A comparison of beta-endorphin levels in regenerating and nonregenerating vertebrates

The mean plasma level of beta-endorphin in the newt, Notophthalmus viridescens, as measured by radioimmunoassay, is significantly higher than the circulating levels of beta-endorphin in the anuran, Rana pipiens, and in mammals (humans and mice). The newt beta-endorphin level is found to be 6-fold greater than mammalian levels and three times greater than the levels observed in Rana pipiens. The high levels are maintained in the newt throughout limb regeneration.