Doxorubicin affects the cardiac muscarinic system in the rat.

During the study on the mechanism of doxorubicin-induced cardiotoxicity, we observed that a long incubation (4 hr) with doxorubicin reduced the maximal negative inotropic effects of a muscarinic receptor agonist, carbachol. The mechanism responsible for this doxorubicin-induced reduction of the efficacy of carbachol was examined in isolated guinea pig hearts. In isolated left atrial muscle preparations, 1 hr incubation with 100 microM doxorubicin caused a parallel right-ward shift of the concentration-response curves for carbachol, but a longer (4 hr) incubation with this agent (30, 100 or 200 microM), caused a significant reduction of the magnitude of the negative inotropic effect of carbachol in addition to the concentration-dependent parallel right-ward shift. The 4-hr incubation with these concentrations of doxorubicin also reduced the maximal negative inotropic effect of an adenosine A1 receptor agonist, R-phenylisopropyl adenosine (R-PIA), without affecting the potency of this agonist. Doxorubicin (1 to 100 microM) reduced [3H]quinuclidinyl benzilate (QNB) binding in a concentration dependent manner, but failed to alter [3HIR-PIA binding. The decrease in the magnitude of the maximal negative inotropic effect by doxorubicin was caused by changes in the muscarinic system at steps common to the transduction of muscarinic and adenosine A1 receptor mechanisms.     

Anticholinergic effects of artemisinin, an antimalarial drug, in isolated guinea pig heart preparations

Concern has been growing about the cardiac toxicity of antimalarial drugs. Artemisinin, a unique type of antimalarial drug originating from a Chinese medicinal plant, has minimal adverse effects, but it has been reported to inhibit delayed rectifier potassium current, a voltage-gated potassium current. However, no studies have been published concerning the effect of artemisinin on ligand-gated potassium currents. Therefore, in the present study, we examined the influence of artemisinin on the acetylcholine receptor-operated potassium current (IK.ACh), a ligand-gated potassium current, in guinea pig atrial myocytes using a patch clamp technique. Artemisinin (1 to 300 microM) inhibited I(K.ACh) induced by extracellular application of both carbachol (1 microM) and adenosine (10 microM) and that induced by intracellular loading of GTPgammaS (100 microM) in a concentration-dependent manner. Artemisinin inhibited carbachol-induced, adenosine-induced, and GTPgammaS-activated IK.ACh within almost the same concentration range. In left atria, artemisinin (1 to 100 microM) partially reversed the shortening of action potential duration induced by carbachol in a concentration-dependent manner. Carbachol-induced negative inotropic action in left atria was also inhibited by artemisinin (10 to 300 microM). In conclusion, we suggest that the anticholinergic action of artemisinin is mediated through inhibition of IK.ACh via inhibition of the muscarinic potassium channel and/or associated GTP-binding proteins.     

Diazepam potentiates the positive inotropic effects of histamine and forskolin in guinea-pig papillary muscles

There have been diverse reports on the effects of diazepam on cardiac contractility. The purpose of this study was to examine whether diazepam modifies the inotropic response elicited by histamine on an isolated guinea-pig papillary muscle. The responses of electrically driven papillary muscle to histamine and cyclic AMP-related inotropic agents were recorded in the absence and in the presence of diazepam. Histamine and forskolin, which directly stimulate adenylate cyclase, significantly increased the contractile force in the papillary muscle in a concentration-dependent manner. A histaminergic H₂-receptor antagonist, cimetidine, but not a H₁-receptor antagonist, diphenhydramine, at 10 μ M produced a rightward shift in the concentration-response curve for histamine. Diazepam (10 μ M ) shifted the concentration-response curve for histamine and forskolin to the left by 1.8 and 1.6 times, respectively. Neither a central type (fulmazenil) nor a peripheral type (PK11195) of benzodiazepine receptor antagonist modified the effect of diazepam on the histaminergic-evoked contraction. Phosphodiesterase blockade by 3-isobutyl-1-methylxanthine shifted the concentration-dependent curve for histamine to the left. A combination of 3-isobutyl-1-methylxanthine also produced a leftward shift of the curve. However, there was no significant difference between the 3-isobutyl-1-methylxanthine only group and the combination group. These results indicate that diazepam potentiates the positive inotropic effect produced by histamine, probably mediated via an increase in cyclic AMP levels induced by histamine.     

