PLASMA THYROID-HORMONE AND GROWTH-HORMONE PATTERNS IN PRECOCIAL JAPANESE-QUAIL AND ALTRICIAL EUROPEAN STARLINGS DURING POSTNATAL-DEVELOPMENT

Plasma concentrations of thyroid hormones (TH) and growth hormone (GH) during postnatal development in the precocial Japanese quail (Coturni x japonica), and the altricial European starling (Sturnus vulgaris) we re measured. Developmental changes in plasma TH found in the starling, differ considerably from those detected in quail. In quail rather hig h triiodothyronine (T-3) values were measured during the first few day s after hatching. Subsequently a steady decrease of plasma T-3, to adu lt levels, was observed. Thyroxine (T-4) concentrations did not change significantly during the period studied. In starlings, on day 1, plas ma T-3 was low and T-4 was at or below the assay detection limit. An i ncrease in concentrations of both hormones occurred between day 1 and day 5 after hatching. A gradual increase of T-4 occurred afterwards, w hile plasma T-3 levels remained nearly constant during this growing pe riod. Plasma GH concentrations showed a similar pattern in both specie s. There was an increase during first days after hatching and GH conce ntrations peaked at day 7 in quail and day 5 in starlings. A subsequen t decrease was observed in both species. Although the GH profiles in s pecies studied were comparable, there were noticeable differences in t heir growth rates. Thus different developmental strategies have been r eflected in different developmental patterns of TH in precocial Japane se quail and altricial European starling whereas developmental changes of GH levels were similar in both species.