How the malaria vector Anopheles gambiae adapts to the use of insecticide-treated nets by African populations

Background

Insecticide treated bed nets have been recommended and proven efficient as a measure to protect African populations from malaria mosquito vector Anopheles spp. This study evaluates the consequences of bed nets use on vectors resistance to insecticides, their feeding behavior and malaria transmission in Dielmo village, Senegal, were LLINs were offered to all villagers in July 2008.

Methods

Adult mosquitoes were collected monthly from January 2006 to December 2011 by human landing catches (HLC) and by pyrethroid spray catches (PCS). A randomly selected sub-sample of 15–20% of An. gambiae s.l. collected each month was used to investigate the molecular forms of the An. gambiae complex, kdr mutations, and Plasmodium falciparum circumsporozoite (CSP) rate. Malaria prevalence and gametocytaemia in Dielmo villagers were measured quarterly.

Results

Insecticide susceptible mosquitoes (wild kdr genotype) presented a reduced lifespan after LLINs implementation but they rapidly adapted their feeding behavior, becoming more exophageous and zoophilic, and biting earlier during the night. In the meantime, insecticide-resistant specimens (kdr L1014F genotype) increased in frequency in the population, with an unchanged lifespan and feeding behaviour. P. falciparum prevalence and gametocyte rate in villagers decreased dramatically after LLINs deployment. Malaria infection rate tended to zero in susceptible mosquitoes whereas the infection rate increased markedly in the kdr homozygote mosquitoes.

Conclusion

Dramatic changes in vector populations and their behavior occurred after the deployment of LLINs due to the extraordinary adaptative skills of An. gambiae s. l. mosquitoes. However, despite the increasing proportion of insecticide resistant mosquitoes and their almost exclusive responsibility in malaria transmission, the P. falciparum gametocyte reservoir continued to decrease three years after the deployment of LLINs.

The rise and fall of malaria in a West African rural community, Dielmo, Senegal, from 1990 to 2012: a 22 year longitudinal study

BACKGROUND

A better understanding of the effect of malaria control interventions on vector and parasite populations, acquired immunity, and burden of the disease is needed to guide strategies to eliminate malaria from highly endemic areas. We monitored and analysed the changes in malaria epidemiology in a village community in Senegal, west Africa, over 22 years.

METHODS

Between 1990 and 2012, we did a prospective longitudinal study of the inhabitants of Dielmo, Senegal, to identify all episodes of fever and investigate the relation between malaria host, vector, and parasite. Our study included daily medical surveillance with systematic parasite detection in individuals with fever. We measured parasite prevalence four times a year with cross-sectional surveys. We monitored malaria transmission monthly with night collection of mosquitoes. Malaria treatment changed over the years, from quinine (1990-94), to chloroquine (1995-2003), amodiaquine plus sulfadoxine-pyrimethamine (2003-06), and finally artesunate plus amodiaquine (2006-12). Insecticide-treated nets (ITNs) were introduced in 2008.

FINDINGS

We monitored 776 villagers aged 0-101 years for 2 378 150 person-days of follow-up. Entomological inoculation rate ranged from 142·5 infected bites per person per year in 1990 to 482·6 in 2000, and 7·6 in 2012. Parasite prevalence in children declined from 87% in 1990 to 0·3 % in 2012. In adults, it declined from 58% to 0·3%. We recorded 23 546 fever episodes during the study, including 8243 clinical attacks caused by Plasmodium falciparum, 290 by Plasmodium malariae, and 219 by Plasmodium ovale. Three deaths were directly attributable to malaria, and two to severe adverse events of antimalarial drugs. The incidence of malaria attacks ranged from 1·50 attacks per person-year in 1990 to 2·63 in 2000, and to only 0·046 in 2012. The greatest changes were associated with the replacement of chloroquine and the introduction of ITNs.

