Submitted to: Poultry Science
Publication Type: Abstract Only
Publication Acceptance Date: May 31, 2004
Publication Date: June 1, 2004
Citation: Lu, J., McMurtry, J.P., Coon, C.N. 2004. Developmental changes of plasma insulin, glucagons, IGF-I, IGF-II, thyroid hormones, and glucose concentration in chick embryo [abstract]. Poultry Science. 83 (Suppl.1):192.
Hatching eggs from a flock of Cobb 500 females were collected and incubated to obtain hormone and glucose data for different ages of chick embryo's. Sampling started with day 10 of embryogenesis (10E) and continued through hatch. Plasma samples were collected to determine the developmental changes of insulin, glucagon, insulin-like grow factor-I and -II (IGF-I, IGF-II), triiodothyronine (T3), thyroxine (T4), and glucose concentration for different ages of the chick embryo.
A significant increase in plasma insulin levels was observed with a large increase from 130pg/ml at 10E to 389pg/ml at 16E. The insulin levels showed two peaks during the late stages of embryogenesis with a peak of 460pg/ml at 17E and a second peak of 488pg/ml at hatch. Plasma glucagon levels significantly increased from 59pg/ml at 10E to 428pg/ml at hatch; however, there was a decrease from 12E to 19E with the lowest level of 60pg/ml at 15E. Previous research has showed glucagon levels in avian plasma is 10-80 times higher than that of mammals (0.05-0.10ng/ml vs 1-4ng/ml plasma). The molar ratio of insulin to glucagon (I/G) from 14E to 17E ranged from 1.7 to 2.2 which was significantly greater than normal I/G ratio in the post-absorptive state in avian species (1.2-1.7). The results indicate that insulin is an important promoter of chick embryo growth by anabolic drive to promote protein deposition especially during the chick embryonic rapid growth period. There also was a significant increase in plasma glucose from 13E to 18E suggesting glucose is an important regulator of protein anabolism in the chick embryo via suppression of amino acid oxidation.
Plasma IGF-1 and IGF-II concentrations increased from 10E to 14E and then IGF-1 slowly decreased until hatch, while IGF-II levels remained constant. IGF-II levels were approximately 10 fold greater than IGF-1 suggesting IGF-II is an important functionary for embryonic development.
Plasma T3 and T4 levels showed a significant increase during the third week of incubation and reached a peak at 19-20 E. The findings are consistent with previous research showing a sharp rise in T3 and T4 activity when the embryo switches to lung respiration. These results indicate that both thyroid hormones play an important role in promoting growth during the final stages of embryogenesis. The T4 level was much greater than that of T3 indicating T4 is the main thyroid hormone during chick embryo development.
Key words: plasma, insulin, glucagon, IGF-I, IGF-II, glucose, thyroid hormones, chick embryo