Peptides in the mammalian cardiovascular system. In: Polak JM, editor. Regulatory Peptides. Basel: Birkhäuser; 1989. pp. 292-316. [DOI: 10.1007/978-3-0348-9136-3_16]

Positive inotropy mediated via CGRP receptors in isolated human myocardial trabeculae

Isometric contractile force were studied on isolated human myocardial trabeculae that were paced at 1.0 Hz in tissue baths. Alpha calcitonin gene-related peptide (alpha-CGRP) had a potent positive inotropic effect in most trabeculae from both the right atrium and left ventricle, and this effect was partially antagonized by the CGRP(1) receptor antagonist alpha-CGRP-(8-37) (10(-6) M). Amylin and the CGRP(2) receptor agonist [Cys(acetylmethoxy)(2, 7)]CGRP had a positive inotropic effect in some trabeculae, whereas adrenomedullin had no inotropic effect. Using reverse transcriptase-polymerase chain reaction (PCR) mRNAs encoding the human calcitonin receptor-like receptor and the receptor associated modifying proteins (RAMPs) RAMP1, RAMP2, and RAMP3 were detected in human myocardial trabeculae from both the right atrium and left ventricle. In conclusion, functional CGRP(1) and CGRP(2) receptors may mediate a positive inotropic effect at both the atrial and ventricular level of the human heart. mRNAs for calcitonin receptor-like receptor and specific RAMPs further support the presence of CGRP receptors.

Positive inotropy of calcitonin gene-related peptide and amylin on porcine isolated myocardium

Isolated porcine myocardial trabeculae from right atria and left ventricles were paced at 1.5 Hz in tissue baths, and changes in isometric contractile force upon exposure to agonist were studied. Alpha calcitonin gene-related peptide (alpha-CGRP) increased contractile force in nearly half of the trabeculae, whereas the selective CGRP(2) receptor agonist [Cys(acetylmethoxy)(2,7)]-CGRP had effect in only a few. Preincubation with the CGRP(1) receptor antagonist alpha-CGRP-(8-37) (10(-6) M) almost completely blocked positive inotropic responses to alpha-CGRP. Amylin had weak positive inotropic effects in some atrial, but not in ventricular trabeculae. Adrenomedullin did not affect contractility in either atrial or ventricular trabeculae. In conclusion, these results suggest that alpha-CGRP has a positive inotropic effect that can be mediated by both CGRP(1) and CGRP(2) receptors. Amylin seems to have a potential positive inotropic effect on atrial tissue, whereas no direct effect of adrenomedullin could be measured.

Vagal nerve stimulation during muscarinic and beta-adrenergic blockade causes significant coronary artery dilation

Vasoactive intestinal peptide (VIP) is present in post-ganglionic vagal nerve fibers in the coronary arteries and right ventricle but no significant amounts are found in the left ventricle. We determined the effects of VIP, released endogenously from cardiac vagal nerves, on the circumflex mean coronary artery pressure and on right and left ventricular (RV and LV) contractility (dP/dtmax) and relaxation (dP/dtmin). In 20 anesthetized, open chest mongrel dogs, the cervical vagus nerves and cardiac sympathetic ansa subclaviae were isolated and transected. Electrodes were applied to the cardiac segments of the right and left vagus nerves for subsequent stimulation. The muscarinic and beta-adrenergic receptors were blocked with atropine and propranolol, respectively. The heart rate was controlled by either producing atrioventricular node block in 10 dogs and pacing the ventricles (series 1) or by right atrial pacing in 10 separate dogs (series 2). Coronary artery blood flow was controlled by perfusing the circumflex coronary artery in each dog with femoral arterial blood at a controlled flow rate. Coronary artery pressure, ventricular and aortic pressures and dP/dt were continuously measured. Experiments were performed prior to and after the administration of [4Cl-D-Phe6,Leu17]VIP, a sensitive and selective VIP antagonist. Vagal nerve stimulation at 20 Hz (0.5 ms, 20 V) for 5 min significantly decreased the circumflex mean coronary artery pressure by 17% from the control value of 95+/-2 mmHg in series 1 and by 13% from the control value of 109+/-2 mmHg in series 2 (both p < 0.005). Aortic, LV and RV systolic and end-diastolic pressures, LV dP/dtmax and dP/dtmin, and the EKG did not change. In contrast, RV dP/dtmax and dP/dtmin increased by 22% (p < 0.04) and 23% (p < 0.02), respectively, in series 1 and by 26% (p < 0.02) and 33% (p < 0.01), respectively, in series 2. The VIP antagonist, [4Cl-D-Phe6,Leu17]VIP, directly injected into the left circumflex coronary artery, had no effect on coronary, aortic or ventricular pressures, ventricular dP/dt or the EKG. However, 20 Hz vagal stimulation in the presence of the VIP antagonist did not decrease circumflex mean coronary artery pressure. In addition, vagal stimulation, in the presence of the VIP antagonist, had no effect on LV pressures or dP/dt but increased RV dP/dtmax and dP/dtmin. RV dP/dtmax increased by 16% (p < 0.01) and RV dP/dtmin increased by 22% (p < 0.04), respectively, in series 1 and by 27 and 24%, respectively, in series 2 (both p < 0.01). Vagal nerve stimulation during muscarinic and beta-adrenergic blockade releases VIP or a 'VIP-like' substance that significantly decreases circumflex coronary artery vascular resistance and increases RV dP/dtmax and dP/dtmin.

