Plasma nitrate accumulation during the development of pacing-induced dilated cardiac myopathy in conscious dogs is due to renal impairment.

Heart failure is associated with an increase in plasma nitrate and nitrite (NOx). To date there is still some controversy regarding the causes of nitrate accumulation during the development of heart failure. The goal of this study was to analyze the underlying mechanisms that cause accumulation of plasma nitrates during the development of heart failure in dogs. Dogs were chronically instrumented for measurement of hemodynamics and renal function. Hearts were paced initially at 210 bpm for 3 weeks and then at 240 until the development of heart failure. Hemodynamics, renal function, renal blood flow, arterial blood gases, hemoglobin, plasma and urine NOx levels, and creatinine levels were measured weekly. Heart failure was assessed by hemodynamic alterations, physical signs such as lethargy, ascites, cachexia, and postmortem evidence of cardiac hypertrophy. LVSP (from 127 +/- 3 to 106 +/- 3 mmHg), LV dP/dt (from 2658 +/- 173 to 1439 +/- 217 mmHg/s), MAP (from 101 +/- 1.9 to 83 +/- 1.8 mmHg) fell, whereas LVEDP tripled (from 6.4 +/- 0.9 to 20 +/- 2.6 mmHg), and heart rate rose (from 101 +/- 4.2 to 117 +/- 6.3 bpm), all changes P < 0.05. RBF (from 146 +/- 10 to 96 +/- 9.9 ml/min), urine output (V) (from 0.26 +/- 0.02 to 0.16 +/- 0.02 ml/min), GFR (from 63 +/- 1.8 to 49 +/- 2 ml/min), and Na excretion (from 45 +/- 4.5 to 14 +/- 4.6 microEq/min) all decreased (P < 0.05), whereas RVR increased (from 0.68 +/- 0.05 to 0.94 +/- 0.1 mmHg/ml/min). These changes took place during a rise in plasma NOx (from 3.7 +/- 0.5 to 16+/-3.3 microM), a decrease in urine NOx (from 33 +/- 9.9 to 8.1 +/- 4.9 microM), and a concurrent increase in NOx reabsorption (from 221 +/- 31 to 818 +/- 166 nmol/min). There was a direct correlation between the increase in plasma NOx levels and an increase in filtered load (r(2) = 0.97, P = 0.02), a negative correlation between NOx levels and NOx excretion (r(2) = 0.65 P < 0.09), and a direct correlation between plasma NOx levels and NOx reabsorption (r(2) = 0.97, P = 0.02). These results indicate that elevated plasma NOx during heart failure are most likely the result of an impairment of the renal function and not increased NOx production. Furthermore, without knowing changes in renal function the measurement of plasma NOx in and of itself is a meaningless index of NO formation.     

Assessment of cardiovascular reflexes: influence of posture and period of preceding rest

The aim of the present study was to investigate the effects of a pretest redistribution of blood volume and of a change in the neurohumoral condition on the blood pressure (BP) and heart rate (HR) responses to three commonly used cardiovascular reflex tests: standing up, forced breathing, and the Valsalva maneuver in 10 healthy male subjects. Base-line conditions were altered by changing posture and the duration of rest preceding the test stimulus. A continuous recording of finger BP was obtained noninvasively by a Finapres. The main observations from this study are with respect to standing up: lengthening the period of preceding rest from 1 to 20 min enlarges the initial BP (systolic/diastolic) decrease (from 8 +/- 10/9 +/- 4 to 27 +/- 8/19 +/- 4 mmHg, P less than 0.01) and the subsequent BP overshoot (from 17 +/- 10/12 +/- 7 to 31 +/- 10/18 +/- 7 mmHg, P less than 0.05); to forced breathing: inspiratory-expiratory changes in BP but not in HR are larger in the upright posture (P less than 0.05); and to the Valsalva maneuver: change in posture from supine to standing increases the phase II BP decrease (from 18 +/- 12/8 +/- 6 to 45 +/- 16/21 +/- 9 mmHg), phase IV systolic BP overshoot (from 26 +/- 16 to 71 +/- 17 mmHg), delta HRmax (from 30 +/- 10 to 47 +/- 12 beats/min), and the Valsalva ratio (HRmax/HRmin), from 2.0 +/- 0.3 to 2.6 +/- 0.7, all significant at P less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of method of preservation on functions of livers from fed and fasted rabbits

