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P H LeBlanc

Publications and source records attributed to P H LeBlanc.

16 recordsLinked to original sources
PubMed1993

In vitro effects of alpha 2-adrenergic receptor stimulation on cholinergic contractions of equine distal airways.

In horses with noninduced, reversible airway obstruction (heaves), pulmonary function is improved after sedation with the alpha 2-adrenergic agonist xylazine. The mechanism of this effect is undetermined. Because the predominant excitatory innervation of equine airways is cholinergic, the influence of alpha 2-adrenergic receptor stimulation on the response of isolated distal airways to cholinergic stimulation was determined. Distal bronchial segments from 22 healthy horses were suspended in isolated organ baths where their mechanical responses to various stimuli could be studied. Each tissue was incubated with one of several concentrations of clonidine, clonidine vehicle, or clonidine plus tolazoline. Then, the contractile response of the tissues to either cumulative acetylcholine (ACh) addition or cumulative electrical field stimulation (EFS) was recorded. All contractile responses evoked by EFS were mediated through stimulation of cholinergic airway nerves. Clonidine had no effect on the contractile response of distal airway segments to exogenous ACh. However, clonidine (at concentrations > 10(-5) M) significantly (P < 0.05) diminished the contractile response of the distal airway segments to EFS. This inhibitory effect of clonidine was not observed in the presence of tolazoline. Similar results were observed when the less-selective alpha 2-adrenergic agonist xylazine was exposed to the isolated segments instead of clonidine. Because EFS-but not exogenous ACh-induced contractions were inhibited, alpha 2-adrenergic receptor stimulation apparently causes presynaptic inhibition of the cholinergic nerves innervating distal portions of the bronchi of horses.

Acetylcholine↗
PubMed1992

Exogenous but not endogenous PGE2 modulates pony tracheal smooth muscle contractions.

The modulatory role of prostaglandin E2 (PGE2) was examined in pony tracheal smooth muscle strips. Although exogenous PGE2 inhibited the contractile response to both electrical field stimulation (EFS) and acetylcholine (ACh) in a dose-dependent manner, the concentration required to inhibit the response to EFS (10 nM) was less than that required to inhibit the response to ACh (0.1 microM). Cyclooxygenase inhibition with aspirin or meclofenamate had no effect on either the response to EFS or to ACh even though PGE2 production was inhibited. Our results demonstrate that in ponies as in other species, exogenous PGE2 can inhibit the airway smooth muscle's response to EFS and ACh. However, the failure of cyclooxygenase inhibition to alter the response to EFS and ACh suggests that endogenous prostanoids do not exert a significant modulatory effect on pony tracheal smooth muscle in vitro.

Acetylcholine↗
PubMed1991

In vitro responses of airway smooth muscle from horses with recurrent airway obstruction.

The in vitro contractile and relaxant responses of tracheal smooth muscle strips (TSM) and third-generation bronchi (3B) of control horses and horses with recurrent obstructive disease (heaves) were compared. Acetylcholine (ACH) sensitivity of the diseased tissues was less than that of tissues from control horses, especially at the level of the third generation (EC50 controls 15 +/- 11 microM vs 81 +/- 17 microM for heaveys). Despite tracheal and bronchial hyporesponsiveness to ACH, these tissues from heavey horses were hyperresponsive to EFS. The inhibitory effect of isoproterenol and electrical field stimulation (EFS) was examined in histamine-precontracted airways pretreated with atropine (1 microM), indomethacin (3 microM), and phentolamine (1 microM). Precontracted tissues of both groups at both levels of airway demonstrated similar concentration-dependent relaxation in response to cumulative doses of isoproterenol (0.1 nM to 0.1 mM). EFS of precontracted tissues caused 80-90% relaxation in the TSM in both groups and 21% relaxation in 3B of the control group. Electrical field stimulation relaxation of precontracted tissues was not seen in the diseased 3B, suggesting a lack of inhibitory innervation. EFS of similarly precontracted tissues plus propranolol (1 microM) resulted in only 46% relaxation in the TSM of both groups but did not reduce the EFS relaxation of control 3B, suggesting the presence of both sympathetic and nonadrenergic noncholinergic nerves (NANC) in the trachea but only NANC in the 3B.

Acetylcholine↗
PubMed1991

Chemical restraint for surgery in the standing horse.