INTERPRETATION

Malaria control policies combining prompt treatment of clinical attacks and deployment of ITNs can nearly eliminate parasite carriage and greatly reduce the burden of malaria in populations exposed to intense perennial malaria transmission. The choice of drugs seems crucial. Rapid decline of clinical immunity allows rapid detection and treatment of novel infections and thus has a key role in sustaining effectiveness of combining artemisinin-based combination therapy and ITNs despite increasing pyrethroid resistance.

FUNDING

Pasteur Institutes of Dakar and Paris, Institut de Recherche pour le Développement, and French Ministry of Cooperation.

MALDI-TOF identification of the human Gut microbiome in people with and without diarrhea in Senegal

Background

In Africa, there are several problems with the specific identification of bacteria. Recently, MALDI-TOF mass spectrometry has become a powerful tool for the routine microbial identification in many clinical laboratories.

Methodology/Principal Findings

This study was conducted using feces from 347 individuals (162 with diarrhea and 185 without diarrhea) sampled in health centers in Dakar, Senegal. Feces were transported from Dakar to Marseille, France, where they were cultured using different culture conditions. The isolated colonies were identified using MALDI-TOF. If a colony was unidentified, 16S rRNA sequencing was performed. Overall, 2,753 isolates were tested, allowing for the identification of 189 bacteria from 5 phyla, including 2 previously unknown species, 11 species not previously reported in the human gut, 10 species not previously reported in humans, and 3 fungi. 2,718 bacterial isolates (98.8%) out of 2,750 yielded an accurate identification using mass spectrometry, as did the 3 Candida albicans isolates. Thirty-two bacterial isolates not identified by MALDI-TOF (1.2%) were identified by sequencing, allowing for the identification of 2 new species. The number of bacterial species per fecal sample was significantly higher among patients without diarrhea (8.6±3) than in those with diarrhea (7.3±3.4; P = 0.0003). A modification of the gut microbiota was observed between the two groups. In individuals with diarrhea, major commensal bacterial species such as E. coli were significantly decreased (85% versus 64%), as were several Enterococcus spp. (E. faecium and E. casseliflavus) and anaerobes, such as Bacteroides spp. (B. uniformis and B. vulgatus) and Clostridium spp. (C. bifermentans, C. orbiscindens, C. perfringens, and C. symbosium). Conversely, several Bacillus spp. (B. licheniformis, B. mojavensis, and B. pumilus) were significantly more frequent among patients with diarrhea.

Conclusions/Significance

MALDI-TOF is a potentially powerful tool for routine bacterial identification in Africa, allowing for a quick identification of bacterial species.

Resistance to DDT and pyrethroids and increased kdr mutation frequency in An. gambiae after the implementation of permethrin-treated nets in Senegal

Introduction

The aim of this study was to evaluate the susceptibility to insecticides of An. gambiae mosquitoes sampled in Dielmo (Senegal), in 2010, 2 years after the implementation of Long Lasting Insecticide-treated Nets (LLINs) and to report the evolution of kdr mutation frequency from 2006 to 2010.

Methods

WHO bioassay susceptibility tests to 6 insecticides were performed on adults F0, issuing from immature stages of An. gambiae s.l., sampled in August 2010. Species and molecular forms as well as the presence of L1014F and L1014S kdr mutations were assessed by PCR. Longitudinal study of kdr mutations was performed on adult mosquitoes sampled monthly by night landing catches from 2006 to 2010.

Findings

No specimen studied presented the L1014S mutation. During the longitudinal study, L1014F allelic frequency rose from 2.4% in year before the implementation of LLINs to 4.6% 0–12 months after and 18.7% 13–30 months after. In 2010, An. gambiae were resistant to DDT, Lambda-cyhalothrin, Deltamethrin and Permethrin (mortality rates ranging from 46 to 63%) but highly susceptible to Fenitrothion and Bendiocarb (100% mortality). There was significantly more RR genotype among An. gambiae surviving exposure to DDT or Pyrethroids. An. arabiensis represented 3.7% of the sampled mosquitoes (11/300) with no kdr resistance allele detected. An. gambiae molecular form M represented 29.7% of the mosquitoes with, among them, kdr genotypes SR (18%) and SS (82%). An. gambiae molecular form S represented 66% of the population with, among them, kdr genotype SS (33.3%), SR (55.6%) and RR (11.1%). Only 2 MS hybrid mosquitoes were sampled and presented SS kdr genotype.

