Hematologic and biochemical changes during canine agility competitions

BACKGROUND: Normal response to different types of exercise needs to be established before performance, training level, or exercise intolerance can be assessed. OBJECTIVES: The aim of this research was to describe the hematologic and biochemical changes that dogs undergo during an agility competition. METHODS: Fifteen dogs were subjected to an agility test that covered a distance of 360-400 m with 40 obstacles. Basal venous blood samples were drawn 1 week before the competition, immediately after exercise, and at 5, 15, and 30 minutes of recuperation. A CBC, plasma biochemical profile, and lactate concentration were determined by standard methods using automated analyzers. Serum cortisol concentration was measured by competitive immune-enzyme analysis; insulin was measured by sandwich ELISA. RESULTS: Hematologic response to the agility test consisted of significant increases in RBC count, hemoglobin concentration, and HCT, with no change in total protein concentration. Serum triglyceride concentrations were increased postexercise, with highest values observed at 30 minutes of recuperation. Postexercise lactate concentrations exceeded the anaerobic threshold of 4 mmol/L. Serum lactate dehydrogenase activity was significantly higher after 30 minutes of recuperation. Significant differences were not observed in other analytes. CONCLUSIONS: Our results indicate that agility competitions induce mild to moderate changes in hematologic and biochemical results consistent with splenic contraction, increased lipolysis, and utilization of anaerobic pathways involved in energy resynthesis in muscle.     

Responses to submaximal treadmill exercise and training in the horse: changes in haematology, arterial blood gas and acid base measurements, plasma biochemical values and heart rate

Four standardbred horses with subcutaneously relocated carotid arteries were given a seven week training programme of treadmill exercise at a gradient of 19 per cent in order to assess if there were any effects of exercise and training on haematology, arterial blood gas and acid base measurements, plasma biochemistry and heart rate. The exercise consisted of one minute walking at 110 metres/minute followed by five minutes trotting at 200 metres/minute, twice daily in the first week. The period of trotting exercise was increased by one minute per week so that by the seventh week the horses were being given 12 minutes trotting twice daily. Before training commenced venous blood samples, for complete blood counts and plasma biochemistry, and arterial samples, for blood gas, acid base and lactate measurements, were taken at rest, after five minutes and 15 minutes of treadmill exercise (200 metres/minute) and 30 minutes and 60 minutes after completing the exercise. Heart rate was measured by telemetric electrocardiogram at similar intervals. This exercise test and blood collection were repeated after one, three, five and seven weeks of training. The only significant changes were a decrease in exercise lactate with training, increases in exercise and recovery total protein. The haematological response to treadmill exercise included an increase in certain red cell parametes and a leucocytosis which was caused by both a neutrophilia and a lymphocytosis. These effects had largely disappeared by 30 minutes after exercise and all values had returned to resting values by one hour after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in haematology and plasma biochemistry during maximal exercise in greyhounds

The haematological and biochemical changes associated with racing over 235 and 420 metres were studied in 23 greyhounds. Blood samples were collected while the dogs were resting and immediately after and 30 minutes after racing. Significant increases in red blood cell count, haemoglobin concentration and haematocrit occurred. The increase in haematocrit was accompanied by increases in total plasma protein and creatinine concentrations. Blood lactate increased to 11.4 and 13.2 mmol/litre over 235 and 420 metres, respectively, and plasma glucose increased to 7.9 and 8.2 mmol/litre. After the 420 metres, the mean plasma ammonia concentration was 256 mumol/litre. Plasma free fatty acid concentrations also increased after dogs had run both distances. The highest concentrations of glycerol and uric acid were found 30 minutes after exercise.     

Effect of acute induced metabolic alkalosis on the acid/base responses to sprint exercise of six racing greyhounds

To investigate the effect of acute induced metabolic alkalosis on the haematological, biochemical and metabolic responses to sprint exercise, six greyhound dogs with previously placed carotid artetrial catheters were raced four times over a distance of 400 metres. Each dog was raced twice after receiving oral sodium bicarbonate solution (NaHCO₃) (400 mg kg⁻¹) or lactated Ringer's solution ( ). Before, and for intervals of up to one hour after, the exercise arterial blood samples were collected for the measurement of blood gases, packed cell volume, total protein, serum biochemistry and plasma lactate. The time to complete the 400 metre sprint ranged from 32·7 seconds to 36·9 seconds. There was no significant difference in racing times between the dogs treated with NaHCO₃ and , and there was no significant difference between the plasma lactate measurements after the treatments with NaHCO₃ or . Serum chloride concentrations were significantly lower after NaHCO₃ than after LRS, and there was a trend towards a lower serum potassium concentration after NaHCO₃ treatment. Plasma lactate concentrations showed a similar increase and time course of disappearance after both LRS and NaHCO₃ treatments. There were significant changes in all the parameters measured after the exercise, but there were large variations between individual dogs and between races when the dogs were receiving the same treatment.     

