HYPOTHALAMIC SECRETION OF THYROTROPHIN RELEASING HORMONE IS DECREASED IN MALE JAPANESE QUAIL EXPOSED TO LONG DAILY PHOTOPERIODS
Osborne F. X. Almeida
Abstract
Osborne F. X. Almeida
Abstract
Adult male Japanese quail held under short daily photoperiods (8 h light: 16 h darkness; 8L: 16D) had significantly higher plasma concentrations of thyroid-stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4) than did those kept under long days (16L:8D). When given a single s.c. injection of 50 microgram thyrotrophin releasing hormone (TRH) the birds held under both the 8L: 16D and 16L: 8D photoperiods showed rapid increases in their blood concentrations of TSH, T4 and T3, the amplitude of the TSH response of the birds exposed to 16L: 8D being particularly marked. These results suggest that, in the male quail, long daily photoperiods produce a hypothyroid state as a result of diminished TRH secretion. The synthetic and secretory capacities of the thyroid gland and pituitary thyrotrophs are apparently unimpaired by long days.
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Adult male Japanese quail held under short daily photoperiods (8 h light: 16 h darkness; 8L: 16D) had significantly higher plasma concentrations of thyroid-stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4) than did those kept under long days (16L:8D). When given a single s.c. injection of 50 microgram thyrotrophin releasing hormone (TRH) the birds held under both the 8L: 16D and 16L: 8D photoperiods showed rapid increases in their blood concentrations of TSH, T4 and T3, the amplitude of the TSH response of the birds exposed to 16L: 8D being particularly marked. These results suggest that, in the male quail, long daily photoperiods produce a hypothyroid state as a result of diminished TRH secretion. The synthetic and secretory capacities of the thyroid gland and pituitary thyrotrophs are apparently unimpaired by long days.
Key concepts: Quail, Internal medicine, Endocrinology, Thyrotropin-releasing hormone, Darkness, Thyroid, Hormone, Biology