Patterns of adrenocorticotropin secretagog release with hypoglycemia, novelty, and restraint after colchicine blockade of axonal transport.

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer hypothalamic ACTH secretagog release in awake rats. Median eminence contents of CRF, arginine vasopressin (AVP) and oxytocin (OT) were determined by RIA after insulin-induced hypoglycemia, restraint, and novelty. Insulin decreased circulating glucose concentrations and increased ACTH and corticosterone values. Median eminence CRF and AVP content declined but OT content did not. Both novelty and restraint stressors increased circulating ACTH and corticosterone concentrations. Secretagog measurements indicated decreases in OT content without concomitant decreases in either CRF or AVP with both stressors. These results indicate that: 1) colchicine blockade of axonal transport is useful in studying patterns of secretagog release in animals undergoing psychological stressors; 2) in contrast to physical stressors, OT appears to be a major component of the hypothalamic-pituitary-adrenal response to psychological stress; 3) the patterns of secretagog release differ with regards to physical and psychological stressors.