Livers from fed, fasted (48 h) and glucose-fed rabbits were preserved for 24 and 48 h by either simple cold storage (CS) or continuous machine perfusion (MP) with the University of Wisconsin preservation solutions. After preservation liver functions were measured by isolated perfusion of the liver (at 37 degrees C) for 2 h. Fasting caused an 85% reduction in the concentration of glycogen in the liver but no change in ATP or glutathione. Glucose feeding suppressed the loss of glycogen (39% loss). After 24 h preservation by CS livers from fed or fasted animals were similar including bile production (6.2 +/- 0.5 and 5.6 +/- 0.4 ml/2 h, 100 g, respectively), hepatocellular injury (LDH release = 965 +/- 100 and 1049 +/- 284 U/liter), and concentrations of ATP (1.17 +/- 0.15 and 1.18 +/- 0.04 mumol/g, glutathione (1.94 +/- 0.51 and 2.35 +/- 0.26 mumol/g, respectively), and K:Na ratio (6.7 +/- 1.0 and 7.7 +/- 0.5, respectively). After 48 h CS livers from fed animals were superior to livers from fasted animals including significantly more bile production (5.0 +/- 0.9 vs 2.0 +/- 0.3 ml/2 h, 100 g), less LDH release (1123 +/- 98 vs 3701 +/- 562 U/liter), higher concentration of ATP (0.50 +/- 0.16 vs 0.33 +/- 0.07 mumol/g) and glutathione (0.93 +/- 0.14 vs 0.30 +/- 0.13 mumol/g), and a larger K:Na ratio (7.4 vs 1.5). Livers from fed animals were also better preserved than livers from fasted animals when the method was machine perfusion. The decrease in liver functions in livers from fasted animals preserved for 48 h by CS or MP was prevented by feeding glucose. Glucose feeding increased bile formation after 48 h CS preservation from 2.0 +/- 0.3 (fasted) to 6.9 +/- 1.2 ml/2 h, 100 g; LDH release was reduced from 3701 +/- 562 (fasted) to 1450 +/- 154 U/liter; ATP was increased from 0.33 +/- 0.07 (fasted) to 1.63 +/- 0.18 mumol/g; glutathione was increased from 0.30 +/- 0.01 (fasted) to 2.17 +/- 0.30 mumol g; and K:Na ratio was increased from 1.5 +/- 0.9 to 5.3 +/- 1.0. This study shows that the nutritional status of the donor can affect the quality of liver preservation. The improvement in preservation by feeding rabbits only glucose suggests that glycogen is an important metabolite for successful liver preservation. Glycogen may be a source for ATP synthesis during the early period of reperfusion of preserved livers.     

Response of thyrotropin, prolactin and free thyroid hormones to graded exercise in normal male subjects

Serum levels of thyrotrophin (TSH), prolactin (PRL), free thyroxine (FT4) and free triiodothyronine (FT3) were determined before and after physical exercise in 21 normal male subjects. The subjects were divided into 3 groups as follows: group I--light exercise (exercise on the Mijnhardt bicycle ergometer at 100 Watts for 15 min); group II--moderate exercise (a 5 km marathon); group III--heavy exercise (a 10 km marathon). In group I, TSH level rose from 1.96 +/- 0.42 mu u/ml (mean +/- SEM) to 2.52 +/- 0.30 mu u/ml (p less than 0.01), and PRL levels rose from 11.0 +/- 2.0 ng/ml to 19.0 +/- 5.2 ng/ml (p less than 0.01). In group II, TSH rose from 2.11 +/- 0.51 mu u/ml to 2.62 +/- 0.56 mu u/ml (p less than 0.05), and PRL rose from 11.2 +/- 1.6 ng/ml to 24.0 +/- 5.2 ng/ml (p less than 0.01). In group III, TSH rose from 2.01 +/- 0.41 mu u/ml to 2.36 +/- 0.45 mu u/ml (p less than 0.02), and PRL rose from 12.1 +/- 2.0 ng/ml to 47.7 +/- 9.3 ng/ml (p less than 0.01). The serum levels of FT4 showed different results among the three groups: Group I showed an increased response from 1.60 +/- 0.12 ng/dl to 1.72 +/- 0.12 ng/dl (p less than 0.01); Group II showed no significant difference; and group III demonstrated a diminished response from 1.61 +/- 0.14 ng/dl to 1.45 +/- 0.16 ng/dl (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of vitamin C administration on blood cholesterol level in man

