Nerve stimulation induced overflow of neuropeptide Y and modulation by angiotensin II in spontaneously hypertensive rats

The Type of Fat in the Diet Influences Regulatory Aminopeptidases of the Renin-Angiotensin System and Stress in the Hypothalamic-Pituitary-Adrenal Axis in Adult Wistar Rats

(1) Background: Prolonged feeding with a high-fat diet (HFD) acts as a stressor by activating the functions of the hypothalamic-pituitary-adrenal gland (HPA) stress axis, accompanied of hypertension by inducing the renin-angiotensin-aldosterone system. Angiotensinases enzymes are regulatory aminopeptidases of angiotensin metabolism, which together with the dipeptidyl peptidase IV (DPP-IV), pyroglutamyl- and tyrosyl-aminopeptidase (pGluAP, TyrAP), participate in cognitive, stress, metabolic and cardiovascular functions. These functions appear to be modulated by the type of fat used in the diet. (2) Methods: To analyze a possible coordinated response of aminopeptidases, their activities were simultaneously determined in the hypothalamus, adenohypophysis and adrenal gland of adult male rats fed diets enriched with monounsaturated (standard diet (S diet) supplemented with 20% virgin olive oil; VOO diet) or saturated fatty acids (diet S supplemented with 20% butter and 0.1% cholesterol; Bch diet). Aminopeptidase activities were measured by fluorimetry using 2-Naphthylamine as substrates. (3) Results: the hypothalamus did not show differences in any of the experimental diets. In the pituitary, the Bch diet stimulated the renin-angiotensin system (RAS) by increasing certain angiotensinase activities (alanyl-, arginyl- and cystinyl-aminopeptidase) with respect to the S and VOO diets. DPP-IV activity was increased with the Bch diet, and TyrAP activity decrease with the VOO diet, having both a crucial role on stress and eating behavior. In the adrenal gland, both HFDs showed an increase in angiotensinase aspartyl-aminopeptidase. The interrelation of angiotensinases activities in the tissues were depending on the type of diet. In addition, correlations were shown between angiotensinases and aminopeptidases that regulate stress and eating behavior. (4) Conclusions: Taken together, these results support that the source of fat in the diet affects several peptidases activities in the HPA axis, which could be related to alterations in RAS, stress and feeding behavior.

The renin-angiotensin system in PTSD: a replication and extension

Prior observational studies have suggested that medications targeting the renin-angiotensin system, such as angiotensin-converting enzyme inhibitors (ACE-Is) and angiotensin receptor blockers (ARBs), may be associated with decreased PTSD symptoms. Given known sex differences in PTSD prevalence and cardiovascular disease, here we tested whether the effects of ACE-I/ARB status on PTSD differ by sex. We also expanded these observations with replication analyses in a large biorepository database. Participants in the initial sample included 840 trauma-exposed individuals recruited as part of the Grady Trauma Project. The Modified PTSD Symptom Scale (M-PSS) was administered and ACE-I/ARB status was determined by self-report. Replication analyses were conducted using a large biorepository database (Partners Healthcare Biobank, N = 116,389) with diagnoses and medication status based on available electronic health records. Among individuals treated with ACE-Is/ARBs in the initial sample, women had significantly higher M-PSS total and Re-experiencing severity compared to men (p's < 0.05). Analyses with the large biorepository sample robustly replicated the overall effects of ACE-I/ARB medication associated with lower rate of PTSD diagnosis (p < 0.001). We also demonstrated that this effect may be specific to the renin-angiotensin system as it did not replicate for beta-blockers, calcium channel blockers, or diuretics. When we examined more specific drug classes, results indicated that the ACE-I/ARB effect on PTSD may be driven more by ARBs (e.g., Losartan) than by ACE-Is. Post-hoc analyses indicated that racial differences may exist in these effects. Overall, our results replicate and extend prior observations that the renin-angiotensin system is associated with PTSD. Medications targeting this system may be worthy of further investigation for PTSD treatment. Our findings suggest that sex and race effects should be considered in future treatment research.

