ABSTRACT
Adenosine plays a role in regulating the contractile function of the heart. This includes a positive ionotropic action via the adenosine A(2A) receptor (A(2A)R) and an inhibition of beta(1)-adrenergic receptor-induced ionotropy (antiadrenergic action) via the adenosine A(1) receptor (A(1)R). Phosphatase activity has also been shown to influence contractile function by affecting the level of protein phosphorylation. Protein phosphatase 2A (PP2A) plays a significant role in mediating the A(1)R antiadrenergic effect. The purpose of this study was to investigate the effects of A(2A)R and A(1)R on the activities of PP2A in hearts obtained from wild-type (WT) and A(2A)R knockout (A(2A)R-KO) mice. PP2A activities were examined in myocardial particulate and cytoplasmic extract fractions. Treatment of wild-type hearts with the A(1)R agonist CCPA increased the total PP2A activity and increased the particulate:cytoplasmic PP2A activity ratio. Treatment with the A(2A)R agonist CGS-21680 (CGS) decreased the total PP2A activity and decreased the particulate:cytoplasmic PP2A activity ratio. This indicated a movement of PP2A activity between cell fractions. The effect of CCPA was inhibited by CGS. In A(2A)R-KO hearts the response to A(1)R activation was markedly enhanced whereas the response to A(2A)R activation was absent. These data show that A(2A)R and A(1)R regulate PP2A activity, thus suggesting an important mechanism for modulating myocardial contractility.
Subject(s)
Heart/physiology , Myocardium/metabolism , Protein Phosphatase 2/metabolism , Receptor, Adenosine A1/metabolism , Receptor, Adenosine A2A/metabolism , Adenosine/analogs & derivatives , Adenosine/metabolism , Adenosine A1 Receptor Agonists , Adenosine A2 Receptor Agonists , Animals , Enzyme Activation , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Myocardial Contraction/physiology , Myocardium/cytology , Phenethylamines/metabolism , Protein Phosphatase 2/genetics , Receptor, Adenosine A1/genetics , Receptor, Adenosine A2A/genetics , Tyrosine/metabolismABSTRACT
The adenosine A1 receptor (A1R) inhibits beta-adrenergic-induced contractile effects (antiadrenergic action), and the adenosine A2A receptor (A2AR) both opposes the A1R action and enhances contractility in the heart. This study investigated the A1R and A2AR function in beta-adrenergic-stimulated, isolated wild-type and A2AR knockout murine hearts. Constant flow and pressure perfused preparations were employed, and the maximal rate of left ventricular pressure (LVP) development (+dp/dt(max)) was used as an index of cardiac function. A1R activation with 2-chloro-N6-cyclopentyladenosine (CCPA) resulted in a 27% reduction in contractile response to the beta-adrenergic agonist isoproterenol (ISO). Stimulation of A2AR with 2-P(2-carboxyethyl)phenethyl-amino-5'-N-ethylcarboxyamidoadenosine (CGS-21680) attenuated this antiadrenergic effect, resulting in a partial (constant flow preparation) or complete (constant pressure preparation) restoration of the ISO contractile response. These effects of A2AR were absent in knockout hearts. Up to 63% of the A2AR influence was estimated to be mediated through its inhibition of the A1R antiadrenergic effect, with the remainder being the direct contractile effect. Further experiments examined the effects of A2AR activation and associated vasodilation with low-flow ischemia in the absence of beta-adrenergic stimulation. A2AR activation reduced by 5% the depression of contractile function caused by the flow reduction and also increased contractile performance over a wide range of perfusion flows. This effect was prevented by the A2AR antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385). It is concluded that in the murine heart, A1R and A2AR modulate the response to beta-adrenergic stimulation with A2AR, attenuating the effects of A1R and also increasing contractility directly. In addition, A2AR supports myocardial contractility in a setting of low-flow ischemia.
Subject(s)
Heart/physiology , Myocardial Contraction/physiology , Receptor, Adenosine A1/physiology , Receptor, Adenosine A2A/physiology , Adenosine/analogs & derivatives , Adenosine/pharmacology , Animals , Heart/drug effects , Isoproterenol/pharmacology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Myocardial Contraction/drug effects , Myocardial Ischemia/physiopathology , Phenethylamines/pharmacology , Xanthines/pharmacologyABSTRACT
OBJECTIVE: To determine the usefulness of the day 10 FSH level of a clomiphene citrate challenge test in predicting IVF outcome in women younger than 40 years of age. DESIGN: Retrospective chart review. SETTING: Academic fertility center. PATIENT(S): Three hundred fifty-three women younger than 40 years of age undergoing 483 IVF cycles. MAIN OUTCOME MEASURE(S): Delivery rates. RESULT(S): An inverse relationship was observed between the likelihood of successful pregnancy and both cycle day 3 and cycle day 10 FSH levels. In women with a normal day 3 FSH level, elevated day 10 FSH levels predicted similarly poor IVF outcomes as for women with an abnormal day 3 FSH level. There was no specific threshold FSH level beyond which pregnancies failed to occur. Successful pregnancies were achieved with aggressive stimulation even in women with FSH levels greater than 20 mIU/mL. CONCLUSION(S): The clomiphene citrate challenge test (CCCT) correlates with IVF outcomes in women younger than 40 years of age. Stimulated day 10 FSH levels are strongly predictive of decreased IVF success even when day 3 FSH levels are normal. Results of the CCCT are useful for patient counseling before the IVF cycle and for choosing the optimal gonadotropin regimen.