Capsaicin-induced relaxation in rabbit coronary artery.

In the present study mechanism of inhibitory effects of capsaicin on the contractility of rabbit coronary artery were studied by measurement of isometric tension and intracellular Ca2+ concentration. Capsaicin (1 microM to 30 microM) relaxed the coronary artery pre-contracted with prostaglandin (PG) F2alpha (1 microM) in a concentration-dependent manner. The PGF2alpha-induced increase in intracellular Ca2+ concentration was also inhibited. The effects of capsaicin were readily reversed by washing capsaicin from the bath. Capsaicin-induced relaxation was not attenuated by pretreatment with capsazepine (1 microM), a blocker of vanilloid receptor or ruthenium red (1 microM), a blocker of non-selective cation channel. Previous exposure to a high concentration of capsaicin (100 microM) or repeated application of capsaicin did not eliminate the relaxation response to subsequent application of capsaicin. Increasing the external K+ concentration to 80 mM significantly attenuated the capsaicin-induced relaxation with simultaneous change in intracellular Ca2+ concentration. Pretreatment with iberiotoxin (100 nM), a blocker of Ca2+-activated K+ channel, only partially inhibited the capsaicin-induced relaxation. However, application of 4-aminopyridine (4-AP, 1 mM), a blocker of delayed rectifier K+ current significantly inhibited the capsaicin-induced relaxation with concomitant attenuation of the effect on intracellular Ca2+ concentration. These results indicate that capsaicin may have a direct relaxing effect on the smooth muscle contractility, and relaxation may be due to activation of the 4-AP-sensitive, delayed rectifier K+ channels in the rabbit coronary artery.     

Mechanisms responsible for reduced cardiotoxicity of mitoxantrone compared to doxorubicin examined in isolated guinea-pig heart preparations

We reported previously that doxorubicin, an anticancer agent that has an anthracycline structure, alters Ca2+ releasing and uptake mechanisms in the sarcoplasmic reticulum of myocardial cells. These effects of doxorubicin are apparently related to its cardiotoxicity. Mitoxantrone is a similar anticancer agent with an anthracenedion structure that has been shown to be significantly less cardiotoxic. In the present study, the effects of mitoxantrone on the functions of the sarcoplasmic reticulum were examined in isolated muscle preparations obtained from the guinea-pig heart. In electrically-stimulated left atrial muscle preparations, incubation in vitro for 4 hr with 30 or 100 microM mitoxantrone significantly prolonged the time to the peak of twitch tension, markedly increased the developed tension observed at lower stimulation frequencies, thereby attenuating the slope of positive force-frequency relationships, and increased the postrest contraction observed after a 60-sec quiescent period. In myocytes isolated from ventricular muscles, 30 microM mitoxantrone increased the peak and the size of intracellular Ca2+ concentrations ([Ca2+] i), and prolonged the time to peak [Ca2+]i. In skinned muscle fiber preparations obtained from the left ventricular muscle, 30 muM mitoxantrone significantly increased the caffeine-induced contraction without affecting the Ca2+ sensitivity of contractile proteins. These results suggest that mitoxantrone enhances Ca2+ release from the sarcoplasmic reticulum in isolated atrial muscle preparations obtained from the guinea-pig heart. Apparent enhancement of the sarcoplasmic reticulum functions, in contrast to anthracyclines that has been shown to suppress these functions, seems to explain the relative lack of marked cardiotoxicity of mitoxantrone.     

