No abstract

Apelin, a peptide recently isolated from bovine stomach tissue extracts, has been identi®ed as the endogenous ligand of the human orphan APJ receptor. We established a stable Chinese hamster ovary (CHO) cell line expressing a gene encoding the rat apelin receptor fused to the enhanced green¯uorescent protein, to investigate internalization and the pharmacological pro®le of the apelin receptor. Stimulation of this receptor by the apelin fragments K17F (Lys1-Phe-Arg-Arg-Gln-Arg-Pro-ArgLeu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe17) and pE13F (pGlu5-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe17) resulted in a dose-dependent inhibition of forskolin-induced cAMP production and promoted its internalization. In contrast, the apelin fragments R10F (Arg8-Leu-Ser-His-Lys-Gly-Pro-Met-ProPhe17) and G5F (Gly13-Pro-Met-Pro-Phe17) were inactive. The physiological role of apelin and its receptor was then investigated by showing for the ®rst time in rodent brain: (i) detection of apelin neurons in the supraoptic and paraventricular nuclei by immunohistochemistry with a speci®c polyclonal anti-apelin K17F antibody; (ii) detection of apelin receptor mRNA in supraoptic vasopressinergic neurons by in situ hybridization and immunohistochemistry; and (iii) a decrease in vasopressin release following intracerebroventricular injection of K17F, or pE13F, but not R10F. Thus, apelin locally synthesized in the supraoptic nucleus could exert a direct inhibitory action on vasopressinergic neuron activity via the apelin receptors synthesized in these cells. Furthermore, central injection of pE13F signi®cantly decreased water intake in dehydrated normotensive rats but did not affect blood pressure. Together, these results suggest that neuronal apelin plays an important role in the central control of body¯uid homeostasis. Keywords: arterial blood pressure, drinking behaviour, internalization, second messenger, vasopressin release.

Despite the success of renin-angiotensin system (RAS) blockade by angiotensin-converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor (AT1R) blockers, current therapies for hypertension and related cardiovascular diseases are still inadequate. Identification of additional components of the RAS and associated vasoactive pathways, as well as new structural and functional insights into established targets, have led to novel therapeutic approaches with the potential to provide improved cardiovascular protection and better blood pressure control and/or reduced adverse side effects. The simultaneous modulation of several neurohumoral mediators in key interconnected blood pressure–regulating pathways has been an attractive approach to improve treatment efficacy, and several novel approaches involve combination therapy or dual-acting agents. In addition, increased understanding of the complexity of the RAS has led to novel approaches aimed at upregulating the ACE2/angiotensin-(1-7)/Mas axis to counter-regulate the harmful effects of the ACE/angiotensin II/angiotensin III/AT1R axis. These advances have opened new avenues for the development of novel drugs targeting the RAS to better treat hypertension and heart failure. Here we focus on new therapies in preclinical and early clinical stages of development, including novel small molecule inhibitors and receptor agonists/antagonists, less conventional strategies such as gene therapy to suppress angiotensinogen at the RNA level, recombinant ACE2 protein, and novel bispecific designer peptides.