Major contribution of vasospasm-induced coronary blood flow reduction to anaphylactic ventricular dysfunction assessed in isolated blood-perfused rat heart

Background: Cardiac anaphylaxis is accompanied by coronary spasm and decreased left ventricular (LV) contractility. However, it has not been determined experimentally whether LV dysfunction during anaphylaxis is induced mainly by reduced coronary blood flow (CBF) or direct negative inotropic actions of chemical mediators. To demonstrate the major role of CBF reduction in anaphylactic LV dysfunction, we determined LV contractility during anaphylaxis and forcible CBF reduction maneuver to reproduce the anaphylaxis-induced CBF reduction in isolated blood-perfused rat hearts.Methods: Isolated hearts from Wistar rats in the ovalbumin-sensitized anaphylaxis, non-sensitized flow reduction, and non-sensitized time control group were subjected to coronary perfusion with blood at a constant pressure and measurements of CBF and LV pressure. Cardiac anaphylaxis was induced by intracoronary injections of ovalbumin antigen.Results: In response to antigen administrations, sensitized anaphylaxis group rat hearts showed decreases in CBF and the maximum increasing rate of systolic LV pressure (dP/dtmax) with an increased coronary vascular resistance as evidence of coronary spasm. The non-sensitized flow reduction group rat hearts whose CBF was forcibly reduced as in anaphylaxis showed the same degree of dP/dtmax reduction.Conclusions: The contractile failure during cardiac anaphylaxis is caused mainly by decreased CBF due to coronary spasm

Blockade of β2-adrenoceptor, rather than β1-adrenoceptor, deteriorates cardiac anaphylaxis in isolated blood-perfused rat hearts

  Background: Cardiac anaphylaxis is one of the features of anaphylactic hypotension. Patients treated with propranolol, a nonselective β-adrenoceptor (AR) antagonist, develop severe anaphylaxis, but the mechanism remains unknown. Under examination were the effects of β1- and β2-AR antagonist on anaphylaxis-induced coronary vasoconstriction and cardiac dysfunction in isolated blood-perfused rat hearts. Methods: Isolated hearts from ovalbumin-sensitized Wistar rats were subjected to coronary perfusion with blood at a constant pressure and measurements were made of coronary blood flow and left ventricu­lar (LV) pressure. Following pretreatment with selective β2-AR antagonist ICI118,551 or selective β1-AR antagonist atenolol, cardiac anaphylaxis was induced by intracoronary injections of ovalbumin antigen. LV contractility was evaluated by the maximum increasing rate of systolic LV pressure (dP/dtmax). Results: In response to antigen administrations, ICI118,551 pretreated hearts showed a greater de­crease in coronary blood flow and consequently a greater increase in coronary vascular resistance than the atenolol pretreated hearts. Pretreatment with ICI118,551 caused a greater decrease in dP/dtmax than those with atenolol. Conclusions: Cardiac anaphylaxis-induced contractile dysfunction and coronary spasm are severe in b2-, rather than β1-AR antagonist, pretreated isolated blood-perfused rat hearts

Establishment of an Endogenous Clostridium difficile Rat Infection Model and Evaluation of the Effects of Clostridium butyricum MIYAIRI 588 Probiotic Strain

Clostridium difficile is well known as an agent responsible for pseudomembranous colitis and antibiotic-associated diarrhea. The hamster model utilizing an oral route for infection of C. difficile has been considered to be the standard model for analysis of C. difficile infection (CDI) but this model exhibits differences to human CDI, most notably as most hamsters die without exhibiting diarrhea. Therefore, we attempted to develop a new non-lethal and diarrheal rat CDI model caused by endogenous C. difficile using metronidazole (MNZ) and egg white. In addition, the effects of probiotic strain Clostridium butyricum MIYAIRI 588 (CBM) on CDI were examined using this model. Syrian Golden hamsters received clindamycin phosphate orally at 30 mg/kg on 5 days before challenge with either C. difficile VPI10463 (hypertoxigenic strain) or KY34 (low toxigenic clinical isolate). Mortality and the presence of diarrhea were observed twice a day for the duration of the experiment. Wistar rats received 10% egg white dissolved in drinking water for 1 week ad libitum following intramuscular administration of 200 mg/kg MNZ twice a day for 3 days. Diarrhea score was determined for each day and fecal water content, biotin concentration, and cytotoxin titer in feces were examined. More than 70% of hamsters orally infected with C. difficile died without exhibiting diarrhea regardless of toxigenicity of strain. The rats receiving egg white after MNZ administration developed diarrhea due to overgrowth of endogenous C. difficile. This CDI model is non-lethal and diarrheal, and some rats in this model were spontaneously cured. The incidence of diarrhea was significantly decreased in C. butyricum treated rats. These results indicate that the CDI model using egg white and MNZ has potentially better similarity to human CDI, and implies that treatment with C. butyricum may reduce the risk of CDI

Effects of anesthetics on the renal sympathetic response to anaphylactic hypotension in rats.

