Plasma steroids in the ammocoete of Petromyzon marinus

Radioimmunoassays revealed the presence of the following steroids (or immunoreactive steroid fractions) in the plasma of larval sea lampreys: progesterone, corticosterone, cortisol, androstenedione, testosterone, dihydrotestosterone, estrone, and estradiol. Several types of stress served to provoke the release of these substances. A statistically significant effect of the treatment was noted under only one condition: squeezing of the body of decapitated ammocoetes during blood collection caused an increase in plasma dihydrotestosterone and a decrease in plasma estradiol. The discovery of all eight steroids (or immunoreactivities) assayed for suggests that the plasma of the ammocoete may contain a considerable number of additional steroids yet to be identified.