759 HERITABILITY OF SODIUM REABSORPTION CAPACITY IN AN EXOCRINE GLAND OF THE RAT

Abstract

In cystic fibrosis (CF) patients Na reabsorption from the primary secretions of exocrine glands is markedly reduced. Because the ducts of rat salivary glands have Na reabsorptive activity levels second only to the kidney tubule and can be inhibited by a component of CF exocrine secretions, they provide a good system for studying factors which alter ion transport in exocrine glands. We found that male rats (n=10) from two different Sprague-Dawley lines (designated OU and SI) produced parotid salivas with intrinsically different Na contents (e.g. 90 vs 30 mEq/L) when induced to salivate with pilocarpine. Serum Na levels were indistinguishable from one another. Crosses between OU and SI lines produced F₁ males (n=12) with parotid Na levels which were intermediate to either parent. Reciprocal crosses gave identical results, i.e. the relative activity of the ductal Na transport system was controlled by a single pair of incompletely dominant autosomal alleles. Reserpineinduced inhibition behaved as a simple dominant. Three daily doses of reserpine had no effect on the Na content of F₁ progeny or the SI line but elevated the Na content of the OU line. Backcrosses of F₁ progeny to each parent line produced males (n=10) with phenotypes of the F₁ hybrid and the appropriate parental type, again, consistent with a single gene autosomal recessive mode of inheritance of the low Na transport capacity phenotype. This gene appears to control a component of the ductal Na transport system which is sensitive to the humoral inhibitor induced by reserpine administration.

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