Effects of tiapride infusion on plasma levels of beta-endorphin, prolactin and dopamine in patients with pain from cancer.

Tiapride, a substituted benzamide, exerts an antalgic effect in man. To examine the possibility that tiapride analgesia might be related to a mechanism involving a release of endogenous opioids, the acute effects of an intravenous injection of the drug on plasma radioimmunoassayable beta-endorphin were studied in patients with pain from cancer (placebo-tiapride double-blind randomized trial). Seeing that substituted benzamides affect prolactin secretion, the plasmatic levels of prolactin and dopamine, a known factor inhibiting prolactin release, were studied as well. The tiapride infusion produced a slight but significant increase in plasma beta-endorphin level, an early and significant increase in plasma prolactin, and a sudden and highly significant decrease in plasma dopamine. These results are compatible with the hypothesis that tiapride influences the neuroendocrine system.