Vitamin C (1.0 g/day) was administered orally to 20 healthy males for 1 month under controlled conditions. The blood ascorbic acid level rose from 0.76 +/- 0.21 mg% to 1.24 +/- 0.19 mg% in young subjects (20-30 years), and from 0.74 +/- 0.29 mg% to 1.22 +/- 0.22 mg% in middle-aged ones (31-50 years). Simultaneously, the serum cholesterol levels decreased from 204 +/- 16 mg% to 177 +/- 21 mg% in the young and from 256 +/- 11 mg% to 225 +/- 36 mg% in the middle-aged, a statistically significant fall of 10-15%, on the average (P less than 0.01). The effect in normo-cholesteraemic subjects, in particular, supports the cholesterol-lowering action of vitamin C.     

Maturation of end-systolic stress-strain relations in chick embryonic myocardium

The embryonic myocardium increases functional performance geometrically during cardiac morphogenesis. We investigated developmental changes in the in vivo end-systolic stress-strain relations of embryonic chick myocardium in stage 17, 21, and 24 white Leghorn chick embryos (n = 10 for each stage). End-systolic stress-strain relations were linear in all developmental stages. End-systolic strain decreased from 0.50 +/- 0.02 to 0.31 +/- 0.01 (mean +/- SE, P < 0.05), while average end-systolic wall stress was similar at 3.29 +/- 0.34 to 4.19 +/- 0.43 mmHg (P = 0.14) from stage 17 to 24. Normalized end-systolic myocardial stiffness, a load-independent index of ventricular contractility, increased from 2.98 +/- 0.19 to 6.03 +/- 0.39 mmHg from stage 17 to 24 (P < 0.05). Zero-stress midwall volume increased from 0.024 +/- 0.002 to 0.124 +/- 0.004 microl from stage 17 to 24 (P < 0.05). These results suggest that the embryonic ventricle increases normalized ventricular "contractility" while maintaining average end-systolic wall stress over a relatively narrow range during cardiovascular morphogenesis.     

Vascularization of the brains of the Atlantic and Pacific hagfishes, Myxine glutinosa and Eptatretus stouti: a scanning electron microscope study of vascular corrosion casts

The microvascularization of the brains of the hagfishes, Myxine glutinosa L. and Eptatretus stouti, were studied by scanning electron microscopy (SEM) of microvascular corrosion casts. Sections of these casts were used to determine the vascular territories of defined brain areas. Histological serial sections (10 microm) of the brains served for correlation of findings. Analysis of the microvascular casts of both species revealed that the blood supply to and from these brains arose ventrally and dorsally, respectively. Neither species possesses an arterial circle (Circulus Willisi) and both have similar microvascular patterns. The only difference between Myxine and Eptatretus was that the posterior cerebral artery in Myxine divides into mesencephalic and rhombencephalic branches, and in Eptatretus a third branch, termed telencephalic branch, arises from the posterior cerebral artery. 3D-morphometry revealed that luminal diameters of: 1) intracerebral arteries and arterioles range from 35.11 +/- 5.66 microm (mean +/- SEM) in the hypothalamus to 92.69 +/- 14.48 microm in the thalamus; 2) capillaries range from 17.8 +/- 0.44 microm in the olfactory bulb to 21.70 +/- 0.87 microm in the basal ganglia; and 3) intracerebral venules and veins range from 49.38 +/- 4.17 microm in the hypothalamus to 75.58 +/- 6.59 microm in the rhombencephalon. Interbranching distances of arteries and arterioles range from 179.19 +/- 11.32 microm in the optic tectum to 235.19 +/- 94.64 microm in the hypothalamus. Capillaries range from 91.07 +/- 6.22 microm in the hypothalamus to 116.15 +/- 9.45 microm in the thalamus, and venules and veins range from 137.30 +/- 18.11 microm in the hypothalamus to 189.83 +/- 17.47 microm in the optic tectum. Intervascular distances range from 70.58 +/- 3.58 microm in the olfactory bulb to 89.52 +/- 5.74 microm in the optic tectum. Branching angles of arteries and arterioles range from 38.39 +/- 10.9 degrees in the olfactory bulb to 100.73 +/- 9.4 degrees in the optic tectum, and the branching angles of capillaries range from 74.40 +/- 5.42 degrees in the optic tectum to 90.24 +/- 4.66 degrees in the olfactory bulb. Finally, the branching angles of the venules and veins range from 67.84 +/- 6.83 degrees in the tegmentum of the mesencephalon to 92.30 +/- 6.35 degrees in the optic tectum.     

