Temporal changes in core body temperature in anesthetized adult horses.

OBJECTIVE: To examine temporal patterns of core body temperatures in adult horses during general anesthesia and to determine the efficacy of forced-air warming blankets in attenuating decreases in core body temperatures. ANIMALS: 5 clinically normal adult horses. PROCEDURE: Horses were assigned to each of 2 trials, warmer and no-warmer, in a randomized crossover design. Horses were instrumented with a thermistor-tipped pulmonary arterial catheter to measure core body temperature. Induction and maintenance of and recovery from general anesthesia were performed in an air-conditioned surgical suite where room temperature and relative humidity were maintained at approximately 21 C and 40%, respectively. Core body temperature measurements were recorded every 5 minutes during 2.5 hours of anesthesia and during recovery until horses could stand. Data were analyzed, using ANOVA for repeated measures. RESULTS: Without warming, mean core body temperature decreased steadily (0.37+/-0.18 C/h). Forced-air warming significantly decreased that rate to 0.19+/-0.09 C/h. In both trials, there was an additional, rapid, significant decrease in core body temperature when horses were moved to the recovery area, which was apparently the result of conductive heat loss to the cold floor. Recovery time and time required for core body temperature to return to baseline were unaffected by forced-air warming during anesthesia and recovery. CONCLUSIONS AND CLINICAL RELEVANCE: Core body temperature decreases steadily in adult horses anesthetized in a cool, dry environment. Forced-air warming devices can attenuate this decrease. Additional body heat can be lost rapidly when anesthetized horses are positioned on cold surfaces during recovery.

Comparison of peripheral and core temperatures in anesthetized horses.

OBJECTIVE: To examine temporal patterns of rectal, nasal, groin, and skin temperatures measured in adult horses undergoing general anesthesia and to determine accuracy and precision of temperatures at these sites, compared with core temperature. ANIMALS: 5 healthy adult horses. PROCEDURE: Induction, maintenance of, and recovery from general anesthesia were performed in an air-conditioned surgical suite. Room temperature and relative humidity were approximately 21 C and 40%, respectively. Anesthesia was maintained for 2.5 hours, and body temperatures were measured and recorded every 5 minutes. Mean values were compared by use of ANOVA for repeated measures. Correlation coefficients for linear regressions of site temperature versus core temperature at 30-minute intervals were used to evaluate precision. RESULTS: Rectal temperature decreased in a linear manner, similar to core temperature. Nasal, groin, and skin temperatures followed a biphasic pattern; they sharply increased initially, peaked, then decreased at a rate similar to that of core temperatures. Rectal temperature always accurately reflected core temperature. Initial significant differences between core temperature and nasal, groin, or skin temperature disappeared as peripheral site temperatures approached peak values. Precision of core temperature estimation was generally poor for rectal, groin, and skin temperatures but was high (r > 0.90) after the first hour of anesthesia. CONCLUSION: Anesthesia-induced core heat redistribution develops with minimal effect on core temperature. Rectal temperature can accurately reflect core temperature.

A preliminary study of the effect of inhaled nitric oxide on lung mechanics in the standing horse with histamine-induced bronchoconstriction.

The effect of inhaled nitric oxide on pulmonary mechanics was studied in normal standing horses with histamine-induced bronchoconstriction. The respiratory health status of 6 normal horses was established on the basis of history, clinical and bronchoalveolar lavage examination. Intrathoracic pressures were estimated using distal oesophageal pressures. Respiratory gas flows were measured using a heated pneumotachograph. Pulmonary mechanics variables were determined from these measurements on a breath by breath basis. Bronchoconstriction was induced by nebulizing a 0.75% w/v solution of histamine over 5 min. Pulmonary function was assessed during 4 periods: 1) while breathing room air prior to histamine challenge; 2) 5 min post histamine challenge; 3) 10 min post histamine challenge and while breathing 5 ppm nitric oxide; and 4) 14 min post histamine challenge while breathing room air. Statistical analysis included Friedman's nonparametric repeated measures analysis of variance followed by Dunn's multiple comparisons tests, where appropriate. Criteria for demonstration of nitric oxide effect on pulmonary mechanics variables were taken as a return of the variable value following nitric oxide administration towards control value and subsequent restoration of the value toward post histamine levels with discontinuation of nitric oxide. Five variables (dynamic compliance, airway resistance, maximum developed pressure, work of breathing, and peak expiratory flow) had significant changes in response to histamine. Three variables (dynamic compliance, airway resistance, and maximum developed pressure) met the above criteria, but only dynamic compliance and airway resistance showed statistical significance (P < 0.05). These results suggest that nitric oxide partly dilates small airways constricted by histamine.

