Effect of prolactin antiserum on growth and resorption of tadpole tail

Rabbit antiserum to bullfrog prolactin (A/S) or normal rabbit serum (NRS) was administered to premetamorphic bullfrog larvae. Collagen synthesis in the tail fin was not affected by A/S. However, the enhancement of collagen synthesis induced by pimozide treatment was completely blocked by A/S. Premetamorphic tadpoles kept in 3 x 10^-8M thyroxine received A/S or NRS. A/S accelerated tail resorption. The results indicate that the endogenous prolactin is acting as an antimetamorphic hormone, although it is not certain that normally circulating level of prolactin contributes to promoting the growth of the tail fin in larval bullfrogs.