This rapid decrease in serum levels parallels the rapid decline in brain and may reflect either elimination or metabolic breakdown of this compound

This rapid decrease in serum levels parallels the rapid decline in brain and may reflect either elimination or metabolic breakdown of this compound. In contrast to the quick accumulation and quick decline of CPT levels in brain, i.p. A2 adenosine receptors. Xanthines have also been shown to reverse the behavioral depressive disorder elicited by adenosine agonists. The potency of xanthine derivatives in locomotor assays, Angiotensin 1/2 (1-5) both as stimulants and as antagonists of agonist-induced depressive disorder, is usually often not commensurate with their potency as adenosine antagonists. Although synthetic analogues of theophylline and various non-xanthine; heterocycles that have 104-fold or greater potency than theophylline in adenosine receptor affinity have been reported [4C6], the relationship between behavioral activation and adenosine receptor antagonism is usually unclear. To properly characterize this relationship binding has been used to measure the ability of a variety of drugs to penetrate into the CNS following intraperitoneal injection [7C9]. Despite its ease and rapidity, this technique has yet to be used in assessing the CNS penetration of adenosine antagonists. The following statement explains the time course for CNS penetration of four adenosine antagonists, 8-cyclopentyl-1,3-dimethylxanthine(CPT),8-cyclopentyl-l,3-dipropylxanthine (CPX), 8-values for the xanthine derivatives were decided using the Cheng-Prusoff equation [14]. Angiotensin 1/2 (1-5) Standard curves were constructed by incubating brain homogenate from untreated mice with numerous concentrations of inhibitor using the identical conditions as above. Each determination was performed in quadruplicate using at least three different animals. The percent brain penetration of test compounds was determined by comparing the amount of inhibition of [3H]PIA binding in homogenates from treated and control brain. By comparing this percent inhibition with that obtained from the standard curve, the concentration of compound entering the brain was determined. One hundred percent brain penetration was defined as the amount of compound reaching the brain in the absence of any permeability barrier, assuming that the injected dose distributed uniformly throughout the mouse. Each determination was performed in quadruplicate and data are expressed as means SD from at least three different animals. Individual adult male mice of NIH (Swiss) strain between 5 and 6 weeks of age weighing at least 25 g were studied in a Digiscan activity monitor (Omnitech Electronics Inc., Columbus, OH) with computerized data analysis (ILAM software). Animals were placed in the cage immediately after injection, and monitoring for three intervals of 10 min each was initiated after 10 min. Total distance travelled was used as a measure of locomotor activity. Xanthines were dissolved in a 20:80 (v/v) mixture of Emulphor EL-620 (GAF Chemicals Corp., Wayne, NJ) and phosphate-buffered saline and injected i.p. in a volume of 5 mL/kg body weight. Control values for vehicle-injected animals were determined for each experiment. RESULTS Scatchard analysis of [3H]PIA binding to membranes from crude homogenates treated with 6 U/mL of ADA revealed two affinities: a high-affinity site with a of 1 1.5 0.2 nM (N = 3) and a (4.5 nM) and lower values consistent with A1-adenosine receptor affinities (8-PST, 2.6 M; CPT, 28 nM; CPX, 4.1 nM; XAC, 8.2 nM). An example of a competition curve for CPT is usually shown in Fig. 2. The detection limits for binding are related to these values. Since brain tissue was diluted a total of 40-fold by homogenization and dilution for binding studies, a concentration of compound 40 occasions its value would be readily detectable in this assay. The detection limits of this method depend on the brain penetrability of the Rabbit polyclonal to EIF4E compound being measured: a highly permeable compound will have a detection limit of around four occasions its value, at which concentration a 10% inhibition in binding would be observed. In this connection, under control Angiotensin 1/2 (1-5) conditions, total [3H]PIA binding amounted to around 5500cpm per 50-L aliquot tested,.