Characteristics of pituitary colloid proteins and their correlation with blood pressure in the rat

Salt resistant rats (R-strain of Dahl) accumulate large amounts of colloid in the pituitary cleft. Such colloid is largely absent in pituitaries of salt susceptible rats (S-strain of Dahl). Polyacrylamide gel electrophoresis of pituitary cleft colloid from R rats shows 4 proteins, designated R1, R2, R3 and R4 in order of decreasing electrophoretic mobility. These proteins have apparent molecular weights of 52,000, 63,000, 130,000 and greater than 235,000, respectively. Their apparent isoelectric points as determined by preparative isoelectric focusing are 4.82, 5.02, 5.54 and 4.35, respectively. Ferguson plots for R1, R2 and rat albumin suggest that R1 and R2 are size isomers of albumin. The molecular weights of R2, R3 and R4 suggest that R2 may polymerize to form a dimer and tetramer. Chronic feeding of 8% NaCl diet for 6 weeks does not influence pituitary accumulation of R1 protein in either R or S rats. Pituitary R1 accumulation does, however, segregate with resistance to salt-induced hypertension in genetic experiments. This strongly suggests that the accumulation of R proteins in the pituitary cleft reflects some genetically controlled change concerned with control of sodium metabolism.