A study of triiodothyronine-catecholamine interactions: their effect on plasma fatty acids in Pacific hagfish...

Plasma circulating levels of fatty acids (PFA) were measured in intact and in triiodothyronine (T3)-treated Pacific hagfish Eptatretus stouti. Intraperitoneal injection of both pharmacological (200 ng/g) and physiological (1 ng/g) doses of T3 caused an elevation of PFA 24 and 48 hr after treatment. The implantation of capsules containing the antithyroid compound, 6-propylthiouracil (6-PTU) decreased PFA levels. Twenty-four hr after T3-injection the norepinephrine (NE) content of plasma declined, whereas epinephrine (E) titres increased. Forty-eight hr after T3-treatment the mean titres of dopamine (D) and NE were lower than in the control group of hagfish. The treatment of hagfish with E in either pharmacological (2-3 micrograms/g) or physiological (2-3 ng/g) doses did not cause any elevation of PFA during the 72 hr following injection. In the same experiment the high dose of E induced long-lasting hyperglycemia, whereas the low dose had no substantial effect on glycemic levels. The data provide evidence that in hagfish, unlike in higher animals, the observed lipolytic effect of administered T3 is not mediated through the potentiation of the fat mobilizing action of catecholamines.