The blood flow and oxygen consumption of brown adipose tissue in the new‐born rabbit

Heim, T; Hull, D

doi:10.1113/jphysiol.1966.sp008019

Cited by 130 publications

(76 citation statements)

References 13 publications

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“…, As a consequence of the changes in metabolic requirements and V02, cardiovascular function and blood gases were also influenced by ambient temperature. The 20% increase in heart rate and cardiac output observed in room air at the lower temperature was probably due to the sympathetic stimulation that mediated the increase in brown fat metabolism (10). Inasmuch as it has been shown that the reserve capacity for increasing cardiac output is decreased in the newborn period, the increase in cardiac output secondary to the exposure to cool environment could considerably affect the potential-circulatory reserve of the normoxic newborn.…”

Section: Discussionmentioning

confidence: 99%

“…Nonshivering thermogenesis is known to be very potent in the newborn lamb and regresses a few weeks after birth (3). Cold exposure is a potent activator of brown fat lipase (12,21), with marked increase in 0 2 uptake in the brown fat both as a result of an increase in blood flow and Oz extraction (10). During hypoxia, brown fat metabolism is inhibited (5,10) and Oz uptake is decreased in brown fat, as a result of both a decrease in blood flow and in oxygen extraction (10).…”

Section: Discussionmentioning

confidence: 99%

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Effects of Ambient Temperature on Oxygen Consumption and the Circulation in Newborn Lambs at Rest and during Hypoxemia

et al. 1983

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SummaryTo assess the effects of environmental temperature on responses to hypoxemia, we studied five unsedated lambs in the first week after birth. We catheterized the carotid artery and pulmonary artery (via the jugular vein). After recovery of at least 1 day, we measured pH, blood gases, arterial and mixed venous blood 0 2 content, oxygen consumption (V02), heart rate, carotid and pulmonary arterial pressures, and cardiac output in both warm (25°C) and cool (17.4 2 l.l°C) environments. In the cool environment, with no shivering, V02 increased 40% (14.9 to 20.8 ml/kg/min). There were also increases of arteriovenous blood 0 2 content difference of 19%, cardiac output of 18%, and heart rate of 14%. In four lambs, we studied the same variables during hypoxemia (Fio2 = 0.09 for 1 h) at both temperatures. In the cool environment, hypoxemia produced a greater fall of V02 (26% versus 6%) and arteriovenous oxygen differences (30% versus 19%) and a smaller increase of cardiac output (8% versus 14%) and heart rate (26% versus 43%). Also in the cool environment, core temperature decreased more (2.1 versus 0.4"C), but base deficit was the same (-6 versus -5 mEq/liter). Despite the greater fall in VO2 during hypoxemia in the cool environment, the lowest value achieved was still higher than the level during normoxemia in the warm environment. Similarly, cardiac output during hypoxemia was greater in the cool than in the warm environment. These findings may explain the variability in reported normal resting values and responses to hypoxemia. Contrary to previous reports, they also indicate that during severe hypoxemia neonates have a decreased reserve of metabolic and cardiovascular responses in a cool compared with a warm environment.Reported values for cardiac output, heart rate, and VO2 in newborn lambs at rest (13,17,20,24,26) and after induced hypoxemia (9, 14, 18, 24) vary greatly. Because newborn homeothermic mammals are very sensitive to cold, we considered that this variability could be explained by differences in ambient temperature.In normoxemic newborns, if ambient temperature is decreased only a few degrees below neutral temperature, the metabolic requirements for maintenance of core temperature increase considerably (22). Because the reserves for increasing cardiac output (13) and Oz delivery to the tissues (17) are limited during the newborn period, the extra metabolism induced by exposure to low ambient temperature could interfere with tissue oxygenation. In hypoxemic newborn humans (19, 23), kittens (1 I), and lambs (4) at low ambient temperature the extra thermogenic metabolism is inhibited and VOz and core temperature decrease. It has been suggested that core temperature may decrease enough to reduce basal metabolism and thereby protect the tissues of the hypoxemic newborn against oxygen lack (1, 2).We have studied the circulatory and metabolic effects of moderate changes in ambient temperature that could occur in a laboratory or nursery in which ambient temperature is not controlled, and address the follow...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Effects of Ambient Temperature on Oxygen Consumption and the Circulation in Newborn Lambs at Rest and during Hypoxemia

et al. 1983

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“…If the tachycardia were in fact caused by increased catecholamine production or adrenergic discharge, inotropic responsiveness to catecholamines must have been blunted, because adrenergic stimulation normally increases cardiac output as well as causing tachycardia. Blunting of adrenergic responsiveness has been described in the metabolism of brown fat under hypoxemic conditions (50). Cardiovascular responsiveness to a and 0 adrenergic stimulation during chronic hypoxemia should be studied to fully explain these findings.…”

