5-Hydroxyeicosatetraenoic Acid and Phorbol Ester Stimulate Prolactin Release from Rat Anterior Pituitary Cells by Different Mechanisms

The relationship between 5-hydroxyeicosatetraenoic acid (5-HETE) and calcium-activated, phospholipid-dependent protein kinase (protein kinase C) in prolactin (PRL) release was investigated in rat anterior pituitary cells. Arachidonic acid or 5-HETE, a 5-lipoxygenase metabolite of arachidonic acid, is known to cause a significant concentration-dependent increase in PRL release. Phorbol 12-myristate 13-acetate (PMA) and dioctanoyglycerol (diC8) have also been known to stimulate PRL release from pituitary cells, so we showed that these PRL releases were correlated with the activation of protein kinase C, that is, they induced dose-dependent translocation of protein kinase C from the cytosol to the membrane. Arachidonic acid, however, did not cause a significant change in the distribution of protein kinase C. We also showed that the PRL release induced by arachidonic acid and that induced by 5-HETE were additional to that by 100nM PMA. Thus we suggested that the signals for the stimulation of PRL release sent by arachidonic acid and 5-HETE would be different from the signal sent through protein kinase C by PMA.