The effect of prolactin on the rate of forelimb regeneration in newts exposed to photoperiod extremes.

Four groups of bilaterally amputated newts were exposed to (1) continuous light, LL; (2) continuous light with daily prolactin injections, LL-PRL; (3) total darkness, DD; or (4) total darkness with daily prolactin injections, DD-PRL. The results confirmed that LL animals regenerate their limbs more rapidly than DD. The results also showed that LL-PRL animals do not respond to the exogenous prolactin but that DD-PRL animals do respond and in fact regenerate at a rate which exceeds not only DD but also LL and LL-PRL. The possible synergism between prolactin and photoperiod is discussed.