Conclusion

Biological evidence of resistance to DDT and pyrethroids was detected among An. gambiae mosquitoes in Dielmo (Senegal) within 24 months of community use of LLINs. Molecular identification of L1014F mutation indicated that target site resistance increased after the implementation of LLINs.

Low and seasonal malaria transmission in the middle Senegal River basin: identification and characteristics of Anopheles vectors

Background

During the last decades two dams were constructed along the Senegal River. These intensified the practice of agriculture along the river valley basin. We conducted a study to assess malaria vector diversity, dynamics and malaria transmission in the area.

Methods

A cross-sectional entomological study was performed in September 2008 in 20 villages of the middle Senegal River valley to evaluate the variations of Anopheles density according to local environment. A longitudinal study was performed, from October 2008 to January 2010, in 5 selected villages, to study seasonal variations of malaria transmission.

Results

Among malaria vectors, 72.34% of specimens collected were An. arabiensis, 5.28% An. gambiae of the S molecular form, 3.26% M form, 12.90% An. pharoensis, 4.70% An. ziemanni, 1.48% An. funestus and 0.04% An. wellcomei. Anopheles density varied according to village location. It ranged from 0 to 21.4 Anopheles/room/day and was significantly correlated with the distance to the nearest ditch water but not to the river.

Seasonal variations of Anopheles density and variety were observed with higher human biting rates during the rainy season (8.28 and 7.55 Anopheles bite/man/night in October 2008 and 2009 respectively). Transmission was low and limited to the rainy season (0.05 and 0.06 infected bite/man/night in October 2008 and 2009 respectively). During the rainy season, the endophagous rate was lower, the anthropophagic rate higher and L1014F kdr frequency higher.

Conclusions

Malaria vectors are present at low-moderate density in the middle Senegal River basin with An. arabiensis as the predominant species. Other potential vectors are An. gambiae M and S form and An. funestus. Nonetheless, malaria transmission was extremely low and seasonal.

[FAV-Africa: a polyvalent antivenom serum used in Africa and Europe]

FAV-Afrique is a polyvalent snake antivenom, elaborated by immunisation of horses with venom from 10 different snake species among the most dangerous in Africa and belonging to Elapidae and Viperidea families. Only F(ab')2 fragments are kept and purified. This serum is able to decrease the quantity of circulating venom and therefore its toxicity. Its use is indicated as soon as the first signs of poisoning are observed (local oedema). Twenty millimetres are administrated via intra-venous route whatever the weight of the patient. Re-administration may be performed if improvement is not sufficient. Treatment should be initiated as soon as possible but can be realized as long as the symptoms are present. Side effects (allergy) should be considered but balanced with the seriousness of poisoning. There is no absolute contraindication or drug interaction reported with FAV-Africa. It is authorized and distributed in several African countries and has a temporary regulatory approval in France. The major limits to its use are high cost and storage conditions (maximum 36 months between +2 degrees C and +8 degrees C). In the future, the new serum Antivipmyn Africa, available as a freeze-dried product, which can be preserved at room temperature, should improve storage conditions and availability of treatment, especially in rural Africa.

Comparative susceptibility to Plasmodium falciparum of the molecular forms M and S of Anopheles gambiae and Anopheles arabiensis

Background

The different taxa belonging to Anopheles gambiae complex display phenotypic differences that may impact their contribution to malaria transmission. More specifically, their susceptibility to infection, resulting from a co-evolution between parasite and vector, might be different. The aim of this study was to compare the susceptibility of M and S molecular forms of Anopheles gambiae and Anopheles arabiensis to infection by Plasmodium falciparum.

