Differential response of embryonic chick pancreas enzymes to glucocorticoids

Glucocorticoids probably play an important role in coordinating the terminal differentiation of several chick embryo tissues, one of which is the pancreas. The chick embryo adrenal cortex is thought to start secreting corticosteroids at 12 days of development. Responsiveness of the pancreas to corticosteroids precedes the normal onset of hormone secretion. There are two developmental patterns of excreted enzyme accumulation in the pancreas: Two step enzymes: amylase and procarboxypeptidase start to accumulate early in development (at the end of the first week) and their specific activities increase in two steps separated by a plateau. Secondly, one step enzymes, chymotrypsinogen and endonuclease, start to accumulate rapidly later in development (after 14 days) and their specific activities rise in a single step that ends around the time of hatching. The response in vivo and in vitro of one-step and two-step enzymes to hydrocortisone is different. In pancreas from embryos of less than 14 days developmental age, hydrocortisone induces one-step enzymes precociously (after a lag of less than a day). Twostep enzymes initially accumulate independently of glucocorticoids until a plateau of specific activity is reached. Glucocorticoids cause the precocious increase of two-step enzymes above plateau levels. The effects of glucocorticoids on two-step enzymes are observed after a lag of a day or more. The observations are consistent with the view that glucocorticoids initiate the rapid accumulation of onestep enzymes at 14 days of development and cause renewed accumulation of two-step enzymes at 17 days of development. A possible role of glucocorticoids in the regulation of two-step enzymes is release of their synthesis from a constraint which comes into effect at the end of the second week of development. The work on pancreas indicates that for each different parameter used to measure the responsiveness of a developing tissue to a hormone, different response times and kinetics may be observed.