Guidelines for evaluation and management of five common podopediatric conditions.

Practice guidelines for five of the most common podopediatric deformities are presented. In establishing these diagnosis and management guidelines, the authors have reviewed an extensive body of literature and considered their experience as clinicians in one of the busiest settings for the evaluation and treatment of disorders of children's feet. No attempt has been made to be encyclopedic; rather, the authors emphasize practical visual descriptors and the rationale for treatment to demonstrate the value of early intervention in moderate-to-severe orthopedic pathology of the foot and leg.

Prostaglandin-concentration-dependent desensitization of adenylate cyclase in human erythroleukaemia (HEL) cells is abolished by pertussis toxin and enhanced by induction by dimethyl sulphoxide.

Prostaglandin-regulated cyclic AMP metabolism in human erythroleukaemia (HEL) cells was similar to that previously described in platelets [Ashby (1989) Mol. Pharmacol. 36, 866-873], displaying prostaglandin-concentration-dependent desensitization that could be explained by the presence of separate stimulatory and inhibitory prostaglandin receptors. Pertussis toxin abolished prostaglandin-concentration-dependent desensitization, indicating that the process is mediated through a pertussis toxin-sensitive GTP-binding protein. Treatment of HEL cells for 4 days with the inducer dimethyl sulphoxide enhanced prostaglandin-concentration-dependent desensitization, but did not alter the initial rate of cyclic AMP synthesis or the amount of Gi2 alpha measured by immunoblotting, suggesting that the inhibitory receptor was selectively induced by changing the cells to a more platelet-like form.

Differences in the mode of action of 1-oleoyl-2-acetyl-glycerol and phorbol ester in platelet activation.

The ADP-hydrolyzing enzyme apyrase inhibited platelet aggregation and phosphorylation of a 40,000 dalton platelet protein (P40) induced by 1-oleoyl-2-acetyl glycerol (OAG), indicating a dependence on secreted ADP. Apyrase also enhanced OAG-induced potentiation of forskolin or prostaglandin I2 activation of cyclic AMP formation in platelets. Cyclic AMP formation induced by OAG alone could be demonstrated in the presence of a phosphodiesterase inhibitor. Elevation of cyclic AMP level inhibits platelet aggregation so that secreted ADP may be required to inhibit OAG-activated adenylate cyclase for aggregation to proceed. In contrast, apyrase only partially affected phosphorylation of P40 and aggregation induced by the tumor promoter 12-0-tetradecanoyl phorbol-13-acetate (TPA). TPA caused marked inhibition of forskolin-stimulated cyclic AMP formation. TPA inhibition of cyclic AMP formation was largely reversed by apyrase, indicating that it was mainly due to release of ADP.

Coformycin inhibition of platelet AMP deaminase has no effect on thrombin-induced platelet secretion nor on glycolysis or glycogenolysis.

Thrombin-stimulated platelet secretion is accompanied by a 30% reduction in the steady state level of cytosolic ATP, a breakdown that proceeds through ADP, AMP, IMP, and inosine to hypoxanthine. The ATP to hypoxanthine conversion could be blocked at the stage of AMP deamination by incubation of platelet-rich plasma for 6 h with 200 microM coformycin, a transition-state analog inhibitor of AMP deaminase. Abolition of AMP deaminase activity had no effect on thrombin-induced secretion from the dense granules, alpha-granules, or acid hydrolases measured in gel-filtered platelets. Coformycin treatment had no effect on thrombin-stimulated lactate production, even when oxidative phosphorylation was blocked by antimycin A, nor on the rate of thrombin-stimulated glycogenolysis. In addition, although it was clear that the adenylate energy charge was maintained by activation of AMP deaminase following thrombin treatment, the adenylate energy charge was also maintained in coformycin-treated platelets, albeit after a short lag, by stimulated ATP production and equilibration through the adenylate kinase reaction. Hydrogen peroxide brings about similar adenylate degradation which could also be inhibited by coformycin. The results indicate that AMP deamination and secretion, although temporally related, are not coupled. The role of AMP deaminase appears to be to maintain the adenylate energy charge in the absence of stimulation of ATP production or to buffer the adenylate charge before ATP production is stimulated.