Methods

F3 progenies of Anopheles gambiae s.l. collected in Senegal were infected, using direct membrane feeding, with P. falciparum gametocyte-containing blood sampled on volunteer patients. The presence of oocysts was determined by light microscopy after 7 days, and the presence of sporozoite by ELISA after 14 days. Mosquito species and molecular forms were identified by PCR.

Results

The oocyst rate was significantly higher in the molecular S form (79.07%) than in the M form (57.81%, Fisher's exact test p < 0.001) and in Anopheles arabiensis (55.38%, Fisher's exact test vs. S group p < 0.001). Mean ± s.e.m. number of oocyst was greater in the An. gambiae S form (1.72 ± 0.26) than in the An. gambiae M form (0.64 ± 0.04, p < 0.0001) and in the An. arabiensis group (0.58 ± 0.04, vs. S group, p < 0.0001). Sporozoite rate was also higher in the molecular form S (83.52%) than in form M (50.98%, Fisher's exact test p < 0.001) and Anopheles arabiensis 50.85%, Fisher's exact test vs. S group p < 0.001).

Conclusion

Infected in the same experimental conditions, the molecular form S of An. gambiae is more susceptible to infection by P. falciparum than the molecular form M of An. gambiae and An. arabiensis.

Malaria morbidity and pyrethroid resistance after the introduction of insecticide-treated bednets and artemisinin-based combination therapies: a longitudinal study

BACKGROUND

Substantial reductions in malaria have been reported in several African countries after distribution of insecticide-treated bednets and the use of artemisinin-based combination therapies (ACTs). Our aim was to assess the effect of these policies on malaria morbidity, mosquito populations, and asymptomatic infections in a west African rural population.

METHODS

We did a longitudinal study of inhabitants of Dielmo village, Senegal, between January, 2007, and December, 2010. We monitored the inhabitants for fever during this period and we treated malaria attacks with artesunate plus amodiaquine. In July, 2008, we offered longlasting insecticide (deltamethrin)-treated nets (LLINs) to all villagers. We did monthly night collections of mosquitoes during the whole study period, and we assessed asymptomatic carriage from cross-sectional surveys. Our statistical analyses were by negative binomial regression, logistic regression, and binomial or Fisher exact test.

FINDINGS

There were 464 clinical malaria attacks attributable to Plasmodium falciparum during 17,858 person-months of follow-up. The incidence density of malaria attacks averaged 5·45 (95% CI 4·90-6·05) per 100 person-months between January, 2007, and July, 2008, before the distribution of LLINs. Incidence density decreased to 0·41 (0·29-0·55) between August, 2008, and August, 2010, but increased back to 4·57 (3·54-5·82) between September and December, 2010--ie, 27-30 months after the distribution of LLINs. The rebound of malaria attacks were highest in adults and children aged 10 years or older: 45 (63%) of 71 malaria attacks recorded in 2010 compared with 126 (33%) of 384 in 2007 and 2008 (p<0·0001). 37% of Anopheles gambiae mosquitoes were resistant to deltamethrin in 2010, and the prevalence of the Leu1014Phe kdr resistance mutation increased from 8% in 2007 to 48% in 2010 (p=0·0009).

INTERPRETATION

Increasing pyrethroid resistance of A gambiae and increasing susceptibility of older children and adults, probably due to decreasing immunity, caused the rebound and age shift of malaria morbidity. Strategies to address the problem of insecticide resistance and to mitigate its effects must be urgently defined and implemented.

FUNDING

Institut de Recherche pour le Développement and the Pasteur Institute of Dakar.