Neuropeptide Y mediates cardiac hypertrophy through microRNA-216b/FoxO4 signaling pathway

Cardiac hypertrophy (CH) is a major risk factor for heart failure accompanied by maladaptive cardiac remodeling. The role and potential mechanism of neuropeptide Y (NPY) in CH are still unclear. We will explore the role and the mechanism of NPY inactivation (NPY-I) in CH caused by pressure overload. Abdominal aortic constriction (AAC) was used to induce CH model in rats. NPY or angiotensin II (Ang II) was used to trigger CH model in vitro in neonatal rat ventricular myocytes (NRVMs). We found that NPY was increased in the heart and plasma of hypertrophic rats. However, Ang II did not increase NPY expression in cardiomyocytes. NPY-I attenuated CH as decreasing CH-related markers (ANP, BNP and β-MHC mRNA) level, reducing cell surface area, and restoring cardiac function. NPY inactivation increased miR-216b and decreased FoxO4 expression in CH heart. Moreover, NPY decreased miR-216b and increased FoxO4 expression in NRVMs which were reversed by NPY type 1 receptor (NPY1R) antagonist BIBO3304. MiR-216b mimic and FoxO4 siRNA (small interfering RNA) inhibited NPY/Ang II-induced myocardial hypertrophy in vitro. Meanwhile, BIBO3304 reversed the pro-hypertrophy effect of NPY in vitro. Collectively, NPY deficiency attenuated CH by NPY1R-miR-216b-FoxO4 axis. These findings suggested that NPY would be a potential therapeutic target for the prevention and treatment of cardiac hypertrophy.

[Angiotensin II Regulates Excitability and Contractile Functions of Myocardium and Smooth Muscles through Autonomic Nervous Transmission]

Angiotensin II (Ang II) is an intrinsic peptide having strong vasopressor effects, and thus, it plays an important role in the physiological regulation of blood pressure. The vasopressor effects of Ang II include direct contraction of myocardium and vascular smooth muscles (SMs) along with aldosterone-mediated sodium retention. In addition, indirect vascular contractions induced by noradrenaline (NA), the release of which is mediated through Ang II receptor type 1 (AT₁) existing at the sympathetic nerve terminals (SNTs), also contribute to the vasopressor effects of Ang II. Stimulation of NA release from SNTs by Ang II also occurs in the myocardium leading to an increase in heart rate and cardiac contraction. Furthermore, Ang II enhances the contractions of non-vascular SMs, such as vas deferens, through induction of NA release from the SNTs. We have found that Ang II attenuated vagus nerve stimulation-induced bradycardia in a losartan-sensitive manner. This suggests that Ang II attenuates vagus nerve stimulation-induced bradycardia by inhibiting acetylcholine (ACh) release from the parasympathetic nerve terminals (PNTs) through activation of the AT₁ receptor. Ang II was also reported to attenuate the release of ACh from the PNTs in SMs, such as stomach and airway, thus suppressing their contractile functions. There are, however, conflicting reports of the effects of Ang II on parasympathetic nerve-mediated contractile regulation of SMs. In this review, we have highlighted the relevant research articles including our experimental reports on the regulation of sympathetic and parasympathetic nerve-mediated excitation and contraction by Ang II along with the future prospects.

Inhibitory effect of D3 dopamine receptors on neuropeptide Y‑induced migration in vascular smooth muscle cells

Abnormal migration of vascular smooth muscle cells (VSMCs) serves an important role in hypertension, atherosclerosis and restenosis following angioplasty, which is regulated numerous hormonal and humoral factors, including neuropeptide Y (NPY) and dopamine. Dopamine and NPY are both sympathetic neurotransmitters, and a previous study reported that NPY increased VSMC proliferation, while dopamine receptor inhibited it. Therefore, the authors wondered whether or not there is an inhibitory effect of dopamine receptor on NPY‑mediated VSMC migration. The present study demonstrated that stimulation with NPY dose‑dependence (10‑10‑10‑7M, 24 h) increased VSMC migration, the stimulatory effect of NPY was via the Y1 receptor. This is because, in the presence of the Y1 receptor antagonist, BIBP3226 (10‑7 M), the stimulatory effect of NPY on VSMC migration was blocked. Activation of the D3 receptor by PD128907 dose‑dependence (10‑11‑10‑8 M) reduced the stimulatory effect of NPY on VSMC migration. The effect of PD128907 was via the D3 receptor, because the inhibitory effect of PD128907 on NPY‑mediated migration was blocked by the D3 receptor antagonist, U99194. The authors' further study suggested that the inhibitory effect of the D3 receptor was via the PKA signaling pathway, in the presence of the PKA inhibitor, 14‑22 (10‑6 M), the inhibitory effect of PD128907 on VSMC migration was blocked. Moreover, the inhibitory effect of PD128907 was imitated by PKA activator, Sp‑cAMP [S], in the presence of Sp‑cAMP [S], the NPY‑mediated stimulatory effect on VSMC migration was abolished. The present study indicated that activation of the D3 receptor inhibits NPY Y1‑mediated migration on VSMCs, PKA is involved in the signaling pathway.