Cardiovascular effects of the macrolide antibiotic tilmicosin, administered alone and in combination with propranolol or dobutamine, in conscious unrestrained dogs

Tilmicosin(TM), a macrolide antibiotic and active ingredient in formulated Micotil 300^TM (Eli Lilly and Co., Indianapolis, IN, USA), is the active ingredient in a formulated animal product used for the treatment of respiratory tract infections in cattle. Owing to the concern of governmental regulatory agencies over the possibility of an accidental injection of the antibiotic to a livestock handler, the cardiovascular effects of sub lethal doses of TM were evaluated in conscious mixed-breed dogs. Left ventricular function, systemic arterial blood pressure, and heart rate (HR) responses to TM alone and in combination with propranolol(P) or dobutamine HCl(DOB) were evaluated. Dogs were instrumented with indwelling micromanometers implanted in the left ventricular chamber and in the thoracic aorta. Cardiovascular variables were recorded, and the peak value of the first derivative of left ventricular pressure (dp/dt_(max)) was used as an index of left ventricular inotropic state. Six treatments were randomly assigned to each of the six dogs using a Latin square design. The six treatments were vehicle, TM alone (2.5 mg/kg of body weight), TM immediately followed by P. and TM immediately followed by 1 of 3 dosages of DOB infused for ?45 min. Additionally, doses of TM alone (0.25, 1.0, 2.5, and 5.0 mg/kg) were administered to complete a dose-response curve. TM caused dose dependent decreases in (dp/dt_(max)) and aortic pulse pressure. HR increased dose-dependently. Left ventricular end-diastolic pressure increased at the 2.5 and 5.0 mg/kg dosages. Left ventricular systolic pressure was reduced dose-dependently at the 2.5 and 5.0 mg/kg dosages. Treatment with P exacerbated the negative inotropic effect and the decrease in left ventricular systolic pressure, but did not attenuate the tachycardia associated with TM treatment. DOB attenuated the changes in ventricular inotropic state in a dose-dependent manner. DOB infusion also restored left ventricular systolic pressure at dosages of 3 or 10 μg/min/kg. Our data indicate that toxic doses of TM may have a negative inotropic effect in conscious dogs. HR increased in a dose-dependent manner and was not the result of β₁-receptor stimulation. DOB reversed some, but not all, of the effects caused by TM administration.     

Conjunctival swab cytology from a guinea pig: it's elementary!

Three 3-month-old guinea pigs (Cavia porcellus) were evaluated for purulent ocular discharge. Conjunctival swabs were obtained for cytologic evaluation of Wright's-Giemsa-stained preparations. The specimen from the most severely affected guinea pig consisted primarily of karyolytic neutrophils and small lymphocytes. Epithelial cells occasionally were observed that contained intracytoplasmic coccoid basophilic organisms, 0.5-1.5 microm in diameter. The intraepithelial inclusions were most consistent with Chlamydia sp elementary and reticulate bodies. Specimens from the other 2 guinea pigs had a similar inflammatory response, but organisms were not observed. Polymerase chain reaction (PCR) analysis of a conjunctival swab from the most severely affected guinea pig was positive for C psittaci, which also is referred to as Chlamydophila caviae, immunotype 8, formerly known as the guinea pig inclusion conjunctivitis strain of C psittaci. Chlamydial conjunctivitis is a common problem in guinea pig populations, with C caviae being specific for this species. Cytologic identification of elementary or reticulate bodies within epithelial cells is diagnostic for the organism in Giemsa-stained preparations. However, PCR is an important complementary tool when organisms are not observed and for accurate classification of the Chlamydia species.     

