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Biomedical subjects

C E Blanco

Publications and source records attributed to C E Blanco.

At least 109 records · Page 6Linked to original sources
PubMed1990

Enzyme profiles of single muscle fibers never exposed to normal neuromuscular activity.

Do muscle fiber properties commonly associated with fiber types in adult animals and the population distribution of these properties require normal activation patterns to develop? To address this issue, the activity of an oxidative [succinic dehydrogenase (SDH)] and a glycolytic [alpha-glycerophosphate dehydrogenase (GPD)] marker enzyme, the characteristics of myosin adenosinetriphosphatase (myosin ATPase, alkaline preincubation), and the cross-sectional area of single fibers were studied. The soleus and medial gastrocnemius of normal adult cats were compared with cats that 6 mo earlier had been spinally transected at T12-T13 at 2 wk of age. In control cats, SDH activity was higher in dark than light ATPase fibers in the soleus and higher in light than dark ATPase fibers in the medial gastrocnemius. After transection, SDH activity was similar to control in both muscles. GPD activity appeared to be elevated in some fibers in each fiber type in both muscles after transection. The cross-sectional areas most affected by spinal transection were light ATPase fibers of the soleus and dark ATPase fibers of the medial gastrocnemius, the predominant fiber type in each muscle. These data demonstrate that although the muscle fibers of cats spinalized at 2 wk of age presumably were never exposed to normal levels of activation, the activity of an oxidative marker enzyme was maintained or elevated 6 mo after spinal transection. Furthermore, although the absolute enzyme activities in some fibers were elevated by transection, three functional protein systems commonly associated with fiber types, i.e., hydrolysis of ATP by myosin ATPase and glycolytic (GPD) and oxidative (SHD) metabolism, developed in a coordinated manner typical of normal adult muscles.

Animals↗
PubMed1990

Effect of hyperoxia (PaO2 50-90 mmHg) on fetal breathing movements in the unanaesthetized fetal sheep.

Hypoxia inhibits fetal breathing movements but after birth it stimulates breathing. These differences have long been thought to involve central nervous inhibitory mechanisms. Such mechanisms might exert a tonic inhibition of fetal breathing movements at normal fetal PaO2 and the rise in PaO2 at birth might lift this inhibitory effect. To test this hypothesis 7 fetal sheep were chronically instrumented at 125-130 days for recording electrocortical activity (ECoG), and the electromyograph (EMG) activity of the diaphragm and neck muscles. Catheters were placed in a fetal carotid and a brachial artery and in the fetal trachea. For an extracorporeal membrane oxygenation system a 12 F gauge silastic catheter was placed in the right atrium for draining fetal blood and a 9.6 F gauge catheter was placed in a carotid artery to return oxygenated blood. Three days after operation the fetuses were connected to the extracorporeal membrane oxygenation system and fetal PaO2 was raised to 65.2 +/- 4.4 mmHg (SEM) for 6 to 19 h without changing pH or PaCO2. Neither the incidence of high voltage ECoG (48.5 +/- SEM 2.0% vs 52.8 +/- 3.3%) nor of fetal breathing movements (37.3 +/- 2.6% vs 23.8 +/- 5.9%) changed during the periods of hyperoxia. Since fetal breathing movements did not become continuous, we conclude that the lower PaO2 in the fetus compared to the neonate does not exert a tonic inhibitory influence on fetal breathing movements.

Animals↗
PubMed1989

Effects of partial plasma exchange transfusion on cerebral blood flow velocity in polycythaemic preterm, term and small for date newborn infants.

Isovolemic haemodilution with plasma was performed in 36 newborn infants with polycythaemia 3h after birth. Continuous wave Doppler ultrasonography was used to study the short and longer term influence of partial plasma exchange transfusion on cerebral blood flow velocity in both the anterior cerebral and mid cerebral arterial system up to 24h after haemodilution. The study group consisted of 11 preterm infants, 12 term infants, and 13 small for date infants. After exchange transfusion peripheral venous haemotocrit decreased from 72.5% to 59.4%. In all experimental groups cerebral blood flow velocity (CBFV) before exchange transfusion was significantly lower (18%-44%) than matched controls, and increased to control levels after exchange transfusion. CBFV improved most in preterm infants. After the transfusion the values were no different from the age-, weight-, sex- and parity-matched control groups, and they remained at this level during the next 24 h. No differences could be found between the anterior and mid-cerebral arterial system. When clinical symptoms were present, they subsided in all infants. In conclusion, partial plasma exchange transfusion has a favourable effect for at least 24 h on cerebral blood flow velocity in newborn infants with polycythaemia.

