Cysteamine inhibition of prolactin immunoassayability and secretion: studies with aminothiophenols and other analogs.

Analogs of the aminothiol cysteamine (CySH) have been studied to clarify the structural features required for exertion of inhibitory effects on PRL. The inhibited functions examined were the detectability of PRL by RIA and the release of PRL from suspensions of isolated secretory granules. The influence on GH assayability and release was also tested. The aromatic compounds 2-aminothiophenol, 3-aminothiophenol, and 4-aminothiophenol shared with CySH the ability to inhibit PRL assayability and release, but were all more potent. Derivatization of the thiol, as in 4-aminothioanisole, was associated with a substantial loss of inhibitory potency, whereas derivatization of the primary amine, as in N-dimethylaminoethanethiol, had no influence. Thiols such as mercaptoethanol, cysteine, glutathione, and others without nearby amino groups were stimulators of PRL assayability and release. The inhibitory effects of the aminothiols were highly pH dependent, being marked at pH 5.5, 6.5, and 7.5, but modest or marginal at 8.5. After CySH exposure, inhibition was reversible in part by extraction of samples with reduced glutathione or at pH 10.5. Though CySH and 4-aminothiophenol induced changes in the electrophoretic migration of granule PRL, similar changes occurred in the migration of standard purified hormone despite the known absence of immunochemical effects. There was close quantitative correlation between the potency of a compound to inhibit PRL assayability and its potency to inhibit PRL release. We conclude that the inhibitory aminothiol action on PRL requires the thiol rather than the sulfide form and involves a reversible interaction which diminishes the immunochemical recognition of granule PRL. This change also results in diminished secretion.