Cardiopulmonary response to an induced pulse in intracranial pressure

Increased intracranial pressure may result in the Cushing response. We applied a short pulse of pressure to the cranial cavity of anesthetized cats which were intubated, curarized, ventilated, and the cranium exposed to an 80- to 100-msec pulse of pressure at 5.3 atm. The following significant increases developed: Intracranial pressure rose from 7.4 +/- 1.5 to 150.6 +/- 19.4 mm Hg, systolic arterial peak pressure from 130.7 +/- 8.1 to 299.0 +/- 11.4, pulmonary peak pressure from 18.9 +/- 1.9 to 42.9 +/- 4.9. Alveolar lavage protein in controls was 6.7 +/- 0.4 mg/g lung compared to 11.9 +/- 2.0 in the experimental group. Extravascular lung water/dry weight ratios increased from 3.36 +/- 0.04 in controls to 3.51 +/- 0.09 but varied inversely with pulmonary systolic peak pressure (r = 0.59). These results showed that a pulse of pressure applied to the cranium of cats produced lung edema which was inversely related to pulmonary artery pressures.     

Effect of reduced uterine blood flow on fetal and maternal cortisol

We have measured the changes in fetal and maternal plasma concentrations of cortisol in relation to blood gases and percent oxygen saturation during 2- and 4-h episodes of reversibly reduced uterine blood flow in sheep between 120 days gestation and term. During that period of reduced uterine blood flow there was a significant decrease in fetal arterial percent oxygen saturation (SaO2), PO2 and pH. Fetal SaO2 decreased from 59.5 +/- 3.2% to 31.8% +/- 2.8% by 15 min, 32.9 +/- 2.9% by 60 min, and 33.5 +/- 2.9% by 120 min. Fetal PO2 decreased from 3.2 +/- 0.1 KPa to 2.0 +/- 0.2 KPa by 15 min, 2.2 +/- 0.2 KPa by 60 min and 2.3 +/- 0.1 KPa by 120 min. Fetal pH decreased from 7.36 +/- 0.01 to 7.30 +/- 0.03 by 15 min, 7.27 +/- 0.02 by 60 min and 7.25 +/- 0.03 by 120 min. During the period of reduced uterine blood flow, fetal plasma concentrations of cortisol increased from 37.1 +/- 10.8 nmol/l to 53.3 +/- 9.2 nmol/l by 15 min, 49.2 +/- 11.4 nmol/l by 60 min and 43.3 +/- 9.0 nmol/l by 120 min. The greatest percentage increase in fetal plasma concentrations of cortisol occurred in fetuses of 126-139 days gestation. There was no significant change in maternal blood gases, SaO2 or plasma concentrations of cortisol. These experiments demonstrate that there is a significant increase in fetal plasma concentrations of cortisol in response to reductions in uterine blood flow from as early as 120 days gestation.     

Exercise responses in pregnant sheep: oxygen consumption, uterine blood flow, and blood volume

In an attempt to explore the acute maternal responses to exercise we measured oxygen consumption, uterine blood flow, and blood volume in 13 chronically catheterized pregnant sheep at rest and while exercising on a treadmill. With maximal exercise O2 consumption increased 5.6 times, from a resting value of 5.8 +/- 0.3 (SE) to 32.1 +/- 2.8 ml X min -1 X kg -1, cardiac output increased 2.7 times, from 149 +/- 8 to 404 +/- 32 ml X min -1 X kg -1, and arteriovenous oxygen content difference increased 2.1 times, from 3.9 +/- 0.2 to 8.0 +/- 0.4 ml X dl -1. Total uterine blood flow decreased from a mean resting value of 292 +/- 6 to 222 +/- 19 ml X min -1 X kg fetus -1 near exhaustion during prolonged (40 min) exercise at 70% maximal oxygen consumption. Maternal blood volume decreased 14% (P less than 0.01) from 67.5 +/- 3.7 to 57.8 +/- 3.6 ml X kg -1 during this exercise period, with a 20% decrease in plasma volume without a change in red cell volume. We conclude that uterine blood flow decreases during maternal exercise. However, hemoconcentration helps to maintain a relatively constant oxygen delivery to the uterus.     

Correlation of acute with chronic hypoxic pulmonary hypertension in cattle.

