Evidence for adrenergic mediation of cholinergic inhibition of prolactin release

Pilocarpine, a cholinergic agonist, significantly reduced the high levels of serum prolactin in estrogen-primed male rats and in female rats on the late afternoon of proestrus. In male rats treated with reserpine, chlorpromazine, haloperidol, or pimozide, serum prolactin levels were greatly elevated. Subsequent treatment with pilocarpine failed to reduce serum prolactin concentrations in these rats. When atropine, a cholinergic antagonist, was injected ip in doses of 3 to 250 mg/kg into male rats, prolactin release was not altered. However, when atropine was injected prior to pilocarpine, it prevented the reduction in serum prolactin by the latter drug. Methyl-atropine, which does not enter the CNS, did not prevent pilocarpine from inhibiting prolactin release. These results suggest that cholinergic inhibition of prolactin release is mediated via adrenergic neurons, and thus support a role for a cholinergic link in hypothalamic regulation of prolactin release.