activities. When combined with arginine‐vasopressin in one injectate, synthetic alpha‐MSH, 1–4 ACTH, 1–13 ACTH‐amide and 1–18 ACTH all showed potentiation of natriuretic activities with no effect on pressor activity. This effect was not shown by synthetic 4–10 ACTH and 5–18 ACTH, or by extracted alpha‐MSH. It was concluded that the 1–4 sequence Ser‐Tyr‐Ser‐Met, regardless of whether the N‐terminal is free or blocked, can potentiate the natriuretic action of vasopressin.