Systemic and colonic venous plasma biochemical alterations in horses during low-flow ischemia and reperfusion of the large colon.

The purpose of this study was to determine the effects of low-flow ischemia and reperfusion (I-R) of the large colon on 16 systemic venous (SV) and colonic venous (CV) plasma biochemical variables in horses. Horses (n = 24) were randomly allocated to 3 groups: sham-operated (n = 6), 6 h ischemia (n = 9), and 3 h ischemia followed by 3 h reperfusion (n = 9). SV and CV heparinized blood was collected at 0, 1, 3, 3.25, 4, and 6 h. The SV-CV difference was calculated for each variable. The SV, CV, and SV-CV difference for albumin, total protein, and calcium decreased significantly (P < 0.05) across time in horses of all groups, but there were no differences among groups. SV phosphorous was significantly increased from baseline (BL) at 1 to 6 h in horses of all groups, but there were no differences among groups. CV phosphorous was significantly greater than BL from 1 to 6 h in group-2 horses and from 1 to 3 h in group-3 horses. SV potassium was not different among groups, but was significantly higher at 6 h, compared with BL in horses of all groups. CV potassium was significantly greater than BL from 1 to 6 h in horses of groups 2 and 3. SV glucose was greater at 6 h compared with all previous times in horses of all groups, but there were no difference among groups. CV glucose was significantly lower than BL and group-1 values in horses of groups 2 and 3 during ischemia, but returned to BL during reperfusion in group-3 horses. CV anion gap was significantly greater and SV-CV anion gap was significantly more negative in horses of groups 2 and 3, compared with group-1 horses during ischemia. The biologic relevance of these alterations is unknown, but they may contribute to histopathologic, hemodynamic, and metabolic alterations characteristic of low-flow I-R. Alternatively, these alterations may simply reflect colonic injury sustained during I-R. Results suggest that the colon utilizes glucose as a fuel and generates acid anions during low-flow ischemia. Increased CV phosphorous and potassium during I-R likely occurs as a result of leakage of intracellular stores subsequent to cellular damage.     

Pulmonary arterial wedge pressures: blood gas tensions and pH in the resting horse.

Blood pressure recordings were made from right atrium, right ventricle, pulmonary trunk, and pulmonary arterial "wedge" positions in the standing, resting, adult horse. Similarly, comparisons were made of blood samples collected from these vascular positions, as well as from jugular vein and carotid artery. A consistently lower partial pressure of carbon dioxide and a greater partial pressure of oxygen and pH were found in blood samples from pulmonary arterial wedge than from carotid artery. A technique for safe and rapid collection of pulmonary trunk and pulmonary arterial wedge blood gases, pH, and pressure data, using a balloon-tipped flow-directed catheter, is described in the nonsedated, nontranquilized, resting, adult horse.     

Pain management in ruminants.

Based on the available literature, the most important tool available in modern veterinary medicine is preemptive analgesia. Veterinarians must capture "opportunities" to prevent the onset of pain, prevent noxious stimuli or their perception, and limit the pain-stress-distress cascade that results in altered behavior and deviation from physiologic norms. Rational treatment of pain requires an appreciation of its consequences, a fundamental understanding of the mechanisms that are responsible for its production,and a practical appreciation of the analgesic drugs that are available. The goal of pain treatment should be to restore normal (physiologic) pain responses and to eliminate pathologic pain processes. In this context, pain therapy should be directed at the multiple mechanisms (multimodal therapy)responsible for its production, and analgesic therapies should be instituted before (preemptive therapy) pain is initiated (eg, surgery) whenever possible.     

Anesthetic and cardiovascular effects of balanced anesthesia using constant rate infusion of midazolam-ketamine-medetomidine with inhalation of oxygen-sevoflurane (MKM-OS anesthesia) in horses

The anesthetic sparring and cardiovascular effects produced by midazolam 0.8 mg/ml-ketamine 40 mg/ml-medetomidine 0.05 mg/ml (0.025 ml/kg/hr) drug infusion during sevoflurane in oxygen (MKM-OS) anesthesia was determined in healthy horses. The anesthetic sparring effects of MKM-OS were assessed in 6 healthy thoroughbred horses in which the right carotid artery was surgically relocated to a subcutaneous position. All horses were intubated and ventilated with oxygen using intermittent positive pressure ventilation (IPPV). The end-tidal concentration of sevoflurane (ET(SEV)) required to maintain surgical anesthesia was approximately 1.7%. Heart rate and mean arterial blood pressure averaged 23-41 beats/min and 70-112 mmHg, respectively. All horses stood between 23-44 min after the cessation of all anesthetic drugs. The cardiovascular effects of MKM-OS anesthesia were evaluated in 5 healthy thoroughbred horses ventilated using IPPV. Anesthesia was maintained for 4 hr at an ET(SEV) of 1.7%. Each horse was studied during left lateral (LR) and dorsal recumbency (DR) with a minimum interval between evaluations of 1 month. Cardiac output and cardiac index were maintained between 70-80% of baseline values during LR and 65-70% of baseline values during DR. Stroke volume was maintained between 75-85% of baseline values during LR and 60-70% of baseline values during DR. Systemic vascular resistance was not different from baseline values regardless of position. MKM-OS anesthesia may be useful for prolonged equine surgery because of its minimal cardiovascular depression in both of lateral and dorsal recumbency.     