Highly protective effects of chronic oral administration of nicorandil on the heart of ageing rats

1. We have tested the effects of 2 month oral treatment with the KATP opener, nitric oxide (NO) donor and anti-oxidant molecule nicorandil (0.1 mg/kg per day) on major physiological parameters and heart function of 4-, 12- and 24-month-old rats. 2. Several methods were used: (i) measurement of blood pressure using a non-invasive tail-cuff method; (ii) perfusion of isolated heart; (iii) lactate dehydrogenase (LDH) dosage; and (iv) measurement of monophasic action potential of rat isolated hearts. 3. Blood pressure and ventricular action potential duration regularly increase with age in control animals, whereas nicorandil restores these parameters in aged animals to levels present in young adult animals. Moreover, following ischaemia, nicorandil treatment improved isolated heart survival rate (100 vs. 50% for nicorandil-treated rats and controls, respectively), heart work and left ventricular developed pressure, whereas it decreased cardiac cell damage (LDH release) and perfusion pressure. 4. This condition of chronic oral nicorandil treatment presents a strong potential in the improvement of cardiac function in normal and pathological ageing.

Endothelial kinin B(1)-receptors are induced by myocardial ischaemia-reperfusion in the rabbit

Kinin B1-receptors are induced by various inflammatory stimuli. Since myocardial ischaemia-reperfusion results in inflammation, we questioned whether it could induce B1-receptor-dependent responses to des-Arg9-bradykinin (DBK). Thirty-six rabbits were submitted either to a 30 min coronary occlusion followed by a 3 h reperfusion or to a sham operation. The response to DBK was then tested in vivo on mean arterial pressure (MAP) and in vitro on isolated hearts and arterial rings. DBK induced a dose-dependent decrease in MAP in the ischaemia-reperfusion group (DBK, 10 microg kg(-1), intra-arterial: -12 +/- 2 vs. -5 +/- 2 mm Hg in the sham group, P < 0.02), which was significantly antagonised by [Leu8]-des-Arg9-bradykinin (LBK), a B1-receptor antagonist. Following ischaemia-reperfusion, isolated hearts responded to DBK by a decrease in coronary perfusion pressure greater than that of the sham group. DBK dose-dependently decreased the isometric force of isolated carotid rings (DBK, 10(-5) M: -9 +/- 2 vs. -1 +/- 2% in the sham group, P < 0.02) and mesenteric arteries (DBK, 10-6 M: -38 +/- 7% vs. -3 +/- 2 % in the sham group, P < 0.001). The vascular effects of DBK seen after ischaemia-reperfusion were significantly antagonised by LBK. The presence of B1-receptors in ischaemia-reperfusion animals was confirmed by immunolocalisation and Western blot analysis. This study demonstrates that myocardial ischaemia-reperfusion induces a global induction of functional kinin B1-receptors in the endothelium.

Delayed myocardial protection induced by endotoxin does not involve kinin B(1)-receptors

Endotoxin is known to confer a delayed protection against myocardial infarction. Lipopolysaccharide (LPS) treatment also induces the de novo synthesis of kinin B(1)-receptors that are not present in normal conditions. The aim of this study was to evaluate whether LPS-induced B(1)-receptors are implicated in the reduction of infarct size brought about by LPS. Rabbits were submitted to a 30-min coronary artery occlusion and 3-h reperfusion sequence. Six groups were studied: pretreated or not (control animals) with LPS (5 microgram kg(-1) i.v.) 24 h earlier and treated 15 min before and throughout ischaemia - reperfusion with either the B(1)-antagonist R-715 (1 mg kg(-1) h(-1)), the B(1)-agonist Sar-[D-Phe(8)]-des-Arg(9)-bradykinin (15 microgram kg(-1) h(-1)) or vehicle (saline). Infarct size and area at risk were assessed by differential staining and planimetric analysis. The presence of B(1)-receptors in LPS-pretreated animals was confirmed by a decrease in mean arterial pressure in response to B(1) stimulation. LPS-pretreatment significantly reduced infarct size (6.4+/-1.7%, of area at risk vs 24.1+/-2.5% in control animals, P<0.05). This protection was not modified by B(1)-receptor antagonism (7.4+/-2.2%, NS) or stimulation (5.2+/-1.2%, NS). Neither antagonist nor agonist modified infarct size in control animals. In conclusion, these data suggest that LPS-induced myocardial protection in the rabbit is not related to concomitant de novo B(1)-receptor induction.

