The effect of salt loading on the urinary excretion of dopamine and sodium transport inhibitor in the rat

1. The temporal relationship between the excretion of dopamine and sodium transport inhibitor (STI) during salt loading was examined in the rat. 2. Urine samples were collected before and during salt loading (given as 18 g/1 NaC1 solution to replace drinking water) for the measurement of sodium, creatinine, dopamine and STI in 6 female rats. Dopamine was measured by HPLC and STI was extracted and measured by its ability to inhibit purified Na⁺, K⁺-ATPase enzyme. 3. Urinary sodium and STI (expressed in relation to creatinine) on day 1 of salt loading were 4.6 and 4.2 times respectively of the control values.