ACE inhibitors in HF restore canine pulmonary endothelial function and ANG II vasoconstriction.

Chronic mitral regurgitation (MR) in dogs results in pulmonary congestion and increased cardiac angiotensin-converting enzyme (ACE) activity and angiotensin (ANG) II levels. ACE could contribute to altered pulmonary vasomotion in heart failure, and ACE inhibitor (ACEI) therapy may normalize pulmonary vasomotion. We evaluated pulmonary artery (PA) responses to ANG II and bradykinin (BK) in control dogs, in dogs with 4 mo of MR, in MR dogs treated with the ACEI ramipril (MR + R), and in control dogs treated with ramipril (C + R). Mean PA systolic pressure increased in MR dogs (21 +/- 4 mmHg) but was normal in MR + R dogs (13 +/- 1 mmHg). Constriction of PA rings to ANG II was depressed in MR dogs. ACEI treatment (MR + R) restored ANG II responsiveness, but peak ANG II response (3.6 +/- 0.2 g) in MR + R dogs remained lower than in C + R dogs (4.7 +/- 0.2 g). Endothelium-dependent relaxation to BK was decreased (-87 +/- 4% C, -65 +/- 4% MR; P < 0.05). Ramipril (MR + R) restored relaxation to BK. This demonstrates that pulmonary congestion results in impaired pulmonary vasomotion to ANG II and BK, which ACEIs could normalize, supporting the use of ACEIs in clinical management of chronic congestive heart failure.

Differential expression of angiotensin-converting enzyme and chymase in dogs with chronic mitral regurgitation.

The current study tested the hypothesis that angiotensin-converting enzyme (ACE) and chymase expression are subject to different regulatory processes in the heart, as well as the lungs and kidneys and, as a result, have an important effect on the efficacy of ACE inhibitor treatment in modulating tissue angiotensin II (ANG II) levels in heart failure. A total of 18 dogs underwent the induction of mitral regurgitation and were followed for 5 months. Eleven dogs were untreated and seven received the ACE-inhibitor ramipril at a dose of 10 mg PO BID. Seventeen dogs underwent a sham-operation: six of these dogs were treated with ramipril for 3 months (10 mg PO BID) and 11 were untreated and followed for 3 months prior to sacrifice. In mitral regurgitation dogs, ANG II levels were increased >2-fold in left ventricle, lungs, and kidney, but were normalized with ACE inhibitor-treatment only in the left ventricle. In the left ventricle and lungs steady state ACE mRNA levels and ACE activities were increased 2-fold in treated and untreated mitral regurgitation dogs compared to shams (P<0.05, ANOVA). In contrast, chymase mRNA levels were decreased by >50% and chymase activity was increased in left ventricle (LV) of mitral regurgitation dogs (P<0.05). Neither chymase mRNA nor chymase activity could be detected in the kidney; however, kidney ACE mRNA and ACE activity were significantly upregulated in treated and untreated mitral regurgitation dogs (P<0. 05). These results suggest that ACE and chymase expression are regulated differentially in the dog in response to chronic mitral regurgitation and ACE inhibitor treatment. Further, these responses, as well as regulation of ANG II formation, are organ specific.

Evidence for angiotensin-converting enzyme- and chymase-mediated angiotensin II formation in the interstitial fluid space of the dog heart in vivo.

BACKGROUND: We have previously demonstrated that angiotensin II (Ang II) levels in the interstitial fluid (ISF) space of the heart are higher than in the blood plasma and do not change after systemic infusion of Ang I. In this study, we assess the enzymatic mechanisms (chymase versus ACE) by which Ang II is generated in the ISF space of the dog heart in vivo. METHODS AND RESULTS: Cardiac microdialysis probes were implanted in the left ventricular (LV) myocardium (3 to 4 probes per dog) of 12 anesthetized open-chest normal dogs. ISF Ang I and II levels were measured at baseline and during ISF infusion of Ang I (15 micromol/L, n=12), Ang I+the ACE inhibitor captopril (cap) (2.5 mmol/L, n=4), Ang I+the chymase inhibitor chymostatin (chy) (1 mmol/L, n=4), and Ang I+cap+chy (n=4). ISF infusion of Ang I increased ISF Ang II levels 100-fold (P<0.01), whereas aortic and coronary sinus plasma Ang I and II levels were unaffected and were 100-fold lower than ISF levels. Compared with ISF infusion of Ang I alone, Ang I+cap (n=4) produced a greater reduction in ISF Ang II levels than did Ang I+chy (n=4) (71% versus 43%, P<0.01), whereas Ang I+cap+chy produced a 100% decrease in ISF Ang II levels. CONCLUSIONS: This study demonstrates for the first time a very high capacity for conversion of Ang I to Ang II mediated by both ACE and chymase in the ISF space of the dog heart in vivo.

