potassium-thiocyanate and potassium-perchlorate

The ability of different goitrogens (anti-thyroid agents) to induce precocious metamorphosis in larval sea lampreys (Petromyzon marinus) was assessed in four separate experiments. Two of these goitrogens (propylthiouracil [PTU] and methimazole [MMI]) are inhibitors of thyroid peroxidase-catalyzed iodination, and three (potassium perchlorate [KClO(4)], potassium thiocyanate [KSCN], and sodium perchlorate [NaClO(4)]) are anionic competitors of iodide uptake. Because, theoretically, all of these goitrogens prevent thyroid hormone (TH) synthesis, we also measured their influence on serum concentrations of thyroxine and triiodothyronine. All goitrogens except PTU significantly lowered serum TH concentrations and induced metamorphosis in some larvae. The incidence of metamorphosis appeared to be correlated with these lowered TH concentrations in that KClO(4), NaClO(4), and MMI treatments resulted in the lowest serum TH concentrations and the highest incidence of metamorphosis in sea lampreys. Moreover, fewer larvae metamorphosed in the KSCN and low-KClO(4) treatment groups and their serum TH concentrations tended to be greater than the values in the aforementioned groups. MMI treatment at the concentrations used (0.087 and 0.87 mM) was toxic to 55% of the exposed sea lampreys within 6 weeks. The potassium ion administered as KCl did not alter serum TH concentrations or induce metamorphosis. On the basis of the results of these experiments, we have made the following conclusions: (i) In general, most goitrogens other than PTU can induce metamorphosis in larval sea lampreys, and this induction is coincident with a decline in serum TH concentrations. (ii) The method by which a goitrogen prevents TH synthesis is not directly relevant to the induction of metamorphosis. (iii) PTU has variable effects on TH synthesis and metamorphosis among lamprey species. (iv) Unlike in protochordates, potassium ions do not induce metamorphosis in sea lampreys and are not a factor in the stimulation of this event.

Topics: Animals; Antithyroid Agents; Iodide Peroxidase; Iodides; Lampreys; Larva; Metamorphosis, Biological; Methimazole; Perchlorates; Potassium; Potassium Chloride; Potassium Compounds; Propylthiouracil; Sodium Compounds; Thiocyanates; Thyroid Hormones; Triiodothyronine

Topics: Animals; Antithyroid Agents; Eukaryota; Fertilization; Larva; Metamorphosis, Biological; Morphogenesis; Perchlorates; Potassium Compounds; Sea Urchins; Thiocyanates; Thiourea; Thyroid Hormones; Thyroxine; Triiodothyronine

Efflux of preloaded I- from the thyroid induced by externally added I- was studied using a biological model of the thyroid I- transport system. Phospholipid vesicles (P-vesicles) made from thyroid plasma membranes and soybean phospholipids were capable of accumulating I- in the presence of external Na+. P-vesicles incubated in 136 mM Na+ containing 0.9 microM I- with 125I- for 2 min accumulated I- so that the I- concentration in the vesicles became about 2 microM. Addition of 5-20 microM stable I- to the incubation mixture at 2 min incubation resulted in a dose-dependent decrease in previously loaded 125I- in the vesicles. In other words, a dose-dependent increase in efflux of preloaded 125I- was observed. While the efflux occurred, Na+-dependent I- influx into P-vesicles was preserved. When 2 mM ClO4-, a specific inhibitor of Na+-dependent I- influx, was added together with 10 microM I-, the external I- failed to diminish preloaded 125I- in P-vesicles. The 125I- efflux did not occur when a large amount of stable I- entered P-vesicles independently of Na+ in the presence of ClO4-. Similar 125I- efflux induced by externally added 5 microM SCN- was also blocked by simultaneously added ClO4-. These observations suggest that such I- efflux from the thyroid is a certain type of uphill I- transport which is closely related to Na+-dependent I- transport and that ClO4- and SCN- act on a common site of the I- transport system.

Topics: Animals; Binding Sites; Biological Transport; Cell Membrane; Chemical Phenomena; Chemistry; In Vitro Techniques; Iodides; Models, Biological; Perchlorates; Potassium; Potassium Compounds; Swine; Thiocyanates; Thyroid Gland