AJP - Endocrinology and Metabolism, Vol 258, Issue 5 E799-E804, Copyright © 1990 by American Physiological Society
Age alters pulsatile prolactin release: influence of dopaminergic inhibition
S. L. Greenspan, A. Klibanski, J. W. Rowe and D. Elahi
Division of Gerontology, Beth Israel Hospital, Boston 02115.
To determine the effect of age on pulsatile prolactin secretion, we
examined prolactin pulse characteristics by cluster analysis in healthy
young and old male subjects during the day and night. Pulsatile prolactin
secretion was identified in all subjects during the day and night, and
prolactin pulse frequency remains stable with age. Younger subjects had a
significantly higher prolactin pulse amplitude, area, and peak interval
during the night compared with older subjects. In contrast, daytime
prolactin pulse characteristics were similar in young and old subjects.
Because the major neuroregulator of prolactin is dopamine and because
normal aging has been reported to be associated with reductions in
hypothalamic dopamine content and effect, we determined whether the
mechanism of altered day-night prolactin pulsatile secretion was due to
changes in dopaminergic tone. We examined endogenous prolactin secretion
after administration of the dopamine antagonist metoclopramide.
Metoclopramide significantly increased mean serum prolactin concentration
and prolactin pulse height and amplitude in all subjects during the day and
night. However, net prolactin pulse amplitude after metoclopramide
stimulation at night was significantly higher in older subjects compared
with younger subjects. We conclude that prolactin pulse amplitude is
blunted in elderly men at night and that daytime pulsatile prolactin
secretion is unaltered by age in normal men. The mechanism for this
alteration of nighttime prolactin pulsatile secretion in elderly men may be
due to age-associated changes in dopaminergic regulation.
