During growth, central venous, right ventricular, pulmonary arterial, Pulmonary capillary wedge, and systemic arterial pressures, heart rate, and cardiac Output were repeatedly measured in 41 Friesian calves, considered as having conventional muscular conformation, and in 19 Belgian White and Blue double-muscled calves. A total of 123 and 70 recordings were collected in conventional and double-muscled calves, respectively. These circulatory indices were calculated: stroke volume, cardiac and stroke indices, pulmonary and systemic pulse pressures, pulmonary and systemic vascular resistance indices, and right and left ventricular work indices. Results indicated that systemic arterial and pulse pressures, as well as cardiac output, stroke volume, cardiac and stroke indices, and right and left ventricular work indices were significantly (P less than or equal to 0.05 to 0.001) lower but, in contrast, pulmonary and systemic vascular resistance indices were significantly (P less than or equal to 0.001) higher in double-muscled than in conventional calves. Right-sided vascular pressures and heart rate were similar in the 2 groups. These results indicated that global cardiac performance may be considerably poorer in double-muscled calves. Diminished cardiac performance of double-muscled calves appears to be related neither to relative bradycardia nor to reduced ventricular preload. The potential role of increased ventricular afterload or of reduced myocardial contractility in double-muscled cattle should be determined by direct measurements.

The uterine hemodynamic response to maternal positioning in dorsal recumbency was evaluated in 7 conscious pregnant cows during the third trimester. Anesthetic or sedative drugs were not administered. Uterine artery flow was measured, using a previously implanted ultrasonic flow probe. Catheters implanted in the uterine artery and vein were used for measurement of blood pressure and for blood sample collections. Heart rate, systemic arterial pressure, uterine arterial blood flow, arterial and venous oxygen and carbon dioxide tensions, and pH were measured in cows in standing position. Cows were cast with ropes and positioned in dorsal recumbency, then measurements were repeated at 15 and 30 minutes. Compared with standing measurements, dorsal recumbency caused 50% increase in heart rate and 44% increase in arterial blood pressure. Uterine artery flow did not change significantly. Despite increased ventilation, arterial oxygenation was reduced during dorsal recumbency. There were minimal differences between measurements at 15 and 30 minutes of dorsal recumbency.

Right atrial, pulmonary artery, pulmonary capillary, pulmonary artery wedge, and systemic blood pressures of strenuously exercising horses increase markedly. As a consequence, myocardial metabolic O2 demand in exercising horses must be high. Experiments were, therefore, carried out on 9 healthy, exercise-conditioned horses (2.5 to 8 years old; 481 +/- 16 kg) to ascertain the regional distribution of myocardial blood supply in the atria and ventricles at rest and during exercise. Blood flow was measured, using 15-micrometer-diameter radionuclide-labeled microspheres that were injected into the left ventricle while reference blood samples were being withdrawn at a constant rate from the thoracic aorta. Myocardial blood flow was determined at rest and during 2 exercise bouts performed on a high-speed treadmill at 8 and 13 m/s (0% grade). The sequence of exercise bouts was randomized among horses, and a 60-minute rest period was permitted between exercise bouts. There was considerable heterogeneity in the distribution of myocardial perfusion in the atria and the ventricles at rest; the right atrial myocardium received significantly (P < 0.05) less perfusion than did the left atrium, and these values were significantly (P < 0.05) less than those for the respective ventricular myocardium. The right ventricular myocardial blood flow also was significantly less than that in the left ventricle. With exercise, myocardial blood flow in all regions increased progressively with increasing work intensity and marked coronary vasodilation was observed in all cardiac regions. During exercise at 8 or 13 m/s, right and left atrial myocardial blood flows (per unit weight basis) were not different from each other. Although at treadmill speed of 8 m/s, left ventricular myocardial blood flow exceeded that in the right ventricle, this was not the case at 13 m/s, when perfusion values (per unit weight basis) became similar.

In an effort to better understand the role of vasodilators in the management of pulmonary hypertension associated with chronic heartworm disease (HWD), pulmonary hemodynamic measurements were obtained from 7 experimentally infected, anesthetized dogs before and after hydralazine administration (mean dose, 1.96 mg/kg of body weight). Five dogs were maintained on room air, while 2 were maintained on 100% oxygen during the hydralazine study. The hemodynamic effect of hydralazine in dogs with HWD was evaluated, using heart rate, cardiac index, mean pulmonary artery pressure, mean arterial pressure, total pulmonary resistance, total systemic resistance, total systemic resistance/total pulmonary resistance, left ventricular dP/dt(max), left ventricular end diastolic pressure, and left and right ventricular double products ([mean arterial pressure X heart rate] and [mean pulmonary artery pressure X heart rate], respectively). Responders were defined as those in which total pulmonary resistance decreased greater than or equal to 20% without an increase in mean pulmonary arterial pressure and in which heart rate increase was less than or equal to 10%. Comparison was also made between maximal hemodynamic effect of hydralazine with that after 100% oxygen administration for 15 minutes to previously normoxemic dogs (n = 5). Significance was determined if P < 0.05, using the paired t-test. Hydralazine induced significant reductions in mean pulmonary and systemic arterial pressures and total pulmonary resistance, with no significant change in heart rate, cardiac index, total systemic resistance, left ventricular dP/dt(max), left ventricular end diastolic pressure, or right and left ventricular double products. Four (57%) of the 7 dogs studied were considered responders. Pretreatment cardiac index, mean pulmonary artery pressure, and total pulmonary resistance did not allow differentiation of responders from nonresponders.

