Quantification of tumour vasculature and hypoxia by immunohistochemical staining and HbO2 saturation measurements.
Despite the possibility that tumour hypoxia may limit radiotherapeutic response, the underlying mechanisms remain poorly understood. A new methodology has been developed in which information from several sophisticated techniques is combined and analysed at a microregional level. First, tumour oxygen availability is spatially defined by measuring intravascular blood oxygen saturations (HbO2) cryospectrophotometrically in frozen tumour blocks. Second, hypoxic development is quantified in adjacent sections using immunohistochemical detection of a fluorescently conjugated monoclonal antibody (ELK3-51) to a nitroheterocyclic hypoxia marker (EF5), thereby providing information relating to both the oxygen consumption rates and the effective oxygen diffusion distances. Third, a combination of fluorescent (Hoechst 33342 or DiOC7(3)) and immunohistological (PECAM-1/CD31) stains is used to define the anatomical vascular densities and the fraction of blood vessels containing flow. Using a computer-interfaced microscope stage, image analysis software and a 3-CCD colour video camera, multiple images are digitized, combined to form a photo-montage and revisited after each of the three staining protocols. By applying image registration techniques, the spatial distribution of HbO2 saturations is matched to corresponding hypoxic marker intensities in adjacent sections. This permits vascular configuration to be related to oxygen availability and allows the hypoxic marker intensities to be quantitated in situ. (+info)
Effect of chronic hypoxia on alpha-1 adrenoceptor-mediated inositol 1,4,5-trisphosphate signaling in ovine uterine artery.
The present study examined the effect of chronic hypoxia on coupling efficiency of alpha-1 adrenoceptors to inositol 1,4,5-trisphosphate (InsP3) signaling in ovine uterine artery. Chronic hypoxia did not change the time course of InsP3 formation, but significantly decreased the potency (pD2: 6.17 +/- 0.09 --> 5.26 +/- 0.12) and the maximal response (220.7 +/- 21.7 --> 147.7 +/- 15.3 pmol/mg protein) of norepinephrine-induced InsP3 synthesis. The coupling efficiency of alpha-1 adrenoceptors to InsP3 synthesis (picomoles InsP3 per femtomoles receptor) was decreased 45% by chronic hypoxia. In addition, simultaneous measurement of norepinephrine-induced contractions and InsP3 synthesis indicated that for a given amount of InsP3 generated, the contractile force of the uterine artery was significantly less in chronically hypoxic than in control tissues (0. 27 +/- 0.01 versus 0.35 +/- 0.02 g tension/pmol InsP3). InsP3 receptors were characterized using radioligand binding techniques. Although the density of InsP3 receptors was not changed by chronic hypoxia (Bmax: 325 +/- 35 --> 378 +/- 18 fmol/mg protein), the dissociation constant (Kd) of InsP3 to its receptors was significantly increased (Kd: 5.20 +/- 0.40 --> 7.81 +/- 0.34 nM). Analysis of InsP3 receptor occupancy-tension development relationship indicated no difference in intrinsic ability of the InsP3-receptor complex in eliciting contractions between the control and hypoxic tissues. Our results suggest that chronic hypoxia attenuates coupling efficiency of alpha-1 adrenoceptors to InsP3 synthesis in the uterine artery. In addition, the tissue contractile sensitivity to InsP3 is reduced, which is mediated predominantly by a decrease in InsP3 binding affinity to InsP3 receptors. (+info)
Nonlinear indicial response of complex nonstationary oscillations as pulmonary hypertension responding to step hypoxia.
This paper is devoted to the quantization of the degree of nonlinearity of the relationship between two biological variables when one of the variables is a complex nonstationary oscillatory signal. An example of the situation is the indicial responses of pulmonary blood pressure (P) to step changes of oxygen tension (DeltapO2) in the breathing gas. For a step change of DeltapO2 beginning at time t1, the pulmonary blood pressure is a nonlinear function of time and DeltapO2, which can be written as P(t-t1 | DeltapO2). An effective method does not exist to examine the nonlinear function P(t-t1 | DeltapO2). A systematic approach is proposed here. The definitions of mean trends and oscillations about the means are the keys. With these keys a practical method of calculation is devised. We fit the mean trends of blood pressure with analytic functions of time, whose nonlinearity with respect to the oxygen level is clarified here. The associated oscillations about the mean can be transformed into Hilbert spectrum. An integration of the square of the Hilbert spectrum over frequency yields a measure of oscillatory energy, which is also a function of time, whose mean trends can be expressed by analytic functions. The degree of nonlinearity of the oscillatory energy with respect to the oxygen level also is clarified here. Theoretical extension of the experimental nonlinear indicial functions to arbitrary history of hypoxia is proposed. Application of the results to tissue remodeling and tissue engineering of blood vessels is discussed. (+info)
Depression of peripheral chemosensitivity by a dopaminergic mechanism in patients with obstructive sleep apnoea syndrome.
