Comparison of the cardiovascular effects of intracellular cyclic adenosine 3',5'-monophosphate (cAMP)-modulating agents in isoflurane-anesthetized cats

Cardiovascular and Gas Exchange Effects of Individualized Positive End-Expiratory Pressures in Cats Anesthetized With Isoflurane

Objectives

To compare the effects of four levels of end-expiratory pressure [zero (ZEEP) and three levels of positive end-expiratory pressure (PEEP)] on the cardiovascular system and gas exchange of cats anesthetized with isoflurane and mechanically ventilated for 3 h with a tidal volume of 10 ml/kg.

Study Design

Prospective, randomized, controlled trial.

Animals

Six healthy male neutered purpose-bred cats.

Methods

Anesthesia was induced with isoflurane and maintained at 1.3 minimum alveolar concentration. PEEP of maximal respiratory compliance (PEEP_maxCrs) was identified in a decremental PEEP titration, and cats were randomly ventilated for 3 h with one of the following end-expiratory pressures: ZEEP, PEEP_maxCrs minus 2 cmH₂O (PEEP_maxCrs−2), PEEP_maxCrs, and PEEP_maxCrs plus 2 cmH₂O (PEEP_maxCrs+2). Cardiovascular and gas exchange variables were recorded at 5, 30, 60, 120, and 180 min (T5 to T180, respectively) of ventilation and compared between and within ventilation treatments with mixed-model ANOVA followed by Dunnet's and Tukey's tests (normal distribution) or Friedman test followed by the Dunn's test (non-normal distribution). Significance to reject the null hypothesis was considered p < 0.05.

Results

Mean arterial pressure (MAP—mmHg) was lower in PEEP_maxCrs+2 [63 (49–69); median (range)] when compared to ZEEP [71 (67–113)] at T5 and stroke index (ml/beat/kg) was lower in PEEP_maxCrs+2 (0.70 ± 0.20; mean ± SD) than in ZEEP (0.90 ± 0.20) at T60. Cardiac index, oxygen delivery index (DO₂I), systemic vascular resistance index, and shunt fraction were not significantly different between treatments. The ratio between arterial partial pressure and inspired concentration of oxygen (PaO₂/FIO₂) was lower in ZEEP than in the PEEP treatments at various time points. At T180, DO₂I was higher when compared to T5 in PEEP_maxCrs. Dopamine was required to maintain MAP higher than 60 mmHg in one cat during PEEP_maxCrs and in three cats during PEEP_maxCrs+2.

Conclusion

In cats anesthetized with isoflurane and mechanically ventilated for 3 h, all levels of PEEP mildly improved gas exchange with no significant difference in DO₂I when compared to ZEEP. The PEEP levels higher than PEEP_maxCrs−2 caused more cardiovascular depression, and dopamine was an effective treatment. A temporal increase in DO₂I was observed in the cats ventilated with PEEP_maxCrs. The effects of these levels of PEEP on respiratory mechanics, ventilation-induced lung injury, as well as in obese and critically ill cats deserve future investigation for a better understanding of the clinical use of PEEP in this species.

Large-Scale Transcriptional Profiling of Molecular Perturbations Reveals Cell Line Specific Responses and Implications for Environmental Screening

Cell-based bioassays represent nearly half of all high-throughput screens currently conducted for risk assessment of environmental chemicals. However, there has long been a concern about the sensitivity and heterogeneity among cell lines, which were explored only in a limited manner. Here, we address this question by conducting a large-scale transcriptome analysis of the responses of discrete cell lines to specific molecules. We report the collections of >223 300 gene expression profiles from a wide array of cell lines exposed to 2243 compounds. Our results demonstrate distinct responses among cell lines at both the gene and the pathway levels. Temporal variations for a very large proportion of compounds occur as well. High sensitivity and/or heterogeneity is either cell line-specific or universal depending on the modes of action of the compounds. Among 12 representative pathways analyzed, distinct cell-chemical interactions exist. On one hand, lung carcinoma cells are always best suited for glucocorticoid receptor agonist identification, while on the other hand, high sensitivity and heterogenic features are universal for histone deacetylase inhibitors and ATPase inhibitors. Our data provide novel insights into the understanding of cell-specific responses and interactions between cells and xenobiotics. The findings have substantial implications for the design, execution, and interpretation of high-throughput screening assays in (eco)toxicology.