Effect of dipeptidyl peptidase 4 inhibition on arterial blood pressure is context dependent

Because the effects of dipeptidyl peptidase 4 (DPP4) inhibitors on blood pressure are controversial, we examined the long-term effects of sitagliptin (80 mg/kg per day) on blood pressure (radiotelemetry) in spontaneously hypertensive rats (SHR), Wistar-Kyoto rats, and Zucker Diabetic-Sprague Dawley rats (metabolic syndrome model). In SHR, chronic (3 weeks) sitagliptin significantly increased systolic, mean, and diastolic blood pressures by 10.3, 9.2, and 7.9 mm Hg, respectively, a response abolished by coadministration of BIBP3226 (2 mg/kg per day; selective Y1-receptor antagonist). Sitagliptin also significantly increased blood pressure in SHR treated with hydralazine (vasodilator; 25 mg/kg per day) or enalapril (angiotensin-converting enzyme inhibitor; 10 mg/kg per day). In Wistar-Kyoto rats, chronic sitagliptin slightly decreased systolic, mean, and diastolic blood pressures (-1.8, -1.1, and -0.4 mm Hg, respectively). In Zucker Diabetic-Sprague Dawley rats, chronic sitagliptin decreased systolic, mean, and diastolic blood pressures by -7.7, -5.8, and -4.3 mm Hg, respectively, and did not alter the antihypertensive effects of chronic enalapril. Because DPP4 inhibitors impair the metabolism of neuropeptide Y1-36 (NPY1-36; Y1-receptor agonist) and glucagon-like peptide (GLP)-1(7-36)NH2 (GLP-1 receptor agonist), we examined renovascular responses to NPY1-36 and GLP-1(7-36)NH2 in isolated perfused SHR and Zucker Diabetic-Sprague Dawley kidneys pretreated with norepinephrine (to induce basal tone). In Zucker Diabetic-Sprague Dawley kidneys, NPY1-36 and GLP-1(7-36)NH2 exerted little, if any, effect on renovascular tone. In contrast, in SHR kidneys, both NPY1-36 and GLP-1(7-36)NH2 elicited potent and efficacious vasoconstriction.

IN CONCLUSION

(1) The effects of DPP4 inhibitors on blood pressure are context dependent; (2) The context-dependent effects of DPP4 inhibitors are due in part to differential renovascular responses to DPP4’s most important substrates (NPY1–36 and GLP-1(7–36)NH2) [corrected]; (3) Y1 receptor antagonists may prevent the prohypertensive and possibly augment the antihypertensive effects of DPP4 inhibitors.

Neuronal and non-neuronal modulation of sympathetic neurovascular transmission

Noradrenaline, neuropeptide Y and adenosine triphosphate are co-stored in, and co-released from, sympathetic nerves. Each transmitter modulates its own release as well as the release of one another; thus, anything affecting the release of one of these transmitters has consequences for all. Neurotransmission at the sympathetic neurovascular junction is also modulated by non-sympathetic mediators such as angiotensin II, serotonin, histamine, endothelin and prostaglandins through the activation of specific pre-junctional receptors. In addition, nitric oxide (NO) has been identified as a modulator of sympathetic neuronal activity, both as a physiological antagonist against the vasoconstrictor actions of the sympathetic neurotransmitters, and also by directly affecting transmitter release. Here, we review the modulation of sympathetic neurovascular transmission by neuronal and non-neuronal mediators with an emphasis on the actions of NO. The consequences for co-transmission are also discussed, particularly in light of hypertensive states where NO availability is diminished.

