Erythropoietin expressed in granular convoluted tubule cells of mice submandibular glands under hypoxia, anemia, and nephrectomy

Immunohistochemically detectable erythropoietin-like substance(Epo) in granular convoluted tubule(GCT) cells of submandibular glands (SMG's) was examined in mice in which hemolytic anemia had been induced by phenylhydrazine (ph), and in mice subjected to hypoxia, nephrectomy, or testosterone (TP) injections. Staining for Epo was negative in GCT cells of SMG's in normal mice, while positive staining occurred in GCT cells of the anemic mice and mice subjected to hypoxia or nephrectomy. A positive Epo reaction was also revealed at the luminal borders of distal tubules, and in cells of proximal and distal tubules in the kidney, and in some hepatic and spleen cells, of mice that had received combination regimens producing anemia and hypoxia, or had been nephrectomized. Increased staining of Epo was found in GCT cells of SMG's, and in proximal and distal kidney tubules of mice given the combination treatment plus TP injections. The detection of Epo in GCT cells suggests these extrarenal cells to be sites of accumulation or biosynthesis of the protein under certain specific conditions such as hemolytic anemia and hypoxia.     

Acidosis, hypoxia and bone

Bone homeostasis is profoundly affected by local pH and oxygen tension. It has long been recognised that the skeleton contains a large reserve of alkaline mineral (hydroxyapatite), which is ultimately available to neutralise metabolic H⁺ if acid-base balance is not maintained within narrow limits. Bone cells are extremely sensitive to the direct effects of pH: acidosis inhibits mineral deposition by osteoblasts but it activates osteoclasts to resorb bone and other mineralised tissues. These reciprocal responses act to maximise the availability of OH⁻ ions from hydroxyapatite in solution, where they can buffer excess H⁺. The mechanisms by which bone cells sense small pH changes are likely to be complex, involving ion channels and receptors in the cell membrane, as well as direct intracellular effects. The importance of oxygen tension in the skeleton has also long been known. Recent work shows that hypoxia blocks the growth and differentiation of osteoblasts (and thus bone formation), whilst strongly stimulating osteoclast formation (and thus bone resorption). Surprisingly, the resorptive function of osteoclasts is unimpaired in hypoxia. In vivo, tissue hypoxia is usually accompanied by acidosis due to reduced vascular perfusion and increased glycolytic metabolism. Thus, disruption of the blood supply can engender a multiple negative impact on bone via the direct actions of reduced pO₂ and pH on bone cells. These observations may contribute to our understanding of the bone disturbances that occur in numerous settings, including ageing, inflammation, fractures, tumours, anaemias, kidney disease, diabetes, respiratory disease and smoking.     

Alveolar hypoxia,alveolar macrophages,and systemic inflammation

Diseases featuring abnormally low alveolar PO₂ are frequently accompanied by systemic effects. The common presence of an underlying inflammatory component suggests that inflammation may contribute to the pathogenesis of the systemic effects of alveolar hypoxia. While the role of alveolar macrophages in the immune and defense functions of the lung has been long known, recent evidence indicates that activation of alveolar macrophages causes inflammatory disturbances in the systemic microcirculation. The purpose of this review is to describe observations in experimental animals showing that alveolar macrophages initiate a systemic inflammatory response to alveolar hypoxia. Evidence obtained in intact animals and in primary cell cultures indicate that alveolar macrophages activated by hypoxia release a mediator(s) into the circulation. This mediator activates perivascular mast cells and initiates a widespread systemic inflammation. The inflammatory cascade includes activation of the local renin-angiotensin system and results in increased leukocyte-endothelial interactions in post-capillary venules, increased microvascular levels of reactive O₂ species; and extravasation of albumin. Given the known extrapulmonary responses elicited by activation of alveolar macrophages, this novel phenomenon could contribute to some of the systemic effects of conditions featuring low alveolar PO₂.     

Acclimation to hypoxia increases survival time of zebrafish, Danio rerio, during lethal hypoxia

Survivorship of zebrafish, Danio rerio, was measured during lethal hypoxic stress after pretreatment in water at either ambient oxygen or at a lowered, but nonlethal, level of oxygen. Acclimation to nonlethal hypoxia (pO(2) congruent with 15 Torr; ca. 10% air-saturation) for 48 hr significantly extended survival time during more severe hypoxia (pO(2) congruent with 8 Torr; ca. 5% air-saturation) compared to survival of individuals with no prior hypoxic exposure. The magnitude of the acclimation effect depended upon the sex of the fish: hypoxia pretreatment increased the survival times of males by a factor of approximately 9 and that of females by a factor of 3 relative to controls. In addition, survival time of control and hypoxia acclimated fish depended upon when in the year experiments were conducted. Survival times were 2-3 times longer when measured in the late fall or winter compared to survival times measured during the spring or summer. These results demonstrate a direct survival benefit of short-term acclimation to hypoxia in this genetically tractable fish. The fact that the acclimation effect depended upon the sex of the fish and the season during which experiments were conducted demonstrates that other genetic and/or environmental factors affect hypoxia tolerance in this species. J. Exp. Zool. 289:266-272, 2001.     

