Albumin synthesis during induced and spontaneous metamorphosis in the bullfrog Rana catesbeiana

Abstract

Treatment of premetamorphic tadpoles with triiodothyronine (T 3) alters the in vivo distribution of radioactive amino acids among serum protein fractions. The effects on the albumin fraction have been interpreted as reflections of the relative rate of synthesis. About 12 hr after intraperitoneal injection of 2.5 × 10 −10 mole of T 3 per gram, there is an increase in the relative rate of albumin synthesis. The effect peaks on day 3 at 5 × the untreated level and returns to near the untreated level by day 6. Continuous immersion in 1 × 10 −7 M T 3 results in a similar stimulation of albumin synthesis, but with no decline after day 3. The timing of the response is independent of dose or route of T 3 administration. The effect of T 3 on the relative rate of albumin synthesis is also observed in froglets. There is a 6-fold increase in the relative rate of albumin synthesis during spontaneous metamorphosis peaking at stage XXI and returning to the premetamorphic level by stage XXV. The following was concluded: (1) The increase in the relative rate of albumin synthesis during metamorphosis results from increased endogenous thyroid levels. (2) Following a peak, the decline in albumin synthesis observed in induced and spontaneously metamorphosing animals is a result of decreasing thyroid hormone levels. (3) The effect of T 3 on albumin synthesis may be the summation of two effects, a direct effect of T 3 and a stimulation by amino acids from the resorbing tail. (4) A decreased relative rate of albumin degradation or a sparing of albumin is probably responsible for the elevated relative concentration of albumin in the serum of postmetamorphic animals.