Effect of intravenous dopamine on blood pressure and plasma insulin in hypertensive patients

Dopaminergic Regulation of Innate Immunity: a Review

Dopamine (DA) is a neurotransmitter in the central nervous system as well as in peripheral tissues. Emerging evidence however points to DA also as a key transmitter between the nervous system and the immune system as well as a mediator produced and released by immune cells themselves. Dopaminergic pathways have received so far extensive attention in the adaptive branch of the immune system, where they play a role in health and disease such as multiple sclerosis, rheumatoid arthritis, cancer, and Parkinson's disease. Comparatively little is known about DA and the innate immune response, although DA may affect innate immune system cells such as dendritic cells, macrophages, microglia, and neutrophils. The present review aims at providing a complete and exhaustive summary of currently available evidence about DA and innate immunity, and to become a reference for anyone potentially interested in the fields of immunology, neurosciences and pharmacology. A wide array of dopaminergic drugs is used in therapeutics for non-immune indications, such as Parkinson's disease, hyperprolactinemia, shock, hypertension, with a usually favorable therapeutic index, and they might be relatively easily repurposed for immune-mediated disease, thus leading to innovative treatments at low price, with benefit for patients as well as for the healthcare systems.

Effects of metoclopramide on duodenal motility and flow events, glucose absorption, and incretin hormone release in response to intraduodenal glucose infusion

The contribution of small intestinal motor activity to nutrient absorption is poorly defined. A reduction in duodenal flow events after hyoscine butylbromide, despite no change in pressure waves, was associated with reduced secretion of the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) and a delay in glucose absorption. The aim of this study was to investigate the effect of metoclopramide on duodenal motility and flow events, incretin hormone secretion, and glucose absorption. Eight healthy volunteers (7 males and 1 female; age 29.8 ± 4.6 yr; body mass index 24.5 ± 0.9 kg/m²) were studied two times in randomized order. A combined manometry and impedance catheter was used to measure pressure waves and flow events in the same region of the duodenum simultaneously. Metoclopramide (10 mg) or control was administered intravenously as a bolus, followed by an intraduodenal glucose infusion for 60 min (3 kcal/min) incorporating the ¹⁴C-labeled glucose analog 3-O-methylglucose (3-OMG). We found that metoclopramide was associated with more duodenal pressure waves and propagated pressure sequences than control (P < 0.05 for both) during intraduodenal glucose infusion. However, the number of duodenal flow events, blood glucose concentration, and plasma 3-[¹⁴C]OMG activity did not differ between the two study days. Metoclopramide was associated with increased plasma concentrations of GLP-1 (P < 0.05) and GIP (P = 0.07) but lower plasma insulin concentrations (P < 0.05). We concluded that metoclopramide was associated with increased frequency of duodenal pressure waves but no change in duodenal flow events and glucose absorption. Furthermore, GLP-1 and GIP release increased with metoclopramide, but insulin release paradoxically decreased.

Effects of metoclopramide and metoclopramide/dopamine on blood pressure and insulin release in normotensive, hypertensive, and type 2 diabetic subjects

The objective is to determine cardiovascular and insulin release effects under metoclopramide (MTC) and dopamine (DA) infusion by using an acute comparative design with the intravenous infusion of both drugs. We evaluated 15 normal (normotensive and normoglycemic) subjects, 13 hypertensive, and 15 type 2 diabetic subjects. Subjects were submitted to an experimental design in which we first gave them a 0.9% saline solution for 30 minutes, and then administered MTC at 7.5 microg kg min through an intravenous infusion during a period of 30 minutes. Although subjects were receiving MTC, we added an intravenous infusion of DA at 1-3 microg kg min during 30 minutes. Blood pressure, heart rate, serum lipid profile, and insulin levels were measured. Sympathetic reactivity by the cold pressor test was also measured. In normotensive subjects, there was a systolic blood pressure and heart rate increase during MTC plus DA infusion. In subjects with diabetes mellitus there was a heart rate increase without changes in blood pressure during the MTC plus DA infusion period. In hypertensive subjects, MTC induced a significant decrease of systolic and diastolic blood pressure. During MTC plus DA period there was an increase of heart rate but no significant changes in blood pressure. During cold pressor test in both diabetic and hypertensive subjects, there were significant increases of both blood pressure and heart rate. Insulin serum levels increased in normotensive and hypertensive subjects but were attenuated in subjects with diabetes mellitus. We conclude that there is a pharmacologic interaction between MTC and DA, that the pressor effects of DA are due to activation to beta and alpha adrenergic receptors, and that the cardiovascular effects of DA in type 2 diabetic subjects are attenuated by a probable defect in sympathetic system and to endothelial dysfunction.

Dopamine type 2 receptor expression and function in rodent sensory neurons projecting to the airways

Agonists of the dopamine receptors have been demonstrated to have bronchodilatory properties in pathologically constricted airways. The mechanism by which these agonists induce bronchodilatation is thought to involve airway sensory nerves. In this study, the expression and function of dopamine D(2) receptor were examined in sensory ganglia supplying the airways. Neuronal dopamine D(2) receptor mRNA expression was demonstrated by single-cell RT-PCR following laser-assisted microdissection. The projection of the neurons to the airways was confirmed by retrograde neuronal labeling. In functional studies, dopamine D(2) receptor agonists (AR-C65116AB and ropinirole) inhibited intraneuronal calcium mobilization in rat capsaicin-sensitive primary sensory neurons and capsaicin-induced plasma extravasation in the rat trachea. Our results provide support to the hypothesis that dopamine D(2) receptor activation inhibits neurogenic inflammation and proinflammatory reflex responses.