Canine bronchoconstriction, gas trapping, and hypoxia with methacholine

The effects of an intravenous methacholine infusion on cardiovascular-pulmonary function were measured in seven mongrel dogs (22.0 +/- 2.8 kg), anesthetized with chloralose and urethan and beta-adrenergically blocked with propranolol. In a volume-displacement plethysmograph, physiological measurements were made at base line and 25 min after establishing a methacholine infusion (0.1-1.0 mg X kg-1 X h-1). Methacholine significantly (P less than 0.05) increased airways resistance (1.9 +/- 0.8 to 8.2 +/- 2.9 cmH2O X l-1 X s), decreased static lung compliance (84.7 +/- 18.5 to 48.2 +/- 9.4 ml/cmH2O), depressed arterial PO2 (81 +/- 17 to 56 +/- 10 Torr), and lowered blood pressure (132 +/- 10 to 69 +/- 18 Torr) and cardiac output (5.7 +/- 1.9 to 4.1 +/- 1.2 l/min). These effects persisted during a further 80 min of methacholine infusion conducted in five of the animals. During the initial 25-min period of methacholine, the end-expired volume (volume-displacement Krogh spirometer) rose in all animals, indicating an increase in functional residual capacity from 997 +/- 115 to 1,623 +/- 259 ml (P less than 0.0005). Analysis of pulmonary pressure-volume curves revealed no change in total lung capacity but an increase in residual volume from 489 +/- 168 to 1,106 +/- 216 ml (P less than 0.001). Thus methacholine caused 617 ml of gas trapping, which was not detected by the Boyle's law principle, presumably because gas was trapped at high transpulmonary pressure. We suggest that intravenous methacholine-induced canine bronchoconstriction, which causes gas trapping and hypoxia, may be a useful animal model of clinical status asthmaticus.     

Laparoscopic nephrectomy.

Since the first clinical operation in June 1990 laparoscopic nephrectomy for benign renal disease has become widely accepted. Although the laparoscopic operation takes much longer than open surgery, there are considerable reductions in the length of postoperative hospital stay and the time taken to return to normal activities and to full recovery. Major complications were relatively common in early operations, but with more experience morbidity has been reduced. Laparoscopic nephrectomy for malignant renal disease is still controversial, largely because of the fear of release of malignant tissue into the abdominal cavity during the morcellation and retrieval of the diseased kidney. To prevent this, the kidney is removed intact through a 5-7 cm incision. Long term follow up is needed, however, before we will know whether the laparoscopic procedure is effective in preventing recurrence of cancer. New developments have improved various technical aspects of the operation, but stringent assessment of new techniques is necessary so that the medical community can decide which procedures should become routine practice.     

Diaphragm, genioglossus, and triangularis sterni responses to poikilocapnic hypoxia

Both isocapnic and poikilocapnic hypoxia may elicit a biphasic respiratory response, during which an initial ventilatory stimulation is followed by a reduction in breathing and diaphragm (DIA) electrical activity. To ascertain whether during adulthood other respiratory muscles have biphasic hypoxic responses similar to the DIA, in nine anesthetized cats electromyograms (EMG) were recorded from the DIA, genioglossus (GG), and triangularis sterni (TS) (n = 7) muscles during poikilocapnic hypoxia. DIA and GG EMG started at 60 +/- 4 and 9 +/- 3 units, respectively, during O2 breathing, increased to a maximum of 100 units during the 10-min hypoxic stimulus, and subsequently declined to 81 +/- 6 and 58 +/- 12 units, respectively, by the end of 10 min of hypoxia. The time course of the increase and subsequent decline was similar for the DIA and GG and for GG activity during both inspiration and expiration. Furthermore the degree to which GG EMG declined after reaching its peak activity level correlated with the magnitude of the respective decline in DIA EMG (r = 0.79, P less than 0.02). The TS, in contrast, was maximally active either during O2 breathing or very early during hypoxia, and its activity declined progressively thereafter (to 13 +/- 6% of its peak value at the end of 10 min of hypoxia). The degree to which TS EMG declined did not correlate with the degree to which DIA or GG EMG declined.(ABSTRACT TRUNCATED AT 250 WORDS)