Evaluation of Indicators of Weight-Carrying Ability of Light Riding Horses

To answer the question of whether horse height, cannon bone circumference, and loin width can be used as indicators of weight-carrying ability in light horses, eight mature horses underwent a submaximal mounted standard exercise test under four conditions: carrying 15, 20, 25, or 30% of their body weight. Heart rate was monitored, plasma lactate concentration was determined in jugular blood samples pre-exercise, immediately post-exercise, and 10 minutes post-exercise, with serum creatine kinase activity determined at the same times as plasma lactate concentrations, with additional samples collected at 24 hours and 48 hours post-exercise. Muscle soreness and muscle tightness scores were determined using a subjective scoring system 24 hours before and 24 hours after exercise. Heart rates remained significantly higher when the horses carried 25 and 30% of their body weight. Plasma lactate concentrations immediately and 10 minutes after exercise differed when horses carried 30% of their body weight compared with 15, 20, and 25% weight carriage. Horses tended to have a greater change in muscle soreness and muscle tightness when carrying 25% of their body weight, and a significant change in soreness and tightness scores was found in horses carrying 30% of their body weight. Loin width and cannon bone circumference were found to be negatively correlated to the changes in muscle soreness and tightness scores. In conclusion, the data suggest that horses with wider loin and thicker cannon bone circumference became less sore when carrying heavier weight loads.     

Effects of nandrolone treatment on recovery in horses after strenuous physical exercise

To test the effect of nandrolone on their recovery, six adult half-bred riding horses performed a competition exercise test (CET) and a standardized exercise test (SET) on consecutive days before and after a 2-week treatment with the anabolic steroid nandrolone laurate. Blood samples were collected during and between these tests for the determination of red cell volume and concentrations of blood lactate, plasma glucose, non-esterified fatty acids, glycerol, triglycrides, erythropoietin, cortisol, insulin, and glucagon. Muscle biopsy specimens were taken immediately after the CET and before the SET for analysis of glycogen content, citrate synthase, and 3-hydroxyacyl CoA dehvdrogenase activity. Nandrolone administration increased the rate of muscle glycogen repletion after exercise, an increase that may be explained by increased glucose output by the liver, higher plasma insulin concentration, and increased insulin-independent glucose transport, but not by better availability of lipid fuels during recovery.     

Bovine longissimus muscle glycogen concentration in response to isometric contraction and exogenous epinephrine

Isometric contraction was elicited in cattle by electrical stimulation (electrical immobilization) and was used as a means of investigating the interaction between muscle contraction and epinephrine-induced muscle glycogen degradation. At 0.5 and 24 hours after a 15-minute period of continuous muscle contraction, glycogen content of longissimus muscle specimens collected via needle biopsy was not different from precontraction concentrations. Epinephrine (13.2 mg/kg of body weight) given subcutaneously resulted in a 30% to 35% reduction of muscle glycogen. Reduction of muscle glycogen was slightly greater when epinephrine was used in conjunction with isometric contraction, compared with epinephrine treatment alone. Muscle glycogen increased, and free glucose, lactate, and glucose-6-phosphate decreased, with increases in body weight. In younger, lighter cattle (370 kg), epinephrine decreased muscle glycogen and lactate concentrations and generally decreased muscle glucose concentrations. Muscle-free glucose and lactate concentrations were increased in older, heavier cattle (446 kg) by contraction and epinephrine injection when the animals were immobilized for 30 minutes, with intermittent periods of muscle relaxation. In these cattle, muscle glycogen concentration slightly decreased with isometric contraction. Data indicate that reports of increased glycogenolysis observed in cattle subjected to stress by mixing strange animals or exercise is due to dynamic muscle contraction and not due to isometric muscle contraction.     

