Serotonin synthesis in mammals is initiated by 2 distinct tryptophan hydroxylases (TPH), TPH1 and TPH2. By genetically ablating TPH2, we created mice ( Tph2 ^−/− ) that lack serotonin in the central nervous system. Surprisingly, these mice can be born and survive until adulthood. However, depletion of serotonin signaling in the brain leads to growth retardation and 50% lethality in the first 4 weeks of postnatal life. Telemetric monitoring revealed more extended daytime sleep, suppressed respiration, altered body temperature control, and decreased blood pressure (BP) and heart rate (HR) during nighttime in Tph2 ^−/− mice. Moreover, Tph2 ^−/− females, despite being fertile and producing milk, exhibit impaired maternal care leading to poor survival of their pups. These data confirm that the majority of central serotonin is generated by TPH2. TPH2-derived serotonin is involved in the regulation of behavior and autonomic pathways but is not essential for adult life.

Mas codes for a G protein–coupled receptor that is implicated in angiotensin-(1-7) signaling. We studied the cardiovascular phenotype of Mas -deficient mice backcrossed onto the FVB/N genetic background using telemetry and found that they exhibit higher blood pressures compared with controls. These Mas ^−/− mice also had impaired endothelial function, decreased NO production, and lower endothelial NO synthase expression. Reduced nicotinamide-adenine dinucleotide phosphate oxidase catalytic subunit gp91 ^phox protein content determined by Western blotting was higher in Mas ^−/− mice than in controls, whereas superoxide dismutase and catalase activities were reduced. The superoxide dismutase mimetic, Tempol, decreased blood pressure in Mas ^−/− mice but had a minimal effect in control mice. Our results show a major cardiovascular phenotype in Mas ^−/− mice. Mas -deletion results in increased blood pressure, endothelial dysfunction, and an imbalance between NO and reactive oxygen species. Our animals represent a promising model to study angiotensin-(1-7)–mediated cardiovascular effects and to evaluate Mas agonistic compounds as novel cardioprotective and antihypertensive agents based on their beneficial effects on endothelial function.

Objective—Angiotensin peptides play a central role in cardiovascular physiology and pathology. Among these peptides, angiotensin II (Ang II) has been investigated most intensively. However, further angiotensin peptides such as Ang 1-7, Ang III, and Ang IV also contribute to vascular regulation, and may elicit additional, different, or even opposite effects to Ang II. Here, we describe a novel Ang II-related, strong vasoconstrictive substance in plasma from healthy humans and end-stage renal failure patients.Methods and Results—Chromatographic purification and structural analysis by matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight (MALDI-TOF/TOF) revealed an angiotensin octapeptide with the sequence Ala-Arg-Val-Tyr-Ile-His-Pro-Phe, which differs from Ang II in Ala¹instead of Asp¹. Des[Asp¹]-[Ala¹]-Ang II, in the following named Angiotensin A (Ang A), is most likely generated enzymatically. In the presence of mononuclear leukocytes, Ang II is converted to Ang A by decarboxylation of Asp¹. Ang A has the same affinity to the AT₁receptor as Ang II, but a higher affinity to the AT₂receptor. In the isolated perfused rat kidney, Ang A revealed a smaller vasoconstrictive effect than Ang II, which was not modified in the presence of the AT2 receptor antagonist PD 123319, suggesting a lower intrinsic activity at the AT₁receptor. Ang II and Ang A concentrations in plasma of healthy subjects and end-stage renal failure patients were determined by matrix-assisted laser desorption/ionisation mass-analysis, because conventional enzyme immunoassay for Ang II quantification did not distinguish between Ang II and Ang A. In healthy subjects, Ang A concentrations were less than 20% of the Ang II concentrations, but the ratio Ang A / Ang II was higher in end-stage renal failure patients.Conclusion—Ang A is a novel human strong vasoconstrictive angiotensin-derived peptide, most likely generated by enzymatic transformation through mononuclear leukocyte-derived aspartate decarboxylase. Plasma Ang A concentration is increased in end-stage renal failure. Because of its stronger agonism at the AT₂receptor, Ang A may modulate the harmful effects of Ang II.

Rat models of hypertension, eg, spontaneously hypertensive stroke-prone rats (SHRSP), display reduced angiotensin-converting enzyme 2 (ACE2) mRNA and protein expression compared with control animals. The aim of this study was to investigate the role of ACE2 in the pathogenesis of hypertension in these models. Therefore, we generated transgenic rats on a SHRSP genetic background expressing the human ACE2 in vascular smooth muscle cells by the use of the SM22 promoter, called SHRSP-ACE2. In these transgenic rats vascular smooth muscle expression of human ACE2 was confirmed by RNase protection, real-time RT-PCR, and ACE2 activity assays. Transgene expression leads to significantly increased circulating levels of angiotensin-(1-7), a prominent product of ACE2. Mean arterial blood pressure was reduced in SHRSP-ACE2 compared to SHRSP rats, and the vasoconstrictive response to intraarterial administration of angiotensin II was attenuated. The latter effect was abolished by previous administration of an ACE2 inhibitor. To evaluate the endothelial function in vivo, endothelium-dependent and endothelium-independent agents such as acetylcholine and sodium nitroprusside, respectively, were applied to the descending thoracic aorta and blood pressure was monitored. Endothelial function turned out to be significantly improved in SHRSP-ACE2 rats compared to SHRSP. These data demonstrate that vascular ACE2 overexpression in SHRSP reduces hypertension probably by locally degrading angiotensin II and improving endothelial function. Thus, activation of the ACE2/angiotensin-(1-7) axis may be a novel therapeutic strategy in hypertension.

Kinins play a central role in the modulation of cardiovascular function and in the pathophysiology of inflammation. These peptides mediate their effects by binding to two specific G‐protein coupled receptors named B1 and B2. To evaluate the full functional relevance of the kallikrein‐kinin system, we generated mice lacking both kinin receptors (B1B2‐/‐). Because of the close chromosomal position of both kinin receptor genes, B1B2‐/‐ mice could not be obtained by simple breeding of the single knockout lines. Therefore, we inactivated the B1 receptor gene by homologous recombination in embryonic stem cells derived from B2‐deficient animals. The B1B2‐/‐ mice exhibited undetectable levels of mRNAs for both receptors and a lack of response to bradykinin (B2 agonist) and des‐Arg ⁹ ‐bradykinin (B1 agonist), as attested by contractility studies with isolated smooth muscle tissues. B1B2‐/‐ mice are healthy and fertile, and no sign of cardiac abnormality was detected. They are nor‐motensive but exhibit a lower heart rate than controls. Furthermore, kinin receptor deficiency affects the pathogenesis of endotoxin‐induced hypotension. While blood pressure decreased markedly in wild‐type mice and B2‐/‐ and moderately in B1 ‐/‐ mice after bacterial lipopolysaccharide (LPS) injection, blood pressure remained unchanged in B1B2‐/‐ mice. These results clearly demonstrate a pivotal role of kinins and their receptors in hypotension induced by endotoxemia in mice.—Cayla C., Todiras, M., Iliescu, R., Saul, V. V., Gross, V., Pilz, B., Chai, G., Merino, V. F., Pesquero, J. B., Baltatu, O. C., Bader M. Mice deficient for both kinin receptors are normotensive and protected from endotox‐in‐induced hypotension. FASEB J. 21, 1689–1698 (2007)