Blood Flow Velocity↗
PubMed1989

Effects of undernutrition on diaphragm fiber size, SDH activity, and fatigue resistance.

The influence of prolonged nutritional deprivation on the succinate dehydrogenase (SDH) activity and cross-sectional areas of individual fibers in the rat diaphragm and deep portion of the medial gastrocnemius (MGr) muscles was determined. Fatigue resistance of the diaphragm was measured by means of an in vitro nerve-muscle strip preparation. Fiber SDH activity and cross-sectional area were quantified by means of an image processing system. Diaphragm fatigue resistance was significantly improved in the nutritionally deprived (ND) group. In both muscles, nutritional deprivation resulted in a significant decrease in fiber cross-sectional area (both type I and II), type II fibers showing greater atrophy. The SDH activities of type I and II fibers in the diaphragm were not affected by nutritional deprivation. This contrasted with a significant decrease in the SDH activity of both type I and II fibers in the MGr of ND animals. An assessment of the interrelationships between fiber atrophy and fiber SDH activity revealed a greater effect of malnutrition on those diaphragm type II fibers that had the lowest relative SDH activities and the largest cross-sectional areas. By comparison, the effect of malnutrition on type I and II fibers in the MGr was nonselective with regard to fiber SDH activity. We conclude that the enhanced diaphragm fatigue resistance in the ND animals does not result from an increase in the oxidative capacity of muscle fibers and is best explained by the pattern of diaphragm muscle fiber atrophy.

Animals↗
PubMed1988

Quantitative histochemical determination of succinic dehydrogenase activity in skeletal muscle fibres.

A histochemical technique was developed for the quantitative determination of succinic dehydrogenase (SDH) activity in muscle cross-sections using 1-methoxyphenazine methosulphate (mPMS) as the exogenous electron carrier, and azide as an inhibitor of cytochrome oxidase. The optimal composition of the incubation medium for the SDH reaction was determined. This histochemical procedure was compared to one using phenazine methosulphate (PMS) instead of mPMS and cyanide instead of azide. The substitution of mPMS and azide resulted in a substantial decrease in the non-specific reduction of nitroblue tetrazolium (NBT; the reaction indicator), i.e., 'nothing dehydrogenase' activity. With mPMS and azide in the reaction medium, the production of NBT formazan was linear for at least 9 min during the enzymic reaction. This compared to a non-linear reduction of NBT during the initial stages of the reactions (SDH and 'nothing dehydrogenase') when using PMS and cyanide. The use of both mPMS and azide also eliminated the production of NBT monoformazan which occurred with PMS and cyanide. This procedure was shown to meet various criteria established for the quantification of histochemical reactions.

Animals↗
PubMed1988

Carotid baroreceptors in fetal and newborn sheep.

The responses of single carotid baroreceptor afferents were determined in anaesthetized fetal lambs at 88-113 and 131-144 days gestation, and in newborn lambs 1-8 and 30-40 days old. The baroreceptors discharged in synchrony with the arterial pressure pulse and increased their discharge rate as pressure was raised by compression of the abdominal aorta. When step increases in pressure were applied to the vascularly isolated carotid sinus, baroreceptor discharge increased abruptly and then showed adaptation to a steady state level. Basal mean arterial pressure increased from 49.1 in the young fetuses to 87.5 mm Hg in the 30- to 40-day-old lambs without an accompanying increase in basal baroreceptor discharge expressed absolutely or as a function of maximum discharge for each unit. The slope of the steep portion of the stimulus-response curve decreased with gestational age from 7.89 +/- 1.57 (mean +/- SE) at 88-113 days gestation to 1.82 +/- 0.37% nerve activity.mm Hg-1 in the 30- to 49-day-old lambs. Dynamic and steady state response curves were determined using step increases in carotid sinus pressure in two fetal lambs of 135 days gestation and two lambs 8 days old. Both the dynamic and the steady state curves were less steep in the older lambs. We conclude that the sensitivity of the carotid baroreceptors is reset as arterial pressure increases throughout the last third of gestation and the first postnatal month. This resetting is seen as a shift to the right of the response curve and a decrease in its slope.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1988

Effects on carotid chemoreceptor resetting of pulmonary ventilation in the fetal lamb in utero.

