Vasoactive intestinal polypeptide antagonists attenuate vagally induced tachycardia in the anesthetized dog

Pseudoaneurysm of thoracic aorta presenting as inappropriate sinus tachycardia: a case report

BACKGROUND

Pseudoaneurysm of thoracic aorta as a complication of blunt trauma to the chest, can present with a variety of symptoms due to mass compression effect. Here we report the first pseudoaneurysm of thoracic aorta presenting with chronic cough and inappropriate sinus tachycardia. The purpose of this case report is to highlight pseudoaneurysm of thoracic aorta as a rare differential diagnosis for inappropriate sinus tachycardia.

CASE PRESENTATION

Here we report a case of 29-year-old white woman, a nurse, with history of a motor vehicle accident. She initially presented to medical attention with inappropriate sinus tachycardia 2 years following the motor vehicle accident during her pregnancy. Six years later she underwent sinoatrial node modification after failing a number of medications. Days prior to the ablation she developed a mild cough which became constant within a week following ablation. A computed tomography scan of her chest performed as part of a workup revealed an outpouching of the inferomedial aspect of the aortic arch, which was compressing her left main bronchus. She underwent arch repair surgery and recovered without complications. Four years later she presented with significant symptomatic sinus bradycardia requiring pacemaker placement.

CONCLUSIONS

This is the first reported case of thoracic pseudoaneurysm of aorta presenting with inappropriate sinus tachycardia due to compression of the vagal nerve and cough as a result of the left main bronchus compressive effect; it highlights the importance of considering structural abnormalities in a differential diagnosis of inappropriate sinus tachycardia before any interventions.

Device-based autonomic modulation in arrhythmia patients: the role of vagal nerve stimulation

OPINION STATEMENT

Vagal nerve stimulation (VNS) has shown promise as an adjunctive therapy for management of cardiac arrhythmias by targeting the cardiac parasympathetic nervous system. VNS has been evaluated in the setting of ischemia-driven ventricular arrhythmias and atrial arrhythmias, as well as a treatment option for heart failure. As better understanding of the complexities of the cardiac autonomic nervous system is obtained, vagal nerve stimulation will likely become a powerful tool in the current cardiovascular therapeutic armamentarium.

Neuronally released vasoactive intestinal polypeptide alters atrial electrophysiological properties and may promote atrial fibrillation

BACKGROUND

Vagal hyperactivity promotes atrial fibrillation (AF), which has been almost exclusively attributed to acetylcholine. Vasoactive intestinal polypeptide (VIP) and acetylcholine are neurotransmitters co-released during vagal stimulation. Exogenous VIP has been shown to promote AF by shortening action potential duration (APD), increasing APD spatial heterogeneity, and causing intra-atrial conduction block.

OBJECTIVE

The purpose of this study was to investigate the effects of neuronally released VIP on atrial electrophysiologic properties during vagal stimulation.

METHODS

We used a specific VIP antagonist (H9935) to uncover the effects of endogenous VIP released during vagal stimulation in canine hearts.

RESULTS

H9935 significantly attenuated (1) the vagally induced shortening of atrial effective refractory period and widening of atrial vulnerability window during stimulation of cervical vagosympathetic trunks (VCNS) and (2) vagal effects on APD during stimulation through fat-pad ganglion plexus (VGPS). Atropine completely abolished these vagal effects during VCNS and VGPS. In contrast, VGPS-induced slowing of local conduction velocity was completely abolished by either VIP antagonist or atropine. In pacing-induced AF during VGPS, maximal dominant frequencies and their spatial gradients were reduced significantly by H9935 and, more pronouncedly, by atropine. Furthermore, VIP release in the atria during vagal stimulation was inhibited by atropine, which may account for the concealment of VIP effects with muscarinic blockade.

CONCLUSION

Neuronally released VIP contributes to vagal effects on atrial electrophysiologic properties and affects the pathophysiology of vagally induced AF. Neuronal release of VIP in the atria is inhibited by muscarinic blockade, a novel mechanism by which VIP effects are concealed by atropine during vagal stimulation.

