Humoral regulation of hemoglobin transition from larval to adult types in a salamander, Hynobius retardatus.

In amphibians hemoglobin (Hb) transition from larval to adult types occurs during metamorphosis. Hemoglobin transition in the salamander Hynobius retardatus also occurs during metamorphosis, but depends on activity of the pituitary gland, rather than that of the thyroid gland. These findings were supported by the fact that the transplanted pituitary gland to hypophysectomized (Hx) larvae exerted accelerating effects on Hb transition. Contrary to this, a homogenate of the pituitary gland from Xenopus laevis had no accelerating effect on Hb transition when injected into Hx larvae of H. retardatus. Whereas exogeneously applied triiodothyronine (T3) or a combination of T3 and hydrocortisone had an accelerating effect on Hb transition in the Hx larvae, a single treatment with hydrocortisone in the Hx larvae had no effect. When an inhibitor of synthesis of adrenocortico-steroid hormones, metyrapone, was applied in combination with goitrogens to intact larvae, Hb transition from larval to adult types was suppressed compared with normal controls, suggesting that the thyroid-corticoid system is involved in Hb transition. These results suggest that Hb transition in H. retardatus is controlled by two independent accelerating factors, from both the pituitary gland and the thyroid-corticoid system. These control mechanisms are different from the general regulation of metamorphosis that occurs in many amphibians. A tentative model of hormonal controls in Hb transition from larval to adult types during the metamorphosis in H. retardatus is presented.