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1.
The influence of dobutamine on glucoregulation has been assessed in the rat during and after an intravenous infusion given at the following doses: 0, 0.1, 1.0, 10, 100, and 1000 micrograms X kg-1 X min-1. Plasma glucose, insulin, and glucagon levels were measured at 15-min intervals in unanesthetized previously cannulated rats. Basal glucose levels were preserved with the less than or equal to 10 micrograms X kg-1 X min-1 doses. At the greater than or equal to 100 micrograms X kg-1 X min-1 doses, a marked hyperglycemic effect was observed, partly attributable to some inhibitory effect of dobutamine on glucose-induced insulin secretion and to its stimulatory effect on glucagon secretion. Such data suggest that dobutamine may disturb the normal glucose homeostasis, particularly in situations of deficient insulin reserve.  相似文献   

2.
We have previously demonstrated a 40% increase in myocardial blood flow (MBF) during hypercapnia but no significant decrease of MBF during hypocapnia. The present study was undertaken to evaluate if epinephrine infusion, which increases both myocardial oxygen consumption (MVo2) and myocardial performance, might influence the effects of hypocapnia and hypercapnia on MBF. Induction of hypocapnia was performed by hyperventilation in closed-chest dogs anesthetized with pentobarbital. By adding carbon dioxide to the inspiratory gas, normocapnia and hypercapnia were created. Epinephrine infusion (0.8 microgram X kg-1 X min-1) increased MBF and cardiac output (CO) by 90 and 140%, respectively, while MVo2 was increased by 45%. Epinephrine had a direct coronary vasodilating effect in excess of myocardial needs evidenced by increased oxygen content of the coronary sinus blood. During epinephrine infusion, induction of hypocapnia effected no change of MBF, while myocardial oxygen extraction increased significantly. Although oxygen saturation (So2) and Po2 in the coronary sinus blood decreased, these values remained well above those with hypocapnia without epinephrine infusion, thereby excluding impaired oxygen supply to the heart. Hypercapnia induced an increase of MBF by nearly 40% despite the coronary vasodilatation already induced by epinephrine infusion.  相似文献   

3.
In adult male rats anaesthetized with pentobarbital the intravenous infusion of 0.5 micrograms.kg-1.min-1 of epinephrine increased liver phosphorylase a activity within 5 min, whereas later a weakening of the hormone effect was observed. After increasing the infusion rate to 1.0 micrograms.kg-1.min-1 and extending the study to more parameters, the diminishing effect on phosphorylase was confirmed and a similar response was established for liver cAMP. Concomitantly, a decrease and recovery of liver glycogen synthase a activity was observed. In rats with permanent catheters in one of their tail arteries for obtaining blood samples, the plasma epinephrine levels were shown to be permanently increased (from cca 1 pmol.ml-1 before infusion of 1.0 micrograms.kg-1.min-1 to more than 30 pmol.ml-1 during infusion) and remained at steady levels throughout the infusion. Therefore, the weakening of the epinephrine effect should be ascribed to changes at (or beyond) the catecholamine receptor level. A hitherto undescribed decrease of total glycogen synthase activity was observed during the infusions.  相似文献   

4.
Chronically elevated plasma norepinephrine has the potential for supporting function of diseased hearts, yet may also initiate harmful biochemical and (or) structural changes in the myocardium. The present study investigated the dosage-related effects of chronic norepinephrine infusion on markers of myocardial damage and then tested the influence of a relatively low norepinephrine infusion rate (0.05 microgram X kg-1 X min-1) on the heart's adaptation to pressure overload in aortic constricted rats. Norepinephrine infusion at 0.50 microgram X kg-1 X min-1 led to significantly increased myocardial hydroxyproline concentration and significant mortality. A rate of 0.25 microgram X kg-1 X min-1 increased myocardial hydroxyproline concentration and mortality in aortic constricted rats but had no such effects on sham-operated rats. The lowest rate tested (0.05 microgram X kg-1 X min-1) significantly increased mean arterial pressure and lung weight of aortic constricted rats, without affecting the degree of left ventricular hypertrophy. This infusion rate and aortic constriction each increased plasma norepinephrine and impaired cardiac performance during rapid preloading, although their combination did not cause further impairment. Thus, it appears that even modest plasma norepinephrine elevation has a negative effect on the heart's adaptation to sustained pressure overload.  相似文献   