We investigated acute and chronic hypoxic pulmonary pressor responses in two groups of calves, one bred to be susceptible, the other resistant to high-altitude pulmonary hypertension. Twelve 5-mo-old susceptible calves residing at 1,524 m increased their mean pulmonary arterial pressure from 26 +/- 2 (SE) to 55 +/- 4 mmHg during 2 h at a simulated altitude of 4,572 m. In 10 resistant calves pressure increased from 22 +/- 1 to 37 +/- 2 mmHg. Five calves were selected from each group for further study. When 9 mo old, the 5 susceptible calves again showed a greater pressor response to acute hypoxia (27 +/- 1 to 55 +/- 4 mmHg) than did 5 resistant calves (23 +/- 1 to 41 +/- 3 mmHg). When 12 mo old, the 5 susceptible calves also developed a greater increase in pulmonary arterial pressure (21 +/- 2 to 9 +/- 4 mmHg) during 18 days at 4,572 m than did the 5 resistant calves (21 +/- 1 to 64 +/- 4 mmHg). Acute and chronic hypoxic pulmonary pressor responses were highly correlated (r = 0.91; P less than 0.001) indicating that they were probably produced through a common mechanism.     

Evaluation of SQ 28,603, an inhibitor of neutral endopeptidase, in conscious monkeys.

The potent neutral endopeptidase inhibitor SQ 28,603 (N-(2-(mercaptomethyl)-1-oxo-3-phenylpropyl)-beta-alanine) significantly increased excretion of sodium from 4.9 +/- 2.3 to 14.3 +/- 2.1 muequiv./min and cyclic 3',5'-guanosine monophosphate from 118 +/- 13 to 179 +/- 18 pmol/min after intravenous administration of 300 mumol/kg (approximately 80 mg/kg) in conscious female cynomolgus monkeys. SQ 28,603 did not change blood pressure or plasma atrial natriuretic peptide concentrations in the normal monkeys. In contrast, 1-h infusions of 3, 10, or 30 pmol.kg-1.min-1 of human atrial natriuretic peptide lowered blood pressure by -3 +/- 4, -9 +/- 4, and -27 +/- 3 mmHg (1 mmHg = 133.322 Pa), increased cyclic guanosine monophosphate excretion from 78 +/- 11 to 90 +/- 6, 216 +/- 33, and 531 +/- 41 pmol/min, and raised plasma atrial natriuretic peptide from 7.2 +/- 0.7 to 21 +/- 4, 62 +/- 12, and 192 +/- 35 fmol/mL without affecting sodium excretion. In monkeys receiving 10 pmol.kg-1.min-1 of atrial natriuretic peptide, 300 mumol/kg of SQ 28,603 reduced mean arterial pressure by -13 +/- 5 mmHg and increased sodium excretion from 6.6 +/- 3.2 to 31.3 +/- 6.0 muequiv./min, cyclic guanosine monophosphate excretion from 342 +/- 68 to 1144 +/- 418 pmol/min, and plasma atrial natriuretic peptide from 124 +/- 8 to 262 +/- 52 fmol/mL. In conclusion, SQ 28,603 stimulated renal excretory function in conscious monkeys, presumably by preventing the degradation of atrial natriuretic peptide by neutral endopeptidase.     

Temperature and the respiratory properties of whole blood in two reptiles, Pogona barbata and Emydura signata

We investigated the capacity of two reptiles, an agamid lizard Pogona barbata and a chelid turtle Emydura signata, to compensate for the effects of temperature by making changes in their whole blood respiratory properties. This was accomplished by measuring the P50 (at 10, 20 and 30 degrees C), hematocrit (Hct), haemoglobin concentration ([Hb]) and mean cell haemoglobin concentration (MCHC) in field acclimatised and laboratory acclimated individuals. The acute effect of temperature on P50 in P. barbata, expressed as heat of oxygenation (deltaH), ranged from -16.8+/-1.84 to -28.5+/-2.73 kJ/mole. P50 of field acclimatised P. barbata increased significantly from early spring to summer at the test temperatures of 20 degrees C (43.1+/-1.2 to 48.8+/-2.1 mmHg) and 30 degrees C (54.7+/-1.2 to 65.2+/-2.3 mmHg), but showed no acclimation under laboratory conditions. For E. signata, deltaH ranged from -31.1+/-6.32 to -48.2+/-3.59 kJ/mole. Field acclimatisation and laboratory acclimation of P50 did not occur. However, in E. signata, there was a significant increase in [Hb] and MCHC from early spring to summer in turtles collected from the wild (1.0+/-0.1 to 1.7+/-0.2 mmol/L and 4.0+/-0.3 to 6.7+/-0.7 mmol/L, respectively).     

