Ontogeny of the sensitivity of the somatotrophes to thyrotrophin releasing hormone (TRH) and growth hormone releasing factor (GRF) in the embryonic and posthatch chick.
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The ontogeny of the in vitro growth hormone (GH) release after stimulation with thyrotrophin releasing hormone (TRH) or growth hormone releasing factor (GRF) has been studied in two strains of chickens during the last week of embryonic development and the first week posthatch. Fourteen-day-old embryos did not yet respond to any of the stimuli applied, while the amplitude of the GH response to the different stimuli increased gradually from 18-day-old embryos to 1-day-old chicks. The evolution of the responses to both stimulating agents was parallel in the two strains of chickens, but the amplitude of the response was always higher in the rapidly growing broiler strain compared to the slowly growing layer strain. The highest GH response was at all stages obtained with the highest dose of GRF (100 nM). At a lower dose (10 nM), however, TRH seemed to be a more effective GH releasing agent than GRF at the posthatch stages.