Evaluation of automated methods of measuring hemoglobin and hematocrit in horses.

OBJECTIVE: To evaluate the accuracy of 3 automated methods of determining Hct and hemoglobin (Hb) concentration, compared with manual methods. Animals-22 clinically normal adult horses of various breeds. PROCEDURE: A blood sample was obtained from each horse. Six dilutions (representing Hct of 0, 10, 20, 40, 60, or 70%) were prepared from each sample and analyzed, using 1 of 2 blood gas analyzers or a hemoximeter (for automated determinations) or the Wintrobe macrohematocrit and cyanmethemoglobin methods (for manual determinations). Regression analysis was used to determine mean slope relationships between Hct and Hb measurements obtained by use of manual versus automated methods. Slopes were compared, using Student's t-test. RESULTS: Of the 3 automated methods examined, only 1 blood gas analyzer reported Hct and Hb values that were not significantly different from those determined by use of manual methods; however, this analyzer could not report Hb concentrations below 2.5 g/dl. The other blood gas analyzer reported values for Hct and Hb concentrations that were consistently higher than those obtained by use of manual methods at Hct < or = 20% and Hb < or = 6.6 g/dl. The hemoximeter yielded more accurate results if the Hb concentration was between 6.6 and 20 g/dl. CONCLUSION: Although there were some limitations in measuring at low Hb concentrations, the method of determining Hb concentration and Hct with blood gas analyzer 2 was more accurate than that with blood gas analyzer 1 (Hct and Hb concentration) or the hemoximeter (Hb only).

Effects of sedation, anesthesia, and endotracheal intubation on respiratory mechanics in adult horses.

OBJECTIVE: To determine the effects of endotracheal intubation on respiratory mechanics during xylazine sedation and xylazine-diazepam-ketamine anesthesia in adult horses. ANIMALS: 5 healthy adult horses. PROCEDURE: Measurements were derived from recordings of respiratory gas flow, and transpulmonary and transtracheal pressures. Total pulmonary resistance (RT) was partitioned into upper airway resistance (extrathoracic portion of trachea, larynx, pharynx, nasal cavity, nares; RUA) and lower airway resistance (intrathoracic portion of trachea, bronchi, bronchioles). Baseline measurements were obtained in unsedated horses, after xylazine administration, and following nasotracheal intubation (ID, 18 mm). Measurements were obtained following induction of xylazine-diazepam-ketamine anesthesia and subsequent to endotracheal intubations (ID, 22, 20, and 16 mm). During recovery, horses were nasotracheally intubated (ID, 18 mm). Measurements were obtained upon standing, and repeated after extubation. Data were examined by use of ANOVA with repeated measures. RESULTS: Significant increases in mean work of breathing (W), RT, and RUA observed with xylazine sedation were variably attenuated by nasotracheal intubation. During xylazine-diazepam-ketamine anesthesia, the highest mean values for W, RT, RUA, transpulmonary and transtracheal pressures developed during non-intubation periods. The magnitudes of resistance and pressure values were inversely proportional to the internal diameter of the endotracheal tube. At recovery, values of the W and all measurements of resistances and pressures were significantly increased, compared with presedation values. Extubation resulted in further increases in these measurements. CONCLUSIONS: Work of breathing in horses is substantially increased when RUA is increased during xylazine sedation and xylazine-diazepam-ketamine anesthesia. Endotracheal intubation reduces W by reducing RUA.

Oncotic, hemodilutional, and hemostatic effects of isotonic saline and hydroxyethyl starch solutions in clinically normal ponies.