Changes in the myocardial performance index during dobutamine administration in anesthetized cats

OBJECTIVE

To investigate the relationship between myocardial performance index (MPI; also known as the Tei index) and cardiac function in anesthetized cats administered dobutamine.

ANIMALS

6 adult cats.

PROCEDURES

Cats were anesthetized by administration of propofol (6 mg/kg, IV), and anesthesia was maintained by administration of isoflurane. Heart rate and systolic arterial pressure (SAP) were monitored. Stroke volume, cardiac output, and aortic blood flow (ABF) were measured by use of transesophageal ultrasonography. Left ventricular fractional shortening (LVFS), mitral E-wave velocity-to-A-wave velocity (E:A) ratio, and ejection time were measured by use of transthoracic echocardiography. Dobutamine was administrated via a cephalic vein at rates of 2.5, 5.0, and 10 microg/kg/min.

RESULTS

Heart rate, SAP, cardiac output, and ABF increased with dobutamine administration, whereas stroke volume significantly decreased. The LVFS significantly increased, and the E:A ratio significantly decreased. Total isovolumic time and the MPI significantly decreased. The MPI was negatively correlated (r=-0.63) with LVFS. Conversely, the MPI was positively correlated with the E:A ratio (r=0.47), stroke volume (r=0.66), and total isovolumic time (r=0.95). However, the MPI was not significantly correlated with heart rate, SAP, cardiac output, or ABF.

CONCLUSION AND CLINICAL RELEVANCE

Analysis suggested that the MPI provides a sensitive clinical assessment of cardiac response to medication in cats, which may be similar to the usefulness of the MPI reported in humans.

Effects of increasing infusion rates of dopamine, dobutamine, epinephrine, and phenylephrine in healthy anesthetized cats

OBJECTIVE

To determine the cardiopulmonary effects of increasing doses of dopamine, dobutamine, epinephrine, and phenylephrine and measure plasma concentrations of norepinephrine, epinephrine, and dopamine in cats anesthetized with isoflurane.

ANIMALS

6 healthy adult cats.

PROCEDURES

Each cat was anesthetized with isoflurane (1.5 X minimum alveolar concentration) on 4 occasions. Cardiopulmonary measurements were obtained after a 30-minute stabilization period; 20 minutes after the start of each infusion dose; and 30, 60, and 90 minutes after the infusion was discontinued. Cats received 5 progressively increasing infusions of epinephrine or phenylephrine (0.125, 0.25, 0.5, 1, and 2 microg/kg/min) or dobutamine or dopamine (2.5, 5, 10, 15, and 20 microg/kg/min). The order of treatment was randomly allocated. Results-All 4 treatments increased oxygen delivery. Heart rate (HR) increased during administration of all drugs except phenylephrine, and mean arterial pressure increased during administration of all drugs except dobutamine. A progressive metabolic acidosis was detected, but whole-blood lactate concentration only increased during administration of epinephrine and dobutamine. Systemic vascular resistance index increased during administration of phenylephrine, decreased during administration of dobutamine, and remained unchanged during administration of dopamine and epinephrine. A positive inotropic effect was detected with all treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

During anesthesia in cats, administration of dopamine, dobutamine, and epinephrine may be useful for increasing cardiac output, with dopamine having the most useful effects. Administration of phenylephrine increased cardiac and systemic vascular resistance indexes with minimal effect on HR and may be useful for increasing mean arterial pressure without increasing HR.