Fetal neurohypophyseal arginine vasopressin and arginine vasotocin in man and sheep.

Immunoreactive arginine vasopressin (AVP) and arginine vasotocin (AVT) were quantitated in 15 of 17 human fetal pituitary glands early in gestation (11-19 weeks) and in 8 of 9 ovine fetal pituitary glands late in gestation (109-137 days). In 14 of 15 human fetal glands, AVT content exceeded that of AVP. There was a significant rise of AVP (as a percentage of total AVP plus AVT content) with gestational age over the period of 12-19 weeks (P less than 00.01). The ovine fetal glands demonstrated a preponderance of AVP over AVT. The mean AVP and AVT content in the ovine glands was 5.7 +/- 2.9 and 0.8 +/- 0.2 mU/mg gland weight, respectively, compared with the values in the human fetal pitiutaries, 0.8 +/- 0.2 and 1.2 +/- 0.2 mU/mg gland weight, respectively. The relative percentage of AVP and AVT in the ovine fetal pituitaries was 76.0+/- 9.6% and 23.9 +/- 9.6%, respectively, as contrasted to the human fetal glands, 36.7 +/- 2.7% AVP and 63.3 +/- 2.7% AVT. The preponderance of AVT over AVP in the early gestational age mammalian fetus may represent a primative first step in molecular evolution of the neurohypophyseal peptides.