Chemical restraint can be a useful pharmacologic tool to assist the veterinarian performing surgery in the standing horse. The agents discussed impose minimal adverse side effects and are considered relatively safe when administered in the doses described. Acetylpromazine, the most widely used tranquilizer, produces mild sedation but no analgesia. The use of tranquilizers for surgical procedures requires the combined use of either a local anesthetic technique or a sedative-hypnotic or opiate to provide analgesia. Sedative-hypnotics such as xylazine and detomidine or opiates such as morphine and butorphanol are commonly used. The sedative-hypnotics also can induce deep CNS depression and may be sufficient alone for many procedures. Opiates may be used to supplement the analgesia produced by sedative-hypnotics or provide analgesia to the tranquilized horse. Opiates are not useful alone because of their potential to cause CNS excitement in the horse. The combination of detomidine and butorphanol is probably the most effective drug combination to facilitate painful surgery in the standing horse.

Animals↗
PubMed1991

In vitro responses of distal airways in horses with recurrent airway obstruction.

Distal airway segments (ID, 3 to 4 mm; length, 5 mm) from 2 groups of horses were isolated and suspended in tissue baths filled with Krebs solution, aerated with 5% CO2 in oxygen and maintained at 37 degrees C. Responses to exogenous acetylcholine, isoproterenol, or electrical field stimulation were compared. Control horses (n = 30) had no history of recurrent airway obstruction, whereas principal horses (n = 15) had recurrent airway obstruction and were studied during an acute episode of airway obstruction. Although the distal airways contracted in response to the cumulative half-logarithmic addition of acetylcholine (10(-10) M to 10(-3) M) in both groups, bronchi obtained from principals were less sensitive to acetylcholine than were bronchi obtained from controls. Tetdrodotoxin-sensitive electrical field stimulation-induced contractions were observed in both groups of airways, but the tension achieved in principal bronchi was less than in controls. All electrical field stimulation-induced contractions were abolished by atropine, indicating that the only excitatory innervation of equine distal airway is through the parasympathetic system. To examine the effect of isoproterenol and determine inhibitory innervation, bronchi were precontracted with histamine. Electrical field stimulation did not cause relaxation of precontracted bronchi in either group, thus indicating that distal airways lack inhibitory innervation. Isoproterenol caused similar, dose-dependent relaxation in both groups.

Acetylcholine↗
PubMed1991

Effects of bovine respiratory syncytial virus on airway function in neonatal calves.

Respiratory syncytial virus (RSV) infection causes severe lower respiratory tract disease in infants and calves. Neonatal respiratory tract infection in children often produces persistent changes in lung function. The specific objective of this study was to determine whether neonatal calves have transient or persistent alterations in pulmonary function and airway reactivity following RSV infection. Six 2- to 3-day-old Holstein bull calves were inoculated with 10 ml of bovine respiratory syncytial virus (BRSV) inoculum (10(2.7) to 10(3.8) cell culture infective doses/ml) intranasally and 10 ml of BRSV inoculum (10(4.8) to 10(5.9) cell culture infective doses/ml) intratracheally for 4 consecutive days, and 5 other calves were sham-inoculated. Prior to inoculation (day 0) and on days 4, 14, and 30 after the last inoculation, body weight (kg), dynamic compliance (Cdyn), pulmonary resistance (RL), and 2 indices of airway reactivity (effective dose [ED] 65Cdyn and ED200RL) were measured. Control calves gained weight progressively throughout the study, whereas RSV-inoculated calves failed to gain weight for 14 days, but equaled control calf weight by 30 days after inoculation. The Cdyn of control calves increased significantly by 30 days, but did not in the RSV-infected calves. Pulmonary resistance was increased significantly at 4, 14, and 30 days, but was unaffected by sham inoculation. The ED65Cdyn and ED200RL indicated an age-dependent increase in reactivity to histamine and an increase in responsiveness in the infected group beginning at 14 days and persisting until the end of the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1990

Regional anesthesia.

Organ toxicity from local anesthetic agents is rare. This makes these agents an attractive option in the high-risk patient. Complications associated with local anesthetics are related to overdosage. Overdosage with local anesthetic agents administered epidurally may cause motor paralysis and hind-limb weakness. Systemic signs of local anesthetic overdosage include changes in central nervous system activity (excitement or depression), muscle tremors, and hypotension. Because the dose required to produce these effects in the horse is high (12 mg/kg), this complication is uncommon. Few side effects and low cost justify the use of local anesthetic techniques in equine practice.

