BACKGROUND AND PURPOSEThe apelin receptor (APJ) is often co-expressed with the angiotensin II type-1 receptor (AT1) and acts as an endogenous counter-regulator. Apelin antagonizes Ang II signalling, but the precise molecular mechanism has not been elucidated. Understanding this interaction may lead to new therapies for the treatment of cardiovascular disease. EXPERIMENTAL APPROACHThe physical interaction of APJ and AT1 receptors was detected by co-immunoprecipitation and bioluminescence resonance energy transfer (BRET). Functional and pharmacological interactions were measured by G-protein-dependent signalling and recruitment of b-arrestin. Allosterism and cooperativity between APJ and AT1 were measured by radioligand binding assays. KEY RESULTSApelin, but not Ang II, induced APJ : AT1 heterodimerization forced AT1 into a low-affinity state, reducing Ang II binding. Likewise, apelin mediated a concentration-dependent depression in the maximal production of inositol phosphate (IP1) and b-arrestin recruitment to AT1 in response to Ang II. The signal depression approached a limit, the magnitude of which was governed by the cooperativity indicative of a negative allosteric interaction. Fitting the data to an operational model of allosterism revealed that apelin-mediated heterodimerization significantly reduces Ang II signalling efficacy. These effects were not observed in the absence of apelin. CONCLUSIONS AND IMPLICATIONSApelin-dependent heterodimerization between APJ and AT1 causes negative allosteric regulation of AT1 function. As AT1 is significant in the pathogenesis of cardiovascular disease, these findings suggest that impaired apelin and APJ function may be a common underlying aetiology. LINKED ARTICLE

Objective To test the hypothesis that apelin protects against AngII-induced cardiovascular fibrosis and vascular remodeling. Methods and Results Wild type mice administered apelin or apelin plus Ang II exhibited less cardiovascular fibrosis and decreased PAI-1 gene expression than mice receiving Ang II, L-NAME, apelin plus L-NAME or apelin plus AngII plus L-NAME. In vitro analysis using a luciferase construct driven by 3.1Kb of the human PAI-1 promoter revealed that apelin blocks Ang II-mediated PAI-1 gene expression. Immunoblotting for phosphorylated myosin phosphatase subunit and myosin light chain revealed that apelin blocked Ang II activation of the Rho kinase pathway, which is associated with induction of PAI-1 gene expression by Ang II. In addition, treatment of human aortic smooth muscle cells with apelin reduced PAI-1 mRNA and protein production in the presence and absence of Ang II. Conversely, L-NAME treatment attenuated the down-regulation of PAI-1 by apelin in cells. Conclusions Apelin protects against cardiac fibrosis and vascular remodeling through direct regulation of PAI-1 gene expression. This protective effect is mediated through the synergistic inhibition of Ang II signaling and increased production of NO by apelin. Our data extend previous findings and provide new insight into the molecular mechanisms by which apelin elicits a cardio-protective effect.

Although thyroid dysfunction will develop in more than 12% of the US population during their lifetimes, true thyroid emergencies are rare. Thyroid storm and myxedema coma are endocrine emergencies resulting from thyroid hormone dysregulation, usually coupled with an acute illness as a precipitant. Careful assessment of risk and rapid action, once danger is identified, are essential for limiting morbidity and mortality related to thyroid storm and myxedema coma. This article reviews which patients are at risk, explains thyroid storm and myxedema coma, and describes pharmacological treatment and supportive cares.

For the purpose of determining the immunogenic potency of polio virus, relatively large amounts of concentrated virus material were prepared which had titres of the order of 1010 T.C.I.D.50 per ml. These were obtained by pervaporating large quantities of tissue culture fluid containing approximately 106.5 T.C.I.D.50 per ml.We wish to acknowledge the valuable assistance received from Dr P. D. Winter and his staff, of the Poliomyelitis Research Foundation, in carrying out the tissue culture titrations of these materials.