Effect of Beta-Casomorphin and Its Analogue on Serum Prolactin in the Rat

Abstract

The effects of exogenous opioid peptides beta-casomorphin Tyr-Pro-Phe-Pro-Gly-Pro-Ile and its analogue Tyr-Pro-Gly-Pro-Phe-Pro-Ile (analogue I) were found to increase prolactin level in plasma after intraperitoneal injection. Analogue I was more potent. This effect of beta-casomorphin and analogue I were blocked by an opioid antagonist, naloxone. These results indicate that the exogenous opioid peptides (exorphins) may participate in the regulation of prolactin secretion. The similarity of analogue I with enkephalin structure was discussed.