Survival in dogs with nasal adenocarcinoma: 64 cases (1981-1995).

Case records of 64 dogs with nasal adenocarcinoma were reviewed. The effects of age, gender, tumor stage, presence of metastatic lesions, and treatment method on survival time were examined. Surgery groups included rhinotomy (n = 9), transnasal curettage (n = 29), and no surgery (n = 26). Chemotherapy groups included fluorouracil-cyclophosphamide combination therapy (n = 15), mitoxantrone (n = 7), and no chemotherapy (n = 42). Fifty-three dogs received fractionated cobalt 60 radiation therapy. Surgical procedure, chemotherapy group, and stage of primary tumor were not significantly associated with survival time (P > .05). Dogs that received radiation therapy had a significantly longer median survival time (424 days) than dogs that did not (126 days)(P = .0001). The presence of either regional lymph node or pulmonary metastasis was associated with significantly shorter median survival time (109 days) when compared to dogs without metastases (393 days)(P = .0125). When only dogs that had received radiation therapy were considered, neither surgical treatment nor chemotherapy group was associated with significant changes in median survival time. An alternate staging system emphasizing the presence or absence of metastases is proposed.

Assessment of current techniques for determining tracheal luminal stenosis in dogs.

OBJECTIVE: To assess the accuracy of current antemortem and postmortem techniques for determining tracheal luminal stenosis. ANIMALS: 15 dogs. PROCEDURE: Percentage of tracheal luminal stenosis (PTLS) was determined by 6 methods, using measurements obtained by radiography, tracheoscopy, and necropsy after selected tracheostomy techniques were performed. To calculate PTLS, dorsoventral tracheal diameter was measured from preoperative and postoperative lateral cervical radiographic views. Preoperative or normal tracheal segments adjacent to the stenotic area were used to obtain normal tracheal diameter measurements. Planimetrically determined cross-sectional area (CSA), obtained from pre- and postoperative tracheoscopic photographs, was used to calculate PTLS. The CSA of tracheal specimens obtained at necropsy was determined, using the formula for an ellipse. Percentage of luminal stenosis was calculated, using CSA of the stenotic site and of segments craniad and caudad to the site obtained at necropsy or at surgery. All methods were compared with the control method of planimetrically determined CSA of sections obtained at necropsy of the tracheostomy and segments craniad and caudad to the site. RESULTS: Correlation was poor for radiographic and tracheoscopic techniques (r = 0.146 to 0.458, P > 0.05) The formula for an ellipse accurately predicted PTLS when measurements obtained at surgery (r = 0.516, P = 0.049) or segments craniad and caudad (r = 0.853, P < 0.001) to the site were used. CONCLUSION: Antemortem methods of assessing PTLS did not correlate with control planimetric methods. Methods using CSA determined by tracheal diameter were weakly correlated to control planimetric techniques. CLINICAL RELEVANCE: Accurate measurement of the degree of tracheal stenosis cannot be made in clinical patients using current techniques.

Volume-overload cardiac hypertrophy is unaffected by ACE inhibitor treatment in dogs.

