The effects of TRH on prolactin, plasma renin activity, water and electrolyte excretion in normal males

The effect of TRH induced secretion of TSH and prolactin (hPrl) on plasma renin activity (PRA), water and electrolyte excretion, was studied in 7 normal males before and after an intravenous injection of 2 ml normal saline or 200 microgram TRH. Plasma hPrl and TSH rose significantly (p less than 0.01) in all 7 subjects after TRH but not after saline injection. No significant differences in the hourly excretion of sodium, potassium and free water clearance were noted before and after either saline or TRH injection. Mean PRA values of the 7 subjects were similar after either the 2 ml saline of TRH injection. Our results indicate that despite a correlation between basal hPrl and sodium excretion as well as free water clearance, acute TRH induced elevation of hPrl is not associated with changes of urinary sodium and potassium excretion, free water clearance and PRA in normal males. These findings provide some evidence against a direct osmoregulatory role of hPrl in man.