5.
This study was undertaken (1) to examine the relation of plasma catecholamine and insulin levels to the blood pressure response during and after submaximal exercise, (2) to verify whether the blood pressure response to an epinephrine infusion is associated with the blood pressure response to a prolonged submaximal exercise, and (3) to study some potential correlates of the hypotensive effect of prolonged aerobic exercise. Nine normotensive young men (mean age 22.0 +/- 1.4 years) were subjected to a 1-h epinephrine infusion protocol and a 1-h submaximal exercise test on a cycle ergometer. The two tests were performed 1 week apart. The physiological and hormonal responses observed during the submaximal exercise test were generally greater than those observed during the epinephrine infusion test. Blood pressure responses in both tests showed no significant association with changes in plasma insulin levels. Changes in plasma norepinephrine concentration were positively correlated with changes in systolic blood pressure during the submaximal exercise test but not during the epinephrine infusion. Results also showed that the blood pressure response to epinephrine infusion was not correlated with the blood pressure response to submaximal exercise. However, post-exercise and post-infusion systolic blood pressure responses (differences between "post-test" and "resting" values) were significantly associated (r = 0.81, p less than 0.01). In addition, a significant hypotensive effect of submaximal exercise was observed for both systolic and diastolic blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

6.
We wished to determine the effect of a 25% hematocrit reduction on glucoregulatory hormone release and glucose fluxes during exercise. In five anemic dogs, plasma glucose fell by 21 mg/dl and in five controls by 7 mg/dl by the end of the 90-min exercise period. After 50 min of exercise, hepatic glucose production (Ra) and glucose metabolic clearance rate (MCR) began to rise disproportionately in anemics compared with controls. By the end of exercise, the increase in Ra was almost threefold higher (delta 15.1 +/- 3.4 vs. delta 5.2 +/- 1.3 mg X kg-1 X min-1) and MCR nearly fourfold (delta 24.6 +/- 8.8 vs. delta 6.5 +/- 1.3 ml X kg-1 X min-1). Exercise with anemia, in relation to controls resulted in elevated levels of glucagon [immunoreactive glucagon (IRG) delta 1,283 +/- 507 vs delta 514 +/- 99 pg/ml], norepinephrine (delta 1,592 +/- 280 vs. delta 590 +/- 155 pg/ml), epinephrine (delta 2,293 +/- 994 vs. delta 385 +/- 186 pg/ml), cortisol (delta 6.7 +/- 2.2 vs. delta 2.1 +/- 1.0 micrograms/dl) and lactate (delta 12.1 +/- 2.2 vs. delta 4.2 +/- 1.8 mg/dl) after 90 min. Immunoreactive insulin and free fatty acids were similar in both groups. In conclusion, exercise with a 25% hematocrit reduction results in 1) elevated lactate, norepinephrine, epinephrine, cortisol, and IRG levels, 2) an increased Ra which is likely related to the increased counterregulatory response, and 3) we speculate that a near fourfold increase in MCR is related to metabolic changes due to hypoxia in working muscle.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

7.
Eight healthy adult grade ponies were studied at rest as well as during maximal exertion carried out with and without adenosine infusion (3 microM X kg-1 X min-1 into the pulmonary artery) on a treadmill to compare levels of blood flow in respiratory muscles with those in other vigorously working muscles and to ascertain whether there remained any unutilized vasodilator reserve in respiratory muscles of maximally exercising ponies. Radionuclide-labeled 15-micron-diam microspheres, injected into the left ventricle, were used to study tissue blood flows. During maximal exertion, there were increases above base-line values in heart rate (336%), mean aortic pressure (41%), cardiac output (722%), and arterial O2 content (56%). The whole-body O2 consumption was 123 +/- 11 ml X min-1 X kg-1, and the stride/respiratory frequency of the galloping ponies was 138 +/- 4/min. With adenosine infusion during maximal exertion, mean aortic pressure decreased (P less than 0.05), but none of the above variables was different from maximal exercise alone. During maximal exertion, blood flow in the adrenal glands, myocardium, respiratory, and limb muscles increased, whereas that in the kidneys decreased and the cerebral perfusion remained unaltered. With adenosine infusion during maximal exercise, renal vasoconstriction intensified, whereas adrenal and coronary beds exhibited further vasodilatation. During maximal exertion, blood flow in the equine diaphragm (265 +/- 36 ml X min-1 X 100 g-1) was not different from that in the gluteus medius (253 +/- 36) and biceps femoris (233 +/- 29); both are principal muscles of propulsion in the equine subjects) or the triceps brachii (227 +/- 26) muscles.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

