AJP - Endocrinology and Metabolism, Vol 247, Issue 6 778-E780, Copyright © 1984 by American Physiological Society
Brief decreases in dopamine result in surges of prolactin secretion in monkeys
L. S. Frawley and J. D. Neill
We have reported previously that the amount of dopamine in hypophysial
stalk blood was sufficient to account for tonic hypothalamic inhibition of
prolactin secretion in rhesus monkeys. In the present study we determined
the effect on prolactin secretion of decreases in dopamine. When
hypophysial stalk-transected, estrogen-treated monkeys were infused with
dopamine at a rate (0.1 microgram X kg-1 X min-1) to achieve peripheral
plasma concentrations similar to those previously measured in stalk blood,
their elevated serum prolactin levels fell to base line (from 47.6 +/- 4.8
to 9.7 +/- 2.7 ng/ml, mean +/- SE, n = 4). Brief interruptions of the
dopamine infusions lasting for 2.5, 5.0, or 7.5 min evoked rapid increases
in serum prolactin concentrations (to 27.5 +/- 8.3, 52.9 +/- 3.6, and 58.9
+/- 8.1 ng/ml, respectively, at 10 min). Maximal prolactin levels were
attained within 10 to 20 min after dopamine removal and serum prolactin
remained elevated for an additional 35 to 150 min. Uninterrupted dopamine
infusions of stalk-transected, estrogen-treated monkeys (n = 3) led to
continuously suppressed prolactin values. These results demonstrate that
brief decreases in dopamine lead to major increases in prolactin secretion.
Thus, if a brief decrease in hypothalamic dopamine secretion occurs after a
suckling stimulus in monkeys, as it does in rats, a decrease in dopamine
secretion alone may account, in part, for suckling-induced prolactin
secretion in monkeys.
