Interaction of arginine vasopressin and corticotropin releasing factor demonstrated with an improved bioassay.

We developed an improved in vivo bioassay for corticotropin releasing factor (CRF) by modifying the injection schedule in the standard chlorpromazine-morphine-pentobarbital assay procedure. A combined injection of chlorpromazine and morphine followed 75 min later by injection of pentobarbital produced low basal levels of corticosterone and rendered the animals highly sensitive to synthetic CRF but insensitive to the stress of ether or histamine. The lowest dose of CRF that significantly elevated plasma corticosterone levels was 0.01 micrograms/kg. Using this assay, we studied CRF-arginine vasopressin (AVP) interactions at doses that were expected to raise systemic peptide concentrations to levels measured in hypophysial portal blood. The threshold for a significant corticosterone response was found to be at least 250-fold lower for CRF-41 than for AVP. The order in which CRF and AVP are injected was also found to be important, potentiation being greater if CRF was given first. In addition, rats deprived of water for 24 hr were more sensitive to CRF than normally hydrated animals.