8.
Epinephrine and norepinephrine together (E + NE) and epinephrine (E) alone were infused intravenously in stepwise increasing doses during progressive isotonic tetanic contractions. The goal was to mimic, for in situ dog skeletal muscle, the concentrations of these catecholamines in the blood and the contractions during progressive exercise. The concentrations of lactate and O2 in arterial and muscle venous blood, the arterial plasma concentration of E and NE, PO2 in arterial and muscle venous blood, and the venous outflow were measured. The infusions caused a rise in plasma E and NE like those seen in progressive exercise. Compared with no-infusion controls, the E + NE infusions and the E alone infusion resulted in significant increases in maximal lactic acid output by the muscles during the contractions from 0.24 mumol X g-1 X min-1 in the controls to 0.44 and 0.54 mumol X g-1 X min-1 during E + NE and E alone infusions, respectively. The venous O2 concentrations and partial pressures were not reduced by the infusions. Both infusions resulted in a rise of arterial lactate concentration that could not be accounted for by the lactic acid output of the contracting muscles. The E alone infusions were associated with a rise in maximal O2 uptake during the contractions. Since the effects of the E + NE and E alone infusions were similar, it was suggested that E is more active than NE. It was suggested that E also increased lactic acid production in tissues other than the working muscles.  相似文献   

9.
Calcium-dependence of the adenosine-induced renal vasoconstriction was studied in dogs anaesthetized with pentobarbital. Close intraarterial (i.a.) infusion of adenosine (40 and 100 micrograms X min-1) elicited a significant blood flow decrease followed by partial recovery during the 2 min infusion periods as measured with an electromagnetic flow probe. I.a. infusion of verapamil (100 micrograms X min-1) blocked the constrictor response. Verapamil also reduced the vasoconstriction produced by i.a. angiotensin II (0.1 micrograms X min-1) or adrenaline (0.6 micrograms X min-1). Blood pressure remained unchanged throughout all the interventions. The results indicate that the adenosine-induced renal vascular response depends on the availability of extracellular Ca2+ to the contractile mechanism of smooth muscle, a property shared by other well known renal constrictor agents.  相似文献   

10.
This study was designed to investigate the effect of short-term, submaximal training on changes in blood substrates, metabolites, and hormonal concentrations during prolonged exercise at the same power output. Cycle training was performed daily by eight male subjects (VO2max = 53.0 +/- 2.0 mL.kg-1.min-1, mean +/- SE) for 10-12 days with each exercise session lasting for 2 h at an average intensity of 59% of VO2max. This training protocol resulted in reductions (p less than 0.05) in blood lactate concentration (mM) at 15 min (2.96 +/- 0.46 vs. 1.73 +/- 0.23), 30 min (2.92 +/- 0.46 vs. 1.70 +/- 0.22), 60 min (2.96 +/- 0.53 vs. 1.72 +/- 0.29), and 90 min (2.58 +/- 1.3 vs. 1.62 +/- 0.23) of exercise. The reduction in blood lactate was also accompanied by lower (p less than 0.05) concentrations of both ammonia and uric acid. Similarly, following training lower concentrations (p less than 0.05) were observed for blood beta-hydroxybutyrate (60 and 90 min) and serum free fatty acids (90 min). Blood glucose (15 and 30 min) and blood glycerol (30 and 60 min) were higher (p less than 0.05) following training, whereas blood alanine and pyruvate were unaffected. For the hormones insulin, glucagon, epinephrine, and norepinephrine, only epinephrine and norepinephrine were altered with training. For both of the catecholamines, the exercise-induced increase was blunted (p less than 0.05) at both 60 and 90 min. As indicated by the changes in blood lactate, ammonia, and uric acid, a depression in glycolysis and IMP formation is suggested as an early adaptive response to prolonged submaximal exercise training.  相似文献   

