DHEA-S (Dehydroepiandrosterone sulfate or DHEA sulfate) is a steroid hormone produced primarily in the adrenal cortex. It is the sulfated version of the human steroid DHEA, and, like DHEA, it is secreted in response to ACTH. DHEA-S been reported to have a diurnal rhythm, but the findings have varied, and some studies found no variation. (1) DHEA-S in the blood stream has a longer half-life, slower clearance, and is more strongly bound to albumin than DHEA, which may affect synchronicity with the DHEA rhythm. (2,3,4) DHEA-S appears to serve largely as a precursor molecule that is circulated to various target tissues in the body. In those locations, the sulfate is removed to yield DHEA, and the DHEA is then further metabolized into various estrogenic and androgenic compounds. This process allows androgens and estrogens to be delivered to the appropriate tissues without leakage of significant amounts into the circulation. (5,6) DHEA-S is also synthesized directly in the central nervous system, where it is thought to help protect nervous tissues against harmful agents. (7,8)
DHEA-S has been investigated for relationships to mental and physical stress and psychological and behavioral disorders. ( 9,10,11,12,13)
DHEA-S is a charged molecule, and it cannot diffuse through the neutral lipid membranes of the salivary cells like the other neutral steroids. The exact mode of entry into saliva is not known. Formerly, it was thought that DHEA-S enters saliva only by squeezing through the tight junctions between cells, and since it is too large to do this readily only small amounts would be present in saliva. (14) More recent work has identified a large family of organic anion transport polypeptides (OATP) that actively transport molecules such as DHEA-S across membranes. It is therefore seems likely that such a mode of entry occurs for DHEA-S into the saliva glands. (15,16) Salivary levels of DHEA-S are quite low–less than 0.1 % of plasma levels in parotid saliva. (14) However, because levels of DHEA-S in blood are 250 and 500 times higher than DHEA in women and men, respectively, (2) the levels found in saliva are high enough to be measurable. Due to the restrictive mode of entry for DHEA-S into saliva, its levels in saliva decrease as salivary flow rates increase. (14) DHEA-S measurements in saliva must therefore be corrected for flow rate. Because of the much higher levels of DHEA-S in blood, it is important to minimize the risk of blood contamination in the saliva samples. Salivary and plasma levels of DHEA-S show a significant positive correlation. (17)
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.