Environmental salinity and the thyroidal response to thyrotropin in juvenile coho salmon (Oncorhynchus kisutch)

Abstract

The effect of environmental salinity on the thyroidal response, measured by plasma concentrations of thyroxine (T4), to exogenous bovine thyrotropin (bTSH) was assessed early and late in the smoltification of coho salmon (Oncorhynchus kisutch). A single injection of 100 mIU bTSH significantly increased plasma T4 concentrations in fish in both fresh water and seawater, and both early (March 19) and late (May 24) in smoltification. In fish transferred to seawater, the increase in T4 titers was somewhat earlier and its duration shorter, suggesting an environmentally induced change in the kinetics of T4 entry and exit from the blood stream. The overall response to TSH was greater near the beginning (March 19) of the smoltification-associated T4 increase than near the end (May 24), suggesting a development-related change in thyroid function.

Measurement and regulation of thyroidal status in teleost fish

“…The response of thyroid tissue to a standa~'xtized TSH dose is not fixed for a given species, but varies with season and physiologic state (Milne and Leatherland, 1980;Grau et al, 1985;Specker and Richman, 1984;Specker and Schreck, 1984;Specker and Kobuke, 1987;Swanson and Dickhoff, 1987). For the killifish (Fundulus heteroclitus, Cyprinodontidae), the seasonal differences in the TSH-induced plasma T4 level were not explained by any alterations in plasma T4 clearance, supporting the view that the seasonal changes in TSH action probably occurred at the level of the thyroid tissue itself (Grau et al, 1985).…”

“…For the killifish (Fundulus heteroclitus, Cyprinodontidae), the seasonal differences in the TSH-induced plasma T4 level were not explained by any alterations in plasma T4 clearance, supporting the view that the seasonal changes in TSH action probably occurred at the level of the thyroid tissue itself (Grau et al, 1985). Photoperiod, temperature, and salinity may in some instances modify teleost thyroidal sensitivity to TSH and TSH efficacy in the control of thyroid function (Olivereau, 1955;Delso and Flatin, 1956;Fontaine and Fontaine 1957;Lysak 1971a,b;Chart and Eales, 1976;Milne and Leatherland, 1980;Specker and Richman, 1984;Grau et al, 1985;Eales and Himick, 1991).…”

Role of thyroid hormones in tilapia larvae (Oreochromis mossambicus): II. Changes in the hormones and 5′-monodeiodinase activity during development

“…T 4 and T 3 contents in the extracted egg and larval samples were measured by RIA using barbital buffer system (0.11 M; pH 8.6) as previously described by Dickhoff et al (1978), Specker and Richman (1984) and Tagawa and Hirano (1987). The antibodies for T 4 and T 3 were purchased from Radioassay Systems Laboratories, Inc. Carson, California and high specific activity (>1200 #ci/txg) 1251-labelled T 4 and T 3 from Radiochemical Centre, Amersham, England.…”

Endocrinology of the Vertebrates

“…As a member of the glycoprotein family, which includes the gonadotropins, TSH may also be regulated by GnRH in some species. Thyroid hormones are legendary with respect to their role in amphibian metamorphosis, but this area requires further clarification beyond the fact that pro-lactin (or its mediator synlactin; 587, 635) is regarded as the "juvenile" and thyroid hormone as the "adult" hormone (450,638,652,657,(921)(922)(923)(924), The developmental associations of thyroidal activities have now been revealed in migratory euryhaline teleost fishes (817)(818)(819)(820)(821), These actions indicate a primary action of thyroid hormones in salinity adaptation in salmonids, both as adults and at the stage of smoltification (809,816,939). As in amphibians, teleostean metamorphosis is under thyroidal control, with the eggs of many species seemingly incorporating maternal hormone (218,477,743,744,(841)(842)(843)926).…”