Inhibitory effects of centrally administered |ASU^1–7| eel calcitonin on basal and stimulated prolactin release in rats

We investigated the effects of /ASU^1–7/eel calcitonin (ASU^1–7 elCT) on basal and stimulated prolactin (PRL) release in male rats. /ASU^1–7/eelCT was administered intracerebroventricularly (icv) into freely moving rats with indwelling catheters. The administration of /ASU^1–7/eelCT (2.5 μ/rat, icv) significantly inhibited basal PRL secretion. When PRL secretion was stimulated by exposing rats to restraint stress, /ASU^1–7/eelCT (250 ng; 800 ng; 2.5 μ/rat, icv) dose-relatedly inhibited the PRL surges at 10 min after stress. The same doses of icv /ASU^1–7/eelCT were effective in inhibiting morphine (6 mg/kg, intracarotid, ia)-induced PRL release. No effect on stress-induced PRL secretion was observed when the peptide was administered intracarotid at the dose of 10 μ/rat. These results demonstrate that /ASU^1–7/eelCT, as we previously observed with salmon calcitonin (sCT), has central inhibitory activity on PRL secretion, probably through enhancement of hypothalamic inhibitory pathways involved in the control of PRL.