Sympathetic nerves and the endothelium influence the vasoconstrictor effect of low concentrations of ouabain in pressurized small arteries

We hypothesized that in salt-dependent forms of hypertension, endogenous ouabain acts on arterial smooth muscle to cause enhanced vasoconstriction. Here, we tested for the involvement of the arterial endothelium and perivascular sympathetic nerve terminals in ouabain-induced vasoconstriction. Segments of rat mesenteric or renal interlobar arteries were pressurized to 70 mmHg at 37 degrees C and exposed to ouabain (10(-11)-10(-7) M). Removal of the endothelium enhanced ouabain-induced vasoconstriction by as much as twofold (at an ouabain concentration of 10(-9) M). A component of the ouabain-induced vasoconstriction is due to the enhanced spontaneous release of norepinephrine (NE) from nerve terminals in the arterial wall. The alpha(1)-adrenoceptor blocker prazosin (10(-6) M) decreased ouabain-induced vasoconstrictions by as much as 50%. However, neither the contraction induced by sympathetic nerve activity (SNA) nor the NE release evoked by SNA (measured directly by carbon fiber amperometry) was increased by ouabain (<10(-7) M). Nevertheless, the converse case was true: after brief bursts of SNA, vasoconstrictor responses to ouabain were transiently increased (1.75-fold). This effect may be mediated by neuropeptide Y and Y(1) receptors on smooth muscle. In arteries lacking the endothelium and exposed to prazosin, ouabain (10(-11) M and greater) caused vasoconstriction, indicating a direct effect of very "low" concentrations of ouabain on arterial smooth muscle. In conclusion, in intact arteries, the endothelium opposes ouabain (10(-11)-10(-7)M)-induced vasoconstriction, which is caused by both enhanced spontaneous NE release and direct effects on smooth muscle. Ouabain (<10(-7)M) does not enhance SNA-mediated contractions, but SNA enhances ouabain-induced contractions. The effects of endogenous ouabain may be accentuated in forms of hypertension that involve sympathetic nerve hyperactivity and/or endothelial dysfunction.

Inhibitory effects of angiotensin-(1-7) on the nerve stimulation-induced release of norepinephrine and neuropeptide Y from the mesenteric arterial bed

Neuropeptide Y (NPY) is a cotransmitter with norepinephrine (NE) and ATP in sympathetic nerves. There is evidence for increased activity of the sympathetic nervous system and the renin-angiotensin system (RAS), as well as a role for NPY in the development of hypertension in experimental animal models and in humans. Angiotensin II (ANG II) is known to facilitate sympathetic neurotransmission, an effect greater in spontaneously hypertensive rats (SHR) than normotensive Wistar-Kyoto (WKY) rats. A newly discovered product of the RAS is angiotensin-(1-7) [ANG-(1-7)]. There is evidence suggesting that ANG-(1-7) opposes the actions of ANG II, resulting in hypotensive effects. The objective of this study was to investigate the role of ANG-(1-7) on the nerve-stimulated overflow of NE and NPY from the mesenteric arterial bed of SHR and the mechanisms involved in mediating any effects produced. ANG-(1-7) (0.001, 0.01, 0.1 microM) decreased nerve-stimulated NE and NPY overflow, as well as perfusion pressure in preparations obtained from SHR. This effect was greater in preparations of SHR than WKY controls. In addition, ANG-(1-7) decreased NE overflow to a greater extent than NPY overflow. Administration of the Mas receptor antagonist, D-Ala(7) ANG-(1-7), attenuated the decrease in both NE and NPY overflow due to ANG-(1-7) administration. However, the angiotensin type 2 receptor antagonist, PD-123391, attenuated the effect of ANG-(1-7) on NE overflow without affecting the decrease in NPY overflow. Moreover, in the presence of N(G)-nitro-L-arginine methyl ester, ANG-(1-7) decreased NPY overflow, but not NE overflow. ANG-(1-7) decreases the nerve-stimulated overflow of NE and NPY in preparations of SHR, whereas ANG II enhances it. Therefore, ANG-(1-7) may counteract the effects of ANG II by acting on ANG type 2 and Mas receptors.