We tested the hypothesis that postnatal resetting of the carotid chemoreceptors is initiated by, and is dependent on, the rise in arterial PO2 (PaO2) which normally occurs after birth as air breathing is established. Previous studies had indicated that this resetting takes at least 24 h. We applied a technique for ventilation of the lungs of fetal sheep in utero to 3 groups of fetuses of 140-142 days gestational age: group 1 were exposed to normocapnic hyperoxia (mean PaO2 179.9 +/- 22.2 mmHg) for 27.4 +/- 0.9 h; group 2 were exposed to normocapnic hyperoxia (mean PaO2 229.4 +/- 77.5 mmHg) for 7.0 +/- 0.3 h; group 3 were ventilated for 21.6 +/- 3.3 h with a nitrogen/CO2 mixture to maintain PaO2 and PaCO2 within the normal fetal range. At the end of the ventilation period the fetuses were delivered by caesarean section, anaesthetized, paralysed and ventilation was continued. The responses of single or few fibre carotid chemoreceptor preparations to isocapnic hypoxia were then determined. To compare their response curves quantitatively, hyperbolic curves were fitted to the data. No significant differences between any of the groups were found in the vertical or the horizontal asymptotes. There was no difference in the slope of the hyperbolic line between group 2 and group 3. However, this slope was significantly greater for Group 1 than for either group 2 or group 3. Our results show that a period of hyperoxia of 24-31 h in utero, although not a similar period of normoxic ventilation, initiates the process of carotid chemoreceptor resetting.

Animals↗
PubMed1988

Changes in fetal organ flow during intrauterine mechanical ventilation with or without oxygen.

To investigate whether the changes in circulation at birth are due to lung ventilation, changes in PaO2 or both we mechanically ventilated in utero the lungs of 10 fetal sheep (120-127 days of gestational age) five days after instrumentation under general anaesthesia. Electrocortical activity (ECoG), eye movements (EOG), electromyographic activity from diaphragm and posterior neck activity (EMG) and electrocardiogram (ECG) were recorded. Fetal catheters (artery and vein of the hindlimb, arteries of both forelimbs which in three occasions were advanced into the left ventricle, fetal trachea and amniotic cavity), and an endotracheal tube were placed. After recovery radioactive 15 mu microspheres (I125, Ce141, Sr85 and Sc46) were injected into the inferior vena cava or left ventricle during high voltage electrocortical activity before and after lung expansion with N2 and after expansion with O2 for two levels of PaO2. PaCO2 did not change. The percentage of spheres trapped in the lungs increased from 9.6% to 44% after expanding the lungs with N2 and to 90% when fetal PaO2 increased (P less than 0.001). Blood flow to different organs did not change during normoxic expansion but it decreased significantly to the brain (91 +/- 25 to 27 +/- 8 ml/min per 100g, [mean +/- SD]) placenta (160 +/- 57 to 54 +/- 33 ml/min/100g) and coronaries (239 +/- 91 to 117 +/- 60 ml/min per 100g) when PaO2 was increased. In conclusion fetal circulation responds to raised levels of PaO2 well before birth probably by a direct action of oxygen on the vessels.

Animals↗
PubMed1987

Breathing activity in fetal sheep during mechanical ventilation of the lungs in utero.

Effects of mechanical ventilation of the lungs of fetal lambs in utero are described. Feasibility studies were performed acutely on four fetuses at 140-142 days gestational age. Five fetuses were prepared for chronic experiments at 122-128 days gestation. Mechanical ventilation was used to produce changes in fetal blood gases for periods of up to 24 h in acute preparations or for repeated periods of 3-9 h on consecutive days in chronic preparations. This technique permits the study of fetal lambs in utero under conditions which normally occur after birth without producing maternal changes or using anesthesia and whilst the umbilical circulation remains open. Four situations were examined using ventilation in these chronic preparations: (1) expansion of the lungs whilst maintaining fetal normoxia and normocapnia; (2) fetal normoxia and hypocapnia; (3) hyperoxia and normocapnia; (4) hyperoxia and hypocapnia. None of these situations produced continuous fetal breathing, either during ventilation or after switching off the ventilator. We conclude that they do not provide appropriate stimuli to mimic those which normally produce continuous breathing after birth.

Animals↗
PubMed1987

Determinants of the onset of continuous air breathing at birth.

We used mechanical ventilation of the fetal lungs in utero on 11 fetal lambs at 140-145 days gestation to alter fetal blood gases and thus separate the influences of PaO2 and PaCO2 on extrauterine breathing after cord clamping. The fetus was delivered either into a 40 degrees C saline bath or onto a cold table. Mechanical ventilation was stopped 2 min after delivery and the time to onset of continuous air breathing was observed. Also two fetuses were ventilated in utero 5 or more days after chronic instrumentation at 127 days gestation; in these animals the time to onset of breathing (diaphragm EMG) was recorded after stopping the ventilator and occluding the cord. We conclude: (a) hypercapnia is a stimulus to breathing even in hyperoxia and at 40 degrees C; (b) hypocapnia delays the start of extrauterine breathing in hyperoxia at 40 degrees C; (c) hypoxia inhibits breathing in the absence of hypercapnia or cold; (d) cold overrides the effects of hypocapnia in normoxia or moderate hypoxia.

