Characterization of Rat Stalk Median Eminence Vasopressin and Its Involvement in Adrenocorticotropin Release

Abstract

The perfused isolated rat anterior pituitary cell column was used as a bioassay for corticotropinreleasing factor (CRF). The system responded to arginine vasopressin (AVP) in a dose-dependent manner with a minimum effective dose of 10^-10 M. Log doseresponse curves for AVP and crude stalk median eminence extract (SME) were statistically significantly nonparallel (P < 0.05) and similar results were found for lysine vasopressin, arginine vasotocin (AVT), oxytocin, and human posterior lobe extract. Vasopressin and its analogs had no effect on LH release. Using RIA for AVP, SME was found to contain 10.83 ng (7.7–14.3 ng, n = 12) AVP, which could account for no more than 30% of its CRF activity. The CRF activity of both SME and AVP was totally quenched by incubation overnight with vasopressin antisera. Partial quenching was obtained with higher dilutions of the antisera. Vasopressin-stimulated ACTH release was affected in a similar way to SME-stimulated ACTH release by the presence of corticosterone (0.2 μg/ml) in the perfusate, by removal of calcium and magnesium ions from the perfusate, and by treatment of AVP or SME with trypsin. These results suggest that the CRF activity of our extract is due to a peptide with a vasopressin-like structure.