Responses upon multiple administration of L-thyroxine in hens.

Studies on the influence of repeated injections of L-thyroxine on enzyme activity and total protein level in the blood plasma of White Rock and Sussex hens have shown that: 1. The total protein level in both races decreased significantly. 2. Activity of aldolase increased in White Rock hens while in Sussex hens it increased considerably only after the last injection. 3. Activity of alanine aminotransferase did not change in White Rock hens and increased in the blood plasma of Sussex hens. 4. In both races, the activity of aspartate aminotransferase increased initially and changed after L-thyroxine injection. 5. Activity of alkaline phosphatase increased in White Rock hens, while in Sussex hens it decreased. 6. Statistically significant differences between activities of examined enzymes in both races after L-thyroxine administration were found.