We tested the hypothesis that angiotensin-converting enzyme (ACE) inhibitor therapy prevents volume-overload hypertrophy in dogs with chronic mitral regurgitation (MR). Seven adult mongrel dogs receiving ramipril (R; 10 mg orally, twice/day) for 4 mo were compared with 11 dogs receiving no R (N) for 4 mo after induction of MR. Cine-magnetic resonance imaging demonstrated that left ventricular (LV) mass increased in the R-MR dogs [80 +/- 4 (SE) to 108 +/- 7 g, P < 0.01] and in the N-MR dogs (92 +/- 7 to 112 +/- 8 g, P < 0.001). LV myocyte cell length was greater in the R-MR and N-MR dogs (203 +/- 6 and 177 +/- 10 microns, respectively) than in normal (144 +/- 4 microns, P < 0.05) dogs. There was significant loss of the collagen weave pattern by scanning electron microscopy in both R-MR and N-MR dogs. LV ACE and chymase activities were significantly elevated in R-MR and N-MR compared with normal dogs. LV angiotensin II (ANG II) levels in the R-MR dogs (28 +/- 12 pg/g) were reduced to levels seen in normal dogs (28 +/- 4 pg/g) compared with N-MR dogs (72 +/- 11 pg/g, P < 0.05). Steady-state AT1-receptor mRNA levels decreased 66% in N-MR compared with normal dogs (P < 0.001) and increased 1.5-fold in R-MR compared with normal dogs (P < 0.01). Thus upregulation of the AT1 receptor in the R-MR hearts may provide a mechanism by which normal intracardiac ANG II levels could continue to mediate LV hypertrophy. However, the mechanism of dissolution collagen weave in both N-MR and R-MR hearts may be related to the stretch of volume overload.

Compartmentalization of angiotensin II generation in the dog heart. Evidence for independent mechanisms in intravascular and interstitial spaces.

Angiotensin-converting enzyme inhibitors have beneficial effects that are presumably mediated by decreased angiotensin II (ANG II) production. In this study, we measure for the first time ANG I and ANG II levels in the interstitial fluid (ISF) space of the heart. ISF and aortic plasma ANG I and II levels were obtained at baseline, during intravenous infusion of ANG I (5 microM, 0.1 ml/min, 60 min), and during ANG I + the angiotensin-converting enzyme inhibitor captopril (cap) (2.5 mM, 0.1 ml/min, 60 min) in six anesthetized open-chested dogs. ISF samples were obtained using microdialysis probes inserted into the left ventricular myocardium (3-4 probes/dog). ANG I increased mean arterial pressure from 102+/-3 (SEM) to 124+/-3 mmHg (P < 0.01); addition of cap decreased MAP to 95+/-3 mmHg (P < 0.01). ANG I infusion increased aortic plasma ANG I and ANG II (pg/ml) (ANG I = 101+/-129 to 370+/-158 pg/ml, P < 0.01; and ANG II = 22+/-40 to 466+/-49, P < 0.01); addition of cap further increased ANG I (1,790+/-158, P < 0.01) and decreased ANG II (33+/-49, P < 0.01). ISF ANG I and ANG II levels (pg/ml) were > 100-fold higher than plasma levels, and did not change from baseline (8,122+/-528 and 6,333+/-677), during ANG I (8,269+/-502 and 6, 139+/-695) or ANG I + cap (8,753+/-502 and 5,884+/-695). The finding of very high ANG I and ANG II levels in the ISF vs. intravascular space that are not affected by IV ANG I or cap suggests that ANG II production and/or degradation in the heart is compartmentalized and mediated by different enzymatic mechanisms in the interstitial and intravascular spaces.

Use of a modified surgical approach to the right atrium for retrieval of heartworms in a dog.

A 2-year-old 2-kg female Maltese dog was referred for treatment of dirofilariosis and mild caval syndrome characterized by hemolysis and lethargy. Ultrasonography revealed worms within the caudal vena cava, right auricle, right ventricle, and pulmonary artery. Because of the mild clinical signs and small size of the dog, jugular venotomy was not performed, and treatment with sodium caparsolate was instituted. A markedly adverse reaction was noticed on initial injection, characterized by cardiac and respiratory arrest. Further treatment with sodium caparsolate was discontinued. Because of progression of the dog's condition surgical removal of heartworms was elected. A modified surgical approach to the right atrium was performed, using a cannula introduced through a pursestring placed in the wall of the right auricle. This technique allowed almost complete removal of heartworms with minimal blood loss. Postoperative ultrasonography revealed a single heart-worm remaining in the distal portion of the left pulmonary artery, but it was subsequently absorbed.