Quantitative electroencephalography for measurement of central nervous system responses to diazepam and the benzodiazepine antagonist, flumazenil, in isoflurane-anaesthetized dogs

Quantitative EEG was assessed in six dogs anaesthetized with 1.8% end-tidal isoflurane concentration and following diazepam (0.2 mg/kg i.v.) administration. Ventilation was controlled to maintain normocapnia. Five dogs were subsequently given the benzodiazepine antagonist, flumazenil (0.04 mg/kg i.v.), and quantitative EEG was recorded. One dog received a saline injection following diazepam (as a control) and quantitative EEG was recorded for an additional 2.5 h. Heart rate, arterial blood pressure, esophageal temperature, arterial pH and blood gas tensions, end-tidal CO2 tension and end-tidal isoflurane concentration were monitored throughout the study. A 21 lead linked-ear montage was used for recording EEG. Quantitative EEG data were stored on an optical disc for analysis at a later date. Values for absolute power of EEG were determined for theta, delta, alpha, and beta frequencies. Cardiovascular parameters remained stable throughout the study. Diazepam administration was associated with decreased absolute power in all frequencies of EEG at all electrode sites. The duration of diazepam-induced decreased absolute power of EEG was at least 3 h in one dog. Administration of flumazenil antagonized diazepam-induced decreased absolute power of EEG in all frequencies at all electrode sites. We conclude that quantitative EEG provides a relatively non-invasive, objective measure of diazepam- and flumazenil-induced changes in cortical activity during isoflurane anaesthesia.     

Effects of diazepam and flumazenil on minimum alveolar concentrations for dogs anesthetized with isoflurane or a combination of isoflurane and fentanyl

OBJECTIVE: To determine the effect of a constant-rate infusion of fentanyl on minimum alveolar concentration (MAC) of isoflurane and to determine the interaction between fentanyl and a benzodiazepine agonist (diazepam) and antagonist (flumazenil) in isoflurane-anesthetized dogs. ANIMALS: 8 mixed-breed adult dogs. PROCEDURE: Dogs were anesthetized with isoflurane 3 times during a 6-week period. After a 30-minute equilibration period, each MAC determination was performed in triplicate, using standard techniques. Fentanyl was administered as a bolus (10 microg/kg of body weight, IV) that was followed by a constant infusion (0.3 microg/kg per min, IV) throughout the remainder of the experiment. After determining isoflurane-fentanyl MAC in triplicate, each dog received saline (0.9% NaCl) solution, diazepam, or flumazenil. After 30 minutes, MAC was determined again. RESULTS: Fentanyl significantly decreased isoflurane MAC (corrected to a barometric pressure of 760 mm Hg) from 1.80+/-0.21 to 0.85+/-0.14%, a reduction of 53%. Isoflurane-fentanyl-diazepam MAC (0.48+/-0.29%) was significantly less than isoflurane-fentanyl-saline MAC (0.79+/-0.21%). Percentage reduction in isoflurane MAC was significantly greater for fentanyl-diazepam (74%), compared with fentanyl-saline (54%) or fentanyl-flumazenil (61%). Mean fentanyl concentrations for the entire experiment were increased over time and were higher in the diazepam group than the saline or flumazenil groups. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl markedly decreased isoflurane MAC in dogs. Diazepam, but not flumazenil, further decreased isoflurane-fentanyl MAC. Our results indicate that diazepam enhances, whereas flumazenil does not affect, opioid-induced CNS depression and, possibly, analgesia in dogs.     

Effects of various selective phosphodiesterase inhibitors on carbachol-induced contraction and cyclic nucleotide contents in guinea pig taenia coli

Effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in guinea pig taenia coli were investigated. Forskolin and sodium nitroprusside inhibited carbachol (CCh)-induced contraction in a concentration-dependent manner. Various selective PDE inhibitors, vinpocetine (type 1), erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20-1724(type 4) and zaprinast (type 5) inhibited CCh-induced contraction in a concentration-dependent manner, but the inhibition of milrinone was noticeably smaller than that of the other PDE inhibitors. The rank order of potency was zaprinast > vinpocetine > EHNA > Ro20-1724 > milrinone. In the presence of CCh (0.3 microM), vinpocetine and Ro20-1724 both increased cAMP content, but not cGMP. By contrast, EHNA and zaprinast both increased cGMP content, but not cAMP. Pretreatment with ODQ (30 microM), a soluble guanylyl cyclase inhibitor, decreased the inhibition of CCh-induced contraction by EHNA or zaprinast. Pretreatment with SQ22536 (100 microM), an adenylyl cyclase inhibitor, decreased the inhibition of CCh-induced contraction by vinpocetine or Ro20-1724. In conclusion, it was indicated that vinpocetine- or Ro20-1724-induced relaxation was correlated with cAMP but EHNA- or zaprinast- induced relaxation was correlated with cGMP.     

