(6R)-5,6,7,8-tetrahydro-alpha-biopterin affects vasopressin and oxytocin release from rat neurointermediate lobe in vitro.

Incubation of neurointermediate lobes in Locke's solution containing 0.13 mumol.l-1 (6R)-5,6,7,8-tetrahydro-alpha-biopterin dihydrochloride (THB4) resulted in an inhibition of bioassayed vasopressin secretion and in an increase of that of oxytocin both under resting conditions as well as during depolarization due to excess potassium. It is suggested that some events related to THB4 and localized in the neural lobe are involved in the mechanism of vasopressin and oxytocin release.