Decreased adrenoceptor stimulation in heart failure rats reduces NGF expression by cardiac parasympathetic neurons

Postganglionic cardiac parasympathetic and sympathetic nerves are physically proximate in atrial cardiac tissue allowing reciprocal inhibition of neurotransmitter release, depending on demands from central cardiovascular centers or reflex pathways. Parasympathetic cardiac ganglion (CG) neurons synthesize and release the sympathetic neurotrophin nerve growth factor (NGF), which may serve to maintain these close connections. In this study we investigated whether NGF synthesis by CG neurons is altered in heart failure, and whether norepinephrine from sympathetic neurons promotes NGF synthesis. NGF and proNGF immunoreactivity in CG neurons in heart failure rats following chronic coronary artery ligation was investigated. NGF immunoreactivity was decreased significantly in heart failure rats compared to sham-operated animals, whereas proNGF expression was unchanged. Changes in neurochemistry of CG neurons included attenuated expression of the cholinergic marker vesicular acetylcholine transporter, and increased expression of the neuropeptide vasoactive intestinal polypeptide. To further investigate norepinephrine's role in promoting NGF synthesis, we cultured CG neurons treated with adrenergic receptor (AR) agonists. An 82% increase in NGF mRNA levels was detected after 1h of isoproterenol (β-AR agonist) treatment, which increased an additional 22% at 24h. Antagonist treatment blocked isoproterenol-induced increases in NGF transcripts. In contrast, the α-AR agonist phenylephrine did not alter NGF mRNA expression. These results are consistent with β-AR mediated maintenance of NGF synthesis in CG neurons. In heart failure, a decrease in NGF synthesis by CG neurons may potentially contribute to reduced connections with adjacent sympathetic nerves.

Vagal postganglionic origin of vasoactive intestinal polypeptide (VIP) mediating the vagal tachycardia

Our aim was to confirm the role of postganglionic vagal fibres and vasoactive intestinal polypeptide (VIP) in mediating the vagal tachycardia in anaesthetised dogs. Vagal postganglionic stimulation after atenolol (1 mg/kg) and hexamethonium (10 mg/kg) caused a bradycardia (40 beats/min, n = 2), after atropine (0.5 mg/kg i.v.) the resulting tachycardia (37 beats/min) was attenuated by VIP receptor antagonism with VIP (6-28) (100 mug i.c.) by approximately 50%. VIP release from vagal postganglionic fibres mediates the vagal tachycardia.

Evidence for a role for vasoactive intestinal peptide in active vasodilatation in the cutaneous vasculature of humans

Active vasodilatation (AVD) in human, non-glabrous skin depends on functional cholinergic fibres but not on acetylcholine (ACh). We tested whether AVD is a redundant system in which ACh and vasoactive intestinal polypeptide (VIP) are co-released from cholinergic nerves. (1) We administered VIP by intradermal microdialysis to four discrete areas of skin in the presence of different levels of the VIP receptor antagonist, VIP(10-28), also delivered by microdialysis. Skin blood flow (SkBF) was continuously monitored by laser Doppler flowmetry (LDF). Mean arterial pressure (MAP) was measured non-invasively and cutaneous vascular conductance (CVC) calculated as LDF/MAP. Subjects were supine and wore water-perfused suits to control whole-body skin temperature (Tsk) at 34 degrees C. Concentrations of 54 microM, 107 microM, or 214 microM VIP(10-28) were perfused via intradermal microdialysis at 2 microl min-1 for approximately 1 h. Then 7.5 microM VIP was added to the perfusate containing VIP(10-28) at the three concentrations or Ringer solution and perfusion was continued for 45-60 min. At the control site, this level of VIP caused approximately the vasodilatation typical of heat stress. All VIP(10-28)-treated sites displayed an attenuated dilatation in response to the VIP. The greatest attenuation was observed at the site that received 214 microM VIP(10-28) (P < 0.01). (2) We used 214 microM VIP(10-28) alone and with the iontophoretically administered muscarinic receptor antagonist atropine (400 microA cm-2, 45 s, 10 mM) in heated subjects to test the roles of VIP and ACh in AVD. Ringer solution and 214 microM VIP(10-28) were each perfused at two sites, one of which in each case was pretreated with atropine. After 1 h of VIP(10-28) treatment, individuals underwent 45-60 min of whole-body heating (Tsk to 38.5 degrees C). VIP(10-28), alone or in combination with atropine, attenuated the increase in CVC during heat stress, suggesting an important role for VIP in AVD.

