Abstract
We investigated the acute stress response in a common carp strain (E5) with interrenal hyperplasia due to 17α-hydroxylase deficiency, and in an isogenic standard (STD) carp strain. Cortisol, corticosterone and the head kidney-somatic index were measured during and after a 3h net confinement stress. Star, cyp17a2, hsd3b, cyp21, hsd11b2 mRNA levels were measured in head kidneys using real-time qPCR. The results show very high corticosterone levels and enlargement of the head kidney in E5 fish. This is the first report in a teleost fish showing a significant increase of corticosterone levels in response to stress due to interrenal hyperplasia. The high levels of corticosterone in E5 suggest that corticosterone is not converted to aldosterone in common carp. star and hsd3b mRNA levels were significantly higher in E5 compared to STD fish, while cyp17a2 levels were significantly lower in E5. In contrast to E5, star levels did not change during stress and recovery in STD, suggesting that the enzyme is regulated in a different manner in E5 and STD fish. In E5, the levels of cyp17a2 dropped below control values after 20min stress. These findings strongly suggest that cyp17a2 is impaired at (post)-transcriptional level. As a consequence the accumulated precursor (pregnenolone) is not converted to cortisol, but to corticosterone. In contrast to STD, significant levels of cortisol could not be detected in E5. Finally, hsd11b2 mRNA levels were significantly lower in E5 compared to STD, and did not change during stress and recovery. These results support the idea that hsd11b2 is involved in the conversion of physiologically active cortisol to inactive cortisone, as reported earlier for STD carp. In conclusion our results show high levels of corticosterone in E5 and differences in star and mRNA levels of steroidogenic genes between E5 and STD carp during net confinement stress.
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