An analysis on the extent of underestimation in fractional rates of protein turnover was conducted by using computer simulation with a two-pool compartmental model in chickens. The extent of underestimation in calculated values for fractional synthesis rates, which was 148 Japan. Poultry Sci., 24(3), 1987 introduced by ignoring isotope recycling, was compared in terms of three isotope administration methods, i.e., pulse injection, continuous infusion and primed infusion. Also tested were the effects on the underestimation of the length of easurement period, varying the fractional rate of protein synthesis per se, and of relative pool size of protein to free amino acid (R).
It was shown that the longer the measurement period, the larger the underestimation resulted in. There was a similar extent of underestimation between the three administration methods within half an hour, while the difference was evident at 6 hours. When fractional rates of protein synthesis per se were high, the extent of underestimation became so large that the effect of isotope recycling was no longer ignorable, especially by the continuous and primed infusion methods at the end of 6-hour measurement period. The R value had a most remarkable effect on the extent of underestimation, which was drastically increased particularly when the R value was low.
The present results suggest that the calculation of fractional rates of protein turnover without consideriog isotope recycling would be underestimated to the extent as large as 70%, depending on the condition employed.

View full abstract

Some aspects of the effects of hypothyroidism on the chicken immune system are described. Two experiments were conducted using different methods to induce hypothyroidism. In Experiment 1, chicks were surgically thyroidectomized at 3 weeks of age (Tx group) and in Experiment 2, hypothyroidism was induced by supplementing the feed with 1% propylthiouracil (PTU) from 3 weeks of age for 6 weeks (PTU group).
1. hypothyroidism was induced in both Tx and PTU treated birds, as indicated by the significant reduction in body weights in both groups, the absence of thyroid gland of in the Tx chicks and enlargement of the thyroid gland in the PTU treated chicks. There were significant decreases in weights of lymphoid organs (bursa of Fabricius, thymus and spleen) and significant increase in the weight of the adrenal in both groups. In the PTU treated chicks, feed efficiency and weight of the liver significantly decreased and increased, respectively.
2. Histological observations indicated that PTU treatment caused notable damage to the lymphoid organs: severe depletion of the cortical lymphocytes in the thymus; reduced number of the bursal follicles; depletion of the lymphoid cells in the cortical region of the bursal follicles; fibroblastic invasion from the interstitial tissue; and the depletion of the lymphoid cells in the white pulp region of the spleen and a reduced number of splenic follicles.
3. PTU treatment reduced the number of the peripheral white blood cells, particularly of lymphoid cells, and the value of the hematocrit.
4. PTU treated chicks had higher antibody responses to sheep red blood cells (SRBC) and Brucella abortus (BA) antigens than untreated control chicks, except for the primary 2-ME resistant antibody (IgG type) response to BA.
5. There was no evidence of any marked changes in the concentration of serum IgG induced by either thyroidectomy or PTU treatment, except in chicks that were not completely thyroidectomized (pTx group).
The result spresented here are consistent with those of previous studies on the effects of thyroidectomy or PTU treatment on the weights of lymphoid organs, the number of the white blood cells and histological observations in mammalian system. However, in the present study, higher antibody responses were contrary to the lower responses of mammalian system and to previous reports of chickens. This suggests that although hypothyroidism results in the impairment of development of the avian immune system, the hypothyroid state may not necessarily be an indicator of the inhibition of immune responsiveness.

View full abstract

[in Japanese]

View full abstract