Some effects of glucagon on chick embryo development

Glucagon concentrations ranging from 1.16 to 300-0 microgram/0.1 ml diluent were injected into the yolk of chick embryos on incubation days 8, 10, and 12. Studies of survival rates, embryo weights, blood sugars, liver and tibiotarsus glycogen histochemistry, and pancreatic alpha and beta tissue histogenesis were undertaken during the 9- to 16-day incubation period. Glucagon dosages of 37.5 and 150.0 microgram/0.1 ml diluent gave the best survival rates. Glucagon caused an increase in embryo weight, increased liver glycogen storage, a chondrocyte glycogen storage pattern which correlated with blood sugar levels, an increase in pancreatic beta tissue and a decrease in pancreatic alpha tissue. Studies of blood sugars following glucagon treatment showed that most concentrations caused an initial (first 16 h) hyperglycemia. Following this, two general patterns were exhibited: (1) the lower glucagon concentrations caused hypoglycemia after about 24 h, and (2) the higher concentrations caused amore prolonged hyperglycemia when administered on incubation day 10 but caused hypoglycemia when administered on incubation day 10 but caused hypoglycemia when administered on days 8 and 12. Interpretation of these results is based on the contribution of three factors to the expression and duration of the glucagon effect: (1) concentration of glucagon administered, (2) insulin secretion, and (3) levels of glycogen storage at the incubation stage of administration.