EFFECTS ON BARORECEPTOR SENSITIVITY OF REPEATED ANESTHESIA WITH MORPHINE-CHLORALOSE IN THE DOG A Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Sciences in the Graduate School of The Ohio State University By Daise Nunes Queiroz da Cunha, DVM ***** The Ohio State University 2005 Master's Examination Committee: , Approved by: Dr. Robert L. Hamlin, DVM, PhD, Adviser Dr. Kathryn Meurs, DVM, PhD V\!\c Adviser Dr. Mark Strauch, PhD Veterinary Biosciences Graduate Pro gram ABSTRACT Systemic arterial blood pressure is regulated mainly by the high-pressure baroreceptor reflex. This reflex is responsible for maintaining systemic arterial pressure despite diseases and pharmacological perturbations. An example of disease would congestive heart failure, in which the increase in sympathetic activity is responsible for reduction in baroreflex sensitivity. The clinical relevance of the baroreflex dysfunction lies in the fact that studies have shown that physical training and beta-adrenergic blockage improves baroreceptor sensitivity, as well as the patient’s prognosis. To investigate the baroreceptors in dogs, we hypothesized that baroreceptor function, as assessed by gain and time-constant, does not change with repeated exposures to morphine-chloralose anesthesia, which is a very common anesthestetic protocol used in laboratories of veterinary research. To study baroreflex, the most used tests are the oxford, neck suction, and tilt. The latter, is discussed in more detail here, since it was the method used to evaluate the baroreceptor response to morphine-chloralose anesthesia. The purpose of this study was to determine the effects of repeated doses of morphine- chloralose anesthesia on baroreceptors function, by tilting the dogs, and histological integrity, by blood profile and blood cell evaluations, as well as histopathology of the important organs. To accomplish these goals, 7 healthy hound-type dogs (20-25 kg) and 3 healthy beagle-hounds (9.5 - 12 kg), males, between 1 and 3 years of age, and healthy were studied. All dogs were given, IV, morphine sulfate (1.5 mg/kg) as a pre-anesthetic. They were then given, IV as a bolus, alpha chloralose (100 mg/kg), after which they received a continuous infusion of alpha chloralose (30 to 40 mg/kg/hour) to sustain ii anesthesia. Animals were ventilated with room air at a rate (12/minute) and a tidal volume (12.5 ml/kg) to sustain systemic arterial PaCO2 of approximately 40mmHg. To access pressure within the carotid sinus, a fluid-filled catheter, attached to a pressure transducer, was advanced retrogradely into the region of the carotid sinus for 4 dogs. To measure aortic arch sinus arterial pressure a fluid-filled catheter attached to a pressure transducer was advanced through a femoral artery into the region of the junction of the ascending aorta with the arch for 4 dogs. Electrodes forming ECG leads I and II were attached to all. Six dogs were studied 3 times with 48 hours between studies. Each time, the dogs were studied 3 times with 30 minutes in between. After baseline measurements of pressures (4 dogs) and ECG’s (6 dogs) were made for 30 seconds, dogs were tilted within <1second to a head-up-position. This head-up tilt was maintained for 20 seconds, after which the dogs were returned to the horizontal. Measurements of pressures (4 dogs) and ECG’s (6 dogs) were made the entire time. The results show that in regards to the baseline heart rate did decrease consistently with days. Neither time (P=0.50) nor day (P=0.92) was significantly associated with the maximum absolute increase in heart rate. As the experiment advances from day 1 to day 2 to day 3, the absolute decrease in heart rate becomes larger. During the initial 5 seconds of the head-up tilt the heart rate increased approximately 12 beats/minute, while peak systolic (p= 0.027), diastolic (p= 0.014), and mean pressures (p= 0.029) decreased more at the carotid sinus than at the aortic sinus. For the calculated gain (6 dogs) there were no differences among means either by day (p=0.14) or by time (p=0.992), nor was there a day-time interaction (p =0.751). The recover from each anesthetic episode was not turbulent or violent. Analysis of the blood constitutes tissues evaluated in the histology showed no alterations due to anesthetic regimen. There were no differences of significance in gain. An important limitation is the lack of assurance that constant levels of anesthesia were maintained over the 3 recordings of each day, or if constant levels were achieved each day. Recovery from this anesthetic protocol is relatively long compared to other anesthetics (e.g. propofol, isoflurane). Finally buffering of the baroreceptor response elicited from changing pressure at the carotid sinus may alter, profoundly, the