Ursodeoxycholic acid (UDCA; 10 mg/kg of body weight) was administered orally to 5 healthy cats for 3 months. Signs of illness were not apparent in any cat during treatment with UDCA. Results of monthly CBC, serum biochemical analysis, and urinalysis were unchanged during drug administration. There was a decrease in serum cholesterol concentration in 4 cats. Total postprandial serum bile acids (PPSBA) concentration was significantly (P = 0.0003) increased over total preprandial serum bile acids (PRSBA) concentration at all sample collection periods. The PRSBA and PPSBA concentrations were significantly (P < 0.05) increased at all sample collection periods after administration of UDCA, compared with baseline values. Ursodeoxycholic and tauroursodeoxycholic acids were not detected in serum prior to initiating administration of UDCA. Both bile acids were detected in the serum of all cats 1 and 2 months after UDCA administration and were detected in the serum of 2 cats 3 months after initiating UCDA administration. Hepatic ultrasonographic findings were normal before and after completion of UDCA administration. A mild, focal lymphocytic infiltrate was observed in 3 cats 3 months after initiating UDCA administration. Results of the study indicate that UDCA is absorbed into the systemic circulation of cats after oral administration, undergoes hepatic conjugation, and appears to be safe.

Seven horses (4 anesthetized and 3 awake) and 2 ponies (anesthetized) were studied to evaluate the high sensitivity of the pulmonary circulation of the horse to various blood-borne particles, and to establish the presence of intravascular macrophages in the lung. Pulmonary and systemic pressures and cardiac output before and during particle injection were measured in some animals. An anesthetized foal had a large increase in pulmonary arterial pressure (32 and 34 mm of Hg) within 1 minute of iv administration of small test doses of radioactively labeled liposomes (2.5 micromoles/kg of body weight) or a 1% suspension of blue pigment (0.3 ml/kg), respectively. Quantitative real-time gamma camera imaging of the foal revealed high retention of the labeled liposomes during the first pass through the lungs; retention persisted throughout the experiment. Postmortem analysis revealed 55 and 47% lung retention of liposomes and blue pigment, respectively. The 2 anesthetized ponies had increased pulmonary artery pressure of 34 +/- 7 mm of Hg, decreased cardiac output, and 42% lung retention after administration of 1% blue pigment (0.2 ml/kg), whereas 3 awake horses had increased pressure of 28 +/- 9 mm of Hg after 1.8 X 10(8) (1.8-micromoles-diameter) latex microspheres/kg. None of the injected particles caused vascular obstruction, and they do not cause pulmonary vascular reactivity in species that lack pulmonary intravascular macrophages. Finally, 3 horses (1 anesthetized and 2 awake) were infused iv with small doses of the blue pigment, and their lungs were perfusion-fixed to identify specific labeling of the pulmonary intravascular macrophages. These cells were fully differentiated macrophages, contained blue pigment in phagocytes, and were tightly adherent to the pulmonary capillary endothelium. At this time, horses (order Perissodactyla) are the only species outside the mammalian order Artiodactyla (sheep, pig, cattle) documented to have reactive intravascular macrophages. Compared with other species, low doses of particles induced marked hemodynamic responses; horses appear to be more sensitive to IV administered particles than are other species studied.

The hypothesis that equine laminitis is caused by thrombosis of vessels in the laminar corium (dermis) was investigated. Hemostatic alterations were evaluated by determining platelet count, platelet survival, platelet adhesiveness to vascular subendothelium, activated clotting time, and whole blood recalcification time. Thrombosis of vessels in the hoof wall was evaluated by scintigraphic studies of the hoof wall after administration of indium-111 ((111)In)- labeled platelets, contrast arteriography, and histologic examination. Platelet count remained constant before and at the onset of lameness; however, survival of (111)In-labeled platelets was shortened. Scintigraphy of affected feet revealed accumulation of (111)In-labeled platelets distal to the coronary band. Arteriography of disarticulated saline-perfused feet revealed marked reduction in blood supply to affected hooves. Histologic examination of the laminar dermis disclosed variable numbers of microthrombi in dermal veins of affected feet from 3 of 4 ponies with laminitis. Whole blood recalcification time was shortened at 8 hours after administration of carbohydrate and was prolonged at the onset of laminitis. Activated clotting time was prolonged at 32 hours after carbohydrate administration and at the onset of lameness. Plasma endotoxin-like activity was detected in 1 of 4 affected ponies. These data confirm that microvascular thrombosis existed at the onset of lameness in ponies with carbohydrate-induced laminitis and indicate that systemic coagulopathy may have preceded development of thrombosis.