Increased ACE and chymase-like activity in cardiac tissue of dogs with chronic mitral regurgitation.

The current study was designed to test the hypothesis that intracardiac angiotensin-converting enzyme (ACE) activity, chymase-like activity, and angiotensin (ANG) peptide levels are increased and are positively related to wall stress estimates in response to the chronic low pressure volume overload of mitral regurgitation produced by percutaneous chordal rupture in the dog. Chronic mitral regurgitation (MR) resulted in an increase in left ventricular (LV) end-diastolic volume [59 +/- 11 (SD) to 103 +/- 32 ml, P < 0.001], LV mass (96 +/- 17 to 114 +/- 23 g, P < 0.001), and a decrease in the LV mass-to-end-diastolic volume ratio (1.64 +/- 0.22 to 1.16 +/- 0.23 g/ml, P < 0.001) measured by magnetic resonance imaging. In vitro studies of heart tissue extracts demonstrated that the majority of ANG II-forming activity was from chymase-like activity rather than from ACE activity in five normal (83.5 +/- 7.5 vs. 6.04 +/- 5.2%) and seven MR hearts (86 +/- 3.9 vs. 2.6 +/- 1.7%). ACE activity (1.22 +/- 0.22 vs. 3.55 +/- 0.62 mU/g, P < 0.05) and chymase-like activity (9.42 +/- 4.64 vs. 20.60 +/- 8.41 nmol.g-1.min-1, P < 0.05) were increased in MR compared with normal hearts. ACE activity correlated with the LV mass-to-volume ratio (r = -0.93, P < 0.001) and LV diastolic wall stress ( r = 0.71, P < 0.05); however, chymase-like activity did not correlate with any hemodynamic parameter. ANG II levels were significantly higher in the midwall of the left ventricle in MR hearts than in normal controls (85 +/- 39 vs. 27 +/- 16 pg/g, P < 0.01). Our results demonstrate a positive correlation between LV diastolic wall stress and increased ACE activity with increased ANG II stores, suggesting that mechanical wall stress activated intracardiac ACE. Although chymase accounted for most ANG II formation in vitro in extracts of both normal and MR dog hearts, the significance of this enzyme in vivo remains unclear.

Effects of lactated Ringer solution and prednisolone sodium succinate on dogs with induced hemorrhagic shock.

Hemorrhagic shock was induced in nonsplenectomized dogs by removing 41% of their blood volume over a 15-minute period. Hemodynamic and metabolic variables were determined prior to and for 3 hours after completion of hemorrhage. One group of 5 dogs was not treated. After the 30-minute sample was collected, a second group of 5 dogs was given lactated Ringer solution (LRS) at 88 ml/kg of body weight, IV. A third group of 5 dogs was given LRS (88 ml/kg, IV) and prednisolone sodium succinate (11 mg/kg, IV) 30 minutes after hemorrhage. The IV administration of LRS was completed within 15 minutes. The glucocorticoid was administered as an IV bolus after 500 ml of LRS had been given. The large volume and administration of LRS significantly (P = 0.05) improved many of the hemodynamic and metabolic effects of acute hemorrhage and hemorrhagic shock. At one time or another during the 2.5-hour observation period after the initiation of treatment, mean arterial pressure, cardiac index, systemic vascular resistance, heart rate, respiratory rate, lactate, glucose, and arterial and venous blood gas values were significantly (P = 0.05) improved, compared with baseline values. The addition of prednisolone sodium succinate to the treatment regimen improved the effectiveness of LRS alone only in some dogs at random sampling times. Significant trends were not observed except, possibly, the improvement of venous pH and A-V pH and PCO2 differences.

Physiological effects of a perfluorochemical blood substitute in beagle dogs.

