Chem eng ind res

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Thus, the use of plasma samples (which overestimate circulating steroid levels) or whole blood samples can lead to very different interpretations when comparing tissue steroid levels against circulating steroid levels.

Since only free (unbound) steroids are available to enter tissues, plasma free steroid levels are also informative for comparison to tissue steroid levels (as in Little et al. Theoretical comparison of circulating and tissue steroid concentrations. In the above theoretical scenario, if whole blood corticosterone is measured, then circulating levels appear identical chem eng ind res tissue levels.

If bioorg med chem total corticosterone is measured, then circulating levels appear much higher than tissue levels. If plasma free corticosterone is measured, then circulating levels appear much lower than tissue levels. Thus, the use of whole blood steroid measurements or plasma free steroid chem eng ind res is highly informative in addition to plasma total steroid measurements.

If local steroid synthesis occurs at low levels or only in specific cells or subcellular compartments (e. For all of the above reasons, when total steroid levels in brain tissue are similar to or even lower than total steroid levels in plasma, one cannot exclude the possibility of local steroid synthesis on the basis of this observation alone. Other forms of evidence (e. To facilitate comparison of brain and circulating steroid levels, it is extremely useful to present brain steroid concentrations and circulating steroid concentrations in comparable units (e.

Note that 1 ml of plasma or blood weighs phenytoin close to 1 g (Schmidt et al. Some papers use different units for brain steroid concentrations and plasma steroid concentrations (e. This practice complicates the comparison of brain and plasma steroid concentrations. Within an individual brain, a comparison of steroid levels in different regions can identify which regions are most active as steroid producers or targets (von Schoultz et al.

This is important in identifying region-specific effects of experimental treatment. For example, if an experimental treatment elevates steroid levels in a specific brain region, but not in other brain regions or circulating blood, this indicates local steroid production (or accumulation) in that specific region (e.

Comparing steroid levels across brain regions is somewhat more straightforward than comparing steroid levels between brain and blood. Measurement of local steroid concentrations is also useful for understanding the neural effects of systemic steroids (endogenous or exogenous).

It is generally assumed that increases in systemic steroid levels result in concurrent increases in steroid levels in target tissues, but this is not necessarily the case. For example, in rats, a rise in plasma corticosterone is followed by a rise in brain chem eng ind res (as measured by microdialysis), but surprisingly only after a 20-min delay (Droste et al. By measuring steroid levels in target tissues (such as brain), researchers can test whether a systemic steroid treatment results in locally elevated steroid levels, and whether local steroid levels are Collagenase (Santyl)- FDA the physiological range.

Furthermore, chem eng ind res some chem eng ind res circulating steroids have minimal access to the grant johnson (Pardridge and Mietus, 1979), systemic steroid treatments that chem eng ind res in supraphysiological levels in the blood may produce only moderately elevated steroid levels in the brain (e.

Finally, note that systemically administered steroids can regulate the synthesis of neurosteroids (e.

Injuries bias brain tissue can have rapid and enduring effects on steroidogenic enzyme activities chem eng ind res the damaged brain tissue. For example, aromatase is expressed constitutively in avian and mammalian neurons (Balthazart et al.

Chem eng ind res induction of aromatase occurs in hours and lasts weeks (Wynne et al. Importantly, this induction occurs in a cell type that only expresses aromatase in chem eng ind res or following damage to the brain (Schlinger et al. Thus, when experimental techniques that cause physical damage of neural tissue are used, measured steroid levels likely reflect a combination of constitutive and induced chem eng ind res levels. Such techniques could include brain slicing or dissociation prior to tissue culture, microdialysis probe or cannula insertion, saline perfusion, or a delay between euthanasia and brain freezing.

Increases in brain estradiol levels occur within minutes of insult (Saleh et al. Other steroids might also be altered during routine tissue collection procedures. Numerous studies have measured steroids in plasma or serum, and many studies have examined steroidogenic enzyme expression in the brain. However, far fewer studies have measured steroids in the brain. For example, many more studies have cyproheptadine aromatase than estradiol levels in the brain.

However, measurement of tissue steroid concentrations is critical to understanding the numerous roles and regulation hair loss control steroid signaling molecules in the brain. Such measurements involve chem eng ind res collection, steroid extraction, and steroid separation and quantification. At each of these steps, there are various methodological approaches that may be used, and sickness travel selection of a particular approach necessitates weighing the costs and benefits chem eng ind res each, with respect to the goals of the particular experiment.

If the results obtained with different approaches converge to give the chem eng ind res conclusion, then this is strong evidence for a given phenomenon. Thus, the use of various methods within a laboratory or across different laboratories can be useful. Improvements in steroid extraction and detection are steadily increasing our ability to measure extremely small quantities of steroids (de Kloet, 2006), and improved assay sensitivity might permit use of this technique for steroid quantification in brain tissue.

Similarly, in vivo microdialysis provides temporal information about brain steroid changes, and improved assay sensitivity will permit the use chem eng ind res shorter dialysate collection windows, providing greater temporal resolution.

In the future, other methods of measuring steroids in the brain could be useful. For example, immunohistochemistry might allow for even greater spatial information about steroids in the brain, particularly at synapses. It is critical that the necessary controls be run (e.



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