Effect of hexavalent chromium exposure on the pituitary–interrenal axis of a teleost, Channa punctatus (Bloch)

The immunocytochemistry of pituitary corticotrophs, interrenal histopathology and serum cortisol assay revealed adverse effects of hexavalent chromium [Cr(VI)] exposure (as potassium dichromate; K2Cr2O7) on the pituitary–interrenal axis of a freshwater fish, Channa punctatus. On acute exposure (10, 20 and 40 mg L−1 for 96 h), corticotrophs showed hypertrophy and intense immunoreactivity to anti-human (h) ACTH1−29. Cytoplasmic degranulations in some of the cells were also noticed. On the contrary, atrophy and weak anti-h ACTH1−29 immunoreactivity of corticotrophs was observed with the chronic exposure (2 and 4 mg L−1 for one month). Exposure-dependent varied effects also reflected in the histopathology of head kidney interrenal tissue and serum cortisol levels. Acute exposure induced hypertrophy and degranulation of interrenal cells along with significant elevation of serum cortisol levels in a concentration-dependent manner (42 ± 0.72, 44.6 ± 1.34 and 52 ± 3.06 ng mL−1, respectively in 10, 20 and 40 mg L−1 group, compared to 36.65 ± 0.83 of control). Atrophy of interrenal cells and low serum cortisol levels as compared to that of control (34.1 ± 0.78 and 29.3 ± 0.92 ng mL−1, respectively in 2 and 4 mg L−1 groups) in chronic-exposed fish indicates attenuated functioning of the hypothalamic–pituitary–interrenal (HPI) axis. The stress response of the fish (under confinement) further confirmed the impairment of the HPI axis, as the elevation in serum cortisol levels were significantly less (258% and 166% of basal level, respectively in 2 and 4 mg L−1 group, compared to 374% of control). The long-term interference of this axis by metal exposure therefore, may pose serious threat to fish making them unable to adapt to stress.