Proglycogen, macroglycogen, glucose, and glucose-6-phosphate concentrations in skeletal muscles of horses with polysaccharide storage myopathy performing light exercise

OBJECTIVE: To determine concentrations of proglycogen (PG), macroglycogen (MG), glucose, and glucose-6-phosphate (G-6-P) in skeletal muscle of horses with polysaccharide storage myopathy (PSSM) before and after performing light submaximal exercise. ANIMALS: 6 horses with PSSM and 4 control horses. PROCEDURES: Horses with PSSM completed repeated intervals of 2 minutes of walking followed by 2 minutes of trotting on a treadmill until muscle cramping developed. Four untrained control horses performed a similar exercise test for up to 20 minutes. Serum creatine kinase (CK) activity was measured before and 4 hours after exercise. Concentrations of total glycogen (G(t)), PG, MG, G-6-P, free glucose, and lactate were measured in biopsy specimens of gluteal muscle obtained before and after exercise. RESULTS: Mean serum CK activity was 26 times higher in PSSM horses than in control horses after exercise. Before exercise, muscle glycogen concentrations were 1.5, 2.2, and 1.7 times higher for PG, MG, and G(t), respectively, in PSSM horses, compared with concentrations in control horses. No significant changes in G(t), PG, MG, G-6-P, and lactate concentrations were detected after exercise. However, free glucose concentrations in skeletal muscle increased significantly in PSSM horses after exercise. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of the results suggests that glucose uptake in skeletal muscle is augmented in horses with PSSM after light exercise. There is excessive storage of PG and MG in horses with PSSM, and high concentrations of the 2 glycogen fractions may affect functional interactions between glycogenolytic and glycogen synthetic enzymes and glycosomes.     

Blood chemistry and skeletal muscle metabolic responses during and after different speeds and durations of trotting

Eight standardbred horses trotted on a treadmill for 55 mins at a sub-maximal speed of 5m/sec and subsequently performed an exercise test consisting of 2 min intervals at increasing speed. Heart (HR) and respiratory (Rf) rates and venous blood samples were obtained before, during and for 5 mins after exercise. Gluteus medius muscle biopsies and rectal temperatures were taken before and after exercise. The mean HR was 132/min and the mean Rf was 156/min during the 5m/sec trotting. With 5m/sec exercise, plasma free fatty acids (FFA), glucose, creatinine and cortisol concentrations increased markedly. Blood lactate increased slightly and plasma potassium increased initially and then decreased with a lengthened duration of trotting. Within 5 mins post exercise plasma FFA, glucose and cortisol concentrations continued to rise, whereas creatinine and lactate levels declined slightly and potassium concentrations declined rapidly to below resting values. The mean intramuscular (im) glycogen utilisation was 86 mmol/kg, no significant changes occurred in creatine phosphate (CP), adenosine triphosphate (ATP) and glucose-6-phosphate (G-6-P) concentrations and muscle lactate decreased significantly. During the second exercise test mean HR was 215/min and Rf 126/min at top speed. No significant change was seen in plasma glucose whereas cortisol levels rose to a lesser extent, and creatinine lactate, ammonia and potassium concentrations to a greater extent, compared to 5 m/sec trotting. Post exercise, these parameters continued to increase except for creatinine which declined slightly and potassium which decreased rapidly. The mean im glycogen utilisation was 144 mmol/kg, ATP concentrations were unaltered, CP declined, lactate and G-6-P increased during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma lactate and purine derivatives accumulation after exercise of increasing intensity in standardbred horses

The aim of the experiment was to study the relationship between plasma lactate and allantoin accumulation in horses undergoing five exercises differing in intensity and length. Twenty-five adult trotter horses were used (18 males, two castrated, and five females), housed in three training centers. The horses were assigned to five groups: slow trot, over 2000 m (Group 1); slow trot over 1600 m (Group 2); fast trot over 1600 m (Group 3); fast trot over 2000 m (Group 4); fast trot over 2400 m (Group 5). Plasma was obtained from blood sampled at rest, at the end of the bout of exercise and after 15 and 45 minutes from the end of the bout of exercise and analyzed for glucose, lactate, uric acid, free fatty acids (FFA) and allantoin concentrations. Accumulations of plasma lactate and allantoin (mmol/sec) were calculated as difference between end of exercise and rest and between 45 minutes sample and rest, respectively.Ranking the intensity of exercise using the lactate concentrations at the end of exercise, the level of exertion was highest for Group 3 horses and lowest for Group 5 horses (20.9 and 2.8 mmol/l, respectively). At the end of exercise, glucose concentrations were much higher for horses undertaking the more intensive exercise (Groups 3 and 4 compared to Group 2). FFA concentrations were highest at the end of exercise for Groups 2 and 3 and after 15 minutes for Groups 4 and 5. Plasma uric acid and allantoin concentrations peaked 15 and 45 minutes from the end of exercise, respectively, independently of exercise intensity. The relationship between accumulation of plasma allantoin (y, dependent variables) and lactate (x, independent variable) was non-linear: y=0.15−2.61^*x+68.3^*x² (r²=0.900; se=0.19). This suggests that allantoin accumulation could be used together with plasma lactate to calibrate the workload to muscle conditions to prevent muscle injury.     

