adrenomedullin and Cardiovascular-Abnormalities

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. To date, numerous in vitro studies have suggested that AM can mediate its biological effects through at least three different receptors. To determine the in vivo importance of the most likely candidate receptor, calcitonin receptor-like receptor, a gene-targeted knockout model of the gene was generated. Mice heterozygous for the targeted Calcrl allele appear normal, survive to adulthood, and reproduce. However, heterozygote matings fail to produce viable Calcrl-/- pups, demonstrating that Calcrl is essential for survival. Timed matings confirmed that Calcrl-/- embryos die between embryonic day 13.5 (E13.5) and E14.5 of gestation. The Calcrl-/- embryos exhibit extreme hydrops fetalis and cardiovascular defects, including thin vascular smooth muscle walls and small, disorganized hearts remarkably similar to the previously characterized AM-/- phenotype. In vivo assays of cellular proliferation and apoptosis in the hearts and vasculature of Calcrl-/- and AM-/- embryos support the concept that AM signaling is a crucial mediator of cardiovascular development. The Calcrl gene targeted mice provide the first in vivo genetic evidence that CLR functions as an AM receptor during embryonic development.

Topics: Adrenomedullin; Animals; Apoptosis; Cardiovascular Abnormalities; Cell Proliferation; Embryo Loss; Fetal Death; Gestational Age; Hydrops Fetalis; Mice; Mice, Knockout; Muscle, Smooth, Vascular; Myocardium; Myocytes, Cardiac; Peptides; Receptors, Calcitonin; Recombination, Genetic

Adrenomedullin (AM) is a vasodilating peptide involved in the regulation of circulatory homeostasis and in the pathophysiology of certain cardiovascular diseases. Levels of AM are markedly increased in the fetoplacental circulation during pregnancy, although its function there remains unknown. To clarify the physiological functions of AM, we chose a gene-targeting strategy in mice.. Targeted null mutation of the AM gene is lethal in utero: the mortality rate among AM(-/-) embryos was >80% at E13.5. The most apparent abnormality in surviving AM(-/-) embryos at E13.5 to E14.0 was severe hemorrhage, readily observable under the skin and in visceral organs. Hemorrhage was not detectable at E12.5 to E13.0, although the yolk sac lacked well-developed vessels. Electron microscopic examination showed endothelial cells to be partially detached from the basement structure at E12.5 in vitelline vessels and hepatic capillaries, which allowed efflux of protoerythrocytes through the disrupted barrier. The basement membrane was not clearly recognizable in the aorta and cervical artery, and the endothelial cells stood out from the wall of the lumen, only partially adhering to the basement structure. AM(+/-) mice survived to adulthood but exhibited elevated blood pressures with diminished nitric oxide production.. AM is indispensable for the vascular morphogenesis during embryonic development and for postnatal regulation of blood pressure by stimulating nitric oxide production.

Topics: Adrenomedullin; Animals; Blood Vessels; Cardiovascular Abnormalities; Embryo Loss; Endothelium, Vascular; Female; Gene Targeting; Genes, Lethal; Genotype; Hemodynamics; Hemorrhage; Heterozygote; Homozygote; Hypertension; Inbreeding; Infusion Pumps; Injections, Subcutaneous; Male; Mice; Mice, Knockout; Nitric Oxide; Peptides; Phenotype; Recombinant Proteins; Vitelline Membrane