Anesthesia, Conduction↗
PubMed1990

Clinical use of epidural xylazine in the horse.

Xylazine was administered into the epidural space of nine horses to facilitate various perineal manipulations (ie rectovaginal laceration repair, replacement of prolapsed rectum and urethral extension). The resulting caudal analgesia was sufficient for all procedures. The duration of analgesia from a single injection of epidural xylazine (0.17 to 0.22 mg/kg bodyweight) was at least 3.5 h. No horses were ataxic during or after the treatment. This trial demonstrates that xylazine given into the epidural space of horses provides prolonged regional analgesia which is sufficient for clinical use.

Analgesia, Epidural↗
PubMed1989

Caudal epidural analgesia in cattle using xylazine.

Each of 25 mature Holstein cows were given a single 5 mL epidural injection of one of four different concentrations of xylazine or saline. The onset, magnitude and duration of caudal epidural analgesia was quantitated with the use of a low voltage DC current applied to the perineal area. The dose that produced the longest duration of analgesia and produced the least ataxia or sedation was approximately 0.05 mg/kg (25 mg in 5 mL diluent). The analgesia produced by this xylazine dose was compared to a standard dose of epidural lidocaine (100 mg/5 mL) by the same method. To investigate the role of systemic absorption in the production of epidural analgesia, the previously utilized epidural xylazine dosage was given intramuscularly to four adult cows. Analgesia was quantitated as before and the results compared with epidural xylazine. Epidural xylazine produced a significantly greater duration of analgesia, as measured by this model, than did epidural lidocaine. Xylazine, given epidurally, produced greater perineal analgesia than did xylazine given intramuscularly.

Analgesia, Epidural↗
PubMed1988

Epidural injection of xylazine for perineal analgesia in horses.

Local anesthetics given in the epidural space of a horse may cause hind limb weakness in addition to analgesia. Because alpha 2 agonists given by epidural injection cause sensory blockade without motor effects in human beings and other species, their use in veterinary anesthesia is appealing. This study was designed to examine the effectiveness of xylazine HCl, an alpha 2 agonist commonly used in horses. Xylazine, 0.9% NaCl, and lidocaine were given by epidural injection to horses subjected to perineal electrical stimulation. Administration of xylazine (0.17 mg/kg of body weight, diluted to a 10-ml volume, using 0.9% NaCl) induced approximately 2.5 hours of local analgesia without apparent side effects. Higher doses of xylazine caused mild hind limb ataxia. Administration of lidocaine induced a similar duration of analgesia, with severe hind limb ataxia (100% incidence). We concluded that xylazine given by epidural injection results in safe, effective perineal analgesia in horses.

Analgesia, Epidural↗
PubMed1988

Effect of withholding feed on ventilation and the incidence of regurgitation during halothane anesthesia of adult cattle.

Six cows were anesthetized for 90 minutes with 1.5 minimal alveolar concentrations of halothane in oxygen, after 48 hours without food and 12 hours without water. On a separate occasion, the cows were allowed access to feed and water up to the time of induction of anesthesia, with the sequence of feeding vs fasting randomized. Every 15 minutes, measurements were made of end-tidal halothane concentration, arterial blood gas tensions, mean arterial blood pressure, heart and respiratory rates, tidal volume, minute volume, airflow rate, and transpulmonary pressure, and calculations were made of dynamic compliance and pulmonary resistance. Any regurgitation was recorded. Hypoventilation was noticed in all cows, but to a greater degree in fed cows. Fed cows became hypoxemic, whereas arterial oxygen tension did not change in nonfed cows. Alveolar-arterial oxygen tension gradient, tidal volume, and minute volume did not change. Arterial pH decreased progressively in all cows. Dynamic compliance also decreased progressively in all cows, and was consistently lower in fed cows. Pulmonary resistance tended to increase in all cows, but the increase was significant only in fed cows at 90 minutes. All fed cows became tympanitic, and 2 cows regurgitated a small volume of fluid at 55 minutes. Three nonfed cows regurgitated larger volumes at times ranging from 8 minutes to 85 minutes.

Airway Resistance↗
PubMed1987

Case report.

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Adolescent↗