The autonomic nervous system plays an important role in rat anaphylactic hypotension. It is well known that sympathetic nerve activity and cardiovascular function are affected by anesthetics. However, the effects of different types of anesthesia on the efferent renal sympathetic nerve activity (RSNA) during anaphylactic hypotension remain unknown. Therefore, we determined the renal sympathetic responses to anaphylactic hypotension in anesthetized and conscious rats and the roles of baroreceptors in these responses. Sprague-Dawley rats were randomly allocated to anesthetic groups that were given pentobarbital, urethane, or ketamine-xylazine and to a conscious group. The rats were sensitized using subcutaneously injected ovalbumin. The systemic arterial pressure (SAP), RSNA and heart rate (HR) were measured. The effects of sinoaortic baroreceptor denervation on RSNA during anaphylaxis were determined in pentobarbital-anesthetized and conscious rats. In all of the sensitized rats, the RSNA increased and SAP decreased after antigen injection. At the early phase within 35 min of the antigen injection, the antigen-induced sympathoexcitation in the conscious rats was significantly greater than that in the anesthetized rats. Anaphylactic hypotension was attenuated in the conscious rats compared to the anesthetized rats. The anesthetic-induced suppression of SAP and RSNA was greater in the order ketamine-xylazine >urethane = pentobarbital. Indeed, in the rats treated with ketamine-xylazine, RSNA did not increase until 40 min, and SAP remained at low levels after the antigen injection. The baroreceptor reflex, as evaluated by increases in RSNA and HR in response to the decrease in SAP induced by sodium nitroprusside (SNP), was suppressed in the anesthetized rats compared with the conscious rats. Consistent with this finding, baroreceptor denervation attenuated the excitatory responses of RSNA to anaphylaxis in the conscious rats but not in the pentobarbital-anesthetized rats. RSNA was increased markedly in conscious rats during anaphylactic hypotension. Anesthetics attenuated this antigen-induced renal sympathoexcitation through the suppression of baroreceptor function

The Role of Lumbar Sympathetic Nerves in Regulation of Blood Flow to Skeletal Muscle during Anaphylactic Hypotension in Anesthetized Rats.

During hypovolemic shock, skeletal muscle blood flow could be redistributed to vital organs via vasoconstriction in part evoked by activation of the innervating sympathetic nerve activity. However, it is not well known whether this mechanism operates during anaphylactic shock. We determined the femoral artery blood flow (FBF) and lumbar sympathetic nerve activity (LSNA) mainly regulating the hindquater muscle blood flow during anaphylactic hypotension in anesthetized rats. Anesthetized Sprague-Dawley rats were randomly allocated to the following groups (n = 7/group): (1) non-sensitized, (2) anaphylaxis, (3) anaphylaxis-lumbar sympathectomy (LS) and (4) anaphylaxis-sinoaortic denervation (SAD) groups. Anaphylaxis was induced by an intravenous injection of the ovalbumin antigen to the sensitized rats. The systemic arterial pressure (SAP), heart rate (HR), central venous pressure (CVP), FBF and LSNA were continuously measured. In the anaphylaxis group, LSNA and HR increased, while SAP and FBF decreased after antigen injection. In the anaphylaxis-SAD group, LSNA did not significantly change during the early phase, but the responses of SAP and FBF were similar to those in the anaphylaxis group. In the anaphylaxis-LS group, both FBF and SAP decreased similarly to the anaphylaxis group during anaphylactic hypotension. These results indicated that LSNA increased via baroreceptor reflex, but this sympathoexcitation or LS did not affect antigen-induced decreases in FBF or SAP. Lumbar sympathetic nerves are not involved in regulation of the blood flow to the hindlimb or systemic blood pressure during anaphylactic hypotension in anesthetized rats