role of only the carotid sinus receptors. Therefore it was concluded that 1.repeated anesthesia with iii morphine/chloralose results in no observable pathological changes monitored by histopathology, blood chemistry, and analysis of blood cellular components; 2.gain of high-pressure baroreceptor reflex may be assessed using the passive head-up tilt; 3.gain did not change significantly within an anesthetic period or on subsequent days; 4.for head-up tilt, the change in pressure on the carotid sinus was greater than the change of pressure on the aortic sinus. iv Dedicated to my family and friends v ACKNOWLEDGMENTS I am thankful to my major adviser, Dr. Robert L. Hamlin, for his genuine and grand enthusiasm to teach, support and guide me throughout this journey. His example of strength and courage has inspired many to pursue their careers with success. For all these reasons, this has been an enjoyable experience of learning. I would like to express my appreciation to my husband, Luis, for his love, incentive and support in the most challenging moments. I am also immensely grateful to my mother, father, and brother for their unconditional love. I thank Dr. March Strauch, for being supportive all the times I needed his assistance, and for his interest with my research. To Dr. Kathryn Meurs, I would like to express my gratitude for her cooperation kindness, and flexibility in the most crucial times. I want acknowledge Dr. Yoshinori Nishijima, Dr. Francesca Travesso, Dr. Adriana Pedraza, Paula Jenkins and Dr. Andy for all the extraordinary help with my experiments, and finally for being such good friends. My special thanks, to Dr. Matthew A. Buccelatto for his help with the histophatology. Finally I would like to recognize and thank Dr. Rajala-Schultz and her colleagues for their assistance with the statistical analysis. VI VITA September 30, 1976 ................ Bom-Ituiutaba, MG, Brazil 1997 - 2002 ...........................DVM University Federal ofUberlandia, MG, Brazil 2002 - 2003 ........................... Internship OARDC - (Ohio Agricultural Research and Development Center) The Ohio State University 2003 - 2004 ........................... Research Assistant OARDC - (Ohio Agricultural Research and Development Center) The Ohio State University 2004 - present. ....................... Graduate Research Associate The Ohio State University vii PUBLICATIONS 1. Moacir Santos Lacerda, Simone Tostes de Oliveira, Daise Nunes Queiroz. Anatomical variations in the Dentition of Dogs crossbreed. In Agricultural Science, Santa Maria, v.30, n.4, p.655-659, 2000. 2. Eduardo Mauricio Mendes de Lima; Frederico Ozanam Carneiro; Renato Souto Severino; Andre Luiz Quagliatto Santos; Sergio Salazar Drummond; Valdiana Araujo Leal; Daise Nunes Queiroz· Topographical study on the medullar cone in crossbreed Zebu bovine fetus. Revista Ciencias. 10-12. art. 13, 2001. 3. Julio Roquete Cardoso, Alan-kardec Martins, Daise Nunes Queiroz, Sergio Salazar Drummond, Francisco Claudio Dantas Mota, Renato Souto Severino, Frederico Ozanam Carneiro e Silva, Andre Luiz Quagliatto Santos. Origin and aspects of ramification of the cranial and caudal mesenteric arteries in chickens. Bioscience Journal. 18, n 1, 2002. 4. Yunusemre Ozkanlar, Yoshinori Nishijima, Daise da Cunha, Robert L. Hamlin. Acute effects of tacrolimus (FK506) on left ventricular mechanics. Pharmacological Research. 52: 2005 FIELDS OF STUDY Major Field: Veterinary Biosciences Specialty: Cardiovascular Physiology, Pharmacology and Clinical Cardiology. Vlll TABLE OF CONTENTS Page Abstract ................................................................................................ .ii Dedication ............................................................................................. v Acknowledgments ...................................................................................vi Vita ....................................................................................................vii List of Tables ..........................................................................................x List of Figures ........................................................................................xi List of Examples ....................................................................................xiv Chapters: 1. Introduction ......................................................................................... 1 2. Literature Review ..................................................................................4 3. Material and Methods ............................................................................34 4. Results ............................................................................................. 46 5. Discussion, Limitations,