Albumin-like proteins from the pituitary glands of Dahl salt-resistant rats.

Dahl selectively bred rats for susceptibility (S strain) or resistance (R strain) to the hypertensive effect of high salt (NaCl) diet. Pituitary glands of R rats accumulate large amounts of four unique proteins not seen in S rats. These proteins were called R1, R2, R3, and R4 in order of decreasing electrophoretic mobility. Albumin, R4, R2, and R1 all bound to an affinity column for albumin (Cibacron blue 3G-A dye coupled to agarose) and were eluted in that order by a KSCN gradient. It was shown by crossed immunoelectrophoresis that R1 and R2 cross-react with plasma albumin. Peptide maps or tryptic digest of R1 and albumin showed that the majority of peptides generated were identical. It was not possible to incorporate labeled amino acid into albumin or the albumin-like R proteins with pituitary incubates, indicating that albumin-like proteins were not synthesized de novo by pituitary glands. R rat pituitary glands showed much greater protease (arginine esterase) activity than did S. This suggests that R proteins are formed locally in the pituitary gland of R proteins are formed locally in the pituitary gland of R rats by cleavabe of specific peptide bonds in albumin. The function of these endogenous albumin fragments is unknown, but albumin fragments produced in vitro by other investigators are known to potentiate bradykinin, a hypotensive peptide.