Animals↗
PubMed1987

Absence of regional differences in the size and oxidative capacity of diaphragm muscle fibers.

The oxidative capacity and cross-sectional area of muscle fibers were compared between the costal and crural regions of the cat diaphragm and across the abdominal-thoracic extent of the muscle. Succinate dehydrogenase (SDH) activity of individual fibers was quantified using a microphotometric procedure implemented on an image-processing system. In both costal and crural regions, population distributions of SDH activities were unimodal for both type I and II fibers. The continuous distribution of SDH activities for type II fibers indicated that no clear threshold exists for the subclassification of fibers based on differences in oxidative capacity (e.g., the classification of fast-twitch glycolytic and fast-twitch oxidative glycolytic fiber types). No differences in either SDH activity or cross-sectional area were noted between fiber populations of the costal and crural regions. Differences in SDH activity and cross-sectional area were noted, however, between fiber populations located on the abdominal and thoracic sides of the costal region. Both type I and II fibers on the abdominal side of the costal diaphragm were larger and more oxidative than comparable fibers on the thoracic side.

Animals↗
PubMed1986

SDH activity and cross-sectional area of muscle fibers in cat diaphragm.

The succinate dehydrogenase (SDH) activity and cross-sectional area of individual muscle fibers in the cat diaphragm were quantified using a computerized image-processing system. The population distributions of fiber-SDH activities and cross-sectional areas showed considerable range within each diaphragm. Despite an overlap in the distribution of SDH activities between fast-twitch (i.e., those staining darkly for myosin ATPase) and slow-twitch (i.e., those staining lightly for myosin ATPase) fibers, differences between the two populations of fibers were observed. Fast-twitch fibers generally had lower SDH activities and greater cross-sectional areas than slow-twitch fibers. However, the range of SDH activities and cross-sectional areas of fast-twitch fibers was much greater than in slow-twitch fibers. The population distributions of SDH activities and cross-sectional areas of both fast- and slow-twitch fibers were unimodal. The unimodal distribution of SDH activities in fast-twitch fibers suggested that these fibers could not be clearly subdivided into two groups based on differences in their oxidative capacity (i.e., high- and low-oxidative fibers). These results were discussed in the context of the classification of fast-twitch glycolytic and fast-twitch oxidative-glycolytic fibers using qualitative histochemistry. In addition, the functional significance of the unimodal distribution of oxidative capacities in fast-twitch fibers was discussed in relation to the distribution of fatigue properties in fast-twitch motor units. A significant negative correlation between cross-sectional area and SDH activity in both fast- and slow-twitch fibers was also observed. The importance of this negative correlation in relationship to the diffusion of energy substrates for oxidative metabolism was discussed.

Adenosine Triphosphatases↗
PubMed1985

Single versus repetitive doses of natural surfactant as treatment of respiratory distress syndrome in premature lambs.

After delivery by caesarean section at 117-120 and 125-130 days gestational age, 20 lambs were supported with infant ventilators at an FiO2 of 1.0. Throughout the experimental period the respiratory settings were held constant. All lambs were treated by tracheal instillation of 50 mg natural sheep surfactant lipid/kg body weight at 1 h of age, after respiratory failure had been documented. All lambs responded with a decrease in PaCO2 and increases in PaO2 and pH, but these responses were of greater magnitude with advancing gestational age. Without waiting for respiratory failure to reappear, repetitive doses of natural surfactant were administered and the effects studied. Retreatment by instillation of 12.5 mg surfactant/kg at 2, 3, 4, 5, and 6 h of age was ineffective at 117-120 days gestational age, but sustained the initial response to the bolus of 50 mg surfactant/kg at 125-130 days gestational age. This indicates that retreatment with natural surfactant should be started before the reappearance of respiratory failure in order to be effective, and that the response to retreatment with small, repetitive doses of surfactant is dependent on gestational age.

Animals↗
PubMed1984

The response to hypoxia of arterial chemoreceptors in fetal sheep and new-born lambs.

