Inheritance of blood pressure and pituitary colloid protein in Dahl rats

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Abstract
Dahi salt resistant (R) rats are characterized by a variable and often marked accumulation of protein rich fluid (colloid) in the cleft between the anterior and intermediate lobes of the pituitary gland. This characteristic was absent in the pituitary glands of DahI salt susceptible (S) rats. Inbreeding of five sublines of R rats without selection resulted in one subline without pituitary colloid accumulation and four sublines with marked pituiiary colloid accumulation. Thus, genes for high colloid were not fixed in the original R stock. Blood pressures of these two kinds of R sublines were similar on 8 percent NaCl diet, but differed when rats were unilaterally nephrectromized as well as fed 8 percent NaCI. Under this severe environmental challenge low pituitary colloid R males had higher blood pressure than high pituitary colloid R males. A high pituitary colloid R line was crossed with S rats. Pituitary colloid protein (R1 protein) was studied by electrophoresis and densitometry in parental, F1 and backcross popula tions, The data suggested that pituitary colloid accumu lation followed polygenic inheritance, but that a single major locus (Pc, pituitary colldid) was discernible. The S allele at the Pc locus was dominant to the R allele in males, but incompletely dominant in females. It was not possible to establish a correlation between the Pc locus and blood pressure in the backcross to the R recessive parental type. This result was different from that obtained previously with two F populations in which pituitary colbid accumulation and blood pressure were inversely related. It was speculated that the blood pressure effect of the Pc locus is difficult to demonstrate on an R genetic background unless the environmental salt challenge is combined with reduced renal mass.