Corticosterone levels in bird eggs corrected by LC/MS, revealing previously unknown patterns

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  • Published: Jul 6, 2015
  • Author: Steve Down
  • Channels: X-ray Spectrometry / Infrared Spectroscopy / Chemometrics & Informatics / Base Peak / NMR Knowledge Base / Raman / MRI Spectroscopy / UV/Vis Spectroscopy / Atomic / Proteomics

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The variation of corticosterone levels in bird eggs has been measured by LC/MS, correcting the gross overestimations of immunoassays and revealing a link with the time of breeding.

The study, reported in Journal of Avian Biology, measured concentrations of this key steroid in the albumen and yolks from eggs in the same clutch and across different clutches and the results were revealing for a number of reasons.

Firstly, the levels in yolk were up to 250-fold lower than those recorded using enzyme and radio immunoassays that did not incorporate preliminary chromatographic separation and 3-6 times lower than those that did. The amounts in albumen were up to 500 times lower than immunoassays but were comparable to those in another study that employed LC/MS. These differences strongly suggest that other steroid hormones were cross reacting in the immunoassays to boost the results.

The extra accuracy introduced by LC/MS revealed patterns in the corticosterone levels that were not otherwise apparent. Over 25 days of testing, a U-shaped relationship emerged between the corticosterone concentrations and the timing of breeding. This was explained in terms of early breeders encountering poor spring weather and limited food, and late breeders having reduced time to breed, fewer breeding sites and increased predation.

Corticosterone, which is a stress hormone, increased with laying order within a clutch of eggs, probably because egg production requires a lot of energy. This is consistent with reports that other egg components were reduced through the laying sequence.

"Future work should also consider applying the LC-MS/MS technique when measuring corticosterone in eggs laid by females experiencing stressful conditions, and when assessing plasma-to-yolk transfer rates," said the researchers. "Moreover, the very low levels of corticosterone in eggs we report may have implications for our understanding of how corticosterone influences the developing embryo."

The study illustrates the importance of choosing the correct analytical technique, one which will allow the accurate estimation of analyte concentrations. In this case, choosing a more expensive technique like LC/MS that is often regarded as “complicated” was shown to pay off by the detail that the results afforded.

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