Peptide mediator effects on bronchial blood velocity and lung resistance in conscious sheep.

Peptide mediators or neuropeptides released from sensory nerves may induce inflammatory effects in airways, but their effects on airway blood velocity and lung resistance have not been previously studied simultaneously in awake animals. Nine adult sheep were chronically prepared for continuous measurement of blood flow velocity to the distal trachea and bronchi by surgical implantation of a 20-MHz pulsed Doppler flow probe on the common bronchial branch of the bronchoesophageal artery. Awake restrained animals were intubated and connected to a pneumotachograph to measure resistance to airflow across the lung (RL). Doubling doses of bradykinin (BK, 0.02-1.51 nmol/kg), calcitonin gene-related peptide (CGRP, 0.004-0.26 nmol/kg), or substance P (SP, 0.02-1.19 nmol/kg) were injected as a bolus into the right atrium while mean arterial pressure (MAP), bronchial blood velocity (Vbr), and RL were measured. BK at 0.76 nmol/kg caused a transient dose-related increase in Vbr from a baseline of 19.3 +/- 2.5 to 41.4 +/- 4.1 (SE) cm/s (P less than 0.05) despite a decrease in MAP from 118 +/- 6 to 80 +/- 6 mmHg. CGRP at 0.26 nmol/kg caused a transient dose-related increase in Vbr from 16.8 +/- 2.7 to 25.3 +/- 4.7 cm/s (P less than 0.05) despite a decrease in MAP from 113 +/- 5 to 87 +/- 8 mmHg. Neither BK nor CGRP affected RL. SP at 1.19 nmol/kg transiently increased Vbr from 18.3 +/- 2.3 to 45.1 +/- 8.3 cm/s (P less than 0.05), MAP from 138 +/- 9 to 162 +/- 15 mmHg, and RL from 4.5 +/- 1.0 to 106.6 +/- 62.1 cmH2O.l-1.s.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxygen consumption is maintained in fetal sheep during prolonged hypoxaemia.

Experiments were conducted in 12 chronically-catheterized pregnant sheep to examine the effect of prolonged hypoxaemia secondary to the restriction of uterine blood flow on fetal oxygen consumption. Surgery was performed at 115 days gestation to place a teflon vascular occluder around the maternal common internal iliac artery and for insertion of vascular catheters. Following a 5-day recovery period, uterine blood flow was reduced in 6 animals for 24 hours and in 6 animals, the occluder was not adjusted. Fetal arterial PO2 decreased from 19.9 +/- 2.0 mmHg to 12.8 +/- 2.0 mmHg and 11.0 +/- 2.0 mmHg at 1 and 24 hours respectively in the experimental group and did not change the control group. Fetal pH decreased from 7.34 +/- 0.01 to 7.25 +/- 0.03 and 7.29 +/- 0.02 at 1 and 24 hours of hypoxaemia respectively. Fetal arterial lactate concentrations remained elevated throughout the experimental period with maximum concentrations of 6.6 +/- 2.1 mmol/l being present at 4 hours compared to 1.3 +/- 0.2 mmol/l during the control period. Umbilical blood flow increased from 186 +/- 19 ml/min/kg to 251 +/- 39 ml/min/kg at 1 h of hypoxaemia and returned to 191 +/- 21 ml/min/kg at 24 h. In association with the progressive fall in oxygen delivery to the fetus, oxygen extraction increased from 0.33 +/- 0.04 to 0.43 +/- 0.04 and 0.54 +/- 0.05 at 1 and 24 hours, respectively. Overall oxygen consumption by the fetus remained unchanged from control values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence of impaired hypoxic vasodilation after intermediate-duration hypoxic exposure in humans

