Increase in vasopressin release into the hypophysial portal blood after superior cervical ganglion stimulation in rat.

The aim of the study was to investigate whether the stimulation of the superior cervical ganglion may influence vasopressin and oxytocin release into the hypophysial portal blood. In urethane-chloralose anaesthesia the pituitary gland was exposed by transpharyngeal approach in rats. The hypophysial portal vessels were transsected in the narrowing between glandular portion of the hypophysis and the infundibulum. The 15 min blood samples from the cut portal vessels were collected before and during electrical stimulation of the superior cervical ganglion. Vasopressin and oxytocin content in the plasma, were determined by radioimmunoassay. In the control samples the vasopressin content amounted to 3.2 +/- 1.03 ng/mL and oxytocin 0.75 +/- 0.3 ng/mL. Stimulation of the superior cervical ganglion evoked an increase (9.6-fold) in vasopressin concentration but not in oxytocin in the blood plasma of hypophysial portal vessels. On the basis of the results obtained, it may be presumed that the sympathetic efferents arising from the superior cervical ganglion induced only vasopressin but not in oxytocin release into the hypophysial portal blood.