Full Length Research Paper

Hormonal responses of the fish, Cyprinus carpio, to environmental lead exposure

Mathan Ramesh*, Manoharan Saravanan and Chokkalingam Kavitha

Unit of Toxicology, Department of Zoology, Bharathiar University, Coimbatore – 641 046, India.

*Corresponding author. E-mail: mathanramesh@yahoo.com

Tel: +91-422-2422222 Ext. (484). Fax: +91-422-2422387.

Accepted 25 January, 2008

The present study reports the acute and sublethal toxicity of lead nitrate on plasma cortisol and prolactin level of a freshwater fish, Cyprinus carpio. The median lethal concentration of lead nitrate to fish for 24 h was found to be 4.10 ppm. 1/10^th of the LC₅₀ concentration of the lead nitrate (0.41 ppm) was taken for sublethal concentration. During acute and sublethal treatment the plasma cortisol level increased throughout the study period showing a direct relationship with exposure period. Similarly, plasma prolactin level was increased during acute treatment. However during sublethal treatment plasma prolactin level was increased up to 14^th day and then declined. The significant increase of plasma cortisol level might have resulted from the release of cortisol from the interrenal tissue as a mechanism of coping up with stress or impaired immune function. The elevated level of plasma prolactin may be a step to re-establish ionic equilibrium due to the disturbances caused by the metal. Whereas the decline in plasma prolactin level indicate the destruction of prolactin cells due to metal toxicity. The alterations of the hormonal levels may be used as a potential biomarker and also can establish the ability of endocrine tissues to respond to their appropriate releasing factors.

Key words: Cortisol, prolactin, lead, Cyprinus carpio.