Source of carbon for the biosynthesis of eggshell carbonate in the hen. Comparison of six 14C labeled compounds as sources of carbon in eggshells, albumen, and yolk.

Laying hens received single-dose intravenous injections of one of six U-14C labeled metabolites (bicarbonate, acetate, D-glucose, glycine, L-leucine, and palmitate) at times coinciding with maximum shell formation. Eggs were collected and 14C activities in shell, yolk, and albumen were measured. Typical patterns of 14C incorporation were observed with each of the three egg fractions; in shells highest 14C activities were obtained on the first postinjection day (D+1 day), albumen on the D+2 day, while yolks increased gradually their activities from zero levels on the D+1 day, reaching a plateau at around the D+4 day. In the second experiment, the 14C entry into albumen was slower than in the first one, with bicarbonate effecting higher albumen activities in D+3 than in D+2 eggs. Levels of 14C entry into shells of eggs laid on the D+1 day by hens injected with bicarbonate, glucose, or acetate were similar; significantly lower levels were obtained with (listed in descending order) glycine, leucine, and palmitate. Highest activities in albumen were induced by the two amino acids, with leucine causing higher activities than glycine; progressively lower entries were obtained with glucose, acetate, bicarbonate, and palmitate. In yolks, highest activities were obtained with glucose, followed by leucine, acetate, glycine, palmitate, and bicarbonate. Unexpectedly high activities obtained in the albumen of the D+1 eggs, particularly with 14C supplied from glucose, indicate that 14C was transported during the shell formation stage into the egg. The physiological implications are discussed and a suggestion is made that the possibility of carbonate for shell formation being delivered to the site of this formation from the inside of the egg should not be overlooked.