CHANGES IN RAT HYPOTHALAMIC CONTENT OF CORTICOTROPHIN-RELEASING FACTOR (CRF) ACTIVITY, PLASMA ACTH AND CORTICOSTERONE UNDER STRESS AND THE EFFECT OF CYCLOHEXIMIDE

Publisher Website
Google Scholar
Abstract
The changes in the hypothalamic content of corticotropin-releasing factor (CRF), the plasma concentrations of ACTH and corticosterone were studied in the intact male rat. CRF activity was estimated by bioassay and plasma ACTH levels by radioimmunoassay. The variation in CRF hypothalamic content reflected CRF secretion since plasma ACTH and corticosterone increased concomitantly. The activity of CRF separated into 2 peaks, one occurring immediately (2 min) and a 2nd about 80 min later after the start of stress. The elevation of plasma ACTH and corticosterone followed the 1st CRF activity peak, and both showed a sustained time course. Cycloheximide pre-treatment (1 mg/100 g i.p.) was used to test whether protein synthesis was required for secretion of CRF. Treatment with cycloheximide reduced the incorporation of [14C]L-alanine into hypothalamic and pituitary proteins. The 2nd CRF activity peak was completely abolished while the 1st activity peak was essentially intact. Plasma ACTH increased in response to the 1st CRF activity peak, but then declined. Plasma corticosterone remained low throughout, possibly as a consequence of inhibition of adrenal protein synthesis. When a 2nd stress stimulus (fracturing of 1 leg without anesthesia) was superimposed, CRF activity and plasma ACTH did not show any incremental response. The 2nd CRF activity peak is apparently sensitive to cycloheximide inhibition of protein synthesis, while the 1st activity peak appears to be cycloheximide resistant.