Effects of maximal exercise on the blood composition of the racing camel

Haematological and blood biochemical changes were studied in nine camels after maximal exercise over 4 or 5 km. There was a lack of splenic reserve for red blood cells, indicated by a minimal increase in haemoglobin concentration and haematocrit. There were marked increases in plasma lactate (to over 20 mmol/litre), plasma ammonia and plasma glucose and a pronounced decrease in circulating free fatty acids. There were small but significant increases in plasma calcium, magnesium, sodium, potassium, chloride and phosphate concentrations.     

Cardiopulmonary effects of a xylazine and ketamine combination in pigs

The carotid and pulmonary arteries were catheterised in six pigs anaesthetised with thiopentone sodium and halothane. A minimum of five days was allowed to elapse before the investigation. The carotid artery pressure, pulmonary artery pressure, cardiac output, arterial pH, PO2, PCO2, plasma glucose and lactate were measured before and after intravenous injection of xylazine (1 mg kg-1) and ketamine 10 mg kg-1). Complete analgesia was produced for 10 minutes in all pigs but by 25 minutes all animals responded to a painful stimulus. The cardiac output and arterial PO2 were significantly decreased for 30 minutes and 10 minutes, respectively. The total vascular resistance was significantly increased. No statistically significant changes occurred in the other variables measured.     

Effects of muscle glycogen depletion on some metabolic and physiological responses to submaximal treadmill exercise.

The aim of this study was to investigate the effects of reduced muscle glycogen concentration on some physiological and metabolic responses during moderate intensity treadmill exercise in horses. Six Thoroughbred geldings were randomly allocated to 2 treatments (protocols A and B) or control in a 3 x 3 replicated Latin square design. In protocol A, horses performed low intensity exercise while horses in protocol B performed short bursts of high intensity exercise. Protocol A was designed to induce glycogen depletion mainly of slow twitch muscle fibers while protocol B aimed to deplete mainly fast twitch muscle fibers. Horses in the control group did not undergo exercise prior to the exercise test. Five hours after glycogen depletion, horses performed treadmill exercise at 60% VO2max at a treadmill slope of 10% until fatigue (20-30 min). The induced glycogen depletion prior to exercise had no significant effect on plasma glucose, insulin, or lactate concentrations during the exercise test, and there was no effect on glycogen utilization rate, although respiratory exchange ratios were lower in the glycogen-depleted groups. The VO2, heart rate and central blood temperature did not vary significantly between the protocols A and B and control throughout the exercise test. It was concluded that 20-30% depletion of glycogen concentration in the middle gluteal muscle resulted in a shift towards fat metabolism, but does not significantly affect heart rate, oxygen uptake, or concentrations of plasma glucose and lactate during moderate intensity exercise.     

Effects of N,N-dimethylglycine on cardiorespiratory function and lactate production in thoroughbred horses performing incremental treadmill exercise

In a crossover study, either a placebo paste or N,N-dimethylglycine was administered orally at a dose rate of 1.2 mg/kg twice daily for five days to six thoroughbred horses, with bodyweights ranging from 424 to 492 kg. Using previously determined regression equations for oxygen uptake (VO2) against speed for each horse, a standardised exercise test was given with speeds equivalent to fixed percentages of the maximum oxygen uptake (VO2max). The test consisted of two minutes at speeds equivalent to approximately 40 per cent and 50 per cent VO2max, and one minute at speeds that produced approximately 60, 70, 80, 90 and 100 per cent VO2max. During the last five seconds of each exercise stage, the values of VO2, carbon dioxide production (VCO2), heart rate, arterial blood and plasma lactate concentrations, arterial blood gases and pH were measured. Before and immediately after the exercise test, muscle biopsies were collected from the middle gluteal muscle to determine the muscle lactate concentrations. The administration of N,N-dimethylglycine produced no significant differences in any of the measured values, and it is concluded that the compound has no beneficial effects on cardiorespiratory function or lactate production in the exercising horse.     

