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1 Chronic hypoxic treatment of rats (to induce pulmonary hypertension, PHT) for 14 days increased cGMP-inhibited cAMP speci®c phosphodiesterase (PDE3) and cGMP binding cGMP speci®c phosphodiesterase (PDE5) activities in pulmonary arteries. The objective of this study was to establish the molecular basis for these changes in both animal and cell models of PHT. In this regard, RT ± PCR and quantitative Western blotting analysis was applied to rat pulmonary artery homogenates and human pulmonary`artery' smooth muscle cell (HPASMC) lysates. 2 PDE3A/B gene transcript levels were increased in the main, ®rst, intrapulmonary and resistance pulmonary arteries by chronic hypoxia. mRNA transcript and protein levels of PDE5A2 in the main and ®rst branch pulmonary arteries were also increased by chronic hypoxia, with no eect on PDE5A1/A2 in the intra-pulmonary and resistance vessels. 3 The expression of PDE3A was increased in HPASMCs maintained under chronic hypoxic conditions for 14 days. This may be mediated via a protein kinase A-dependent mechanism, as treatment of cells with Br-cAMP (100 mM) mimicked chronic hypoxia in increasing PDE3A expression, while the PKA inhibitor, H8 peptide (50 mM) abolished the hypoxic-dependent increase in PDE3A transcript. 4 We also found that the treatment of HPASMCs with the inhibitor of kB degradation TosylLeucyl-Chloro-Ketone (TLCK, 50 mM) reduced PDE5 transcript levels, suggesting a role for this transcription factor in the regulation of PDE5 gene expression. 5 Our results show that increased expression of PDE3 and PDE5 might explain some changes in vascular reactivity of pulmonary vessels from rats with PHT. We also report that NF-kB might regulate basal PDE5 expression.

Cyclic nucleotide phosphodiesterases (PDEs) comprise a family of enzymes (PDE1-PDE11) which hydrolyse cyclic AMP and cyclic GMP to their biologically inactive 5′ derivatives. Cyclic AMP is an important physiological amplifier of glucose-induced insulin secretion. As PDEs are the only known mechanism for inactivating cyclic nucleotides, it is important to characterise the PDEs present in the pancreatic islet beta cells. Several studies have shown pancreatic islets or beta cells to contain PDE1C, PDE3B and PDE4, with some evidence for PDE10A. Most evidence suggests that PDE3B is the most important in relation to the regulation of insulin release, although PDE1C could have a role. PDE3-selective inhibitors augment glucose-induced insulin secretion. In contrast, activation of beta-cell PDE3B could mediate the inhibitory effect of IGF-1 and leptin on insulin secretion. In vivo, although PDE3 inhibitors augment glucose-induced insulin secretion, concomitant inhibition of PDE3B in liver and adipose tissue induce insulin resistance and PDE3 inhibitors do not induce hypoglycaemia. The development of PDE3 inhibitors as anti-diabetic agents would require differentiation between PDE3B in the beta cell and that in hepatocytes and adipocytes. Through their effects in regulating beta-cell cyclic nucleotide concentrations, PDEs could modulate beta-cell growth, differentiation and survival; some work has shown that selective inhibition of PDE4 prevents diabetes in NOD mice and that selective PDE3 inhibition blocks cytokine-induced nitric oxide production in islet cells. Further work is required to understand the mechanism of regulation and role of the various PDEs in islet-cell function and to validate them as targets for drugs to treat and prevent diabetes. [Diabetologia (2003[Diabetologia ( ) 46:1179[Diabetologia ( -1189

Cyclic 3'5'AMP (cAMP) is an important physiological amplifier of glucose-induced insulin secretion by the pancreatic islet beta-cell, where it is formed by the activity of adenylyl cyclases, which are stimulated by glucose, through elevation in intracellular calcium concentrations, and by the incretin hormones (GLP-1 and GIP). cAMP is rapidly degraded in the pancreatic islet beta-cell by various cyclic nucleotide phosphodiesterase (PDE) enzymes. Many steps involved in glucose-induced insulin secretion are modulated by cAMP, which is also important in regulating pancreatic islet beta-cell differentiation, growth and survival. This chapter discusses the formation, destruction and actions of cAMP in the islets with particular emphasis on the beta-cell.

cGMP signaling regulates epithelial fluid transport by Drosophila Malpighian (renal) tubules. In order to directly evaluate the importance of cGMP-degrading phosphodiesterases (PDEs) in epithelial transport, bovine PDE5 (a bona fide cGMP-PDE), was ectopically expressed in vivo. Transgenic UAS-PDE5 Drosophila were generated, and PDE5 expression was driven in specified tubule cells in vivo by cell-specific GAL4 drivers. Targeted expression was verified by PCR and Western blotting. Immunolocalization of PDE5 in tubule confirmed specificity of expression and demonstrated localization to the apical plasma membrane. GAL4/UAS-PDE5 tubules exhibit increased cG-PDE activity and reduced basal cGMP levels compared with control lines. We show that wild-type and control tubules are sensitive to the PDE5-specific inhibitor sildenafil and that GAL4/UAS-PDE5 tubules display enhanced sensitivity to sildenafil, compared with controls. cGMP content in GAL4/UAS-PDE5 tubules is restored to control levels by treatment with sildenafil. Thus bovine PDE5 retains cGMP-degrading activity and inhibitor sensitivity when expressed in Drosophila. Expression of PDE5 in tubule principal cells results in an epithelial phenotype, reducing rates of basal and cGMP-/Cardioaccelatory peptide 2b (CAP 2b )-stimulated fluid transport. Furthermore, inhibition of PDE5 activity by sildenafil restores basal and cGMP-stimulated fluid transport rates to control levels. However, corticotrophin releasing factorlike-stimulated transport, which is activated by cAMP signaling, was unaffected, confirming that only cGMPstimulated signaling events in tubule are compromised by overexpression of PDE5. Successful ectopic expression of a vertebrate cG-PDE in Drosophila has shown that cG-PDE has a critical role in tubule function in vivo and that cG-PDE function is conserved across evolution. The transgene also provides a generic tool for the analysis of cGMP signaling in Drosophila.