Galpha(i2)-mRNA and -protein regulation as a mechanism for heterologous sensitization and desensitization of insulin secretion

Prolonged exposure of cells to an agonist of a G-protein-coupled receptor usually results in an attenuation of the cellular response. To elucidate the cellular mechanisms of sensitization or desensitization in an insulin secretory cell system (INS-1 cells), we investigated a regulatory link between G-protein alpha(s)- and alpha(i2)-subunits mRNA, their protein levels and insulin secretion as the biological effect using various compounds. Incubation with epinephrine (50 microM) for 8 h decreased alpha(s)- and alpha(i2)-mRNA levels to 58% and 72%, respectively, which is reversed after a longer incubation. From results using isoprenaline and the alpha2-agonist UK 14,304 epinephrine is shown to mediate its actions via alpha2- but not beta-adrenoceptors. The insulin inhibitory neuropeptide galanin (50 nM) caused a decrease of alpha(s)- and alpha(i2)-mRNA levels, whereas insulinotropic compounds (incretin hormones) such as GIP or GLP-1 (both 10 nM) led to an increase of alpha(s)- and alpha(i2)-mRNA levels. By using the Ca2+ channel blocker verapamil (50 microM) alpha(i2)-mRNA changes clearly depend on Ca2+ influx. The effects on alpha(i2)-mRNA were accompanied by a parallel, albeit weaker effect on the protein level (only GIP and UK 14,304 were investigated). The changes in alpha(i2)-mRNA levels by either compound were paralleled by inverse changes in insulin secretion: preincubation with UK 14,304 for 8 h led to an increased insulin secretion when challenged by either GLP-1, GIP or glucose (8.3 mM). This was similar for galanin, another potent inhibitor of insulin release. On the other hand, exposure to the incretins GIP or GLP-1 for 8 h induced a smaller insulin release when challenged afterwards by either UK 14,304, galanin, GIP, GLP-1, or glucose. Thus the influence on insulin secretion of various compounds is reciprocal to the regulation of alpha(i2)-mRNA levels but not alpha(s)-mRNA levels. There is, therefore, evidence from all the manoeuvres used that alpha(i2)-mRNA regulation may play a role in heterologous sensitization and desensitization of insulin secretion.

Histamine H3-receptor stimulation is unable to modulate noradrenaline release by the isolated rat heart during ischaemia-reperfusion

The aim of this study was to evaluate the ability of H3-histaminergic prejunctional receptors to modulate the noradrenaline release induced by myocardial ischaemia in the rat, and the effects of an eventual modulation on haemodynamic, biochemical and electrophysiological parameters. Isolated rat hearts were perfused according to the Langendorff technique. Control hearts (n = 13) were not treated; two groups were treated with the H3-agonist R-alpha-methyl-histamine at 0.3 microM (n = 14) and 1 microM (n = 11) and one group, used as positive control, was treated with the selective alpha 2-agonist Mivazerol at 0.5 microM (n = 14) added to the perfusion medium. Noradrenaline, lactate and transaminase output in the coronary effluent, as well as various haemodynamic and electrophysiological parameters, were measured during global and total ischaemia (30 min) and reperfusion (30 min). alpha 2-receptor stimulation increased ischaemia-induced noradrenaline release during reperfusion (195 +/- 13 vs. 145 +/- 12 pmol.g-1 in control group, P < 0.05). In contrast, R-alpha-methyl-histamine, at both doses, did not significantly modify these parameters. Both treatments did not affect ischaemia- and reperfusion-induced haemodynamic (decrease in heart rate or in left ventricular developed pressure), biochemical (lactate and GOT release) and electrophysiological (arrhythmias or increase in action potential duration) alterations. Unlike other species, the rat appears to be insensitive to H3-histaminergic receptor modulation of ischaemia-induced noradrenaline release, although a modulation can be seen with other prejunctional receptor agonists.