Systemic hemodynamics, including forearm blood flow and ventilatory parameters, were evaluated in 21 subjects before and after exposure to 8 h of poikilocapnic hypoxia. To evaluate the role of sympathetic nervous system activation in the changes, in 10 of these subjects, we measured muscle sympathetic nerve activity (MSNA) before and after exposure, and the remaining 11 subjects received intra-arterial phentolamine infusion in the brachial artery to define vascular tone in the absence of sympathetically mediated vasoconstriction. Short-term ventilatory acclimatization occurred as evidenced by a decrease in resting Pco(2) (from 42 +/- 1.4 to 37 +/- 0.96 mmHg) and by an increase in the slope of the ventilatory response to acute hypoxia [from 0.7 +/- 0.1 to 1.2 +/- 0.2 l.min(-1).%Sp(O(2)) (blood O(2) saturation from pulse oximetry)] after exposure. Subjects demonstrated a significant increase in resting heart rate (from 61 +/- 2 to 65 +/- 2 beats/min) and diastolic blood pressure (from 64.8 +/- 2.7 to 70.4 +/- 2.0 mmHg). MSNA did not change significantly after exposure, although there was a trend toward a decrease in burst frequency (from 19.8 +/- 4.1 to 14.3 +/- 1.2 bursts/min). Forearm vascular resistance showed a significant decrease after termination of exposure (from 37.7 +/- 3.6 to 27.6 +/- 2.7 mmHg.ml(-1).min.100 g tissue, P < 0.05). Initially, progressive isocapnic hypoxia elicited significant vasodilation, but after 8 h of poikilocapnic hypoxic exposure, the acute challenge failed to change forearm vascular resistance. Local alpha-blockade with phentolamine restored the vasodilatory response to acute hypoxia in the postexposure setting.     

Acute anemic hypoxemia produces a transient depression in fetal respiratory activity

Isovolemic anemia was produced in 11 unanesthetized fetal sheep by withdrawal of blood and replacement with saline-dextran. Fetal hematocrit fell from 36 +/- 1 to 19 +/- 1% (SE). Fetal breathing movements, which were present during 34.4 +/- 5.5% of 3 h before the anemia, occurred 10.1 +/- 5.3, 14.8 +/- 4.4, and 27.1 +/- 6.7% in the 3 h following. The anemia caused a fall in arterial O2 concentration from 8.4 +/- 0.3 to 3.6 +/- 0.1 vol% and sagittal vein PO2 fell from 15.4 +/- 0.5 to 12.4 +/- 0.3 Torr. Cerebral metabolic rate during the period of anemia was 2.9 +/- 0.1 ml.100 g-1.min-1, which was unchanged from the control value of 3.0 +/- 0.2 ml.100 g-1.min-1. Sagittal vein PCO2 (54.2 +/- 1.4 Torr) remained constant after the fetus was made anemic. We conclude that respiratory activity in the sheep fetus is depressed by anemic hypoxemia but that the effect is transient.     

Blood-brain barrier to hydrogen ion during acute metabolic acidosis in piglets

The present study investigates the integrity of the blood-brain barrier to H+ or HCO3- during acute plasma acidosis in 35 newborn piglets anesthetized with pentobarbital sodium. Cerebrospinal fluid acid-base balance, cerebral blood flow (CBF), and cerebral oxygenation were measured after infusion of HCl (0.6 N, 0.191-0.388 ml/min) for a period of 1 h at a constant arterial PCO2 of 35-40 Torr. HCl infusion resulted in decreased arterial pH from 7.38 +/- 0.01 to 7.00 +/- 0.02 (P less than 0.01). CBF measured by the tracer microsphere technique was decreased by 12% from 69 +/- 6 to 61 +/- 4 ml.min-1.100 g-1 (P less than 0.05). Infusion of 0.6 N NaCl as a hypertonic control had no effect on CBF. Cerebral metabolic rate for O2 and O2 extraction was not significantly changed from control (3.83 +/- 0.20 ml.min-1.100 g-1 and 5.7 +/- 0.6 ml/100 ml, respectively) during acid infusion. Cerebral venous PO2 was increased from 41.6 +/- 2.1 to 53.8 +/- 4.0 Torr by HCl infusion (P less than 0.02) associated with a shift in O2-hemoglobin affinity of blood in vivo from 38 +/- 2 to 50 +/- 1 Torr. Cisternal cerebrospinal fluid pH decreased from 7.336 +/- 0.014 to 7.226 +/- 0.027 (P less than 0.005), but cerebrospinal fluid HCO3- concentration was not changed from control (25.4 +/- 1.0 meq/l). These data suggest that there is a functional blood-brain barrier in newborn piglets, that is relatively impermeable to HCO3- or H+ and maintains cerebral perivascular pH constant in the face of acute severe arterial acidosis. (ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of storage temperatures and annealing conditions on the structure and properties of potato (Solanum tuberosum) starch

