Dopamine-1 receptor stimulation attenuates the vasoconstrictive response to gut ischemia

DR1 Activation Inhibits the Proliferation of Vascular Smooth Muscle Cells through Increasing Endogenous H2S in Diabetes

Tissue ischemia and hypoxia caused by the abnormal proliferation of smooth muscle cells (SMCs) in the diabetic state is an important pathological basis for diabetic microangiopathy. Studies in recent years have shown that the chronic complications of diabetes are related to the decrease of endogenous hydrogen sulfide (H₂S) in diabetic patients, and it has been proven that H₂S can inhibit the proliferation of vascular SMCs (VSMCs). Our study showed that the endogenous H₂S content and the expression of cystathionine gamma-lyase (CSE), which is the key enzyme of H₂S production, were decreased in arterial SMCs of diabetic mice. The expression of PCNA and Cyclin D1 was increased, and the expression of p21 was decreased in the diabetic state. After administration of dopamine 1-like receptors (DR1) agonist SKF38393 and exogenous H₂S donor NaHS, the expression of CSE was increased and the change in proliferation-related proteins caused by diabetes was reversed. It was further verified by cell experiments that SKF38393 activated calmodulin (CaM) by increasing the intracellular calcium ([Ca²⁺]_i) concentration, which activated the CSE/H₂S pathway, enhancing the H₂S content in vivo. We also found that SKF38393 and NaHS inhibited insulin-like growth factor-1 (IGF-1)/IGF-1R and heparin-binding EGF-like growth factor (HB-EGF)/EGFR, as well as their downstream PI3K/Akt, JAK2/STAT3 and ERK1/2 pathways. Taken together, our results suggest that DR1 activation up-regulates the CSE/H₂S system by increasing Ca²⁺-CaM binding, which inhibits the IGF-1/IGF-1R and HB-EGF/EGFR pathways, thereby decreasing their downstream PI3K/Akt, JAK2/STAT3 and ERK1/2 pathways to achieve the effect of inhibiting HG-induced VSMCs proliferation.

Effects of dobutamine, dopamine, phenylephrine and noradrenaline on systemic haemodynamics and intestinal perfusion in isoflurane anaesthetised horses

BACKGROUND

In the horse, effects of cardiovascular-active drugs on local perfusion of the gastrointestinal tract are poorly understood.

OBJECTIVES

To determine the effect of drugs commonly used to support blood pressure, on local intestinal blood flow and tissue oxygenation under isoflurane anaesthesia.

STUDY DESIGN

In vivo randomised crossover experiment.

METHODS

Ten horses were anaesthetised with isoflurane. After 90 min of equilibration three doses (μg/kg bwt/min) of dobutamine (DOB 0.5/1/3), dopamine (DA 1/2/5), noradrenaline (NA 0.1/0.2/0.5) and phenylephrine (PHE 0.5/1/3) were infused for 15 min, in a randomised order, with a 45 min washout-period. Blood flow and tissue oxygenation (sO₂ ) of jejunum, colon and stomach were measured using white light remission spectrophotometry and laser doppler flowmetry; heart rate (HR), mean arterial blood pressure (MAP), cardiac output (CO) were measured and systemic vascular resistance (SVR) calculated.

RESULTS

Compared to baseline high dose dobutamine significantly increased CO, HR, MAP (P<0.001) and blood flow to the jejunum (+47 ± 26%, P = 0.001) and colon (+29 ± 15%, P<0.001) (mean ± s.d.). Dopamine (DA5) increased CO but decreased colonic blood flow (-39 ± 21% from baseline, P<0.001), as well as SVR and MAP compared to baseline (P<0.001). Noradrenaline had no significant influence on intestinal perfusion, but increased MAP and SVR from baseline (P<0.001). Phenylephrine (PHE3) caused a significant decrease in blood flow and sO₂ , most profoundly at the colon compared to baseline (flow -44 ± 21%; sO₂ -16 ± 3%, P<0.001), while MAP and SVR increased and CO and HR decreased (P<0.001).

MAIN LIMITATIONS

The measurement technique only allows for flow measurements in arbitrary units, which can limit comparability to other techniques.

CONCLUSION

At the investigated doses dobutamine improved systemic and peripheral haemodynamics, while dopamine decreased MAP and peripheral perfusion. Noradrenaline increased MAP and SVR while peripheral blood flow was maintained, phenylephrine increased MAP, but reduced both local and systemic perfusion.

