Temperature and prolactin as control factors in newt forelimb regeneration

Temperature and prolactin were studied as control factors in the process of newt forelimb regeneration. Temperature was varied in five steps from 10° to 30°C under otherwise constant environmental conditions. Longitudinal new growth and limb differentiation were observed. Temperature was found to have a profound effect upon both developmental processes. Maximal longitudinal new growth resulting from changes in temperature alone occurred at 25°C with maximal limb differentiation at 30°C. At each temperature studied, prolactin enhanced both new growth and limb differentiation. With prolactin, maximum new growth also occurred at 25°C, but maximum limb differentiation occurred at 20°C. For our purposes optimum limb development was defined as the greatest new growth commensurate with full normal development. This optimum was reached by prolactin treated animals at 20°C when the regenerating limbs studied achieved 100% maximum normal differentiation and 87% maximum new growth. It was possible by employing a combination of temperature changes and hormone administration to control newt forelimb regeneration and produce a whole spectrum of limb development.