Urinary excretion of free dopamine and digoxinlike substances correlates with endogenous secretion of insulin in normotensive adults, but not in hypertensive subjects.

We investigated whether urinary excretion of free dopamine is related with the humoral factors which affect Na+, K+ ATPase activity in the kidneys. Subjects were 51 adults admitted in a hospital without renal insufficiency: they were divided into normotensive (n = 36, 60 +/- 3 years old, 122 +/- 3/73 +/- 2 mmHg) and hypertensive groups (n = 15, 65 +/- 5 years old, 157 +/- 6/91 +/- 2 mmHg). Urinary excretion of free dopamine was significantly and positively correlated with urinary excretion of C-peptide immunoreactivity of insulin (CPR) (r = 0.451, p = 0.014) in normotensive subjects, but not in hypertensive subjects (r = 0.155, p = 0.668). Urinary excretion of endogenous digoxinlike substances (EDLS) was also significantly and positively correlated with urinary CPR (r = 0.500, p = 0.006) in normotensive subjects, but not in hypertensive subjects (r = 0.275, p = 0.363). In normotensive subjects, urinary excretion of free dopamine and EDLS may be regulated at least in part by insulin secreted endogenously. In hypertensive subjects, however, this regulatory mechanism of the diuretic factors, such as insulin, EDLS and dopamine, is thought to be deranged, which might result in decompensation of a diuretic and antidiuretic balance leading to blood pressure elevation.