Episodic patterns of growth hormone secretion and growth hormone status of normal and tibial dyschondroplastic chickens.

Growth hormone status of normal and tibial dyschondroplastic (TD) birds was determined in 25 d old male chicks genetically selected for high and low incidence of TD. Birds were surgically prepared with indwelling venous catheters and blood samples remotely removed at 20 min intervals for 6 h to establish secretory patterns. Birds were maintained under a 16L:8D cycle, with free access to feed and water at all times. In a second experiment, secretory capacity was evaluated by administering a 10 micrograms/kg body weight dose of thyrotrophin releasing hormone (TRH). Blood samples were removed at 0, 5, 10, 20, 30, 60 and 120 min post-infusion of either TRH or saline (control). All birds displayed pulsatile patterns of GH secretion, with an average peak duration of 60 min and a 90 min inter-peak interval. Dyschondroplastic birds exhibited 50% higher mean peak amplitudes than normal birds (P less than .06), however, this difference was not translated into overall mean or total (curve area) differences. The magnitude of response to a TRH challenge was greater (P less than .10) for TD than for normal birds. In view of the relationships observed in other species between secretory pattern characteristics such as peak amplitude, and growth characteristics, it is suggested that differences in GH status of dyschondroplastic relative to normal birds may be related to initiation of the TD lesion.