Plasma thyroid hormones in cyclostomes: do they have a role in regulation of glycemic levels?
Plasma levels of thyroxine (T4) and triiodothyronine (T3) were measured by radioimmunoassay in intact Pacific lamprey (Entosphenus tridentatus) undergoing the period of natural fasting and in Pacific hagfish (Eptatretus stouti) maintained unfed in the laboratory. Plasma T3 levels in both lamprey and hagfish were always severalfold lower than T4 levels. The influence of thyroid hormones on glycemic level was studied following intraperitoneal injection of T4 or T3 (13-20 micrograms/100 g body wt), as well as after implantation of sealed Silastic capsules containing the goitrogen, 6-propylthiouracil (6-PTU), or after intraperitoneal injections of an antithyroglobulin serum (ATgS) exhibiting both anti-T4 and anti-T3 activities. Measured plasma T4 and T3 levels after hormonal injection were extremely high and could be considered pharmacological. The 6-PTU treatment decreased plasma levels of both T4 and T3 within several weeks. The glycemic levels in lampreys and hagfish after thyroid hormone treatment were lower than in control animals, whereas in animals treated with either 6-PTU or ATgS, hyperglycemic levels prevailed. It is concluded that thyroid hormones, possibly acting with other hormones, may participate in the maintenance of glycemic levels in cyclostomes and that their action is to reduce glycemic levels.
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D005215:Fasting; D005260:Female; D005399:Fishes / Q000097:blood*; D006003:Glycogen / Q000378:metabolism; D006196:Hagfishes / Q000097:blood*; D007106:Immune Sera / Q000494:pharmacology; D007798:Lampreys / Q000097:blood*; D008297:Male; D011441:Propylthiouracil / Q000494:pharmacology; D013954:Thyroglobulin / Q000276:immunology; D013974:Thyroxine / Q000097:blood* / Q000494:pharmacology; D014284:Triiodothyronine / Q000097:blood* / Q000494:pharmacology
D001786:Blood Glucose; D007106:Immune Sera; D014284:Triiodothyronine; D011441:Propylthiouracil; D006003:Glycogen; D013954:Thyroglobulin; D013974:Thyroxine