LIVER METABOLISM DURING MALIGNANT HYPERTHERMIA IN THE PIETRAIN PIG

Liver function was systematically investigated in 7 malignant hyperthermia (MH) susceptible Pietrain pigs (mean weight 67 kg ± 7 kg SEM) to determine the contribution of hepatic metabolism to circulating substrates (Hall, Lucke, Lovell and Lister 1978). It was considered that the progressive lactic acidosis observed in MH may be a result, not only of impaired hepatic uptake of lactate but also production of lactate by the liver as is said to occur in Type II lactic acidosis (Cohen and Simpson 1975). These authors suggested that as the enzyme pyruvate decarboxylase is pH sensitive, and because it is rate limiting in the gluconeugenic pathway of lactate to glucose, under conditions of severe acidosis (pH 7.1) hepatic lactate uptake will be inhibited and there will be production of lactate by the liver. Pigs were prepared with hepatic vein, right ventricle and common carotid artery cannulae. Control measurements were made before inducing MH by ventilating with 1% halothane for 10 minutes together with intravenous injection of 1 mg suxamethonium chloride per kg body weight. Paired arterial and hepatic venous samples were collected at 10 minute intervals for the following estimations: pH, oxygen content, glucose, potassium, lactate, pyruvate, alanine, free fatty acids and glycerol. Hepatic blood flow was estimated by continuous infusion of Indocyanine green (Lucke and Hall 1978). All pigs developed MH with a rise in mean muscle temperature from 37.8°C to 41.5°C after 40 minutes. Mean hepatic blood flow decreased to 25% of control value but, because there was a concomitant increase in oxygen extraction by the liver, hepatic oxygen consumption did not change significantly. At 20 minutes after MH there was a 7-fold increase in glucose efflux from the liver with an arterial glucose concentration of 12.6 mmol/1. There was a massive efflux of 1.1 mmol K+/min early in the response showing that the characteristic hyperkalaemia is not only due to potassium loss from muscle but mainly hepatic in origin. The mean lactate uptake by the liver increased from the control 0.21 mmol/min to 1.19 mmol/min after 10 minutes MH. Even in the presence of gross acidosis (mean pH 6.75) and hepatic blood flow 25% of control, hepatic lactate uptake was still 3 times that recorded in the resting state. It is important to note, however, that although hepatic lactate uptake was increased under these conditions, it was still insufficient in the presence of gross muscle stimulation with a mean arterial lactate concentration of 19.3 mmol/l. It is concluded that the lactic acidosis in porcine MH is due to peripheral overproduction with some impairment of hepatic uptake. The gluconeugenic capacity of the liver was never completely inhibited despite the severity of the metabolic acidosis and hyperthermia and at no stage was there production of lactate by the liver.     

Effects of submaximal exercise on adenine nucleotide concentrations in skeletal muscle fibers of horses with polysaccharide storage myopathy

OBJECTIVE: To determine whether disruption of adenine triphosphate (ATP) regeneration and subsequent adenine nucleotide degradation are potential mechanisms for rhabdomyolysis in horses with polysaccharide storage myopathy (PSSM) performing submaximal exercise. ANIMALS: 7 horses with PSSM and 4 control horses. PROCEDURES: Horses with PSSM performed 2-minute intervals of a walk and trot exercise on a treadmill until muscle cramping developed. Control horses exercised similarly for 20 minutes. Serum creatine kinase (CK) activity was measured 4 hours after exercise. Citrate synthase (CS), 3-OH-acylCoA dehydrogenase, and lactate dehydrogenase activities prior to exercise and glucose-6-phosphate (G-6-P) and lactate concentrations before and after exercise were measured in gluteal muscle specimens. Adenine triphosphate, diphosphate (ADP), monophosphate (AMP), and inosine monophosphate (IMP) concentrations were measured before and after exercise in whole muscle, single muscle fibers, and pooled single muscle fibers. RESULTS: Serum CK activity ranged from 255 to 22,265 U/L in horses with PSSM and 133 to 278 U/L in control horses. Muscle CS activity was lower in horses with PSSM, compared with control horses. Muscle G-6-P lactate, ATP, ADP, and AMP concentrations in whole muscle did not change with exercise in any horses. Concentration of IMP increased with exercise in whole muscle, pooled muscle fibers, and single muscle fibers in horses with PSSM. Large variations in ATP and IMP concentrations were observed within single muscle fibers. CONCLUSIONS AND CLINICAL RELEVANCE: Increased IMP concentration without depletion of ATP in individual muscle fibers of horses with PSSM during submaximal exercise indicates an energy imbalance that may contribute to the development of exercise intolerance and rhabdomyolysis.     