OBJECTIVE: To evaluate the oncotic, hemodilutional, and hemostatic effects of IV infusions of a large volume of isotonic saline solution and 2 doses of 6% hydroxyethyl starch (HES) in clinically normal ponies. ANIMALS: 12 adult ponies. PROCEDURE: Ponies were assigned to 3 treatment groups and received the following IV infusions: 80 ml of 0.9% sodium chloride/kg; 10 ml of 6% HES (in 0.9% sodium chloride)/kg; or 20 ml of 6% HES (in 0.9% sodium chloride)/kg. Blood samples were collected for determination of colloid oncotic pressure (COP), PCV, plasma total protein concentration, platelet count, von Willebrand factor antigen (vWf:Ag) activity, fibrinogen concentration, prothrombin time, activated partial thromboplastin time (APTT), and factor VIII coagulant (FVIII:C) activity. A rocket immunoelectrophoretic procedure was used for determination of vWf:Ag activity. A modification of the APTT assay was used for determination of FVIII:C activity. Cutaneous bleeding time was determined, using a template method. RESULTS: Mean COP was persistently increased over baseline values in the face of hemodilution in HES-treated ponies. Prothrombin time, APTT, and fibrinogen concentrations decreased after infusions and vWf:Ag and FVIII:C activities were decreased in dose-dependent manner in HES-treated ponies. Though cutaneous bleeding time was not significantly affected in ponies of any group, a trend toward prolongation of bleeding time was evident in ponies receiving 20 ml of HES/kg. This trend appeared to be associated with marked decrement in vWf:Ag activity at this dosage. CONCLUSIONS AND CLINICAL RELEVANCE: Infusion of HES in clinically normal ponies increases COP, and exerts dose-dependent hemodilutional effects and dose-dependent effects on specific hemostatic variables. Thus, HES may be useful for resuscitative fluid treatment of horses.

Gene transfer by adenovirus in smooth muscle cells.

We report adenovirus-mediated gene transfer into airway smooth muscle cells in cultured cells and organ-cultured tracheal segments. Incubation of cultured rat tracheal myocytes with virus (5 x 10(8) pfu/ml) for 6 h resulted in beta-galactosidase expression in 94.8 +/- 2.5% of cells (n = 4). Following incubation of thin (less than 200 microns diameter) equine trachealis muscle segments with virus in organ culture (5 x 10(8)-5 x 10(10) pfu/ml) the average expression of the Lac Z gene was approximately 19 +/- 10% (n = 9). Expression was markedly improved, however, in segments from neonatal rats (13-21 days). In two experiments in which the mucosa and serosa were removed, nearly all cells expressed beta-galactosidase, whereas in a third experiment in which the tissue was not dissected, about 40% of cells were stained. Viral infection had no effect on tension development of strips following organ culture. In vitro gene transfer may provide a useful method to alter protein expression and examine the effect of this alteration on excitation/contraction coupling in smooth muscle.

Use of a bovine hemoglobin preparation in the treatment of cyclic ovarian hemorrhage in a miniature horse.

Anemia that was secondary to ovarian hemorrhage in a 4-year-old miniature horse mare was treated prior to laparotomy with polymerized ultrapurified bovine hemoglobin (PUBH). Two previous whole-blood transfusions had resulted in acute transfusion reaction, and a suitable blood donor could not be found among 9 horses, necessitating use of the blood substitute. Subsequent blood typing revealed the mare to be Aa-negative, with allo-antibodies against Aa in serum. Serious adverse reactions were not observed after infusion of PUBH, and the mare recovered. Although the safety and efficacy of using PUBH in horses has not been established, PUBH may prove to be an excellent alternative to whole-blood transfusions, when indicated.

The application of double fluorescence to the rapid selection of atypical cervical epithelial cells spread in monolayers.

Monolayer spreads of cervical cells were prepared and reacted in sequence with two fluorescent probes. The nuclei were reacted with 4,6-Diamidino-2-phenylindole (DAPI), resulting in white fluorescence of all cell nuclei. Those cells possessing active guanidinobenzoatase (GB) bound the second probe, rhodamine-alpha-N-agmatine (Rh-Agm), resulting in orange cell surface fluorescence. Atypical epithelial cells possessed both active GB and enlarged nuclei; such cells could easily be recognised by their cytological appearance. We illustrate our results in the form of colour prints which are representative of our observations of cells in both normal and abnormal cervical spreads.

Contractile agonists activate voltage-dependent calcium channels in airway smooth muscle cells.

