Thyroid status alters gill ionic metabolism and chloride cell morphology as evidenced by scanning electron microscopy in a teleost Anabas testudineus (Bloch): short and long term in vivo study.

Gill is the main organ of osmotic regulation in teleosts and chloride cells are the sites of ion transport across gill epithelium. Thyroid hormones are implicated in the regulation of osmotic balance in teleosts also. Treatment with 6-propyl thiouracil (6-PTU) inhibited the membrane bound enzyme Na+K+ ATPase in the gill while triiodothyronine (T3) injection stimulated it in a short-term in vivo study in the teleost Anabas testudineus. Na+, K+ and Ca2+ ions were also decreased in the 6-PTU treated fish and the T3 treatment increased their concentrations in the gill lamellae. The gill morphology also changed according to the thyroid status in the long term study. 6-PTU treatment altered the typical serrated morphology of the gill lamellae, while the T3 treatment reversed it. T3 injection increased the density of pavement and chloride cells as evidenced by scanning electron microscopy. The results demonstrate that physiological status of the thyroid influences gill Na+ pump activity and chloride cell morphological changes. Further, the study suggests a regulatory role of T3 on gill ions (Na+, K+ and Ca2+), Na+K+ and Ca2+ ATPase activity and the different gill cell types in A. testudineus.

Rapid action of glucocorticoids on branchial ATPase activity in Oreochromis mossambicus: an in vivo and in vitro study.

The rapid action of cortisol and corticosterone on branchial Na(+)-K(+) ATPase, Ca(2+) ATPase activity and Na(+), K(+) and Ca(2+) ion contents was studied both in vivo and in vitro employing transcription inhibitor actinomycin D in Oreochromis mossambicus. Cortisol and corticosterone administration had significantly increased the activity of branchial Na(+)-K(+) ATPase and Ca(2+) ATPase in vivo after 30 min of injection, and the trend continued for 60 and 120 min for cortisol. The ionic contents were also significantly increased after 30 min in vivo. Na(+)-K(+) ATPase activity was significantly increased 5 min after hormone application in the in vitro system. Actinomycin D did not inhibit the effect of glucocorticoids on ATPase activity both in vivo and in vitro. It is concluded from the present study that cortisol and corticosterone produced a rapid stimulatory effect on branchial ATPase activity and ions in O. mossambicus both in vivo and in vitro. This effect could be due to a non-genomic action of these hormones since the enzyme activity was insensitive to actinomycin D.