Marked synergism between vasopressin and angiotensin II in a human isolated artery

Impaired angiotensin II signaling in septic shock

Recent years have seen a resurgence of interest for the renin-angiotensin-aldosterone system in critically ill patients. Emerging data suggest that this vital homeostatic system, which plays a crucial role in maintaining systemic and renal hemodynamics during stressful conditions, is altered in septic shock, ultimately leading to impaired angiotensin II-angiotensin II type 1 receptor signaling. Indeed, available evidence from both experimental models and human studies indicates that alterations in the renin-angiotensin-aldosterone system during septic shock can occur at three distinct levels: 1. Impaired generation of angiotensin II, possibly attributable to defects in angiotensin-converting enzyme activity; 2. Enhanced degradation of angiotensin II by peptidases; and/or 3. Unavailability of angiotensin II type 1 receptor due to internalization or reduced synthesis. These alterations can occur either independently or in combination, ultimately leading to an uncoupling between the renin-angiotensin-aldosterone system input and downstream angiotensin II type 1 receptor signaling. It remains unclear whether exogenous angiotensin II infusion can adequately address all these mechanisms, and additional interventions may be required. These observations open a new avenue of research and offer the potential for novel therapeutic strategies to improve patient prognosis. In the near future, a deeper understanding of renin-angiotensin-aldosterone system alterations in septic shock should help to decipher patients' phenotypes and to implement targeted interventions.

Multimodal strategy to counteract vasodilation in septic shock

Early initiation of a multimodal treatment strategy in the management of vasopressors during septic shock has been advocated to reduce delays in restoring adequate organ perfusion and to mitigate side effects associated with the administration of high-dose catecholamines. We provide a review that summarises the pathophysiology of vasodilation, the physiologic response to the vascular response, and the different drugs used in this situation, focusing on the need to combine early different vasopressors. Fluid loading being insufficient for counteracting vasoplegia, norepinephrine is usually the first-line vasopressor used to restore hemodynamics. Norepinephrine sparing is discussed in further detail through the concomitant use of adrenergic, vasopressinergic, and renin-angiotensin systems and the optimisation of endothelial reactivity with methylene blue. A blueprint for the construction of new studies is outlined to address the question of vasopressor selection and timing in septic shock.

Selepressin in Septic Shock

ABSTRACT

Sepsis and septic shock usually show a high mortality rate and frequently need of intensive care unit admissions. After fluid resuscitation, norepinephrine (NE) is the first-choice vasopressor in septic shock patients. However, high-NE doses are associated with increased rates of adverse effects and mortality. In this perspective, many authors have proposed the administration of non-adrenergic vasopressors (NAV). Selepressin is a selective vasopressin type 1A (V1A) receptor agonist and may be a valid option in this field, because it can decrease NE requirements and also limit the deleterious effects induced by high doses of catecholamines. Only few clinical data actually support selepressin administration in this setting. Here, we review the current literature on this topic analyzing some pathophysiological aspects, the rationale about the use of NAV, the possible use of selepressin differentiating animal, and human studies. Various issues remain unresolved and future trials should be focused on early interventions based on a multimodal activation of the vasopressive pathways using both alpha and V1A receptors pathways.

Effect of adding vasopressin on the distribution of lidocaine in tissues, anesthetic action, and circulatory dynamics

We examined whether vasopressin affects the distribution, anesthesia duration, and circulatory dynamics of lidocaine. Blood flow was measured after injecting 0.003, 0.03, or 0.3 U/mL vasopressin and 2% lidocaine (L) to the upper lip of rats. Radioactivity and distribution of ¹⁴C-labeled L (CL) in the palate, palatal mucosa, maxilla bone, and blood was measured by autoradiography after injecting CL and CL + 0.03 U/mL vasopressin. To evaluate anesthesia duration, somatosensory-evoked potentials, blood pressure, and pulse rate were measured after L, 0.03 U/mL vasopressin, and L + 0.03 U/mL vasopressin injection to the palatal mucosa. Blood flow from 10 to 60 min was significantly lower with 0.03 U/mL vasopressin and L + 0.03 U/mL vasopressin than with L. Radioactivity in the palatal mucosa and maxilla bone was significantly higher at 5-60 min and 2-60 min with CL + 0.03 U/mL vasopressin than with CL. Blood radioactivity reached the maximum at 0.5 and 50 min with CL and CL + 0.03 U/mL vasopressin, respectively. Autoradiogram showed higher distribution with CL + 0.03 U/mL vasopressin than CL. Peak-to-peak amplitude 30-60 min was significantly lower with L + 0.03 U/mL vasopressin than with L. Lidocaine did not affect blood pressure and pulse rate with 0.03 U/mL vasopressin-only or combined with 2%-lidocaine. Topical 0.03 U/mL vasopressin injection reduced the tissue blood flow, promoted the localization and retention, and extended the anesthesia duration of lidocaine, leaving circulatory dynamics unaffected.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Sympathetic innervation of the splanchnic region mediates the beneficial hemodynamic effects of 8-OH-DPAT in hemorrhagic shock

