Abstract
Summary
A single intraperitoneal injection of L-dopa, the precursor of dopamine, into female rats significantly reduced serum prolactin concentration at 30 min, 1 hr, and 2 hr after injection compared to pretreatment levels or control rats not given this drug. A single injection of each of 3 monoamine oxidase inhibitors, pargyline, iproniazid or Lilly-15641, also significantly decreased serum prolactin below pretreatment values. Injection of L-dopa and pargyline together was more effective than either alone in lowering serum prolactin. Each of the above drugs is believed to reduce pituitary prolactin release because it increases catecholamine activity in the hypothalamus. By contrast, a single injection of methyldopa, which inhibits catecholamine synthesis, increased serum prolactin many fold over pretreatment levels. A single injection of d-amphetamine, a sympatheticomimetic drug, also greatly increased serum prolactin concentration.
Addendum
The hypothalami of the rats treated with saline (controls), iproniazid, pargyline, L-dopa or pargyline and L-dopa together, were assayed for PIF activity by our standard in vitro procedure. All drugs increased hypothalamic PIF activity and the combination of pargyline and L-dopa was more effective than either alone. These observations suggest that the increase in hypothalamic catecholamines produced by these drugs results in increased hypothalamic PIF activity, and this in turn depresses prolactin release by the pituitary.
Get full access to this article
View all access options for this article.