Dehydroepiandrosterone (DHEA; androstenolone; 3ß-hydroxy-5-androsten-17-one) is a steroid hormone produced principally in the adrenal cortex. In men, it is estimated that 10-25% of the circulating DHEA is secreted by the testes. (1) DHEA and its sulfated analog DHEA-S serve primarily as precursors that circulate to peripheral tissues, where they are converted to androgens and estrogens. (1,2) This allows androgens and estrogens to be delivered to the appropriate tissues without leakage of significant amounts into the circulation. (3,4,5) In addition to serving as a precursor for other steroid hormones, DHEA is also believed to have some physiological properties of its own. It is known to have anti-glucocorticoid, anti-oxidant, anti-inflammatory, and immunomodulatory effects. (1,5) The mechanisms of these effects are not well understood and currently under investigation. (5,6,7) Circulating levels of DHEA peak around the age of 20 to 30, then decline to only 20-30% of peak level by the age of 70 to 80; it has been explored as a marker of aging and for possible anti-aging therapeutic uses.
Low levels have been associated with a range of diseases. (1,5) DHEA is also produced in the brain, where is serves as a protective neurosteroid. (8,9)
Like cortisol, DHEA synthesis in the adrenal gland is affected by HPA axis activity and the release of ACTH, and DHEA levels increase in response to stress. (10) Differences in the secretion of the two hormones can exist, however, and changes in the ratio of cortisol to DHEA have been observed in connection with various disorders, including depression, psychiatric conditions, and HIV infection. (11,12,13,14) DHEA exhibits a diurnal rhythm synchronized with cortisol, with highest values in the morning and a nadir in the late evening. (15)
In blood DHEA is only weakly bound to albumin or sex hormone binding globulin (SHBG). (16,17) Unbound DHEA enters saliva from blood via intracellular mechanisms, and the serum-saliva correlation is high. (18,19)
The effects of freeze thaw on most biological measures, regardless of biospecimen type, can be dramatic. Analytes in oral fluid are not distinct or different in this way. As a general rule, multiple freeze-thaws should be avoided. The most practical way to address this concern is by aliqouting samples after collection. Some analytes are more resistant to freeze thaw than others. We recommend that investigators consult the literature for the analytes of interest. If there is freeze thaw data for a specific biological measure in traditional biospecimens, it is reasonable to assume this would also be true for saliva.
No, but the literature is rather extensive on this subject for several salivary analytes; especially for salivary alpha-amylase and cortisol. We do not track that information internally.
With modern search tools online, we no longer maintain records of this type. We suggest that you use Pubmed or Psychlit to search the literature or you can Ask An Expert and we will be happy to assist you in your search.
If the analyte you are interested in is not noted in our website, please contact Dr. Granger at [email protected] to find out what developments are in the pipeline.
Salimetrics does not release products for sale if the quality control (QC) testing shows any issues. Here are some probable causes:
1) Can timing of adding reagents be off? For instance with a multichannel you can pipette the conjugate and TMB so many times before you refill, but you can pipette the stop twice as fast because it is a smaller volume. If you do this, it shortens the time the bottom rows have with TMB.
2) Can your washer be uneven and sheering off antibody in the bottom corner? Aspirate and check the amount of fluid left. It should be even in all wells and no wells should be completely dry.
3) Are you mixing faster than recommended? Or slower?
4) Are all reagents completely at room temperature? A bottle of assay diluent takes 2 hours to come to RT. You can pour some off into a smaller tube to warm up quicker for the zero and nsb.
5) Are you leaving the plate come to room temperature BEFORE opening the bag? (Otherwise moisture due to humidity may form in the wells and this is particularly a problem in this high humidity weather)
6) Are your multichannel pipettes dispensing the same amount each time reliably? We discard the first and last dispenses as they are not as reliable.
7) Are you incubating with TMB in the dark? (We no longer recommend aluminum foil.)
8) Are you testing one plate at a time? For example, do not put the standards on 5 plates then go back and fill in with samples. This delays the addition of conjugate to the plates.
9) Clean your plate reader filter. Dust from the lab can collect on the filter.
10) Are you adding assay diluent to the zero in sequence after the standards and not the last thing?
11) Never put the multichannel pipette tips into the wells as you can drag down standard from the wells above it causing lower readings in other wells.
12) Thoroughly blot all wells just before adding TMB but do not let the plate dry out.