Administration of the 5-HT(1A) receptor agonist, 8-OH-DPAT, improves cardiovascular hemodynamics and tissue oxygenation in conscious rats subjected to hypovolemic shock. This effect is mediated by sympathetic-dependent increases in venous tone. To determine the role of splanchnic nerves in this response, effects of 8-OH-DPAT (30 nmol/kg iv) were measured following fixed-arterial blood pressure hemorrhagic shock (i.e., maintenance of 50 mmHg arterial pressure for 25 min) in rats subjected to bilateral splanchnic nerve denervation (SD). Splanchnic denervation decreased baseline venous tone as measured by mean circulatory filling pressure (MCFP) and accelerated the onset of hypotension during blood loss. Splanchnic denervation did not affect the immediate pressor effect of 8-OH-DPAT but did reverse the drug's lasting pressor effect, as well as its ability to increase MCFP and improve metabolic acidosis. Like SD, adrenal demedullation (ADMX) lowered baseline MCFP and accelerated the hypotensive response to blood withdrawal but also reduced the volume of blood withdrawal required to maintain arterial blood pressure at 50 mmHg. 8-OH-DPAT raised MCFP early after administration in ADMX rats, but the response did not persist throughout the posthemorrhage period. In a fixed-volume hemorrhage model, 8-OH-DPAT continued to raise blood pressure in ADMX rats. However, it produced only a transient and variable rise in MCFP compared with sham-operated animals. The data indicate that 8-OH-DPAT increases venoconstriction and improves acid-base balance in hypovolemic rats through activation of splanchnic nerves. This effect is due, in part, to activation of the adrenal medulla.

Vascular reactivity in human arteries: from experimental study to clinical application

The principal function of VSM cells in mature animals is contraction. The endothelium is now recognized to elaborate various vasoactive factors and to play a critical part in regulation of vascular tone. Many circulating mediators and hormones have effects on vascular tone that are mediated via multiple receptors. Vasoactive agents also exert their effects on tissues by acting on one or more processes in the contraction–relaxation cycle in VSM. In humans,systemic, pulmonary, and various organ circulation(s) are maintained by an intricate and complex cardiovascular system. We expect future studies to clarify the sophisticated but complex mechanisms of VSM in humans.

Vasopressin-induced vasoconstriction: two concentration-dependent signaling pathways

Current scientific literature generally attributes the vasoconstrictor effects of [Arg(8)]vasopressin (AVP) to the activation of phospholipase C (PLC) and consequent release of Ca(2+) from the sarcoplasmic reticulum. However, half-maximal activation of PLC requires nanomolar concentrations of AVP, whereas vasoconstriction occurs when circulating concentrations of AVP are orders of magnitude lower. Using cultured vascular smooth muscle cells, we previously identified a novel Ca(2+) signaling pathway activated by 10-100 pM AVP. This pathway is distinguished from the PLC pathway by its dependence on protein kinase C (PKC) and L-type voltage-sensitive Ca(2+) channels (VSCC). In the present study, we used isolated, pressurized rat mesenteric arteries to examine the contributions of these different Ca(2+) signaling mechanisms to AVP-induced vasoconstriction. AVP (10(-14)-10(-6) M) induced a concentration-dependent constriction of arteries that was reversible with a V(1a) vasopressin receptor antagonist. Half-maximal vasoconstriction at 30 pM AVP was prevented by blockade of VSCC with verapamil (10 microM) or by PKC inhibition with calphostin-C (250 nM) or Ro-31-8220 (1 microM). In contrast, acute vasoconstriction induced by 10 nM AVP (maximal) was insensitive to blockade of VSCC or PKC inhibition. However, after 30 min, the remaining vasoconstriction induced by 10 nM AVP was partially dependent on PKC activation and almost fully dependent on VSCC. These results suggest that different Ca(2+) signaling mechanisms contribute to AVP-induced vasoconstriction over different ranges of AVP concentration. Vasoconstrictor actions of AVP, at concentrations of AVP found within the systemic circulation, utilize a Ca(2+) signaling pathway that is dependent on PKC activation and can be inhibited by Ca(2+) channel blockers.