Perfluorochemical (PFC) emulsions have been examined for use as erythrocyte substitutes in the treatment of various disease states. The physiological changes induced by PFC infusion would be an important determinant of successful clinical therapy. Previous studies have reported PFC induced changes in the disposition of drugs. This report describes some physiological (hematology, cardiovascular, liver enzyme) changes resulting from a 30% blood exchange with a PFC emulsion in Beagle dogs. A 30% blood exchange with hydroxyethylstarch (HES) also was evaluated and compared to the PFC emulsion exchange. The blood pressure was markedly reduced shortly after PFC infusion while HES infusion produced only minor changes. Changes in the heart rate following blood replacement were similar for PFC and HES treated dogs. Hematology profiles also were similar for the PFC and HES treatment groups. The liver enzyme levels in PFC treated dogs showed marked elevations beginning shortly after PFC infusion and remained elevated for months after the initial PFC blood replacement. In contrast, HES treated dogs exhibited no observable changes in liver enzyme levels over the time course of the study.

Comparative study of ultrasonography and arteriography of the carotid artery of xylazine-sedated and halothane-anesthetized goats.

The carotid artery of clinically normal goats was examined, using duplex ultrasonography and arteriography. The diameter of the carotid artery was measured by use of two-dimensional ultrasonography and Doppler ultrasonography, respectively, before and after xylazine administration. The diameter of the artery was also measured by use of an arteriography technique in halothane-anesthetized goats. There was no significant difference between the mean diameter of the carotid artery measured by ultrasonography in conscious nonsedated goats and that determined by arteriography in goats under halothane anesthesia. On the other hand, ultrasonography of xylazine-sedated goats revealed an increase of carotid artery diameter of 20 to 30%. There was no change in the velocity of blood flow after xylazine administration.

The pony as an animal model for vascular implants.

This study evaluated the pony as a potentially suitable model for vascular implant research. Healthy, conditioned ponies were randomly assigned to one of three groups: group I, carotid artery autografts (n = 6); group II, e-PTFE carotid interpositional grafts (n = 5); and group III, e-PTFE carotid interpositional grafts plus aspirin (10 mg/kg) and dipyridamole (3.5 mg/kg) drug administration. It was found that autografts remained patent longest (mean = 396.2 days; grafts were still patent at time of writing) followed by group III grafts (157.5 days), with group II grafts remaining patent for the shortest duration (61.1 days), (p less than 0.01). Patency was determined using two-dimensional real-time ultrasonography with Doppler velocimetry and/or arteriography. It was demonstrated that the pony's response to antithrombotic drugs was consistent and comparable to that in other animal models, both with respect to platelet function and affect on patency rate. The combination of the ease of surgical manipulation, drug administration, and platelet function testing, the comparable size of the pony and its heart and blood vessels to that of an adult human, the long life span of ponies, and the patency results of this study have demonstrated that the pony is a valuable animal model for vascular research.

Platelet function testing in the pony.

Platelet isolation techniques and platelet function were evaluated in 35 adult ponies. Platelet recovery from whole blood was consistent and the preparation of platelet rich plasma was facilitated by an enhanced erythrocyte sedimentation rate. All platelet samples aggregated in response to 10 microM ADP. However, concentrations of ADP as high as 100 microM did not elicit significant 14C-serotonin release. Collagen induced irreversible platelet aggregation and 14C-serotonin release in all samples. The threshold dose for collagen in most ponies was 1.5 micrograms. Arachidonic acid (500 microM) failed to induce irreversible platelet aggregation or 14C-serotonin release in any of the samples evaluated. Pony platelets were nonresponsive to epinephrine (5.5 microM).

Biologic characterization of canine melanoma cell lines.

Eight canine melanoma cell lines were established from tissues from 6 dogs with spontaneous primary or metastatic melanomas. Cell lines were characterized for morphologic features and growth patterns on plastic, pigmentation, ultrastructure, cloning efficiency in soft agar, and tumorigenicity in nude mice. Biologic properties of cell lines were distinct and preserved during 40 to 120 passages in vitro. All cell lines were clonogenic and tumorigenic.

Ureterocolonic anastomosis in a dog with transitional cell carcinoma of the urinary bladder.

