Levels of vasopressin and oxytocin in neurohypophysis and plasma of the postnatally developing rat and the influence of hypothyroidism on rat fetuses.

Arginine vasopressin (AVP) and oxytocin (OXT) were measured simultaneously by radioimmunoassay in neurohypophyses of rats immediately before birth (fetal day 22) onward to day 50 of life. The neurohypophysial content of AVP exceeded that of OXT by factor 17 at fetal day 22, by 20 immediately post natum, and by 2 at day 21 of life, respectively. As compared to day 0, the content at day 21 is considerably higher (AVP 24 fold, OXT 270 fold). The poor correlation between neurohypophysial AVP and OXT content suggests the possibility of a different onto-genetic development of both neuropeptide systems. Both AVP and OXT were detected in pooled rat plasma at various postnatal stages. Hypo- and hyperthyroidism induced experimentally during gestation did not result in a significant change in neuropeptide content of fetal neural lobes.