Assays and dynamics of corticotropin-releasing factor activity in rat hypothalamus

Features of several assays for corticotropin-releasing factor (CRF) were compared, with reference to sensitivity, precision, specificity and convenience. In general, in vivo assays are less specific, whereas in vitro assays with isolated pituitary cells appear to suffer from vulnerability. Promising approaches for overcoming this difficulty are appearing: one is the cell culture technique and the other is the perfusion of pituitary cell column. However, the findings with vasopressin are again discordant. So far, the in vivo-in vitro assay system appears to be the most satisfactory. In this connection, special emphasis was laid on the CRF assay by out intrapituitary injection technique through the parapharyngeal approach, which has features of both in vivo and in vitro systems. The drawbacks with this assay are its complexity and relatively lower precision. Problems of the use of dexamethasone are discussed from a viewpoint of possible multistage feedback inhibition, as postulated by Yates et al. Several findings on the CRF dynamics were mentioned, in order to exemplify the findings obtained with our assay: it was shown that the two-peaked changes of CRF after ether-laparotomy stress in adult rats were composed of heterogeneous components, as revealed by differential effect of cycloheximide. Pretreatment with cycloheximide similarly abolished the delayed CRF peak that was observed in 2-day-old neonatal rats under stress. These findings suggest an operation of a biochemical denominator in common with both cases.