Food deprivation and feeding of broiler chickens is associated with rapid and interdependent changes in the somatotrophic and thyrotrophic axes

1. In several experiments, hormonal changes in the somatotrophic axis, grow th hormone (GH) sensitivity to a GH-secretagogue, thyroid hormones and thei r metabolising enzymes and plasma glucose levels were measured in relation to food deprivation and reinitiation after a single daily meal in 4- to 5-w eek-old male broiler chickens. 2. Floor-reared male broiler chickens were fed ad libitum or were restricte d to a daily food intake of 40 or 45 g per d from the age of 2 weeks onward s. The daily food allowance was consumed in 0.5 h. 3. Food deprivation increased plasma GH concentrations but decreased GH-dep endent variables such as plasma insulin-like growth factor-I and 3,3',5-tri iodothyronine (T-3) Concentrations. Hepatic inner ring deiodinating type II I activity was markedly elevated, presumably as a consequence of low hepati c GH receptor numbers, and is thought to be the causal mechanism for the lo w plasma T-3 concentrations. Food intake reversed these variables in a time -related manner. 4. GH pulsatility characteristics, as calculated by deconvolution analysis, revealed profound changes between food restricted and ad libitum fed anima ls. Chickens deprived of food for about 23.5 h were characterised by an enh anced pulsatile GH release as reflected in the higher GH secretory burst am plitude, GH mass per burst, GH production rate and GH pulse frequency. Thes e variables returned very quickly to normal values after refeeding. 5. In summary, these experiments taken together demonstrate very clearly th e interdependent and time-related changes of the somatotrophic and thyroid axes upon a single meal in previously food-deprived broiler chickens.