Effects of Prolactin on Tadpoles

Prolactin is a growth hormone secreted by the pituitary gland. Prolactin is necessary for normal growth in tadpoles. In August of 1968, a study conducted by Patricia Stocking Brown and B.E. Frye (published in "General and Comparative Endocrinology,") reviewed how a tadpole's growth is affected by an increase in prolactin. No changes were reported when the dose was increased up to 1 pg per day. When increased up to or over 1 pg per day, four areas of tadpoles were affected by this increase.

  1. Body Weight

    • Prolactin in doses of 1 pg per day or greater produced significant increases in weight. One-half microgram per day did not produce a significant effect on growth. The time of day also made a difference. When given an increase of prolactin in the morning, the tadpoles had no change in weight. When given the increase midday, researchers observed a 100 percent increase in weight. The tadpoles were weighed wet and dry. Both had an increase in weight after the increase of prolactin.

    Body Length

    • Total body length was also measured weekly, along with body weight. To achieve full body length, the tail was included in the measurement. An increase in prolactin resulted in significant increases in the body length of tadpoles. The stage of metamorphosis was noted each time researchers measured the length. Toward the end of metamorphosis, the tail is resorbed, which would change the length of the tadpole.

    Hind Leg Length

    • Hind leg length was measured weekly. The hind legs of tadpoles initially increased in length with an increase in prolactin. However, one to two weeks into the treatment, the hind legs actually decreased in length, along with the tail resorption. This decrease appears to be related to the retardation of metamorphosis with increased doses of prolactin.

    Metamorphosis

    • Metamorphosis is the biological process in which a frog develops after birth into an adult. The decrease in length of the hind legs suggests that increased prolactin retards metamorphosis. After about two to three weeks of increased Prolactin, frogs were metamorphosing slower than normal. According to this study, "the initial metamorphic stages for all of the tested groups ranged between XII and XIV. The prolactin-treated groups advanced to stages XVI-XVII during the first week or two of treatment, after which they remained stationary." They did not continue to advance to metamorphic climax.