Tadpoles were treated with intraperitoneal injections of mammalian prolactin and growth hormone (NIH). The growth rate of hypophysectomzied tadpoles (R. pipiens) was accelerated by both hormones, prolactin having the greater effect. Metamorphosis in the bullfrog (R. catesbeiana) was inhibited by prolactin but not by growth hormone. The results are interpreted to indicate a general antagonism between prolactin and thyroid hormone in amphibian development with respect to both growth rate and metamorphosis.
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Etkin et al. (1967) studied this question.