Continuous measurement of blood flow in the superior sagittal sinus of the lamb

Grant, Daniel; Franzini, Carlo; Wild, Jennene; Walker, Adrian M.

doi:10.1152/ajpregu.1995.269.2.r274

Cited by 25 publications

(47 citation statements)

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“…The present study utilized a continuous intravenous infusion of L- [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]leucine to investigate leucine metabolism in the near-term ovine fetal brain. This was accomplished with the measurement of tissue protein leucine specific activity, which reflects the unidirectional flux of leucine into cerebral protein, i.e., protein synthesis, and using Fick methodology to measure the uptake of labeled/unlabeled leucine by the brain, which reflects that utilized for protein synthesis/accretion, plus any leucine that is oxidized.…”

Section: Discussionmentioning

confidence: 99%

“…A-V differences were collected in both the LV/REM and HV/NREM behavioral states to determine the relationship between cerebral leucine metabolism and behavioral state activity during brain development. The label on L- [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]leucine at the carboxyl position can be measured in leucine that has been incorporated into protein, or it can be followed through the catabolic pathway, which involves the reversible transamination with ␣-ketoglutarate to form ␣-KIC, followed by oxidative decarboxylation to form 14 CO 2 , which diffuses out of the tissue (8). The measurement of tissue SA PB leucine along with that of the precursor pool at a defined time from the start of the tracer infusion provides a means of estimating the fractional synthetic rate of brain proteins, i.e., the percentage of brain proteins newly synthesized per unit time.…”

Section: Discussionmentioning

confidence: 99%

“…The superior sagittal sinus drains regions of the frontal cortex and anterior regions of the parietal cortex as measured in the newborn lamb and represents ϳ20% of total brain blood flow (7). Cerebral blood flow and leucine uptake per unit mass of brain tissue were then calculated assuming the respective relative values to be reflective of ϳ20% of brain tissue mass (7), thus allowing for comparison with previous studies.…”

Section: Methodsmentioning

confidence: 99%

“…Significance is based on paired data analysis. Cerebral blood flow, leucine uptake, and [ 14 C]leucine uptake were calculated assuming the respective sagittal sinus blood flow (Qss) or cortical uptake values to be reflective of ϳ20% of brain tissue mass (7). A-V, arterial-venous; ␣-KIC, ␣-ketoisocaproic acid; LV/REM, low-voltage electrocortical state in presence of rapid eye movement; HV/NREM, high-voltage electrocortical state with no rapid eye movement present; NS, not significant.…”

Section: Cerebral Leucine and [mentioning

confidence: 99%

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Cerebral leucine uptake and protein synthesis in the near-term ovine fetus: relation to fetal behavioral state

Czikk

Sweeley

Homan

et al. 2003

American Journal of Physiology-Regulatory, Integrative and Comp

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leucine uptake and protein synthesis in the near-term ovine fetus: relation to fetal behavioral state. Am J Physiol Regul Integr Comp Physiol 284: R200-R207, 2003; 10.1152/ ajpregu.00190.2002-Behavioral/sleep state activity may impact on synthetic processes within the brain, thus accounting for the developmental change in such activity and suggesting a role in the brain's growth and development. We have therefore determined the cerebral uptake of leucine and [ 14 C]leucine during continuous tracer infusion as measures of leucine metabolism in relation to behavioral state activity, as well as the regional flux of leucine into brain tissue in the ovine fetus near term. The cerebral fractional protein synthetic rate and the absolute protein synthetic rate averaged ϳ20%/day and ϳ1 g/day, respectively, as measured for the whole brain, which is considerably higher than anticipated protein accretion and indicates a high rate of protein turnover with protein synthesis closely linked to protein degradation. Measures of protein synthesis were significantly higher in the pituitary gland, which may be attributed to the active synthesis and export of peptide hormones from this region. Cerebral leucine and [14 C]leucine uptakes averaged ϳ630 and ϳ1,000 nmol ⅐ 100 g Ϫ1 ⅐ min Ϫ1 , with the latter higher than leucine unidirectional flux and thus supporting a degree of leucine oxidation by the brain. Cerebral leucine metabolism as studied was affected by behavioral state activity, with uptake measurements for both leucine and [ 14 C]leucine significantly increased during the high-voltage electrocortical/non-rapid eye movement state by 1.7-fold and 2.8-fold, respectively, indicating that protein synthesis and degradation must also be increased at this time, and supporting a role for behavioral state activity in the brain's growth and development. brain development; leucine metabolism CEREBRAL PROTEIN SYNTHESIS has been studied during brain growth and development, both pre-and postnatally in sheep (1, 24) and postnatally in the rat (6, 26), because proteins are integral components of structural elements in brain tissue and with the metabolism of brain protein directly related to maturational events (26). Initial study in the near-term ovine fetus by Schaefer and Krishnamurti (24) using a tyrosine isotopic-dilution technique showed high rates of cerebral protein synthesis with a fractional protein synthetic rate between 14 and 37%/day and an absolute rate of synthesis of ϳ1 g/day. A subsequent study in fetal sheep by Abrams and colleagues (1) using [14 C]leucine autoradiography reported a rate of leucine incorporation into brain protein of ϳ5 nmol ⅐ g Ϫ1 ⅐ min Ϫ1 , with an overall increase through the latter part of gestation and into the early postnatal period likely reflecting cerebral myelination. Postnatal studies in rats have similarly shown high rates of brain protein synthesis during early development, with peak values occurring shortly after birth and gradually decreasing thereafter (6, 26). While high rates of cerebral pr...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Cerebral Leucine and [mentioning