Comparison of plasma benzodiazepine concentrations following intranasal and intravenous administration of diazepam to dogs

OBJECTIVE: To determine whether plasma concentrations of benzodiazepines (BDZ) in dogs following intranasal (IN) administration of diazepam are comparable to concentrations following IV administration. ANIMALS: 6 (4 male, 2 female) healthy adult Greyhounds. PROCEDURE: Dogs were randomly assigned to 2 groups of 3 dogs in a crossover design. Diazepam (0.5 mg/kg of body weight) was administered intravenously to dogs in group 1 and intranasally to dogs in group 2. Blood was collected from the jugular vein of each dog into tubes containing lithium heparin before and 3, 6, 9, 12, 15, 20, 30, 60, 120, 240, and 480 minutes following diazepam administration. After a 4-day washout period, dogs in group 1 received diazepam intranasally, dogs in group 2 received diazepam intravenously, and blood was again collected. Plasma concentration of BDZ was determined by use of a fluorescence polarization immunoassay. RESULTS: Mean (+/- SD) peak plasma concentration of BDZ following IV administration (1,316 +/- 216 microg/L) was greater than that following IN administration (448 +/- 41 microg/L). Time to peak concentration was < or = 3 minutes following IV administration and 4.5 +/- 1.5 minutes following IN administration. Mean bioavailability of BDZ following IN administration was 80 +/- 9%. CONCLUSIONS AND CLINICAL RELEVANCE: Diazepam is rapidly and efficiently absorbed following IN administration of the parenteral formulation. Plasma concentrations match or exceed the suggested therapeutic concentration (300 microg/L). Intranasal administration of diazepam may be useful for treatment of seizures in dogs by owners or when intravenous access is not readily available.     

Osteodystrophia fibrosa in two guinea pigs.

Two adult guinea pigs were examined because they were lethargic and reluctant to walk. Additionally, I guinea pig had otitis media, and the other had dental malocclusion. Both guinea pigs had been fed a commercially available diet of cereals and pellets enriched with vitamin C and formulated for this species. Radiographically, the guinea pigs had coarse trabecular bone patterns, skeletal deformations, pathologic fractures, and polyarthritic degenerative joint disease. A double cortical line was also evident on several long bones, the pelvis, and the vertebrae. A diagnosis of osteopenia was confirmed by use of dual-energy x-ray absorptiometry. Analysis of a food sample fed to 1 guinea pig revealed calcium and phosphorus contents of 0.524 and 0.425%, respectively (Ca:P ratio, 1.23:1). Microscopic examination of bone tissue from both guinea pigs revealed severe fibrous osteodystrophy. Nutritional secondary hyperparathyroidism caused by calcium-phosphorus imbalance was considered to be the underlying cause of osteodystrophia fibrosa in both guinea pigs.     

Effects of substance P on nicotine-induced intracellular Ca2+ dynamics in bovine adrenal chromaffin cells

