Developmental Changes in Thyrotropic and Somatotropic Effect of TRH in Precocial Japanese Quail and Altricial European Starlings

Abstract

The thyrotropic and somatotropic effects of thyrotropin releasing hormone (TRH) in precocial Japanese quail (Coturnix japonica) and altricial European starlings (Sturnus vulgaris) during postnatal ontogeny were studied. Concentrations of thyroid hormones (TH) and growth hormone (GH) in the circulation were determined 60 min after the subcutaneous administration of TRH. In quail, TRH caused an increase of triiodothyronine (T3) in plasma during the phase of rapid growth, whereas thyroxine (T4) concentrations were not affected. In starlings, with a different developmental pattern of TH concentrations, TRH induced an increase of plasma T3 concentrations on all analyzed days, whereas a significant increase of T4 occured on day 1 only. Concentrations of GH were stimulated by TRH in both species. Although growth rate is nearly two times higher in starlings than in quail, differences in the control of the thyrotropic and somatotropic axes do not parallel this difference and tissue sensitivity to other hormonal signals are expected in both developmental strategies.