A Novel Type of Vasopressin Receptor on Anterior Pituitary Corticotrophs?*

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Abstract
Suspensions of rat anterior pituitary cells were exposed to corticotropin-releasing factor (CRF) (5 nM) and various neurohormones (0.002-1000 nM). CRF-induced secretion of ACTH was doubled by 0.1 nM arginine vasopressin (AVP), 0.2 nM arginine vasotocin, 1 nM oxytocin, 10 nM angiotensin II and 100 nM noradrenaline [norepinephrine]; vasoactive intestinal peptide had no effect at 0.2-200 nM. CRF potentiation by AVP was also observed at lower concentrations of CRF. Since AVP appeared to be the most potent modulator of CRF-induced ACTH seretion, potentiation was further tested with specific antidiuretic and oxytocic agonists. Potentiation was clearly related to pressor biological activity, less so to antidiuretic, and hardly at all to oxytocin activities. Even at 200 nM, the antipressor antagonists dPTyr(Me) AVP and d(CH2)5Tyr(Me)AVP had no effect on potentiation by AVP. The lack of antagonism was partly due to the agonist effects of the antagonists on the pituitary gland, an effect not observed with vascular tissue. Apparently, anterior pituitary vasopressin receptors resemble (but are not identical to), V1 (pressor and hepatic), do not resemble the V2 (renal), and might be classified as V3 (pituitary) receptors.