Clinical Pharmacology

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This division was known as Pharmacology until 27 June 2013.

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Browsing Clinical Pharmacology by browse.metadata.advisor "Lopes, J."

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    The role of Phosphodiesterase (PDE3) in heart protection.
    (Stellenbosch : Stellenbosch University, 2016-03) Labuschagne, S. W.; Lopes, J.; Naidoo, G.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine. Clinical Pharmacology.
    ENGLISH ABSTRACT: Introduction: During a heart attack the blood supply to the heart is reduced significantly, known as ischemia (Reimer & Jennings, 1991). Energy generating pathways that require oxygen become inhibited in the ischemic tissue. The energy decline leads to an increase in ions (calcium, hydrogen, sodium) inside the ischemic heart cells, leading to tissue damage, which is enhanced by reperfusion (Nakamura et al 1999, Piper et al 2004). Hypercontracture, mitochondrial membrane potential and cell death are the hallmarks of ischemia/reperfusion injury. β-adrenergic receptor (β-AR) activation by sympathetic stimuli increases the intracellular cyclic AMP levels, which activates PKA and enhance cell damage during ischemia. Phosphodieterases (PDEs) have been found to play a role in the sensitivity of cardiomyocytes to anoxia induced cell death (Geisbuhler et al., 2002), and PDE3 is known to play a role in β-AR mediated signalling (Christ et al., 2009). Therefore the involvement of PDE3 was evaluated as a regulator of cell survival in the presence and absence of β-AR stimulation (β1-, β2- and β3-AR, separately and together), and insulin administration. Aims: The main aim of this study is to investigate the effective role of the PDE isoform 3, in the cardioprotection induced by insulin versus damage induced by the β-AR and to identify the possible mechanisms involved. Methods: Cardiomyocytes were isolated from Male Wistar rat hearts and cultured overnight in 96-well plates for simulated ischemia/reperfusion experiments the next day. Twelve experimental groups were tested in all objectives including (1) Control; (2) Control + PDE 3 inhibitor; (3) Insulin; (4) Insulin + PDE 3 inhibitor; (5) Dobutamine; (6) Dobutamine + PDE 3 inhibitor; (7) Formoterol; (8) Formoterol + PDE 3 inhibitor; (9) Isoproterenol; (10) Isoproterenol + PDE 3 inhibitor; (11) BRL-37344; and (12) BRL-37344 + PDE 3 inhibitor. These treatments were applied during 20 minutes simulated ischemia induced by 3mM SDT and 10mM 2DG, followed by 60 minutes reperfusion. Cell viability was determined by staining cells with JC-1 and images of cells were captured using fluorescence microscopy. The cells were analysed according morphology and fluorescence intensity. Results: In cardiomyocytes that were subjected to 20 minutes simulated ischemia and 60 minutes reperfusion, 3mIU insulin mediated cardioprotection through decreasing cell hypercontracture and increasing cell viability. β2-AR stimulation through the agonist 10uM formoterol also led to protection regarding the cell parameters. Cardiomyocyte protection during ischemia was also elicited when the PDE3 enzyme were inhibited by 10uM milrinone. β1-AR stimulation with 10uM dobutamine appears to have no significant effect regarding damage or protection, while β3-AR stimulation with 10uM BRL37344 resulted in protection. Conclusion: Cardioprotection was elicited with the inhibition of the PDE3 enzyme, but did not have any significant effect on insulin-mediated cell protection. One of the most remarkable observations made, was the fact that β2-AR stimulation with formoterol and β3-AR stimulation with BRL-37344 the most effective triggers of cardioprotection.