Role of PAC(1) receptor in adrenal catecholamine secretion induced by PACAP and VIP in vivo

The present study was conducted to investigate the functional implication of the pituitary adenylate cyclase-activating polypeptide (PACAP) type I (PAC(1)) receptor in the adrenal catecholamine (CA) secretion induced by either PACAP-27 or vasoactive intestinal polypeptide (VIP) in anesthetized dogs. PACAP-27, VIP, and their respective antagonists were locally infused to the left adrenal gland via the left adrenolumbar artery. Plasma CA concentrations in adrenal venous and aortic blood were determined by means of a high-performance liquid chromatograph coupled with an electrochemical detector. Adrenal venous blood flow was measured by gravimetry. The administration of PACAP-27 (50 ng) resulted in a significant increase in adrenal CA output. VIP (5 microg) also increased the basal CA secretion to an extent comparable to that observed with PACAP-27. In the presence of PACAP partial sequence 6--27 [PACAP-(6--27); a PAC(1) receptor antagonist] at the doses of 7.5 and 15 microg, the CA response to PACAP-27 was attenuated by approximately 50 and approximately 95%, respectively. Although the CA secretagogue effect of VIP was blocked by approximately 85% in the presence of PACAP-(6--27) (15 microg), it remained unaffected by VIP partial sequence 10--28 [VIP-(10--28); a VIP receptor antagonist] at the dose of 15 microg. Furthermore, the CA response to PACAP-27 did not change in the presence of the same dose of VIP--(10--28). The results indicate that PACAP-(6--27) diminished, in a dose-dependent manner, the increase in adrenal CA secretion induced by PACAP-27. The results also indicate that the CA response to either PACAP-27 or VIP was selectively inhibited by PACAP-(6--27) but not by VIP-(10--28). It is concluded that PAC(1) receptor is primarily involved in the CA secretion induced by both PACAP-27 and VIP in the canine adrenal medulla in vivo.

Characterization of VIP receptor-effector system antagonists in rat and mouse peritoneal macrophages

In the present study we show that the synthetic peptides [4-Cl-D-Phe6,Leu17]VIP and the growth hormone releasing factor (GRF) analog [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 inhibit in a competitive manner the specific [125I]VIP binding to both rat and mouse peritoneal macrophages. In rat peritoneal macrophages, the order of potency of the different peptides, as expressed by the IC50 values was: VIP (IC50 = 1.90 +/- 0.16 nM) > [4-Cl-D-Phe6,Leu17]VIP (IC50 = 125.8 +/- 13.2 nM) > [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 (IC50 = 354.8 +/- 21.2 nM). In mouse peritoneal macrophages a similar pattern of potency was observed: VIP (IC50 = 1.58 +/- 0.12 nM) > [4-Cl-D-Phe6,Leu17]VIP (IC50 = 110.8 +/- 10.7 nM) > [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 (IC50 = 251 +/- 19.2 nM). The behavior as VIP receptor antagonists of both [4-Cl-D-Phe6,Leu17]VIP and [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 in rat and mouse peritoneal macrophages was confirmed by: (a) the shift to the right of VIP dose-stimulated cyclic AMP production curves in the presence of the two antagonists; (b) the agreement between the order of efficacy of the two peptides in competition experiments with the corresponding inhibition of cyclic AMP production; (c) the inefficiency of the two antagonists on the stimulation of cyclic AMP production by the beta-adrenoceptor agonist isoproterenol, which indicates the specificity of the interaction; (d) the synergic effect of VIP on isoproterenol-stimulated cyclic AMP production was completely abolished by [4-Cl-D-Phe6,Leu17]VIP or [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2, suggesting that both antagonists acted via specific VIP receptors. Moreover, propranolol, a beta-adrenoceptor antagonist, did not affect the VIP-stimulated cyclic AMP production and the antagonist role of [4-Cl-D-Phe6,Leu17]VIP or [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2; (e) in cross-linking experiments, the intensity of the labeling of the [125I]VIP/receptor complexes was significantly lower with the antagonists than in the control experimental situation in both mouse and rat peritoneal macrophage membranes.