title: Observations on the interaction of prolactin and thyroxine in the tail of the bullfrog tadpole.
abstract: Explants of tail fin from tadpoles of Rana catesbeiana maintained in tissue culture underwent resorption when exposed to a medium containing 150 nM thyroxine (T4). Increases in the specific activity of hexosaminidase (Hex) and of acid phosphatase (AP) were associated with this response. Ovine prolactin inhibited resorption of explants in a dose-responsive manner; however, prolactin had no influence on the specific activity of either Hex or AP cultured explants. This result contrasted with the effect of prolactin in vivo, where it inhibited both the resorption of the tail and the increase in specific activity of hydrolytic enzymes induced by T4. The actions of both hormones, when applied in vivo, were more pronounced in the tail fin than in the muscular core of the tail at the stage of regression tested, indicating that the failure of prolactin to influence enzyme induction in vitro did not result from an incapacity of the fin to respond to prolactin in this fashion. It is suggested that the inhibition of T4-induced enzymic activity by prolactin which is observed in the intact animal may come about in response to some related but indirect systemic action of prolactin that is lacking when explants are cultured in vitro. It is concluded that inhibition of the induction of hydrolytic enzymes is not an essential factor in the inhibitory effect of prolactin on the resorption of the tail fin.
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D046508:Culture Techniques; D006596:Hexosaminidases / Q000378:metabolism; D007814:Larva; D008675:Metamorphosis, Biological; D011388:Prolactin / Q000494:pharmacology*; D011892:Rana catesbeiana / Q000254:growth & development*; D013623:Tail / Q000254:growth & development; D013974:Thyroxine / Q000494:pharmacology*
chemical_list: D011388:Prolactin; D000135:Acid Phosphatase; D006596:Hexosaminidases; D013974:Thyroxine