11.
The effects of exercise conditioning on the myocardium were studied in seven instrumented pigs strenuously exercised for 12 wk by treadmill running. Data were compared with eight instrumented untrained pigs. O2 consumption measured during maximum exercise effort was significantly elevated in the trained pigs (71.7 +/- 4.0 vs. 56.3 +/- 3.0 ml X ml-1 X kg-1). Absolute right and left ventricular mass increased by 20 and 13%, respectively, in response to exercise. Myocyte cross-sectional area increased by 21% in the trained hearts compared with the untrained hearts. Transmural left ventricular myocardial blood flow (ml X min-1 X g-1) was not significantly different at rest, during maximum exercise, or during exercise with adenosine infusion. However, training caused an elevation of the regional epicardial blood flow noted during exercise and exercise with adenosine. In the trained pigs mean aortic pressure during maximum exercise with adenosine infusion was not significantly different compared with untrained pigs. Coronary resistance during exercise with adenosine infusion was the same in both animal groups. In the trained group capillary numerical (no./mm2) and length (mm/mm3) densities were reduced, whereas arteriolar numerical and length densities were significantly increased compared with the untrained group. Measurements of capillary luminal surface density (mm2/mm3) in the trained group were unchanged compared with the untrained group. These results suggest that strenuous exercise does not stimulate the production of new capillaries, but this is modified by the ability of existing capillaries to increase their luminal surface area to parallel increases in myocyte growth. The arteriolar data suggest that exercise promotes the formation of new arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

12.
To examine the relationship between fetal O2 consumption and fetal breathing movements, we measured O2 consumption, umbilical blood flow, and cardiovascular and blood gas data before, during, and after fetal breathing movements in conscious chronically catheterized fetal lambs. During fetal breathing movements, O2 consumption increased by 30% from a control value of 7.7 +/- 0.7 (SE) ml X min-1 X kg-1. Umbilical blood flow was 210 +/- 21 ml X min-1 X kg-1 before fetal breathing movements; in 9 of 16 samples it increased by 52 +/- 12 ml X min-1 X kg-1, while in the other 7 it decreased by 23 +/- 9 ml X min-1 X kg-1. Umbilical arterial and venous O2 partial pressures and pH fell during fetal breathing movements, and the fall was greater when umbilical blood flow was decreased. Partial CO2 pressure rose in both vessels, and again the increase was greatest when umbilical blood flow fell during fetal breathing movements. Also associated with a fall in umbilical blood flow was the transition from low-amplitude irregular to large-amplitude regular fetal breathing movements. It is concluded that fetal breathing movements increase fetal O2 demands and are associated with a transient deterioration in fetal blood gas status, which is most severe during large-amplitude breathing movements.  相似文献   

13.
M D Johnson 《Life sciences》1987,41(16):1945-1951
Previous experiments have shown that epinephrine-induced renin secretion in vivo apparently is initiated by activation of extrarenal adrenoceptors. However the location of these receptors has not been determined despite considerable search. The present experiments were designed to evaluate the hypothesis that epinephrine-induced renin secretion is initiated by a change in blood composition, independent of the passage of the blood through any organ. Accordingly, the left kidneys of anesthetized dogs were perfused with femoral arterial blood via an extracorporeal circuit. The circuit consisted of large-bore Tygon tubing (157 ml volume) with an infusion port and a mixing chamber near the femoral arterial origin, and a blood sampling and pressure-monitoring site near the renal artery. A roller pump was used to maintain renal perfusion pressure approximately equal to femoral arterial pressure, and renal blood flow was measured with an electromagnetic flowmeter. Transit time (of a dye) in the extracorporeal circuit was approximately 40 seconds. Intravenous infusion of epinephrine at 25 ng X kg-1 X min-1 increased renin secretion significantly. However, infusion of epinephrine into the extracorporeal circuit at a rate of 5 ng X kg-1 X min-1 did not alter renin secretion, even though epinephrine concentration in the renal perfusate was higher than during intravenous infusion. The data do not support the hypothesis that epinephrine-induced renin secretion is initiated by a direct effect of epinephrine on blood composition, independent of the passage of blood through any organ.  相似文献   

