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Department of Animal Physiology, Faculty of Science, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands

(Requests for offprints should be addressed to P H M Klaren; Email: p.klaren{at}science.ru.nl)

(E J W Geven and F Verkaar contributed equally to this work)

The effect of experimental hyperthyroidism, realized by T₄ injection, on central mediators of the hypothalamo–pituitary–interrenal axis (HPI-axis) in common carp (Cyprinus carpio L.) was studied. Our results show that hyperthyroidism evokes a marked 3.2-fold reduction in basal plasma cortisol levels. Corticotropin-releasing hormone-binding protein (CRH-BP) mRNA levels in the hypothalamus, measured by real-time quantitative PCR, were significantly elevated by 40%, but CRH, urotensin-I, prepro-TRH, prohormone convertase-1 (PC1), and POMC mRNA levels were unchanged. In the pituitary pars distalis, PC1, CRH receptor-1, and POMC mRNA levels were unaffected, as was ACTH content. Plasma -MSH concentrations were significantly elevated by 30% in hyperthyroid fish, and this was reflected in PC1 and POMC mRNA levels in pituitary pars intermedia that were increased 1.5- and 2.4-fold respectively. The -MSH content of the pars intermedia was unchanged. Hyperthyroidism has profound effects on the basal levels of a central mediator, i.e., CRH-BP, of HPI-axis function in unstressed carp in vivo, and we conclude that HPI- and hypothalamo–pituitary–thyroid-axis functions are strongly interrelated. We suggest that the changes in plasma cortisol, thyroid hormone, and -MSH levels reflect their concerted actions on energy metabolism.

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				E. J. W. Geven, N.-K. Nguyen, M. van den Boogaart, F. A. T. Spanings, G. Flik, and P. H. M. Klaren Comparative thyroidology: thyroid gland location and iodothyronine dynamics in Mozambique tilapia (Oreochromis mossambicus Peters) and common carp (Cyprinus carpio L.) J. Exp. Biol., November 15, 2007; 210(22): 4005 - 4015. [Abstract] [Full Text] [PDF]