Carotid chemoreceptor activity was detected in each of fourteen halothane or pentobarbitone anaesthetized exteriorized fetal lambs of 90-143 days gestational age. Activity was about 5 Hz at a Pa,O2 of 25 mmHg and it increased as Pa,O2 was reduced, either by compressing the umbilical cord or by reducing the (FIO2) oxygen fraction of the gas used to ventilate the ewe. Activity increased briskly when 1-2 ml CO2-saturated saline was injected retrogradely into the lingual artery, but not when saline of pH 7.4 or fetal arterial blood was injected. In two fetuses near-term chemoreceptor activity was recorded continuously whilst the umbilical cord was ligated and ventilation with air started. Activity increased 200-500% as Pa,O2 fell, but then fell to below control as Pa,O2 rose. We suggest that these changes in activity reflect those occurring naturally at birth. No spontaneous chemoreceptor activity could be detected on the day of birth in twelve pentobarbitone anaesthetized lambs delivered vaginally or by Caesarean section at 135-146 days. Single baroreceptor activity could however be recorded in these lambs, and chemoreceptor activity could be elicited by hypercapnia. Spontaneous chemoreceptor activity was detected in six of seven lambs more than 2 days old. In eight conscious lambs the steady-state respiratory response to isocapnic hypoxia was variable on the day of birth. In six of these lambs the response was significantly greater by the third day. We conclude that the arterial chemoreceptors are active and responsive in the fetus, but quiescent in the lamb on the day of birth when Pa,O2 has risen. The hypoxic sensitivity of the chemoreceptors is reset from the fetal to the adult range over the next few days.

Action Potentials↗
PubMed1984

Breathing pattern of kittens during hypoxia.

In 19 pentobarbital sodium-anesthetized kittens aged 5-34 days, inspired O2 was reduced from 21 to 6-12%. Respiratory frequency (f) and tidal volume (VT) increased within 30 s. Over 5 min f fell to about 60% below control; VT usually fell but remained above control. Arterial pressure fell in 80% of trials, sometimes before f fell. Arterial CO2 was below control, but raising inspired CO2 to keep expired CO2 at control did not prevent the fall in f and VT. The relation between VT and esophageal pressure or diaphragm electromyogram (EMG) did not change consistently, nor was the ratio of high to low frequencies in the diaphragm EMG altered. Carotid chemoreceptor discharge increased within 15 s, and at 5 min it was much above control. We conclude that the change in the breathing pattern in hypoxia is probably due to the activation of a central mechanism.

Abdominal Muscles↗
PubMed1983

Effect of hypoxia on polysynaptic hind-limb reflexes of unanaesthetized fetal and new-born lambs.

Polysynaptic reflex excitation of the hind-limb flexor muscles was produced by stimulation of the distal peroneal or common sciatic nerve in ten fetal and six new-born unanaesthetized lambs. In the fetal lambs, stimulation at 1.1-3.25 times threshold for direct activation of the nerve produced a reflex response which was greatest during high-voltage electrocortical activity, being reduced 69 +/- 5.0% (mean +/- S.E. of the mean) during low-voltage electrocortical activity. Reduction of the fetal arterial PO2 from 23.3 +/- 0.58 to 12.2 +/- 0.4 mmHg caused a rapid and reversible reduction of the reflex in all fetal lambs with intact spinal cord, including two whose brain stems were transected at the level of the colliculi. Hypoxia did not alter the amplitude of the reflex in two fetuses in which the spinal cord at L1-2 had been cut several days previously. In new-born lambs reduction of the arterial PO2 to 43 mmHg did not change the reflex amplitude during episodes of quiet wakefulness or slow-wave sleep. Brief reduction of the Pa,O2 to 20-30 mmHg caused a statistically insignificant reduction of reflex amplitude during quiet sleep before behavioural arousal. It is concluded that hypoxaemia activates reticular mechanisms in the pons and medulla of fetal lambs which decrease the excitability of spinal reflex pathways. In the new-born lamb such effects are counteracted or prevented by mechanisms associated with arousal.

Animals↗
PubMed1983

Effects of hypoxia on polysynaptic hind-limb reflexes in new-born lambs before and after carotid denervation.

Polysynaptic reflex responses in the hind limb were obtained by stimulating the peroneal nerve in unanaesthetized lambs between 4 and 12 days from birth, before and after carotid denervation. In intact lambs isocapnic reduction of the Pa,O2 from 88 to 31 or to 23 mmHg caused an insignificant decrease in reflex amplitude. Denervation of the carotid bifurcations induced hypoventilation. When the Pa,O2 was then reduced to 22 mmHg the reflex amplitude fell by 77%. In carotid denervated lambs after complete transection of the spinal cord at T12-L1, reduction of the Pa,O2 to 23 mmHg did not alter the size of the reflex. The same result was observed after section of the dorsal part of the lateral funiculi. It is concluded that, in the young lamb a few days after birth, the afferent activity of the carotid chemoreceptors during hypoxia plays an important role in maintaining the excitability of motor reflexes. The possible mechanisms are discussed.

Animals↗