INFLUENCE OF CORTICOTROPIN-RELEASING FACTOR ON THE IN-VITRO THYROXINEAND THYROTROPIN SECRETION IN NEWLY-HATCHED FOWL

Injections of ovine corticotropin-releasing factor (oCRF) are known to increase circulating thyroid hormone levels in the chicken embryo (ME EUWIS et al., 1989). This can in part be explained by a direct effect of the hypothalamic hormone on the thyroid gland and/or the stimulatio n of the thyrotropin (TSH) release from the pituitary. We tested these two assumptions in two separate perifusion experiments. Our results c learly indicate that oCRF does not influence the in vitro thyroxine (T -4) secretion from the thyroid. The pituitaries of the newly hatched c hickens, however, released significant amounts of TSH after in vitro t reatment with oCRF. Growth hormone and luteinizing hormone secretions were also elevated after the oCRF stimulation period, but this release was less pronounced compared to the TSH release. As a conclusion we p ostulate that oCRF mediates its effect on the thyroidal status of the chicken through stimulation of TSH release and not through a direct ef fect on the thyroid.