Starches were extracted from freshly harvested potatoes (12 cultivars, grown in Perthshire) and the properties of the starches of six cultivars were compared with starches extracted from the same samples but stored at 5, 25 or 55 degrees C for 7 days before extraction. The amylose (total) content of the freshly extracted starches from tubers stored at 5, 25 or 55 degrees C was on average 27.9+/-2.3, 28.3+/-1.7, 29.2+/-2.2 and 28.8+/-1.5%, respectively, with corresponding phosphorus representing 60+/-16, 64+/-9, 61+/-5 and 63+/-9 mg 100 g(-1). The unit chain distribution by chromatography of the amylopectin molecules from the starches extracted from the different conditions was very similar with an average degree of polymerisation (DP) of 26+/-2 where the two major fractions (F1 and F2) represented 54+/-2 and 19+/-1, respectively. Peak gelatinisation temperatures (Tp) and enthalpies (DeltaH) for the freshly extracted starches and from tubers stored at 5 or 25 degrees C were very similar (63.3+/-1.5 degrees C and 18.6+/-0.8 J g(-1); 63.1+/-1.0 degrees C and 17.7+/-1.5 J g(-1) and; 62.9+/-0.7 degrees C and 18.7+/-1.1 J g(-1), respectively) although starches stored at 55 degrees C were annealed, where Tp represented 71.1+/-1.1 degrees C and DeltaH 18.1+/-1.4 J g(-1). These in situ-annealed starches were comparable in terms of gelatinisation characteristics to annealed freshly extracted starches where on average, T(p) represented 72.7+/-1.0 degrees C and DeltaH 20.8+/-1.0 J g(-1). Annealing of tubers in situ prior to processing might be beneficial with respect to developing new potato-based products.     

Age-dependent activation of PKC isoforms by angiotensin II in the proximal nephron

ANG II increases fluid absorption in proximal tubules from young rats more than those from adult rats. ANG II increases fluid absorption in the proximal nephron, in part, via activation of protein kinase C (PKC). However, it is unclear how age-related changes in ANG II-induced stimulation of the PKC cascade differ as an animal matures. We hypothesized that the response of the proximal nephron to ANG II decreases as rats mature due to a reduction in the amount and activation of PKC rather than a decrease in the number or affinity of ANG II receptors. Because PKC translocates from the cytosol to the membrane when activated, we first measured PKC activity in the soluble and particulate fractions of proximal tubule homogenates exposed to vehicle or 10(-10) M ANG II from young (26 +/- 1 days old) and adult rats (54 +/- 1 days old). ANG II increased PKC activity to the same extent in homogenates from young rats (from 0.119 +/- 0.017 to 0.146 +/- 0.015 U/mg protein) (P < 0.01) and adult rats (from 0.123 +/- 0.020 to 0.156 +/- 0.023 U/mg protein) (P < 0.01). Total PKC activity did not differ between groups (0.166 +/- 0.018 vs. 0.181 +/- 0.023). We next investigated whether activation of the alpha-, beta-, and gamma-PKC isoforms differed by Western blot. In homogenates from young rats, ANG II significantly increased activated PKC-alpha from 40.2 +/- 6.5 to 60.2 +/- 9.5 arbitrary units (AU) (P < 0.01) but had no effect in adult rats (46.1 +/- 5.1 vs. 48.5 +/- 8.2 AU). Similarly, ANG II increased activated PKC-gamma in proximal tubules from young rats from 47.9 +/- 13.2 to 65.6 +/- 16.7 AU (P < 0.01) but caused no change in adult rats. Activated PKC-beta, however, increased significantly in homogenates from both age groups. Specifically, activated PKC-beta increased from 8.6 +/- 1.4 to 12.2 +/- 2.1 AU (P < 0.01) in homogenates from nine young rats and from 19.0 +/- 5.5 to 25.1 +/- 7.1 AU (P < 0.01) in homogenates from 12 adult rats. ANG II did not alter the amount of soluble PKC-alpha, -beta, and -gamma significantly. The total amount of PKC-alpha and -gamma did not differ between homogenates from young and adult rats, whereas the total amount of PKC-beta was 59.7 +/- 10.7 and 144.9 +/- 41.8 AU taken from young and adult rats, respectively (P < 0.05). Maximum specific binding and affinity of ANG II receptors were not significantly different between young and adult rats. We concluded that the primary PKC isoform activated by ANG II changes during maturation.