Effect of freeze-drying on measurements of pH in biopsy samples of the middle gluteal muscle of the horse: comparison of muscle pH to the pyruvate and lactate content

Muscle biopsies taken after exercise, in comparison to those at rest, contain increased amounts of blood and this is a particular problem in studies of the horse. The inclusion of blood in muscle will introduce an upward bias in values of pH measured in muscle homogenates. In an attempt to control this, muscle biopsy samples of the middle gluteal from Thoroughbred horses were freeze-dried and dissected free of blood before determination of pH. Following exercise, muscle pH measured after freeze-drying was similar to that measured in homogenates prepared from frozen samples. In contrast, freeze-drying appeared to increase muscle pH in samples taken at rest. This was probably the result of loss of CO2 during freeze-drying. Muscle pH determined in freeze-dried samples taken at rest and after exercise was linearly related to pyruvate and lactate content (P less than 0.001). It is concluded that muscle samples taken after exercise can be freeze-dried and dissected free from blood before determination of pH, whereas this procedure will cause an alkaline shift in samples taken at rest.     

Acid-base values of standardbred horses recovering from strenuous exercise.

Blood gases, lactic acid concentrations, and pH were measured in arterial and mixed venous blood in moderately conditioned Standardbred horses after a standardized exercise load of 1.6 km in 2 minutes, 40 seconds. Samples were obtained at rest, immediately after exercise, and at 3, 6, 15, 30, and 60 minutes after exercise. Arterial oxygen tension and mixed venous oxygen tension increased after exercise, reaching peak values at 6 minutes. Arterial oxygen tension returned to the resting (preexercise) value by 15 minutes, and mixed venous oxygen tension by 30 minutes. Arterial carbon dioxide tension decreased immediately after exercise, reaching its lowest value at 6 minutes, and returned to resting value by 30 minutes. Mixed venous carbon dioxide tension reached its highest value immediately after exercise, then decreased to less than the resting value, reaching its lowest value by 15 minutes, and returned to normal by 60 minutes. Lactic acid concentration increased immediately after exercise, reaching its highest value at 6 minutes, and returned toward normal by 60 minutes. Arterial pH decreased immediately after exercise, reaching its lowest value at 6 minutes, and returned to normal by 60 minutes. Mixed venous pH reached its lowest value immediately after exercise, then began to increase, and returned to normal by 60 minutes. The decrease in mixed venous pH was more pronounced than that in arterial blood since, in addition to the increase in lartic acid, there was a considerable increase in mixed venous carbon dioxide tension.     

Cardiopulmonary effects of prostacyclin infusion in anesthetized horses

Prostacyclin was infused IV into 6 horses anesthetized with halothane. Three dosage rates (10, 30, and 100 ng/kg of body weight/min) were evaluated in each horse. Facial and pulmonary artery pressures, heart rate, cardiac output, blood temperature, and arterial and mixed venous pH, PCO2, and PO2 were measured. Arterial blood was collected for determination of glucose, lactate, and PCV. Mixed venous blood was sampled for assay of 6-keto-prostaglandin F1 alpha and catecholamines. Infusion of prostacyclin at 10 ng/kg/min had no effect on the variables measured, whereas the 30 ng/kg/min dosage decreased diastolic and mean arterial pressure at 15 and 30 minutes and PaO2 at 15 minutes (P less than 0.05). Prostacyclin infusion at 100 ng/kg/min significantly decreased arterial pressure, total vascular resistance, and total pulmonary resistance. Heart rate increased slightly, and cardiac output increased by 44%. Arterial PO2 decreased from 311 mm of Hg to 137 and 135 mm of Hg at 15 and 30 minutes, respectively. Blood glucose was increased. Prostacyclin infusions of 30 and 100 ng/kg/min increased blood concentrations of 6-keto-prostaglandin F1 alpha by factors of 5 and 40, respectively. Significant changes in catecholamine concentrations did not occur.