Monophosphoryl lipid A, a derivative of bacterial lipopolysaccharide, fails to induce B1-receptor-dependent responses to (des-Arg9)-bradykinin in the rabbit in vivo

OBJECTIVE

The aim of this study was to evaluate whether monophosphoryl lipid A (MLA) was able to induce a hypotensive response to (des-Arg9)-bradykinin in the rabbit in vivo, by inducing B1-receptor synthesis.

MATERIALS AND METHODS

Arterial pressure was measured after intra-arterial administration of B1- and B2-receptor agonists and antagonists in control rabbits and in rabbits pre-treated 24 h earlier with MLA (100 microg kg(-1) i.v.) or lipopolysaccharide (LPS) (10 microg kg(-1) i.v.).

RESULTS

Intra-arterial bradykinin administration induced a similar dose-dependent hypotension in all groups (BK 0.25 microg kg(-1), 36 +/- 3 mm Hg, BK 1 microg kg(-1), -39 +/- 3 mm Hg, p < 0.05 vs. control conditions) that was significantly antagonised by intra-arterial HOE 140 (2 microg kg(-1)) (-5 +/- 2 mm Hg, p < 0.05). Intra-arterial (des-Arg9)-bradykinin induced a hypotensive response in the LPS-pre-treated group (DBK 1 microg kg(-1), -6 +/- 1 mm Hg, DBK 10 microg kg(-1), -10 +/- 1 mm Hg, p < 0.05 vs. control conditions) that was totally abolished by intra-arterial (des-Arg9, Leu8)-bradykinin (10 microg kg(-1) min(-1)) (+1 +/- 2 mm Hg, p < 0.05). In the control and MLA-pre-treated groups, (des-Arg9)-bradykinin had no effect.

CONCLUSION

MLA pre-treatment did not induce a hypotensive response to (des-Arg9)-bradykinin. We conclude that, in contrast to LPS, MLA does not induce B1-receptor synthesis, 24 h after its administration in the rabbit. Thus, the cardioprotective effects of MLA do not appear to be related to the kinin pathway.

In vivo demonstration of H3-histaminergic inhibition of cardiac sympathetic stimulation by R-alpha-methyl-histamine and its prodrug BP 2.94 in the dog

1. The aim of this study was to investigate whether histamine H3-receptor agonists could inhibit the effects of cardiac sympathetic nerve stimulation in the dog. 2. Catecholamine release by the heart and the associated variation of haemodynamic parameters were measured after electrical stimulation of the right cardiac sympathetic nerves (1-4 Hz, 10 V, 10 ms) in the anaesthetized dog treated with R-alpha-methyl-histamine (R-HA) and its prodrug BP 2.94 (BP). 3. Cardiac sympathetic stimulation induced a noradrenaline release into the coronary sinus along with a tachycardia and an increase in left ventricular pressure and contractility without changes in mean arterial pressure. Intravenous administration of H3-receptor agonists significantly decreased noradrenaline release by the heart (R-HA at 2 micromol kg(-1) h(-1): +77 +/- 25 vs +405 +/- 82; BP 2.94 at 1 mg kg(-1): +12 +/- 11 vs +330 +/- 100 pg ml(-1) in control conditions, P < or = 0.05), and increases in heart rate (R-HA at 2 micromol kg(-1) h(-1): +26 +/- 8 vs +65 +/- 10 and BP 2.94 at 1 mg kg(-1): +30 +/- 8 vs 75 +/- 6 beats min(-1), in control conditions P < or = 0.05), left ventricular pressure, and contractility. Treatment with SC 359 (1 mg kg(-1)) a selective H3-antagonist, reversed the effects of H3-receptor agonists. Treatment with R-HA at 2 micromol kg(-1) h(-1) and BP 2.94 at 1 mg kg(-1) tended to decrease, while that with SC 359 significantly increased basal heart rate (from 111 +/- 3 to 130 +/- 5 beats min(-1), P < or = 0.001). 4. Functional H3-receptors are present on sympathetic nerve endings in the dog heart. Their stimulation by R-alpha-methyl-histamine or BP 2.94 can inhibit noradrenaline release by the heart and its associated haemodynamic effects.