Effects of Prolactin and Somatotropin on Growth and Metamorphosis of Amphibians

Mammalian prolactin stimulates growth and inhibits metamorphosis of larvae of several species of amphibians. Mammalian somatotropin has little or no effect upon larval growth or metamorphosis unless used in high concentrations. The evidence behind these statements and some of the implications are critically evaluated. Growth of postmetamorphic amphibians is stimulated by somatotropin but not by prolactin. The possible biological significance of this apparent transition from prolactin to somatotropin regulation of growth in the preand postmetamorphic stages of development is discussed in terms of possible mechanisms involved in the transition, and in terms of the adaptive significance of the change.