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Stimulation and production of 11-deoxycortisol in the stress response of lamprey Roberts, Brent Warren William


This study is the first to provide direct physiological evidence that lamprey have a hypothalamus-pituitary-interrenal (HPI) axis that functions in a manner similar to that of more derived vertebrates. In teleost fishes, the hypothalamus produces corticotropin-releasing hormone (CRH), which stimulates the anterior pituitary to produce adrenocorticotropic hormone (ACTH), which in turn stimulates production of cortisol (F) from the interrenal cells of the head kidney. Although it has recently been shown that 11-deoxycortisol (S) is the functional corticosteroid in lamprey, no studies have yet determined its mechanism of regulation or site of production. This study demonstrated that 1) exposure to acute stress by air-exposure caused plasma S concentrations to increase, supporting its role as a stress hormone; 2) intraperitoneal injections of lamprey-CRH (0.1, 50, and 100 µg/kg) stimulated an increase in plasma S concentrations that was sensitive to dose, 3) intraperitoneal injection of four isoforms of lamprey-ACTH (each at 1.0 and 10 µg/kg) increased plasma S concentrations, although rates of production were low and varied by isoform between male and female subjects. Confirmation of the identity of 11-deoxycortisol was obtained by demonstrating that plasma extracts fractionated by high performance liquid chromatography (HPLC) had peaks of immunoreactive S that co-eluted with standard S using RIA. Finally, this study demonstrated that 4) lamprey mesonephric kidneys produced S in vitro when incubated in the presence of tritiated 17α-hydroxyprogesterone (17αP), as well as in the absence of any precursor hormones. The identity of the tritiated S produced in vitro was determined by co-elution with standard S on HPLC, and confirmed by co-migration with standard and acetylated S on thin-layer chromatography (TLC) after purification by HPLC. Together, these results provide supporting evidence that the stress response of lamprey, one of the oldest extant vertebrates, may be controlled through an axis similar to the hypothalamus-pituitary-interrenal (HPI) axis of teleost fishes, although additional studies in this area will be required for further confirmation.

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