confidence: 99%

See 2 more Smart Citations

Cerebral leucine uptake and protein synthesis in the near-term ovine fetus: relation to fetal behavioral state

Czikk

Sweeley

Homan

et al. 2003

American Journal of Physiology-Regulatory, Integrative and Comp

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“…Based on this, it is reasonable to anticipate that cortical tPO 2 also may not be altered significantly by tissue trauma. Also, the sagittal sinus drains blood from the anterior one-third of the fetal lamb brain (20), and its oxyhemoglobin saturation is considered to represent global cerebral oxygenation. Nonetheless, this value is an indirect estimation of cerebral (chiefly cortex and partly white matter; in this study) oxygenation, and small contributions by extracerebral contamination cannot be excluded.…”

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confidence: 99%

Fetal Hypercapnia and Cerebral Tissue Oxygenation: Studies in Near-Term Sheep

2006

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The precise role of CO 2 in cerebral oxygenation is not as well defined as O 2 , especially in the immature brain. In the ovine fetus, we tested the hypotheses that arterial PCO 2 (PaCO 2 ) plays a critical role not only in the regulation of cerebral blood flow but also in the regulation of cerebral tissue oxygenation. I n the developing fetus and newborn infant, as well as the adult, the maintenance of optimal cerebral oxygenation is of critical importance, as the brain is highly dependent on a continuous and adequate O 2 supply to maintain structural and functional integrity. Cerebral tissue oxygenation is maintained and carefully regulated by the balance of several factors. These include CBF, arterial O 2 partial pressure (PaO 2 ) and content, cerebral metabolic rate for O 2 (CMRO 2 ), and the relative position of the Hb-oxygen dissociation curve (1,2). Arterial CO 2 tension (PaCO 2 ) long has been recognized as playing a major role in CBF regulation of the fetus (3) as well as the adult (4,5). Thus, it is reasonable to anticipate that CO 2 , as well as O 2 , plays a significant role in cerebral tissue oxygenation.Variation of PaCO 2 commonly occurs in the management of the fetus and newborn during the perinatal period. During labor, fetal hypercapnia with respiratory acidosis, in part resulting from transient compression of the umbilical cord, is not uncommonly seen (6). In addition, vaginal delivery itself may be associated with respiratory acidosis and hypoxia (7). Alternatively, with moderate to severe maternal hyperventilation, particularly during the later stages of labor, fetal hypocapnia with respiratory alkalosis may develop (8,9). In addition, among critically ill newborn infants, significant changes in PaCO 2 can present problems. Under some circumstances, hypocapnia is believed to be of value to prevent an excessive increase in CBF. In other instances, "permissive" hypercapnia is practiced to optimize CBF, to reduce the risk of periventricular leukomalacia, and to minimize ventilator-associated lung injury (10). Nonetheless, despite the critical importance of these issues, and knowledge that cerebrovascular PaCO 2 reactivity differs dramatically between the immature and mature organism (11), the role of CO 2 in cerebral tissue oxygenation has received relatively little attention, especially in the immature brain. (12)(13)(14). MATERIALS AND METHODSExperimental animals and instrumentation. For these studies, we used six pregnant Western ewes and their singleton fetuses obtained from Nebeker Ranch (Lancaster, CA). All surgical and experimental procedures were performed within the regulations of the Animal Welfare Act, the National Institutes of Health Guide for the Care and Use of Laboratory Animals, "The Guiding Principles in the Care and Use of Animals" approved by the Council of the American Physiologic Society, and the Animal Care and Use Committee of Loma Linda University.Pregnant ewes and their fetuses were instrumented at 122 Ϯ 3 d of gestation (term 145 d), as we have described in...

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