In the present study, respiratory drives to chemical stimuli and peripheral chemosensitivity were evaluated in patients with obstructive sleep apnoea (OSAS). The effects of oral administration of domperidone, a selective dopamine D2-receptor antagonist, were also examined, to study the respiratory effects of endogenous dopamine on peripheral chemoreceptors. Sixteen patients with OSAS and nine normal control subjects were studied. Respiratory responses to hypercapnia and hypoxia were measured using the rebreathing method and isocapnic progressive hypoxia method, respectively. The hypoxic withdrawal test, which measures the decrease in ventilation caused by two breaths of 100% O2 under mild hypercapnic hypoxic conditions (end-tidal oxygen and carbon dioxide tensions approximately 8.0 kPa and 5.3-6.7 kPa, respectively), was used to evaluate peripheral chemosensitivity. In the patients with OSAS, ventilatory responses to hypercapnia and hypoxia were significantly decreased compared with those of control subjects. Hypoxic withdrawal tests showed that peripheral chemosensitivity was significantly lower in patients with OSAS than in normal subjects. Hypercapnic ventilatory response and peripheral chemosensitivity were enhanced by administration of domperidone in the patients with OSAS, although no changes in either of these were observed in the control subjects. The hypoxic ventilatory response and peripheral chemosensitivity in the patients with OSAS were each significantly correlated with severity of hypoxia during sleep. These findings suggest that peripheral chemosensitivity in patients with obstructive sleep apnoea syndrome may be decreased as a result of abnormality in dopaminergic mechanisms and that the reduced chemosensitivity observed in patients with obstructive sleep apnoea syndrome may affect the severity of hypoxia during sleep. (+info)
Evidence of O2 supply-dependent VO2 max in the exercise-trained human quadriceps.
Maximal O2 delivery and O2 uptake (VO2) per 100 g of active muscle mass are far greater during knee extensor (KE) than during cycle exercise: 73 and 60 ml. min-1. 100 g-1 (2.4 kg of muscle) (R. S. Richardson, D. R. Knight, D. C. Poole, S. S. Kurdak, M. C. Hogan, B. Grassi, and P. D. Wagner. Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1453-H1461, 1995) and 28 and 25 ml. min-1. 100 g-1 (7.5 kg of muscle) (D. R. Knight, W. Schaffartzik, H. J. Guy, R. Predilleto, M. C. Hogan, and P. D. Wagner. J. Appl. Physiol. 75: 2586-2593, 1993), respectively. Although this is evidence of muscle O2 supply dependence in itself, it raises the following question: With such high O2 delivery in KE, are the quadriceps still O2 supply dependent at maximal exercise? To answer this question, seven trained subjects performed maximum KE exercise in hypoxia [0.12 inspired O2 fraction (FIO2)], normoxia (0.21 FIO2), and hyperoxia (1.0 FIO2) in a balanced order. The protocol (after warm-up) was a square wave to a previously determined maximum work rate followed by incremental stages to ensure that a true maximum was achieved under each condition. Direct measures of arterial and venous blood O2 concentration in combination with a thermodilution blood flow technique allowed the determination of O2 delivery and muscle VO2. Maximal O2 delivery increased with inspired O2: 1.3 +/- 0.1, 1.6 +/- 0.2, and 1.9 +/- 0.2 l/min at 0.12, 0.21, and 1.0 FIO2, respectively (P < 0.05). Maximal work rate was affected by variations in inspired O2 (-25 and +14% at 0.12 and 1.0 FIO2, respectively, compared with normoxia, P < 0.05) as was maximal VO2 (VO2 max): 1.04 +/- 0.13, 1. 24 +/- 0.16, and 1.45 +/- 0.19 l/min at 0.12, 0.21, and 1.0 FIO2, respectively (P < 0.05). Calculated mean capillary PO2 also varied with FIO2 (28.3 +/- 1.0, 34.8 +/- 2.0, and 40.7 +/- 1.9 Torr at 0.12, 0.21, and 1.0 FIO2, respectively, P < 0.05) and was proportionally related to changes in VO2 max, supporting our previous finding that a decrease in O2 supply will proportionately decrease muscle VO2 max. As even in the isolated quadriceps (where normoxic O2 delivery is the highest recorded in humans) an increase in O2 supply by hyperoxia allows the achievement of a greater VO2 max, we conclude that, in normoxic conditions of isolated KE exercise, KE VO2 max in trained subjects is not limited by mitochondrial metabolic rate but, rather, by O2 supply. (+info)
Mechanisms of hypoxic vasodilatation of isolated rat mesenteric arteries: a comparison with metabolic inhibition.