Substance P (SP) is colocalized with ACh in splanchnic nerves that innervate into adrenal medulla and the peptide has been shown to inhibit nicotinic agonists-induced catecholamine secretion. To elucidate the effects of SP on cytosolic Ca2+ dynamics, the present study was conducted using fura-2-loaded isolated bovine adrenal chromaffin cells. Stimulation of the cells with nicotine (10-100 microM) produced a rapid rise of cytosolic Ca2+ concentration ([Ca2+]i), the peak level of which increased in a dose-dependent manner, followed by a gradual decay. In the presence of 10 microM SP, the dose-response relationship of the peak levels shifted downward. Quantitative analyses implied that SP inhibits the nicotine-induced Ca2+ influx in a noncompetitive manner. Nicotinic acetylcholine receptor is composed of two major functional domains: an agonist-binding site and an ionophore or channel domain. Agonist binding activates ionophore/channel domain and causes mainly Na+ influx. This Na+ influx depolarizes the cell and activates voltage-dependent Ca2+ channels. Based on this fact, the present results indicate that SP dose not block nicotine binding sites but interferes with other sites of nicotinic receptor/channel molecule, most probably a channel domain. It was suggested that SP colocalized with ACh in splanchnic nerves functions as a physiological modulator of catecholamine secretion by non-competitively suppressing ACh-induced cytosolic Ca2+ dynamics in bovine adrenal chromaffin cells.     

Characterization of somatotropin binding sites in pig skeletal muscle.

The present study was conducted to determine whether somatotropin (ST) binding sites are present in crude membrane preparations containing sarcolemma of pig skeletal muscle. Initial characterization experiments indicated that binding of bovine ST (bST) was time- and temperature-dependent and that binding was reversible. At 23 degrees C, binding was maximized between 36 and 48 h, whereas at 4 degrees C binding had not reached a maximum by 96 h. Somatotropin binding was stable between pH 5.5 and 8.5 and increased linearly between 100 and 600 micrograms of membrane protein. Addition of unlabeled bST decreased specific binding of [125I]bST in a dose-dependent manner (ED50: 1 to 1.6 ng/mL). The binding sites for bST were specific because porcine prolactin poorly inhibited bST binding. Scatchard analysis revealed the presence of a single class of binding sites (Ka: 9 to 15 x 10(9)M-1; Bmax: 5 to 6 fmol/mg of protein). In summary, the present report is the first to demonstrate that specific ST receptors are present in pig skeletal muscle. The role that ST plays in directly stimulating muscle growth and(or) muscle synthesis of insulin-like growth factor I (IGF-I) in pST-treated pigs as opposed to changes that occur as the result of an increase in plasma IGF-I concentration remains to be resolved.     

Mechanisms of acetylcholine-induced vasorelaxation in high K+-stimulated rabbit renal arteries

To characterize the mechanisms of acetylcholine (ACh)-induced vasorelaxation in rabbit renal arteries precontracted with high K+ (100 mM), muscle tension and cytosolic free Ca2+ concentration ([Ca2+]i) were measured simultaneously in the fura-2-loaded arterial strips. In the artery with endothelium, high K+ increased both [Ca2+]i and muscle tension. Addition of ACh (10 microM) during high-K+ induced contraction significantly relaxed the muscle and induced additional increase in [Ca2+]i. In the presence of NG-nitro-L-arginine (L-NAME, 0.1 mM). ACh increased [Ca2+]i without relaxing the muscle. In the artery without endothelium, high K+ increased both [Ca2+]i and muscle tension although ACh was ineffective, suggesting that ACh acts selectively on endothelium to increase [Ca2+]i. 4-DAMP (10 nM) or atropine (0.1 microM) abolished the ACh-induced increase in [Ca2+]i and relaxation. However, pirenzepine (0.1 microM), AF-DX 116 (1 microM) and tropicamide (1 microM) were ineffective. The ACh-induced increase of [Ca2+li and vasorelaxation was significantly reduced by 3 microM gadolinium, 10 microM lanthanum or 10 microM SKF 96365. These results suggest that, in rabbit renal artery, ACh-evoked relaxation of 100 mM K+-induced contractions is mediated by the release of endothelial NO. ACh may stimulates the M3 subtype of muscarinic receptor in the endothelial cells, resulting in the opening of the nonselective cation channels followed by an increase of [Ca2+]i and stimulation of NO synthase.     