Dopamine under α1-blockade, but not dopamine alone or fenoldopam, increases depressed gastric mucosal oxygenation*

OBJECTIVE

To compare the effects of dopamine, both in the presence and absence of alpha1-blockade, and fenoldopam on microvascular gastric mucosal oxygenation and systemic oxygen transport under compromised circulatory conditions, both without and with fluid resuscitation.

DESIGN

Randomized controlled animal study.

SETTING

University department of anesthesiology.

SUBJECTS

Eight anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output.

INTERVENTIONS

On different days, the dogs received in random order either dopamine (2.5 and 5.0 microg.kg(-1).min(-1), with or without alpha1-blocker pretreatment), the selective DA1-agonist fenoldopam (0.1 and 1.0 microg.kg(-1).min(-1), with and without DA1-blocker pretreatment), or saline (control). These interventions were performed under compromised cardiocirculatory conditions (induced by ventilation with positive end-expiratory pressure [PEEP] of 10 cm H2O), both without and with fluid resuscitation.

MEASUREMENTS AND MAIN RESULTS

We continuously measured regional microvascular hemoglobin saturation (microHbO2) in gastric mucosa by reflectance spectrophotometry and systemic oxygen transport ([U1E0A]O2). Ventilation with PEEP significantly decreased [U1E0A]O2 (from 19 +/- 2 to 9 +/- 1 mL.kg(-1).min(-1), mean +/- sem) and gastric mucosal microHbO2 (from 57 +/- 2% to 37 +/- 3%). Fluid resuscitation restored [U1E0A]O2 back to baseline (from 9 +/- 1 to 19 +/- 2 mL.kg(-1).min(-1)) but only partially restored microHbO2 (from 37 +/- 3% to 50 +/- 4%). Under both conditions, dopamine with and without alpha1-blockade significantly increased [U1E0A]O2 (by about 5 mL.kg-1.min-1 in the nonresuscitated state and 10 mL.kg-1.min-1 in the fluid resuscitated state, respectively), but only dopamine in the presence of alpha1-blockade also significantly increased gastric mucosal microHbO2 (by 5 +/- 1% and 7 +/- 2% in the nonresuscitated and fluid resuscitated states, respectively). Fenoldopam under all study conditions did not significantly affect [U1E0A]O2 or microHbO2, either in the presence or absence of DA1-blockade.

CONCLUSIONS

During compromised cardiocirculatory conditions, alpha1-receptor activation during dopamine infusion prevented an increase in gastric mucosal oxygenation. Furthermore, selective DA1-stimulation (by fenoldopam) was insufficient to overcome the PEEP-induced depression of microHbO2. The responses of gastric mucosal oxygenation did not parallel changes in systemic oxygen transport. These findings were independent of fluid resuscitation.

Fenoldopam--but not dopamine--selectively increases gastric mucosal oxygenation in dogs

OBJECTIVE

To compare the effects of fenoldopam and dopamine on gastric mucosal and systemic oxygenation, and to identify the receptors involved.

DESIGN

Randomized controlled animal study.

SETTING

University research department of experimental anesthesiology. SUBJECTS Seven anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output.

INTERVENTIONS

On different days, the dogs received in random order either the selective DA(1)-agonist fenoldopam (0.1 and 1.0 microg x kg-1.= x min-1, with or without DA(1)-blocker pretreatment), dopamine (2.5 and 5.0 microg.kg-1 x min-1, with or without alpha(1)-blocker pretreatment), or saline (control).

MEASUREMENTS AND MAIN RESULTS

We continuously measured regional microvascular hemoglobin oxygen saturation (muHbO(2)) in gastric mucosa by reflectance spectrophotometry, and systemic oxygen delivery. Fenoldopam increased gastric mucosal muHbO(2) by approximately 20%, and this effect was prevented by selective DA(1)-receptor blockade. In contrast, dopamine neither alone nor during alpha(1)-blockade altered muHbO(2). With respect to systemic measures of oxygen transport, fenoldopam had negligible effects, whereas dopamine (with and without alpha(1)-blocker pretreatment) dose-dependently increased cardiac output and systemic oxygen delivery by approximately 30%.

CONCLUSIONS

Fenoldopam dose-dependently increased microvascular oxygenation of the gastric mucosa without changing systemic oxygen transport, i.e., this drug acted selectively on the splanchnic mucosa. The increase in gastric mucosal oxygenation was mediated by DA(1)-receptors. In contrast, dopamine markedly increased systemic oxygen transport, but did not affect microvascular oxygenation of gastric mucosa. This lacking effect on gastric mucosal oxygenation was not caused by alpha(1)-mediated vasoconstriction. The regional effects of both catecholamines could not be deduced from systemic hemodynamics and oxygenation.