14.
To determine whether the reduced blood lactate concentrations [La] during submaximal exercise in humans after endurance training result from a decreased rate of lactate appearance (Ra) or an increased rate of lactate metabolic clearance (MCR), interrelationships among blood [La], lactate Ra, and lactate MCR were investigated in eight untrained men during progressive exercise before and after a 9-wk endurance training program. Radioisotope dilution measurements of L-[U-14C]lactate revealed that the slower rise in blood [La] with increasing O2 uptake (VO2) after training was due to a reduced lactate Ra at the lower work rates [VO2 less than 2.27 l/min, less than 60% maximum VO2 (VO2max); P less than 0.01]. At power outputs closer to maximum, peak lactate Ra values before (215 +/- 28 mumol.min-1.kg-1) and after training (244 +/- 12 mumol.min-1.kg-1) became similar. In contrast, submaximal (less than 75% VO2max) and peak lactate MCR values were higher after than before training (40 +/- 3 vs. 31 +/- 4 ml.min-1.kg-1, P less than 0.05). Thus the lower blood [La] values during exercise after training in this study were caused by a diminished lactate Ra at low absolute and relative work rates and an elevated MCR at higher absolute and all relative work rates during exercise.  相似文献   

15.
We evaluated whether elevated blood lactate concentration during exercise in anemia is the result of elevated production or reduced clearance. Female Sprague-Dawley rats were made acutely anemic by exchange transfusion of plasma for whole blood. Hemoglobin and hematocrit were reduced 33%, to 8.6 +/- 0.4 mg/dl and 26.5 +/- 1.1%, respectively. Blood lactate kinetics were studied by primed continuous infusion of [U-14C]lactate. Blood flow distribution during rest and exercise was determined from injection of 153Gd- and 113Sn-labeled microspheres. Resting blood glucose (5.1 +/- 0.2 mM) and lactate (1.9 +/- 0.02 mM) concentrations were not different in anemic animals. However, during exercise blood glucose was lower in anemic animals (4.0 +/- 0.2 vs. 4.6 +/- 0.1 mM) and lactate was higher (6.1 +/- 0.4 vs. 2.3 +/- 0.5 mM). Blood lactate disposal rates (turnover measured with recyclable tracer, Ri) were not different at rest and averaged 136 +/- 5.8 mumol.kg-1.min-1. Ri was significantly elevated in both control (260.9 +/- 7.1 mumol.kg-1.min-1) and anemic animals (372.6 +/- 8.6) during exercise. Metabolic clearance rate (MCR = Ri/[lactate]) did not differ during rest (151 +/- 8.2 ml.kg-1.min-1); MCR was reduced more by exercise in anemic animals (64.3 +/- 3.8) than in controls (129.2 +/- 4.1). Plasma catecholamine levels were not different in resting rats, with pooled mean values of 0.45 +/- 0.1 and 0.48 +/- 0.1 ng/ml for epinephrine (E) and norepinephrine (NE), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

16.
Exercise training has been found to increase coronary vascularity of the heart in experimental animals. Maximum coronary flow and minimum coronary resistance were determined in 16 dogs with the injection of microspheres (15 micron) into the left atrium at rest and during the intravenous infusion of adenosine (0.7 mg X min-1 X kg-1). Heart rate was paced at 150 beats/min. Dogs were divided into three groups with microsphere injections made before and after 4-5 wk of daily exercise (group 1); before and after 8-10 wk of daily exercise (group II); and before and after 8-10 wk of cage rest (group III). Results of average left ventricular maximum myocardial flow before and after daily exercise were 4.08 +/- 0.34 and 4.89 +/- 0.33 ml X min-1 X g-1 for group I, 5.13 +/- 0.32 and 5.55 +/- 0.56 ml X min-1 X g-1 for group II, and 5.24 +/- 0.43 and 4.34 +/- 0.55 ml X min-1 X g-1 for group III. Arterial pressure, maximum coronary flow, and minimum coronary resistance were not significantly different before and after any condition in all three groups of dogs. Peak reactive hyperemia coronary flow was not altered by daily exercise. These results indicate that maximum coronary flow and minimum coronary resistance were not altered by either 4-5 or 8-10 wk of exercise training.  相似文献   