1. Hypoxia (PO2 < 5 mmHg) decreased vessel tone in isolated rat mesenteric arteries precontracted with either high [K+] or the thromboxane analogue U46619. This response was not altered by N-nitro-L-arginine (L-NA) and indomethacin. 2. Simultaneous measurement of pHi and tension showed that the decrease in vessel tone was accompanied by an intracellular acidification. Similar reductions in tone and pHi were observed with the metabolic inhibitors 2,4-dinitrophenol (DNP) and sodium azide. 3. The presence of the lactate transport inhibitor alpha-cyano-4-hydroxy-cinnamic acid (CHC) increased the magnitude of the acidification and resulted in a significantly faster reduction in tone in response to hypoxia. Addition of CHC to normoxic tissues caused both a vasodilatation and a reduction of pHi. 4. A decrease in pHi induced on washout of ammonium chloride (NH4Cl) resulted in an increase in tone. 5. Relaxation to hypoxia or metabolic inhibition was unaffected when the change in pHi was neutralized by addition of the weak base trimethylamine (TMA). 6. It is concluded that severe hypoxia decreases tone in isolated rat mesenteric arteries by a mechanism which is independent of nitric oxide and prostaglandins. Both severe hypoxia and metabolic inhibition reduced pHi, although this does not appear to be contributing to the changes in tone observed. (+info)
Comparison of vascular reactivity in spinal cord and brain.
The local tissue PO2 in the brain cortex and in the spinal cord of rats was examined with ultramicroelectrodes. In the spinal cord the PO2 was highest in white matter, intermediate in dorsal horn gray matter, and lowest in the ventral horn gray matter. In the gray matter of the cord, as well as in the brain, the PO2 at a fixed locus was found normally to oscillate. CO2 responses were more brisk in the cord than in the brain while the responses to hypoxia were similar. Therefore, it appears that the physiological regulation of blood flow in the spinal cord is qualitatively similar to that of the brain. (+info)
Estimation of corneal endothelial pump function in long-term contact lens wearers.
PURPOSE: To study the effects of long-term contact lens wear on morphologic and physiologic properties of corneal endothelial cells. METHODS: The endothelial permeability to fluorescein and the rate of corneal deswelling from hypoxia-induced edema were measured in 20 long-term (mean, 17+/-9 years; range, 5-33 years) contact lens wearers and 20 age-matched control subjects. From these data, the relative endothelial pump rate in each subject was estimated, based on the pump-leak hypothesis of corneal hydration control. Corneal autofluorescence and the aqueous humor flow rate were determined by fluorescein fluorophotometry. Images of corneal endothelial cells were recorded by using specular microscopy, and morphologic indices (cell density, coefficient of variation of cell area, percentage of hexagonal cells, and skewness) were determined. RESULTS: No statistically significant differences were found between the contact lens and control groups in endothelial permeability, corneal deswelling, relative endothelial pump rate ([mean +/- SD] 1.07+/-0.33 relative pump units versus 1.01+/-0.25 relative pump units; contact lens versus control; P = 0.57), and endothelial cell density. Contact lens wearers had a significantly higher aqueous humor flow rate (3.57+/-1.03 microl/min versus 2.77+/-0.51 microl/min; P = 0.005), coefficient of variation of cell area (0.35+/-0.09 versus 0.28+/-0.04; P = 0.006), and corneal autofluorescence (3.1+/-0.6 ng/ml versus 2.3+/-0.3 ng/ml fluorescein equivalents; P < 0.001) than did non-contact lens wearers. CONCLUSIONS: Despite the known effects of long-term contact lens wear on corneal endothelial morphometry, no effect on endothelial function was found. (+info)