Splanchnic blood flow in low-flow states

IMPLICATIONS

Insufficient splanchnic blood flow in critically ill patients is the result of a multitude of different diseases, treatment modalities and their interplay, and is associated with increased morbidity and mortality. A combination of diminished and heterogeneous mesenteric blood flow, impaired or exhausted regulatory mechanisms and adverse drug effects may coexist with normal systemic hemodynamics.

Effect of extracellular volume expansion and surgical stress on splanchnic blood flow and cardiac output in anesthetized rats: role of nitric oxide

In a normal volume state, surgical stress decreases rather than increases nitric oxide (NO) production in the vascular system. In our studies, the effect of minor and major surgical stress and three different degrees of volume expansion on systemic and splanchnic circulatory parameters and on the NO dependence of the circulation have been investigated. When the degree of volume expansion was increased, cardiac output and organ blood flow increased without significant change in vascular resistances. Major surgical stress reduced the increase in cardiac output and organ blood flow elicited by the volume expansion. NO synthase (NOS) inhibition significantly increased blood pressure and total peripheral resistance (TPR) and decreased cardiac output in all groups of animals. As the degree of volume expansion was increased, the NO dependence of the circulation in the surgically less- and more-stressed animals was inversely influenced in some cases. With the three degrees of volume expansion (20, 40, and 60 ml/kg), the NOS inhibition increased the TPR from 30.7 R/kg +/- 1.90 to 73.6 R/kg +/- 5.00, from 20.7 R/kg +/- 1.43 to 66.7 R/kg +/- 3.88, and from 19.9 R/kg +/- 1.25 to 49.1 R/kg +/- 3.84 in the surgically less-stressed animals and from 38.6 R/kg +/- 2.14 to 59.8 R/kg +/- 5.62, from 31.9 R/kg +/- 2.70 to 81.7 R/kg +/- 9.89, and from 29.1 R/kg +/- 2.49 to 91.1 R/kg +/- 6.36 in the surgically more-stressed animals. Volume expansion increases the NO dependence of the vascular resistance in the surgically more-stressed animals but decreases it in the surgically less-stressed animals.

Dopamine-1 receptor stimulation impairs intestinal oxygen utilization during critical hypoperfusion

Effects of a dopamine-1 (DA-1) receptor agonist on systemic and intestinal oxygen delivery (Do(2))-uptake relationships were studied in anesthetized dogs during sequential hemorrhage. Control (group 1) and experimental animals (group 2) were treated similarly except for the addition of fenoldopam (1.0 microg x kg(-1) x min(-1)) in group 2. Both groups had comparable systemic critical Do(2) (Do(2crit)), but animals in group 2 had a higher gut Do(2crit) (1.12 +/- 1.13 vs. 0.80 +/- 0.09 ml. kg(-1) x min(-1), P < 0.05). At the mucosal level, a clear biphasic delivery-uptake relationship was not observed in group 1; thus oxygen consumption by the mucosa may be supply dependent under physiological conditions. Group 2 demonstrated higher peak mucosal blood flow and lack of supply dependency at higher mucosal Do(2) levels. Fenoldopam resulted in a more conspicuous biphasic relationship at the mucosa and a rightward shift of overall splanchnic Do(2crit) despite increased splanchnic blood flow. These findings suggest that DA-1 receptor stimulation results in increased gut perfusion heterogeneity and maldistribution of perfusion, resulting in increased susceptibility to ischemia.

Clinical review: splanchnic ischaemia

Inadequate splanchnic perfusion is associated with increased morbidity and mortality, particularly if liver dysfunction coexists. Heart failure, increased intra-abdominal pressure, haemodialysis and the presence of obstructive sleep apnoea are among the multiple clinical conditions that are associated with impaired splanchnic perfusion in critically ill patients. Total liver blood flow is believed to be relatively protected when gut blood flow decreases, because hepatic arterial flow increases when portal venous flow decreases (the hepatic arterial buffer response [HABR]). However, there is evidence that the HABR is diminished or even abolished during endotoxaemia and when gut blood flow becomes very low. Unfortunately, no drugs are yet available that increase total hepato-splanchnic blood flow selectively and to a clinically relevant extent. The present review discusses old and new concepts of splanchnic vasoregulation from both experimental and clinical viewpoints. Recently published trials in this field are discussed.