Basal serum prolactin levels and prolactin responses to constant infusions of thyrotropin releasing hormone in healthy aging men

We measured serum prolactin (PRL) levels by RIA before and during a 240-min constant infusion of TRH (0.4 μg/min iv) in three similarly sized groups of healthy aging men 30 to 49, 50 to 69, and 70 to 96 years. Basal data were evaluated by analysis of variance with Duncan's multiple range test and regression analysis. Mean basal serum PRL level was elevated (p < .05) in the oldest group, attributable to PRL elevations (between 20 and 40 ng/ml) in 4 men over 75 years. Serum PRL levels decreased (p < .001) from -30 min to 0 min before TRH infusion in all groups, but there was no age-dependent difference (p > .3) in the magnitude of the reduction. Repeated measures analysis of variance showed increased serum PRL levels (p < .001) during TRH infusion in all age groups, and an age-dependent increase (p < .05) in magnitude of peak PRL response. This significant difference was between the two oldest age groups early in the infusion. Chi-square analysis revealed an increased (p < .05) frequency of early (less than 120 min) peak responses in the oldest age group. The present data suggest that basal and TRH-stimulated PRL secretion may be augmented in some healthy older men.