Hormonal profiles correlated with season, cold, and starvation in Rana catesbeiana (bullfrog) tadpoles

• Published in: Comparative biochemistry and physiology. C, Comparative pharmacology and toxicology Vol. 124; no. 1; pp. 109 - 116
• Main Authors: Wright, Mary L, Proctor, Krista L, Alves, Christina D
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.1999
• Subjects: Adrenal Cortex Hormones - blood; Aldosterone; Aldosterone - blood; Animals; Cold Temperature - adverse effects; Cortisol; Eye - metabolism; Freshwater; Hydrocortisone - blood; Larva - metabolism; Melatonin; Melatonin - blood; Melatonin - metabolism; Rana catesbeiana; Rana catesbeiana - metabolism; Seasonal changes; Seasons; Starvation; Starvation - metabolism; Thyroid gland; Thyroid Gland - drug effects; Thyroid Gland - metabolism; Thyroid sensitivity to TSH; Thyrotropin - pharmacology; Thyroxine; Thyroxine - secretion; Seasonal changes; Melatonin; Starvation; Thyroid sensitivity to TSH; Thyroxine; Thyroid gland; Cortisol; Aldosterone
• ISSN: 0742-8413; 1367-8280
• DOI: 10.1016/S0742-8413(99)00060-2

Bullfrog ( Rana catesbeiana) tadpoles are of value to amphibian researchers because of their large size, and year-round availability due to overwintering in many latitudes. Concern over a possible difference in hormonal parameters in tadpoles obtained at different times of the year prompted us to investigate thyroid gland secretion in vitro, plasma and ocular melatonin, and plasma corticosteroids in late pre- to early prometamorphic larvae on 12L:12D. Winter tadpoles exposed to 22°C for 3 weeks of acclimation (winter group) were compared to summer tadpoles kept at 22°C (summer group), as well as to summer tadpoles exposed to cold (12°C) for the 3 weeks (cold group), or kept at 22°C and starved for the last week of acclimation (starved group). Thyroids from the summer group had a significantly higher response to 0.2 μg/ml ovine thyrotropin (TSH) than the other groups, indicating that cold and starvation inhibited subsequent in vitro thyroid sensitivity to TSH. The thyroids of the starved tadpoles had significantly higher baseline (unstimulated) thyroxine (T 4) secretion into the culture media, a finding that might be related to starvation-induced acceleration of metamorphosis. Plasma melatonin was lower, and ocular melatonin significantly higher in both summer and starved groups, while the reverse occurred in the winter and cold groups. Thus, seasonal or induced cold brought on a shift in the relationship of plasma to ocular melatonin but starvation had no effect. There were no significant differences among the treatment groups in plasma hydrocortisone (HC) and aldosterone (ALDO) levels, except that HC was lower than ALDO only in the plasma of winter tadpoles. We conclude that seasonal variation needs to be taken into account in endocrine experiments utilizing tadpoles obtained at different times of the year.