Inhibition of the antimetamorphic action of prolactin in larval Ambystoma tigrinum by lysine vasopressin, arginine vasotocin, and aldosterone

Ontogenic screening of aldosterone in the South American toad Bufo arenarum (Hensel)

The content of aldosterone in the South American toad Bufo arenarum embryos developed in Holtfreter's 10% solutions and in distilled water was measured. The screening was carried out on embryos from the following periods of their development: 15 min after fertilization; gray crescent-32 cells; mid cleavage-late gastrula; neural plate-neural tube; tail bud-heart beat; gill circulation-tail fin circulation and operculum fold-complete operculum. The aldosterone content of embryos incubated both in Holtfreter and in distilled water decreased gradually up to gill circulation-tail fin circulation stages. The steroid content of both groups of embryos rose sharply at the end of their development (operculum fold-complete operculum); the observed increase was significantly higher in distilled water animals.

Secretion of prolactin-synergizing activity (synlactin) by the liver of ectothermic vertebrates in vitro

Recent work in our laboratory indicated that the liver of rats and pigeons secretes a prolactin synergist (synlactin) in vitro. We have investigated the secretion of this activity by the liver of nine species of ectothermic vertebrates. Liver from three teleosts (goby, salmon, and tilapia), four amphibians (Ambystoma, Necturus, bullfrog, and grass frog) and two reptiles (turtle and anole) was diced, washed, and incubated for 3 hr in isotonic medium. After dialysis, the liver incubation media (LIM) were tested with and without prolactin (PRL) in the local pigeon crop-sac bioassay. The LIM for turtle, larval bullfrog, freshwater salmon, and 5% seawater-adapted goby significantly augmented the local crop-sac response to PRL, but the LIM from anole, adult bullfrog, grass frog, fasted larval Ambystoma, Necturus, 100% seawater-adapted goby, and tilapia did not contain synergizing activity. We conclude that synlactin is secreted by the liver of several species representing three of the major ectothermic classes of vertebrates. It is significant that in two cases, larval bullfrog and 5% seawater-adapted goby, the presence of synlactin occurs in physiological states in which PRL is active. In the opposite cases (adult frog and 100% seawater-adapted goby) the activity was not detectable. We also found that the liver of larval and adult bullfrogs and tilapia released a factor in vitro that had proliferative activity in the crop-sac. This activity appears to be distinct from synlactin.

Antagonistic effects of prolactin and oxytocin on tail fin regression and acid phosphatase activity in metamorphosing Ambystoma tigrinum

We have found that the inhibition of thyroxine-induced tail fin regression by prolactin in larval tiger salamanders is antagonized by oxytocin. Other workers have shown that prolactin blocks the rise in activity of several hydrolytic enzymes that occurs in regressing tissue during metamorphosis. Here, we examine the effects of prolactin and oxytocin--given alone and in combination--on tail fin regression and acid phosphatase specific activity in this tissue. Both long-term (12-day) and short-term (48-hr) treatment paradigms using prolactin and oxytocin are investigated. The results show that long-term prolactin treatment of metamorphosing larvae blocks fin regression and the rise in acid phosphatase specific activity seen in metamorphosing controls; short-term prolactin treatment of metamorphosing larvae inhibits fin regression within 48 hr, but does not block the rise in acid phosphatase activity seen in controls; oxytocin antagonizes the effects of prolactin on tail fin regression; and oxytocin treatment (long-term or short-term) of metamorphosing larvae causes an elevation of acid phosphatase activity above that seen in metamorphosing controls. With long-term treatment, this effect of oxytocin is slightly antagonized by prolactin; with short-term treatment, no antagonism is observed even though an effect of prolactin on fin height is still evident. We have interpreted these results as suggesting that the effect of prolactin on hydrolase activity is not a prerequisite for its inhibitory effect on fin regression to occur.