Regional vascular and cardiac responses to systemic neuropeptide-Y in normal and diabetic rats

Diabetes is associated with altered autonomic activity, and both the peripheral and central nervous content of NPY is altered in diabetes suggesting that part of the cardiovascular dysfunction of diabetes may be associated with altered responses to NPY. We evaluated the mean arterial pressure (MAP), heart rate (HR) and regional blood flow (BF) in response to NPY in normal and diabetic rats. Male Wistar rats were made diabetic using streptozotocin and maintained without insulin treatment for 28-30 days. Normal and diabetic animals were anesthetized, the femoral artery cannulated, and flow probes placed around the iliac, renal and superior mesenteric arteries. Dose dependent responses to NPY infusion were determined for MAP, HR and BF. Conductance was calculated from BF/MAP. In normal rats NPY increased the MAP in a dose-dependent fashion but did not alter the HR. NPY decreased the BF in the iliac artery in a dose-dependent fashion while the renal BF was decreased only at the highest dose, and the superior mesenteric BF was not affected. The conductances in all vascular beds were decreased dose dependently. NPY in diabetic rats also increased MAP and did not affect HR. In diabetic rats NPY also decreased BF in iliac and renal arteries but contrastingly increased BF in the superior mesenteric artery. Again conductances in all three vascular beds were decreased by NPY. When comparing diabetic response to NPY to normals we noted that the MAP response was less in the diabetic, but the HR and regional BF were not different. The vascular conductances in response to NPY were attenuated in the diabetic vessels especially the iliac and superior mesenteric. We conclude that systemic NPY increases MAP as a result of decreased vascular conductance and this vasopressive effect of NPY is diminished in diabetics.

Hypotensive effect of intravenous injection of tachykinins in conscious, freely moving spontaneously hypertensive and Wistar Kyoto rats

The present study evaluated the sensitivity of spontaneously hypertensive (SHR) and of Wistar Kyoto (WKY) rats to the hypotensive effect of tachykinins (TKs). Eledoisin, substance P, and the NK-1-selective agonist [Sar9,Met(O2)11]substance P evoked a smaller hypotensive response in SHR than in WKY rats. The hypotensive effect of NKA was slightly smaller in SHR, but no significant strain difference was observed. The NK-2-selective agonist [beta Ala8]NKA(4-10) was a very weak hypotensive agent in WKY rats, while being completely inactive in SHR. The NK-3-selective agonists [Asp5,6,MePhe8]substance P(5-11) and [MePhe7]NKB did not modify blood pressure in both strains. Heart rate was essentially unmodified following the NK-3 agonists, while it was increased after injection of substance P, [Sar9,Met(O2)11]substance P, and neurokinin A, the increase being greater in WKY than in SHR. Surprisingly, eledoisin increased heart rate in SHR, but not in WKY rats, despite the greater hypotensive effect elicited in the latter strain. The present results confirm that the hypotensive effect of peripheral TKs is mediated by NK-1 receptors and show that SHR are less sensitive than WKY rats to this effect.

Occurrence of CGRP receptors on dedifferentiated smooth muscle cells from media of rat thoracic aorta

Autoradiographic studies with [125I]-CGRP did not demonstrate receptors on sections from two different regions of 5-week-old rat aorta (of both sexes). By contrast, cultured smooth muscle cells isolated from similar aortic media and passaged 5 to 7 times exhibited specific binding.

Sprouting of aberrant neuropeptide Y-immunoreactive sympathetic nerves into neonatally denervated smooth muscle

Sympathetic nerves normally project ipsilaterally to lateral cranial targets. Following unilateral superior cervical ganglionectomy in neonatal rats, however, neurons from the contralateral superior cervical ganglion sprout into the denervated region. In the present study we examined neuropeptide Y immunoreactivity (NPY-ir) of neurons comprising ipsilateral (control) and denervation-induced contralateral pathways to the superior tarsal smooth muscle of the eyelid. Fluoro-Gold injection of the control muscle retrogradely labelled 133 +/- 18 neurons in the ipsilateral superior cervical ganglion; of these, 21 +/- 3% displayed detectable NPY-ir. Fluoro-Gold injections of the reinnervated muscle labelled 20 +/- 4 neurons in the contralateral superior cervical ganglion, of which 85 +/- 3% contained detectable NPY-ir. Examination of the control tarsal muscle revealed DBH-ir noradrenergic nerves throughout the muscle and vasculature, while NPY-ir nerves were present primarily around blood vessels. In the reinnervated preparation, NPY-ir fibers innervated both blood vessels and tarsal muscle in a pattern similar to that of DBH-ir innervation. Acute excision of the remaining superior cervical ganglion eliminated all DBH-ir fibers bilaterally; NPY-ir was reduced markedly in the reinnervated preparations, though some fibers remained. We conclude that, following neonatal denervation, the tarsal muscle is reinnervated by a subpopulation of sympathetic neurons that differs in neuropeptide phenotype from that of the normal ipsilateral innervation.