Effect of diclofenac sodium on the arachidonic acid cascade.

The anti-inflammatory activity of nonsteroidal anti-inflammatory drugs is primarily attributed to inhibition of distinct steps in the arachidonic acid cascade, particularly, the cyclo-oxygenase pathway. Diclofenac sodium, a compound of this class of drugs, appears to have a dual effect since it also regulates the lipoxygenase pathway. Study of appropriate cell systems (leukocytes and whole blood in rats) demonstrates that diclofenac's potent inhibition of cyclo-oxygenase activity causes a sharp reduction in the formation of prostaglandin, prostacyclin, and thromboxane products, all key mediators of inflammation. Recent work discloses that at higher concentrations, diclofenac sodium also reduces the formation of products of the lipoxygenase pathway (5-hydroxyeicosatetraenoic acid, leukotrienes). The mechanism by which this evolves, however, appears to be unrelated to direct inhibition of lipoxygenase. Instead, by enhancing its reincorporation into triglycerides, diclofenac sodium reduces the intracellular level of free arachidonic acid.

Pharmacology of diclofenac sodium.

Diclofenac sodium is the active ingredient in Voltaren, a nonsteroidal anti-inflammatory drug designed by selection of appropriate physicochemical and steric properties. Its pharmacologic activity, specifically its effects in acute and subchronic inflammation, and its analgesic activity have been assessed in animal models. The tolerability of the compound as judged by several parameters (i.e., ratio between the acute lethal dose or the dose inducing gastrointestinal blood loss and the desired pharmacologic activity) is favorable in comparison with other nonsteroidal anti-inflammatory drugs. Diclofenac sodium acts by potent cyclo-oxygenase inhibition, reduction of arachidonic acid release, and enhancement of arachidonic acid uptake. It thereby results in a dual inhibitory effect on both the cyclo-oxygenase and lipoxygenase pathways.

Glucocorticoid receptors in rat kidney cortical tubules enriched in proximal and distal segments.

Cytoplasmic and nuclear binding of [3H]triamcinolone acetonide was assessed in isolated rat kidney cortical tubules, enriched in distal (fraction A) or in proximal segments (fraction B). The concentration dependence of specific [3H]triamcinolone acetonide binding in cytoplasm was determined (range = 4.4 X 10(-10) to 2.1 X 10(-7) M) and analyzed by a least-squares curve-fitting method. A single, high-affinity binding class with a dissociation constant of 1 X 10(-8) M (25 degrees C) was obtained in both fractions A and B. Based on competition for the [3H]triamcinolone acetonide sites, the following sequence of affinities was obtained: triamcinolone acetonide = dexamethasone > progesterone = corticosterone > d-aldosterone > 17 beta-estradiol. These specificities imply that these sites are glucocorticoid receptors. Fraction B contained 1.6 times more cytosol sites for [3H]triamcinolone acetonide than fraction A (5.0 +/- 0.5 X 10(-13) vs. 3.0 +/- 0.5 X 10(-13) mol/mg protein). In the presence of a onefold excess of d-aldosterone specific cytoplasmic binding of [3H]triamcinolone acetonide was 1.4-fold greater in fraction B than in fraction A, and specific nuclear binding was 1.3-fold greater in fraction B than in fraction A (5.1 +/- 0.6 X 10(-13) vs 4.0 +/- 0.5 X 10(-13) mol/mg DNA). These results and the measured lengths of proximal and distal tubules yielded estimates of a higher proximal content (three- to sixfold) compared to distal content of glucocorticoid receptors.

Isolation of epithelial cells from toad bladder.

The epithelial cells of the toad bladder have been isolated by brief exposure to ethylenediaminetetraacetic acid followed by treatment with collagenase, DNAse, and the application of shearing forces. This approach eliminates the need for scraping of the mucosal surface and reduces mechanical damage during harvesting of the epithelium. The method yields intact, isolated epithelial cells and few clumps. The three major types of epithelial cells described in the intact toad bladder were present in the final preparation. The cellular contents of nucleic acids and proteins (in pg/cell) were: DNA 22.5 +/- 1.1; RNA, 12.9 +/- 0.6; and protein, 192 +/- 9. The isolated cells possess rates of oxygen consumption and amino acid incorporation higher than those of epithelial sheets obtained by collagenase treatment and scraping of the intact bladder. However, the production of cyclic nucleotides in response to stimulation by vasopressin and carbachol is comparable in both preparations.