Tonicity measurement

The dynamic range of the fluorescence experiment is related to a number of factors but it can be orders of magnitude. It is possible, for example, to determine quinine in water from nanomolar to millimolar concentration by direct measurement. Quinine fluorescence is familiar to most people that have noticed the blue glow of quinine tonic water in sunlight. 

Anandamide may reduce pain by a peripheral action, by acting on CB 1-like receptors located outside the CNS (Calignano et al. 1998). Palmitylethanolamide (PEA) is an endocannabinoid that is coreleased with anandamide and activates peripheral CB2 receptors. When the two are administered together, they show a 100-fold synergistic effect on analgesic measures. Measurements of anandamide and PEA levels in the skin show that there are sufficient amounts to create tonic activation of local cannabinoid receptors. Thus, endocannabinoids may tonically inhibit cutaneous pain. 

Moss DE, Johnson RL. (1980). Tonic analgesic effects of delta 9-tetrahydrocannabinol as measured with the formalin test. EurJ Pharmacol. Feb. 8 61(3) 313-15. 

Results obtained in this way were helpful, but of limited value. The analyses told us whether or not the bile was supersaturated with cholesterol, but did not tell us whether the abnormality was due to too much cholesterol, too few bile acids, too few phospholipids or to some combined defect. The next step, therefore, was to measure the hour-by-hour bile lipid-secretion rates using marker-corrected perfusion techniques. These assume that, in response to the perfusion stimulus (such as an intra-duodenal amino acid mixture), the gallbladder remains tonically contracted throughout and steady-state conditions ensue. 

The tension or osmotic pressure of a solution also, ionic strength, usually measured as weight percentage. Often the tonicity of a solution is presented as relative to some physiological solution (e.g., blood plasma). See Hypertonic Hypotonic Isotonic Isotonic Buffers... 

The clinical examination of an ocular chemical bum victim includes all the steps of the ophthalmologic examination measurement of visual ACUITY, slit lamp, and evaluation of the ocular tonicity. 

Hormones are exceptionally potent chemicals that operate at concentrations so low that they can be measured only by the most sensitive analytical methods. Their concentrations are typically expressed as parts per trillion, one thousand times lower than parts per billion. This magnitude of dilution can be dramatized by thinking of a drop of gin dissolved in a train of tank cars containing tonic. It has been calculated that one drop in 660 tank cars would approximate one part in a trillion such a train would be 6 miles long. 

The measured HF vibrational population distribution from the reaction F + HN3 peaks in v = 1 v = 0 was not observed) and decreases mono-tonically to the maximum observed level, v = 4 [563]. The distribution... 

With the ECS threshold procedure, the primary measure is the mean electroshock intensity administered per group of 15 animals. If less current is required to induce a clonic-tonic convulsion after a particular treatment, this is reflected by a decrease in the mean intensity administered (proconvulsant effect). Conversely, if more current is required to induce a clonic-tonic convulsion, this is reflected by an increase in the mean intensity (anticonvulsant effect). In other words, the mean intensity administered is a direct representation of the electroconvulsive threshold. 

With the PTZ procedure, pro- or anti-convulsant activity is indicated both by the frequency of the convulsant events (clonic convulsions, tonic convulsions, deaths) and by their latency of occurrence. Latency is the measure which most clearly identifies pro-convulsant activity, whereas frequency is the measure most useful for detecting anticonvulsant activity. A statistical problem arises when the test substance completely blocks convulsions in some of the animals. 

What is the actual concentration of dopamine at the dopamine receptors associated with each mode of firing of the dopamine cells The tonic level of dopamine measured using dialysis is 6.5 nM (Sam and Justice, 1996), consistent with predictions that the spatially averaged concentration of extracellular dopamine in the striatum is in the low nanomolar range (Kawagoe et ah, 1992). 

The two phases of prolactin activation of TIDA neurons (rapid tonic and delayed induction components) suggest that the level of activity of these DA neurons reflects both amount of circulating prolactin at the time of measurement (tonic component) and the past history of blood levels of this hormone (induction component). That is, animals treated chronically in such a way as to maintain high circulating concentrations of prolactin exhibit an exaggerated stimulatory response to acute injections of prolactin. Conversely, chronic hypoprolactinemia causes a reduced response to the acute administration of this hormone (Demarest et al., 1985a). 

The rapid (i.e. less than 4 h) activation of TH in the median eminence by prolactin that constitutes the tonic component of prolactin stimulation does not require protein synthesis, but is probably associated with effects on the catalytic properties of this enzyme. Pasqualini and coworkers (1994) demonstrated in vitro that prolactin acts directly on TH in the mediobasal hypothalamus to trigger the phosphorylation of this enzyme. This effect, possibly mediated by protein kinase C, makes the enzyme less susceptible to inhibition by newly synthesized DA. That is, prolactin-induced short-term activation of TH results from the removal of end-product inhibition of the enzyme. Conversely, the acute reduction in TH activity measured in vitro in median eminence removed from rats 4 h after administration of bromocriptine is prevented by the coadministration of prolactin (Arbogast and Voogt, 1995). This can also be prevented by an inhibitor of phosphoprotein phosphatases, suggesting that rapid suppression of TH activity secondary to the bromocriptine-induced hypoprolactinemia may also result from dephosphorylation of the enzyme. 

The four colligative properties that are of importance are 1) the vapor pressure lowering 2) the elevation of boiling point 3) the freezing-point depression and 4) the osmotic pressure. An attempt is made below to describe qualitatively and quantitatively each colligative property of solutions, with an emphasis on their interrelationship and their application later in measurement and adjustment of the tonicity of solutions, with particular reference to parenteral formulations. Although theoretical derivations based on thermodynamics can be used to show how each of the colligative properties of solution arises and relate to each other, textbooks on physical chemistry for theoretical derivations are recommended. 

The most direct method for measurement of tonicity obviously would be to observe changes in erythrocytes on mixing solution with blood. If hemolysis or crenation or a marked change in the appearance of erythrocytes occurs, the solution is not isotonic. If the cells retain their normal size and shape, the solution is isotonic. Grosicki and Husa used this method early on ... 

Boiling-point elevation can also be used to measure osmotic pressure and tonicity of a solution using just a reflux condenser and a thermometer. The commercially available instrument is the Cottrell boiling-point apparatus. However, this method is affected by the ambient barometric pressure and the presence of volatile solvents in the solution. 

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