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confidence: 99%

Chronic Hypoxemia in the Newborn Lamb: Cardiovascular, Hematopoietic, and Growth Adaptations

et al. 1985

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ABSTRAm. We have created a model of chronic hypoxemia in the newborn lamb by decreasing pulmonary blood flow in the presence of an atrial septal defect. Via a left lateral thoracotomy, we place an inflatable balloon around the pulmonary artery and perform an atrial septostomy under direct vision. We also insert several vascular catheters and place an electromagnetic flow transducer around the ascending aorta. Three days after surgery, we inflated the balloon in 11 lambs such that arterial oxygen saturation decreased to 60 to 75%. Studies were performed on these lambs twice weekly and weekly on 12 normoxemic lambs. Growth decreased sharply (47 2 123 versus 221 f 82 g/ day) at the onset of hypoxemia and remained low, although oxygen consumption followed the normal gradual decline. Heart rate remained elevated throughout the study. Arterial Pcoz levels decreased from 40 + 5 to 35 f 7 torr and remained low. Systemic blood flow decreased at balloon inflation but quickly returned to normal. Mixed venous saturation was low, but could decrease further with shivering. Systemic oxygen delivery decreased initially but returned to normal as Hb concentration rose (from 9.4 f 1.5 to 12.5 f 2.2 g/dl). P50 increased normally over the study period. Four of the 11 hypoxemic lambs died during the study. These data show that, in the chronically hypoxemic newborn, systemic oxygen delivery is maintained primarily by a rising Hb. Total body oxygen consumption is maintained at rest but is redistributed away from anabolic requirements and toward cardiorespiratory work. This signal to decrease growth occurs despite less than maximal oxygen extraction at rest. (Pediatr Res 19: 1004Res 19: -1010Res 19: ,1985 developed a model of a common cyanotic heart lesion to assess some of its cardiovascular and metabolic effects on the newborn lamb.Several authors have studied acute hypoxemia in the developing organism and elucidated its effects on general cardiovascular function (1-3), regional blood flow (1, 4, 5), metabolic activity (6, 7), and course of decompensation (1). The effects of sympathetic blockade (8, 9) and decreasing Hb oxygen affinity (10, 11) on the response to acute hypoxemia have also been addressed. Few studies have been performed on the chronically hypoxemic developing organism to understand the change from acute to chronic adaptations and the sequelae of these adaptations. Those studies have involved rodents and calves and have focussed on growth (1 2) and the development of the pulmonary (1 3) and coronary (14) vascular beds.We have designed a model to produce chronic hypoxemia in the newborn lamb and have studied lambs over several days of hypoxemia. We created a model of severe pulmonary stenosis with atrial septal defect. This simulates cyanotic lesions in which total pulmonary blood flow is reduced, which occurs in more than half of the infants with cyanotic heart disease (15). The degree of right ventricular outflow obstruction determines the drop in pulmonary blood flow and thus the magnitude of rightto-left atrial shu...

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“…In the present study, an increase in the plasma concentration of T× following cold exposure is likely to be the result of cold stimulation of the hypothalamic-pituitary-thyroidal axis (Hefco et al 1975;Cabello, 1983). At 4 days of age effects of hypoxia on metabolism and thyroid hormone secretion may be exacerbated as a result of a decrease in Oµ extraction, blood flow (Heim & Hull, 1966) and therefore T× production (Fernandez et al 1987) by brown adipose tissue.…”

Section: Statistical Analysesmentioning

confidence: 90%

The Influence of Acute Hypoxia and Carotid Body Denervation on Thermoregulation During Non‐Rapid Eye Movement Sleep in the Developing Lamb

Symonds

Andrews

Johnson

1999

Experimental Physiology

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summaryWe investigated the influence of ambient temperature on the thermoregulatory response to hypoxia in developing lambs before (at 4 and 14 days of age) and after (17 and 30 days of age) carotid body denervation (CBD). Lambs were studied during non-rapid eye movement sleep at thermoneutral (23-15°C) and cool (10-5°C) ambient temperatures, during normoxia and acute hypoxia (inspired oxygen content of 13%). Measurements of oxygen consumption, arterial partial pressures of Oµ and COµ, colonic temperature, incidence of shivering and plasma concentrations of thyroid hormones, cortisol, insulin and glucose were made under each condition. Oxygen consumption was higher at cool compared with thermoneutral ambient temperatures and decreased during hypoxia during cooling at all stages. At 4 days of age, only one lamb shivered during cooling in normoxia, but 4 out of 12 lambs shivered during hypoxia and colonic temperature fell, significantly, by 0·2°C. At 14 days, 8 out of 12 lambs shivered during cooling, of which 6 continued to shiver during hypoxia but colonic temperature did not change significantly. Plasma triiodothyronine concentrations increased on cooling at 4 and 14 days, an affect that was inhibited by hypoxia at 4, but not 14 days of age. At 17 days of age, i.e. post-CBD, plasma thyroid hormone concentrations and oxygen consumption were lower during cold exposure compared with intact lambs at 14 days of age. In CBD lambs, imposing further hypoxia resulted in colonic temperature falling 0·6°C during cooling, with only 2 out of 10 lambs shivering. Plasma glucose and insulin, but not cortisol, concentrations decreased during hypoxia, irrespective of age or CBD. It is concluded that hypoxia has an important influence on metabolism and thermoregulation, which is modulated by age and environmental conditions. Compromised carotid body function, in lambs older than 2 weeks of age, can result in severe hypoxia and thermoregulatory dysfunction even with modest environmental cooling.

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The blood flow and oxygen consumption of brown adipose tissue in the new‐born rabbit

Cited by 130 publications

References 13 publications

Effects of Ambient Temperature on Oxygen Consumption and the Circulation in Newborn Lambs at Rest and during Hypoxemia

Effects of Ambient Temperature on Oxygen Consumption and the Circulation in Newborn Lambs at Rest and during Hypoxemia

Chronic Hypoxemia in the Newborn Lamb: Cardiovascular, Hematopoietic, and Growth Adaptations

The Influence of Acute Hypoxia and Carotid Body Denervation on Thermoregulation During Non‐Rapid Eye Movement Sleep in the Developing Lamb

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