Inhibition by melittin of phosphorylation by protein kinase C of annexin I from cow mammary gland

Protein kinase C (PKC) is a phosphotransferase activated by diacylglycerols, phospholipids and Ca(2+), that regulates a wide variety of biological functions by phosphorylating multiple protein substrates such as annexin I. Annexin I is a phospholipid/Ca (2+)-binding protein distributed in various tissues, including the mammary gland, and is thought to mediate the anti-inflammatory actions of glucocorticoids by inhibiting phospholipase A(2). Melittin, a phospholipase A(2) activator in bee venom, is known to inhibit PKC activity when lysine-rich histone is used as the substrate. The purpose of the present study was to examine whether phosphorylation by PKC of annexin I from cow mammary gland was inhibited by melittin. Melittin inhibited annexin I phosphorylation by PKC in a dose-dependent manner, and its IC(50) value (concentration causing 50% inhibition) was 0.8 microM. The phosphorylation of annexin I was also inhibited by the amphiphilic polypeptides mastoparan and polymyxin B, and their inhibitory effects were comparable to that of melittin. The surface-inactive polypeptide bacitracin was less effective. The inhibition by melittin was effectively reversed by the excess addition of phosphatidylserine, but not distinctly by 1-oleoyl-2-acetyl-sn-glycerol or Ca(2+), suggesting that melittin inhibited the phosphorylation of annexin I by interacting with phosphatidylserine. The inhibition by melittin of PKC phosphorylation of annexin I seems to be pathophysiologically important, because a melittin-like phospholipase A(2)-stimulatory protein is present in bovine endothelial cells.     

A dose titration study into the effects of diazepam or midazolam on the propofol dose requirements for induction of general anaesthesia in client owned dogs,premedicated with methadone and acepromazine

ObjectiveTo assess the effect of a benzodiazepine co–induction on propofol dose requirement for induction of anaesthesia in healthy dogs, to describe any differences between midazolam and diazepam and to determine an optimal benzodiazepine dose for co–induction.Study designProspective, randomised, blinded placebo controlled clinical trial.AnimalsNinety client owned dogs (ASA I–III, median body mass 21.5kg (IQR 10–33)) presented for anaesthesia for a variety of procedures.MethodsDogs were randomised to receive saline 0.1 mL kg^?1, midazolam or diazepam at 0.2, 0.3, 0.4 or 0.5 mg kg^?1. All dogs received 0.01 mg kg^?1 acepromazine and 0.2 mg kg^?1 methadone intravenously (IV). Fifteen minutes later, sedation was assessed and scored prior to anaesthetic induction. Propofol, 1 mg kg^?1, was administered IV, followed by the treatment drug. Further propofol was administered until endotracheal intubation was possible. Recorded data included patient signalment, sedation score, propofol dosage and any adverse reactions.ResultsMidazolam (all groups combined) significantly reduced propofol dose requirement compared to saline (p < 0.001) and diazepam (p = 0.008). Midazolam (0.4 mg kg^?1) significantly reduced propofol dose requirement (p = 0.014) compared to saline, however other doses failed to reach statistical significance. Diazepam did not significantly reduce propofol dose requirement compared to saline (p = 0.089). Dogs weighing <5 kg, regardless of treatment group, required a greater propofol dose than those weighing 5–40 kg (p = 0.002) and those >40 kg (p = 0.008). Dogs which were profoundly sedated required less propofol than those which were mildly sedated (p < 0.001) and adequately sedated (p = 0.003).Conclusions and clinical relevanceMidazolam (0.4 mg kg^?1) given IV after 1 mg kg^?1 of propofol significantly reduced the further propofol dose required for intubation compared to saline. At the investigated doses, diazepam did not have significant propofol dose sparing effects.     