Ureterocolonic anastomosis and cystectomy were performed in a dog for treatment of transitional cell carcinoma of the urinary bladder. The dog remained an acceptable house pet for 10 months after surgery. However, the tumor recurred 10 months after surgery, and the dog was euthanatized. Our results indicated that the combination of ureterocolonic anastomosis and cystectomy can be an acceptable form of palliative treatment for transitional cell carcinoma of the urinary bladder in the dog.

Pharmacokinetics of prednisolone sodium succinate and its metabolites in normovolemic and hypovolemic dogs.

Tritium-labeled prednisolone sodium succinate was administered IV to 4 healthy, awake, nonsplenectomized dogs. The concentration of prednisolone and its metabolites in the plasma were measured for 10 hours. Forty-one percent of the blood volume of these dogs was removed, and plasma prednisolone was measured again. The data before and after hemorrhage were fitted to a 2-compartment open model. From plasma profiles, a rapid distributional phase, followed by a slower phase, was observed in control and shock groups. Volume of the central compartment of prednisolone before and after hemorrhage was 165 ml/kg of body weight and 110 ml/kg, respectively; and the difference was significant (P less than 0.05). The rate of total body clearance of prednisolone before and after hemorrhage was 3.96 ml/min/kg and 2.53 ml/min/kg, respectively; the difference was significant. The mean plasma half-lives for prednisolone sodium succinate and its metabolites, before and after hemorrhage, were 166 and 197 minutes, respectively; the difference was not significant. The mean half-life data indicated that prednisolone sodium succinate may be repeated in a patient 2.5 to 3 hours after onset of treatment if signs of hypovolemic shock reappear.

Surgical management of cancer.

In cancer surgery, operating time, tissue trauma and other stress should be minimized because circulating dormant tumor cells may be reactivated by stress, including that of anesthesia. Rectal polyps and Sertoli-cell tumors should be removed as soon after diagnosis as possible. Neutering is recommended to reduce the risk of certain tumors. Biopsies should contain tissue from the center and periphery of the lesion. Laparotomy or thoracotomy may be necessary to visually inspect internal tumors. Debulking or partial resection of large tumors may render them more susceptible to chemotherapy or irradiation. Palliative surgery may be desirable to comfortably prolong an animal's life. In curative surgery, enlarged local lymph nodes should also be resected, hemorrhage controlled and lavage used to prevent tumor-cell seeding. Complete resection should take precedence over reconstructing the defect created by resection.

Experimental hemorrhage in splenectomized and nonsplenectomized dogs.

Ten splenectomized and ten nonsplenectomized conscious dogs were subjected to hemorrhage of 41% of their blood volume over a 15-minute period. Hemodynamic and metabolic variables were monitored for 4 hours after hemorrhage. Mortality (100%) occurred in the splenectomized group. Significant (P < 0.001) hemodynamic responses after hemorrhage included hypotension, tachycardia, low central venous pressure, and decreased ECG voltage of the R wave. Tachypnea was noted in the absence of hypoxia, hypercapnia, and acidosis inthe nonsplenectomized dogs. Significant (P < 0.001) hypocapnia and mean PCO2 values of 13.9 MM of Hg and 23.5 mm of Hg in splenectomized and nonssplenectomized dogs, respectively, was noted. Mean hemoglobin levels were significantly (P < 0.001) decreased after hemorrhage in the splenectomized dogs. The absence of a change in hemoglobin in thenonsplenectomized dogs was attributed to the translocationof extracellular fluid into the vascular space which diluted the high concentration of RBC from splenic contraction. Other changes noted after hemorrhage were hyperglycemia, increased blood cortisol, and increased pyruvate and lacte levels. Changes were not noted in pyruvate-to-lactate ratios.

Microscopic tissue alterations following cryosurgery of canine skin.

Cryosurgery of cutaneous tissue of 6 dogs was followed by serial biopsies throughout the necrotizing and healing periods. The duration of cold application was controlled by thermocouple monitoring in 3 dogs and by a standard time in 3 dogs. Tissue changes following cryosurgery were consistent in all 6 dogs and were composed of edema, erythema, necrosis, sloughing, granulation, and epithelialization.