Effect of normal aging on the prolactin response to graded doses of sulpiride and to arginine.

The prolactin (PRL) response to placebo, sulpiride (2.5, 5, 10 and 20 mg im) and arginine HC1 infusion (0.33G/kg) was examined in young (18-25 yrs) and old (65-75 yrs) normal men. Analysis of variance for the sulpiride data showed no significant dose x age group interaction or dose X age group X period interaction. There was, however, a significant age group X period interaction (p less than 0.05). PRL concentrations were significantly lower in the old subjects (N = 9) compared with the young (N = 9) 15 min after 2.5, 5, or 10 mg but not significantly after 20 mg sulpiride or at any other time interval. The areas under the concentration-time curves and the mean individual peak PRL concentrations were not significantly different between the two groups. The pattern of findings suggests a delayed absorption of sulpiride in the elderly rather than a change in pituitary dopamine (DA) receptor sensitivity to account for the lower PRL concentrations at 15 min. Differences in magnitude of the PRL response between the four doses of sulpiride were small and results suggest that the 2.5 mg dose is close to that required to saturate DA receptors on the lactotrophe and that the 10 and 20 mg doses are sufficient to completely block pituitary DA receptors. There was no significant age effect on arginine-induced PRL secretion (N = 11 in each group).(ABSTRACT TRUNCATED AT 250 WORDS)