Effects of xylazine on canine coronary artery vascular rings

OBJECTIVE: To determine the effects of xylazine on canine coronary artery smooth muscle tone. SAMPLE POPULATION: Hearts of 26 healthy dogs. PROCEDURE: Dogs were anesthetized with pentobarbital, and vascular rings of various diameters were prepared from the epicardial coronary arteries. Vascular rings were placed in tissue baths to which xylazine was added (cumulative concentrations ranging from 10(-10) to 10(-4) M), and changes in vascular ring tension were continuously recorded. Effects of the nitric oxide inhibitor NG-nitro-L-arginine methyl ester (L NAME; 5 mM), the alpha1-adrenoceptor antagonist prazosin (10 mM), and the alpha2-adrenoceptor antagonist atipamezole (10 mM) on xylazine-induced changes in vascular ring tension were determined. Results were expressed as percentage of maximal contraction for each vascular ring preparation. RESULTS: Xylazine induced vasoconstriction of small (< 500-microm-diameter) and medium (500- to 1,000-microm-diameter) vascular rings but not of large (> 1,000-microm-diameter) rings. For large vascular rings, L-NAME, atipamezole, and prazosin did not significantly affect the contractile response to xylazine. For small vascular rings, the contractile response following addition of xylazine to rings treated with L-NAME was not significantly different from the contractile response following addition of xylazine to control rings, except at a xylazine concentration of 10(-6) M. Xylazine-induced vasoconstriction of small vascular rings was blocked by atipamezole, but the addition of prazosin had no effect on xylazine-induced vasoconstriction. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that xylazine increases smooth muscle tone of small canine coronary arteriesand that this effect is predominantly mediated by stimulation of alpha2adrenoceptors.     

Partial and conditional maximum likelihood for variance-component estimation

SUMMARY: Patterson and Thompson's idea of 'error contrasts' (or restricted maximum likelihood) (1971) was extended to multiple sets of linear contrasts for variance component estimtion. The error contrasts were established in such a way that only errors are retained in the model. The error variance was then estimated by maximizing the likelihood function obtained from the error contrasts. More sets of linear contrasts were then progressively established such that each set of linear contrasts contains only one class of random effects and the errors. A likelihood function was constructed and maximized for each variance of random effects given the error variance held at its estimated value. The likelihood function for estimating the covariance component between two classes of random effects was established such that all other random effects are treated as fixed effects. The likelihood function was then maximized with respect to the covariance given the two variance components fixed at their estimated values. The multidimensional optimization problem in the traditional restricted maximum-likelihood problem was then turned into several one-dimensional optimization problems by using this technique. Inasmuch as the error variance was estimated using a partial likelihood function and the other variance components are estimated using likelihood functions conditional on the estimated error variance, the method is referred to as partial and conditional maximum likelihood (PCML). ZUSAMMENFASSUNG: Partielle und bedingte Maximum Likelihood zur Sch?tzung von Varianzkomponenten Die Patterson und Thompson Vorstellungen von 'Fehlerkontrasten' (1971) (oder beschr?nkte maximale Likelihood) wurde auf multiple Gruppen linearer Kontraste für Varianzkomponenten- sch?tzung ausgedehnt. Die Fehlerkontraste erfolgen in der Form, da? nur Fehler im Modell verbleiben. Die Fehlervarianz wurde dann durch Maximierung der Likelihood Funktion von Fehlerkontrasten gesch?tzt. Weitere Gruppen linearer Kontraste wurden nacheinander etabliert dergestalt, da? jede Gruppe linearer Kontraste nur eine Klasse zuf?lliger Wirkungen und die Fehler enth?lt. Eine Likelihood Funktion wurde konstruiert und für jede Varianz von Zufallsgr??en maximiert unter der Voraussetzung, da? die Fehlervarianz auf ihrem gesch?tzten Wert verbleibt. Die Likelihood Funktion zur Sch?tzung der Ko-Varianzkomponenten zwischen zwei Klassen zuf?lliger Wirkungen wurde in der Form aufgestellt, da? alle anderen Zufallswirkungen als fixe behandelt werden. Die Likelihood Funktion wurde maximiert im Hinblick auf Ko-Varianz bei gegebenen gesch?tzten Varianzkomponenten. Das multidimensionale Optimierungsproblem der traditionellen restringierten Maximum Likelihood wurde auf diese Weise in ein eindimensionales Optimierungsproblem verwandelt. Nachdem die Fehlervarianz aus der partiellen Likelihood Funktion und die anderen Varianzkomponenten unter Verwendung der bedingten Likelihood Funktionen gesch?tzt worden waren, wurde die Methode als partielle und bedingte Maximum Likelihood (pcml) bezeichnet.     

Corpus Luteum–Endometrium–Embryo Interactions in the Dairy Cow: Underlying Mechanisms and Clinical Relevance

Conception rates of dairy cows are currently declining at an estimated 1% every year. Approximately, 35% of embryos fail to prevent luteolysis during the first three weeks of gestation. Interactions between the corpus luteum, endometrium and embryo are critical to the successful establishment of pregnancy and inadequacies will result in the mortality of the embryo. For example, as little as a one day delay in the post-ovulatory rise of progesterone has serious consequences for embryo development and survival. Recently, we found that LH support, degree of vascularization and luteal cell steroidogenic capacity were not the major factors responsible for this luteal inadequacy, but are nevertheless essential for luteal development and function. Progesterone acting on its receptor in the endometrium stimulates the production of endometrial secretions on which the free-living embryo is dependent. However, their exact composition and effects of inadequate progesterone remains to be determined. The embryo is recognized through its secretion of interferon tau (IFNT), which suppresses luteolytic pulses of prostaglandin F_2α. In the cow, it is most likely that IFNT inhibits oxytocin receptor up-regulation directly and does not require the prior inhibition of oestrogen receptor α (ESR1). Unravelling the precise luteal-endometrium and embryo interactions is essential for us to understand pregnancy establishment and development of strategies to reverse the declining fertility of dairy cows.