Salsolinol. is a putative endogenous neuro-intermediate lobe prolactin-releasing factor

The isolation and identification of a prolactin-releasing factor (PRF) from the neuro-intermediate lobe of the pituitary gland has been pursued for ov er a decade. Using high-pressure liquid chromatography with electrochemical detection (HPLC-ECD) and gas chromatography/mass spectrometry (GUMS) (R)-s alsolinol (SAL) (a dopamine-related stereo-specific tetrahydroisoquinoline) was found to be present in neuro-intermediate lobe as well as median emine nce extracts of male, intact-, and ovariectomized female rats. Moreover, an alysis of SAL concentrations in neuro-intermediate lobe revealed parallel i ncreases with plasma prolactin in lactating rats exposed to a brief (10 min ) suckling stimulus following 4-h separation. SAL appears to be a selective and potent stimulator of prolactin secretion in vivo and it was without ef fect on the secretion of, other pituitary hormones. We have also found that SAL can elevate prolactin release, although to a lesser extent, in pituita ry cell cultures as well as in hypophysectomized rats bearing anterior lobe transplants under the kidney capsule. Lack of interference of SAL with [H- 3]-spiperone binding to AP homogenates indicates that SAL does not act at t he dopamine D-2 receptor. Moreover, [H-3]-SAL binds specifically to homogen ate of AL as well as neuro-intermediate lobe obtained from lactating rats. Taken together, our data clearly suggest that SAL is synthesized in situ an d this compound can Play a role in the regulation of pituitary prolactin se cretion.