17.
Ten foxhounds were studied during maximal and submaximal exercise on a motor-driven treadmill before and after 8-12 wk of training. Training consisted of working at 80% of maximal heart rate 1 h/day, 5 days/wk. Maximal O2 consumption (VO2max) increased 28% from 113.7 +/- 5.5 to 146.1 +/- 5.4 ml O2 X min-1 X kg-1, pre- to posttraining. This increase in VO2max was due primarily to a 27% increase in maximal cardiac output, since maximal arteriovenous O2 difference increased only 4% above pretraining values. Mean arterial pressure during maximal exercise did not change from pre- to posttraining, with the result that calculated systemic vascular resistance (SVR) decreased 20%. There were no training-induced changes in O2 consumption, cardiac output, arteriovenous O2 difference, mean arterial pressure, or SVR at any level of submaximal exercise. However, if post- and pretraining values are compared, heart rate was lower and stroke volume was greater at any level of submaximal exercise. Venous lactate concentrations during a given level of submaximal exercise were significantly lower during posttraining compared with pretraining, but venous lactate concentrations during maximal exercise did not change as a result of exercise training. These results indicate that a program of endurance training will produce a significant increase in VO2max in the foxhound. This increase in VO2max is similar to that reported previously for humans and rats but is derived primarily from central (stroke volume) changes rather than a combination of central and peripheral (O2 extraction) changes.  相似文献   

18.
The influence of dopamine as compared with dobutamine on glucose homeostasis has been assessed in thyroidectomized euthyroid rats. Both sympathomimetic agents were given intravenously over 6 h at four dosages, varying from 2 to 30 micrograms.kg-1.min-1. Immediately before the end of the infusion period, serum concentrations of glucose and insulin as well as plasma glucagon concentrations were measured. Dobutamine infusions did not exert any influence on these parameters. At a dose of 7.5 micrograms.kg-1.min-1, dopamine infusion caused a decrease in glucose concentrations, accompanied by a rise of glucagon and insulin levels. Glucose levels were significantly increased in the presence of unaltered insulin and decreasing glucagon levels at higher dopamine doses. The rise in glucose levels was reversed by 8 micrograms.kg-1.min-1 and inverted to a decrease by 12 micrograms.kg-1.min-1 of the alpha-adrenergic blocking agent phentolamine, simultaneously infused with 15 micrograms.kg-1.min-1 dopamine, while the insulin levels were increased and glucagon levels remained elevated. These findings demonstrate that dopamine acts on glucoregulation divergently, according to the dosage applied. The data suggest that dopamine rather than dobutamine treatment may disturb glucose homeostasis.  相似文献   

19.
The effects of supramaximal exercise on blood glucose, insulin, and catecholamine responses were examined in 7 healthy male physical education students (mean +/- SD: age = 21 +/- 1.2 years; VO2max = 54 +/- 6 ml X kg-1 X min-1) in response to the following three dietary conditions: a normal mixed diet (N); a 24-h low carbohydrate (CHO) diet intended to reduce liver glycogen content (D1); and a 24-h low CHO diet preceded by a leg muscle CHO overloading protocol intended to reduce hepatic glycogen content with increased muscle glycogen store (D2). Exercise was performed on a bicycle ergometer at an exercise intensity of 130% VO2max for 90 s. Irrespective of the dietary manipulation, supramaximal exercise was associated with a similar significant (p less than 0.01) increase in the exercise and recovery plasma glucose values. The increase in blood glucose levels was accompanied by a similar increase in insulin concentrations in all three groups despite lower resting insulin levels in conditions D1 and D2. Lactate concentrations were higher during the early phase of the recovery period in the D2 as compared to the N condition. At cessation of exercise, epinephrine and norepinephrine were greatly elevated in all three conditions. These results indicate that the increase in plasma glucose and insulin associated with very high intensity exercise, persists in spite of dietary manipulations intended to reduce liver glycogen content or increase muscle glycogen store.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

20.
O2 chemoreflex drive of ventilation was studied before and after an intravenous infusion of L-norepinephrine (9 microgram/min), inducing a plasmatic hormone concentration similar to that obtained during submaximal exercise. The ventilation increasing rapidly at the beginning of the infusion was stabilized after 30 min : the ventilation was two times the reference value. The O2 chemoreflex drive of ventilation increased during norepinephrine infusion. When man was transiently switched from hypoxia to pure O2 (O2 test) the maximal fall of ventilation was two times the reference response. This increase in the chemoreflex drive, although the physico-chemical blood state was unchanged, may be explained by a norepinephrine chemoreceptor sensitization. Such a mechanism could partly explain the increase of O2 chemoreflex drive observed during muscular exercise.  相似文献   

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