Rat corticostatin R4: synthesis, disulfide bridge assignment, and in vivo activity.

We have synthesized significant amounts of the most potent member of the rat corticostatins that inhibits ACTH-induced corticosteroid and compared its structure to that of the natural hormone. The cystine bridging arrangement that corresponds to that reported for a human defensin (3-31, 5-20, 10-30) was determined. The in vitro corticostatic activity of the synthetic rat corticostatin R4 paralleled that of the natural R4. Biological studies in vivo showed that doses of 8 or 12 mg corticostatin/kg effectively interfered with corticosterone release in stressed rats. We conclude that in the assays that were used, the biological activity of the synthetic and natural molecules was identical. The availability of significant amounts of synthetic material will make possible studies investigating the physiological role played by corticostatins in modulating the activity of the hypothalamic-pituitary-adrenal axis.