To determine whether agents that cause contraction of airway smooth muscle affect sarcolemmal calcium channel activity, unitary calcium channel currents (using Ba2+ as the charge carrier) were recorded in on-cell configuration from acutely dissociated (dog, pig, and ferret) and cultured (human) airway smooth muscle cells. Addition of the contractile agonists methacholine or bradykinin increased the open-state probability of the large-conductance calcium channel 37.2- and 45-fold, respectively. The increase in open-state probability was not due to cellular depolarization because increases occurred in the absence of depolarization. Channel activation by the agonist was determined to result in the favoring of a long (16.5 +/- 5.0 ms) open lifetime for the channel, which was not observed under control conditions, in the absence of BAY K 8644. We also report the unitary calcium channel currents from a second, smaller conductance calcium channel. This channel was present in all cell types and had a mean conductance of 9.5 +/- 0.8 pS (80 mM Ba2+). Exposure of cells to agonist also resulted in an increase in the open-channel probability of the small-conductance calcium channel (10.4-fold), which did not result from cellular depolarization. These experiments demonstrate that the molecular pathways exist between contractile agonist receptors and sarcolemmal calcium channels in airway smooth muscle cells. Because membrane patches were not directly exposed to agonist, receptor-channel linkage probably occurs via a second messenger-coupling pathway.

Delayed rectifier potassium channels in canine and porcine airway smooth muscle cells.

1. In order to define the ion channels underlying the inactivating, calcium-insensitive current in airway smooth muscle cells, unitary potassium currents were recorded from canine and porcine trachealis cells, and compared with macroscopic currents. On-cell and inside-out single-channel currents were compared with whole-cell recordings made in dialysed cells. 2. Depolarizing voltage steps evoked outward unitary currents. In addition to a large conductance, calcium-activated potassium channel (KCa), a lower conductance potassium channel was identified. This channel has a conductance of 12.7 pS (on-cell; 1 mM-K+ in the pipette). 3. The lower conductance channel (Kdr) was not sensitive to cytosolic Ca2+ concentration and unitary current openings occurred following a delay after the voltage step. The time course of activation of the current composed of averaged single-channel events was very similar to that of the whole-cell, delayed rectifier potassium current (IdK), recorded under conditions of low intracellular calcium (Kotlikoff, 1990). 4. Kdr channels also inactivated with kinetics similar to those of the macroscopic current. Averaged single-channel records revealed a current that inactivated with kinetics that could be described by two exponentials (tau 1 = 0.14 s, tau 2 = 1.1 s; at 5 mV). These values corresponded well with previously determined values for time-dependent inactivation of IdK. Inactivation of Kdr channels was markedly voltage dependent, and was well fitted by a Boltzmann equation with V50 = -53 mV; this was similar to measurements of the macroscopic current, although the V50 value was shifted to more positive potentials in whole-cell measurements. When only the inactivating component of the macroscopic current was considered, the voltage dependence of inactivation of the single-channel current and macroscopic current were quite similar. 5. Single-channel kinetics indicated that Kdr channels occupy one open and two closed states. The mean open time was 1.7 ms. Inactivation results in a prominent increase in the long closed time, with little effect on the mean open time or short closed time. 6. The Kdr channel was not blocked by tetraethylammonium (TEA; 1 mM), charybdotoxin (ChTX; 100 nM) or glibenclamide (20 microM), but was blocked by 4-aminopyridine (4-AP; 1 mM). Similarly, 4-AP blocked the inactivating component of the macroscopic current, but a non-inactivating current remained. KCa currents were blocked by TEA (0.5-1 mM) and charybdotoxin (40 nM), but were insensitive to to 4-AP (1 mM) and glibenclamide (20 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Muscarinic regulation of membrane ion channels in airway smooth muscle cells.

We have demonstrated that stimulation of airway smooth muscle by muscarinic agonists results in a coordinated modulation of two membrane ion channel proteins. Both channels are modulated in a similar way, although their effects on open-channel probability are opposite. The voltage-dependence of channel activity is shifted to more positive potentials in the case of KCa, and to more negative potentials in the case of the voltage-dependent calcium channels. Similarly, KCa channel dwell-time kinetics are shifted to short open lifetimes, whereas the long open state is favored for the large-amplitude voltage-dependent calcium channel. Although little is known about the molecular coupling of calcium channels, muscarinic inhibition of KCa channels is mediated through a pertussis toxin-sensitive guanine nucleotide binding protein.