Prolactin responses to vasoactive intestinal polypeptide and thyrotropin releasing hormone in chronic renal failure

Prolactin response to iv bolus injection of 1 micrograms/kg vasoactive intestinal polypeptide was determined in 8 patients with chronic renal failure undergoing chronic hemodialysis and in 8 normal controls, age- and sex-matched. Plasma prolactin in the patients showed a blunted response following vasoactive intestinal polypeptide injection, whereas the controls showed significantly higher mean peak prolactin value over the baseline value (p less than 0.002). The net rise (peak levels minus basal levels) in plasma prolactin and area under the curve after vasoactive active intestinal polypeptide injection in the controls were significantly greater than those in the patients (p less than 0.001). On a separate day, each individual underwent a TRH (500 micrograms) challenge with the prolactin response determined. The patients had significantly higher peak prolactin values over baseline levels (p less than 0.02) which, however, were not significantly different from those in the control group. In the patients, the peak net prolactin increments and area under the curve were significantly higher following TRH than following vasoactive intestinal polypeptide (p less than 0.05). The net prolactin increments to TRH challenge were significantly higher in the control group than in the patients (p less than 0.001). The results demonstrate the blunted prolactin response to the stimulatory effect of vasoactive intestinal polypeptide and TRH in chronic renal failure. In chronic renal failure prolactin release after vasoactive intestinal polypeptide is more blunted than after TRH. These data suggest that the responsiveness of plasma prolactin to vasoactive intestinal polypeptide is defective in these patients, though the mechanism(s) are yet to be defined.