Abstract
Abstract
The effects of morphine, pilocarpine, and two anticholinergic drugs on serum prolactin (PRL) levels were studied in unanesthetized male rats, each previously implanted with an atrial cannula for collection of blood for radioimmunoassay. Morphine induced a threefold increase in serum PRL levels, whereas pilocarpine, a cholinergic agonist, significantly decreased serum PRL levels. When given together, the two drugs partially counteracted each other's effects on PRL release. Atropine, an anticholinergic drug, had no effect on serum PRL levels when injected alone, but when given together with morphine, significantly enhanced morphine induced PRL release. This enhancing effect of muscarinic blockade on morphine induced PRL release was confirmed in a second experiment by using scopolamine, another anticholinergic drug. These results suggest that the stimulating effect of morphine on PRL release may be mediated in part by a decreased activity in the central cholinergic system.
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