The actions of dopamine on the airways

BACKGROUND

Dopamine exerts inhibitory and excitatory effects on different systems. In the lungs, dopamine modulates respiratory functions through carotid bodies and modulates pulmonary blood vessel tone, alveolar liquids, and bronchial exchange, and possibly participates in the regulation of airways diameter. It has been reported that dopamine has no acute effect on human airways in normal subjects or those with asthma background. However, inhaled or infused dopamine decreased histamine-induced bronchoconstriction in both normal and asthmatic subjects. We have examined the possible modulating effect of dopamine on bronchial diameter by administering inhaled dopamine and the DA2 dopaminergic blocker metoclopramide to subjects with various degrees of bronchial tone.

METHODS

We examined 56 volunteers. Arterial blood pressure and heart rate were determined in every subject. By means of spirometry, we measured forced vital capacity, forced expiratory volume in the first second, maximal forced expiratory flow, and forced expiratory flow at 50% of vital capacity, before and after each treatment. By inhalation with a nebulizer, we administered dopamine (0.5 microg/kg/min) to 10 healthy subjects, 10 subjects with asthma without acute bronchospasm, and 16 subjects with acute asthma attack; intravenous metoclopramide (7 microg/kg/min) was administered to 10 healthy subjects and 10 subjects with asthma without acute bronchospasm. For ethical reasons, metoclopramide was not used in subjects with acute asthma attack.

STATISTICS

non-parametric Wilcoxon tests for paired samples, ANOVA tests, and Bonferroni multiple comparison tests were performed.

RESULTS

Inhaled dopamine increased forced expiratory volume in the first second, forced vital capacity, maximal forced expiratory flow, and forced expiratory flow at 50% of vital capacity in the acute asthma attack group, but there were no modifications in the healthy group or in the asthma without acute bronchospasm group. Metoclopramide did not induce changes in respiratory parameters in healthy individuals or in those with asthma without acute bronchospasm.

CONCLUSIONS

Inhaled dopamine was able to induce bronchodilatation when the bronchial tone was already increased by acute asthma attack, but it did not modify the resting bronchial tone in normals or in asthmatics without acute bronchospasm. DA2 blockade with metoclopramide did not modify resting bronchial tone either. We suggest that dopamine exerts a modulatory effect on bronchial tone of human airways depending on the degree of existing basal tone.

Dopamine, hypertension and obesity

Dopamine, a neurotransmitter, precursor of noradrenaline, is responsible for cardiovascular and renal actions, such as increase in myocardial contractility and cardiac output, without changes in heart rate, producing passive and active vasodilatation, diuresis and natriuresis. These cardiovascular and renal actions take place through the interaction with dopamine receptors, D(1), D(2), D(3), D(4), and D(5). Recent findings point to the possibility of D(6) and D(7)receptors. Dopamine is known to influence the control of arterial pressure by influencing the central and peripheral nervous system and target organs such as kidneys and adrenal glands, in some types of hypertension. Although dopamine and its derivatives have been shown to have antihypertensive effects, these are still being studied; therefore it is important to explain some physiological and pharmacological aspects of dopamine, its receptors, and the clinical uses it could have in the treatment of arterial hypertension and more recently in obesity, based on evidence proving a clear association between obesity and the decrease in the expression of D(2) receptors in the brain of obese persons.

Dopaminergic modulation of human bronchial tone

BACKGROUND

Dopamine exerts inhibitory and excitatory effects on different systems. Its effect on human bronchial tone is controversial. It has been reported that dopamine has no acute effect on human airways from normal subjects or those with asthma background. However, inhaled or infused dopamine decreased histamine-induced bronchoconstriction in both normal and asthmatic subjects.

METHODS

We examined the possible modulating effect of dopamine on bronchial diameter by administering inhaled dopamine and the DA(2) dopaminergic blocker metoclopramide (MTC) to subjects with various degrees of bronchial tone. We examined 50 volunteers. Arterial blood pressure and heart rate were determined in each subject. By means of spirometry, we measured forced vital capacity (FVC), forced expiratory volume in the first second (FEV(1)), maximal forced expiratory flow (FEF(max)), and forced expiratory flow at 50% of vital capacity (FEF(50)), before and after each treatment. By inhalation with a nebulizer, we administered the following: a) dopamine (0.5 microg/kg/min) to 10 healthy subjects, 10 subjects with asthma without acute bronchospasm (AWAB), and nine subjects with acute asthma attack (AAA), and b) intravenous (i.v.) metoclopramide (7 microg/kg/min) was administered to 10 healthy subjects and 11 subjects with AWAB. For ethical reasons, MTC was not used in subjects with acute asthma attack. Non-parametric Wilcoxon test for paired samples, ANOVA test, and Bonferroni multiple comparison test were performed. Inhaled dopamine increased FEV(1) and FVC, FEF(max), and FEF(50) in the AAA group, but there were no modifications in the healthy group or in the AWAB group. Metoclopramide did not induce changes in respiratory parameters in healthy individuals or in those with AWAB.

CONCLUSIONS

Inhaled dopamine is able to induce bronchodilatation when the bronchial tone is already increased by acute asthma attack but did not modify the resting bronchial tone in normal subjects or in asthmatics without acute bronchospasm. Additionally, DA(2) blockade with metoclopramide did not modify resting bronchial tone. Dopamine exerts a modulatory effect on the bronchial tone of human airways depending on the degree of preexisting tone.