Schirmer tear test, phenol red thread tear test, eye blink frequency and corneal sensitivity in the guinea pig

OBJECTIVE: To establish reference values for Schirmer tear tests (STT) I and II, phenol red thread (PRT) tear test and eye blink frequency, and to determine corneal sensitivity for normal guinea pigs. ANIMALS STUDIED: One hundred and eight eyes of 54 adult Duncan-Hartley guinea pigs. PROCEDURE: Schirmer tear test (STT) I and then STT II were performed in 36 guinea pigs. PRT and STT I were compared in 18 adult Duncan-Hartley guinea pigs. Corneal sensitivity was determined in 23 guinea pigs by evaluating the corneal touch threshold (CTT) of five different regions using a Cochet-Bonnet esthesiometer. Eye blink frequency was measured in 10 guinea pigs over a period of 20 min and in 17 guinea pigs over a period of 10 min. RESULTS: Mean STT I was 0.36 mm +/- 1.09 mm (wetting/min) and mean STT II was 0.43 mm +/- 1.29 mm (wetting/min). There was no significant difference between mean STT I and mean STT II (P = 0.79). The mean PRT-value was 16 +/- 4.7 mm (wetting/15 s), and the mean STT I-value in the same guinea pigs was 0.6 +/- 1.83 mm (wetting/min). Corneal sensitivity was significantly higher in the center than in the four limbal regions. The mean CTT for central, ventral, nasal, temporal and dorsal regions was 2, 1.7, 1.7, 1.7 and 1.6 cm or 3.7, 5.2, 5.6, 5.7 and 6.4 g/mm(2), respectively. Eye blink frequency was between two to five (mean 3.4 +/- 1.04) blinks per eye over 20 min in guinea pigs in their home environment, while in handheld and restrained guinea pigs eye blink frequency showed a variation between 0 and 17 blinks per eye (mean 3.24 +/- 3.64 blinks per eye) over 10 min. CONCLUSIONS: As there were no significant differences between STT I and STT II results, reflex tear secretion in the guinea pig may not exist. The most likely explanation is a lower corneal sensitivity in the guinea pig than in other species, such as cats, dogs and horses. Because of the small amount of tears, PRT is the preferred test for tear measurement in the guinea pig.     

Bovine reaginic antibody III. Cross-reaction of antihuman IgE and antibovine reaginic immunoglobulin antisera with sera from several species of mammals.

Using antisera specific for the heavy chain of human IgE and bovine reaginic immunoglobulin, the degree of cross-reaction amongst sera from pig, rat, rabbit, guinea pig, goat, cow, horse, dog, cat and human was tested. Antihuman IgE antiserum gave strong reactions with pig, rabbit, cow, goat and human sera (100% to 15.1%) and weak reactions with rat, guinea pig, horse, dog and cat sera (10.1% to 3.22%). Antibovine reagin antiserum produced a considerable amount of cross-reaction with sera from pig, rat, rabbit, goat, horse and human (43.6% to 20.1%) with limited reactions with guinea pig, dog and cat sera (13.9% to 9.3%).     

A comparative study on S-100 protein-immunoreactive cells in lymph nodes

S-100 protein-immunoreactive cells of the lymph node were examined in the duck and 9 mammalian species, such as guinea pigs, dogs, cats, horses, pigs, goats, cows, Japanese serows and crab-eating monkeys. S-100 protein was detected in follicular dendritic cells (FDC) and tangible-body macrophages (TBM), sinus and parenchymal macrophage (MP), sinus endothelial cells (SEC) and interdigitating reticulum-like cells (IRC) in the node of mammalian species, but not in the duck except nervous elements. S-100-positive FDC and TBM were detected in germinal centers of the nodes in all mammalian species, but immunoreactivity of the other 3 cell types varied according to animal species and individuals of the same species. S-100 alpha subunit was detected in FDC, with the exception of those of the duck and guinea pig. The subunit was also detected in SEC of the dog, cow and Japanese serow. In the guinea pig, a unique S-100 alpha-positive giant dendritic cell (GDC) was found in the subsinusal cortical area. In addition, S-100 immunoreactive lymphocytes were observed in the paracortex-equivalent area of pig nodes. Arterial endothelial cells of the pig and cow were immunoreactive to S-100 beta subunit.