Modulation of cAMP levels by β-stimulation and PDE3 inhibition during hypothermia. An in vitro study on embryonic cardiac cells from rat

Abstract

Introduction: Accidental hypothermia is defined as an involuntary drop in core body temperature below 35 °C and is associated with acute cardiac dysfunction. The PDE3 inhibitor milrinone and β-agonist isoprenaline provide positive inotropic effects during normothermia by elevating intracellular levels of cAMP in cardiac cells. Rat models have demonstrated that milrinone has more favorable hemodynamic effects during cooling and rewarming compared to isoprenaline, but the exact mechanism for this is not clear. <p>

<p>Methods: Embryonic cardiac cells were incubated at 37, 30 and 20 °C. Intracellular levels of cAMP were quantified with LC-MS/MS in control cells and after exposure with milrinone and isoprenaline after 3, 15 and 30 minutes. <p>

<p>Results: Significant elevation of cAMP was observed after incubation with 100 μM and 1 mM milrinone at all temperatures (p<0.05). Similarly, isoprenaline induced significant cAMP elevations at all temperatures, but only in a concentration of 10 μM (p<0.05). Incubating control cells, not exposed to any drug, resulted in significant cAMP elevation after 3 and 15 minutes during moderate hypothermia (30 °C) compared to normothermia (p<0.05). Corresponding cAMP elevation was not present during severe hypothermia (20 °C). <p>

<p>Conclusion: The present findings demonstrate that milrinone and isoprenaline elevates cAMP at temperatures down to 20 °C. In contrast, the relation between basal levels of cAMP and temperature seems non-linear, as only moderate hypothermia induces a significant elevation of cAMP compared to normothermia.