Salt preference in rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain)

Brattleboro rats are homozygous for diabetes insipidus (HO-DI), lacking the ability to synthesize vasopressin. Besides increasing water consumption, HO-DI rats may compensate for their excessive renal water loss by reducing their intake of and preference for substances that elevate plasma osmolarity. In two experiments we assessed this possibility. In Experiment 1, salt preference of HO-DI and control Long-Evans (LE) rats was measured by presenting the rats with two tubes: one filled with water and the other with NaCl. In the first part of the experiment, 18 NaCl concentrations were presented in increasing order (from 6 to 300 mM). In the second part, other groups of HO-DI and LE rats were presented with 6 concentrations of NaCl, ranging from 6 to 450 mM in either increasing or decreasing order of concentrations. In Experiment 2, preference for 6 concentrations of citric acid ranging from 0.1 to 6 mM was assessed. With NaCl concentrations greater than 100 mM, intake and preference declined rapidly for the HO-DI group but very gradually for the LE group. In contrast, the HO-DI rats preferred all citric acid solutions more than LE rats. The results suggest that HO-DI rats compensate for their inability to concentrate urine not only by increasing water consumption, but also by decreasing consumption of and preference for salty solutions.