Showing papers by "Aarhus University published in 1978"

A comparison of methods for the quantification of bacterial sulfate reduction in coastal marine sediments

Abstract: A radiotracer technique for measuring in situ rates of sulfate reduction in marine sediments is described. Microliter portions of labeled‐sulfate solution are injected into undisturbed sediment cores, and the amount of labeled sulfide produced is analyzed. This tracer method is experimentally compared with a method that mixes label into the sediment. Controls and methodological problems of both methods are discussed.

A comparison of methods for the quantification of bacterial sulfate reduction in coastal marine sediments

Abstract: Rates of bacterial sulfate reduction are calculated from the accumulation of reduced sulfur compounds in coastal sediments. The method is found to underestimate the in situ metabolism 10‐fold because it neglects diffusional losses of produced sulfide. In relation to this result, the quantitative connection between the pyrite, HCl‐extractable iron, and organic carbon contents of the sediments and the intensity of sulfate reduction are disussed. A comparison is made between colony counts of sulfate‐reducing bacteria and the rate of sulfate reduction in coastal sediments. The number of bacteria is roughly proportional to their measured rate of metabolism both when different sediment types and different depths are compared. The colony counts, however, seem to underestimate the true numbers of sulfate reducers by 1000‐fold or more.

Denitrification rates in a marine sediment as measured by the acetylene inhibition technique.

Abstract: A method has been developed for measurement of denitrification activity in sediments by application of the acetylene inhibition technique. Acetylene-saturated water was injected, at close intervals, into sediment cores which were then incubated for a few hours at the in situ temperature. Frozen segments of the cores were assayed for accumulation of N2O by a combined gas extraction and detection system. The segments were thawed under a stream of helium from which N2O (and other gases) was collected in a liquid N2 trap, and the quantity of N2O was measured by gas chromatography. The maximum rate of denitrification in a coastal marine sediment was 35 nmol of N per cm3 of sediment per day at 2.5°C, and the rate of denitrification for the total sediment was 0.99 nmol of N per m2 per day.

Capacity for Denitrification and Reduction of Nitrate to Ammonia in a Coastal Marine Sediment

Abstract: The capacity for dissimilatory reduction of NO3− to N2 (N2O) and NH4+ was measured in 15NO3−-amended marine sediment. Incubation with acetylene (7 × 10−3 atmospheres [normal]) caused accumulation of N2O in the sediment. The rate of N2O production equaled the rate of N2 production in samples without acetylene. Complete inhibition of the reduction of N2O to N2 suggests that the “acetylene blockage technique” is applicable to assays for denitrification in marine sediments. The capacity for reduction of NO3− by denitrification decreased rapidly with depth in the sediment, whereas the capacity for reduction of NO3− to NH4+ was significant also in deeper layers. The data suggested that the latter process may be equally as significant as denitrification in the turnover of NO3− in marine sediments.

Polarity of actin at the leading edge of cultured cells

Abstract: VERTEBRATE non-muscle cells are known to contain considerable amounts of actin and myosin1–3, but the mechanisms underlying their motility have yet to be elucidated. Various theories have been proposed1,4–7 to explain the well known phenomena of cell migration, membrane ruffling and unidirectional growth processes, different emphasis being placed on the involvement of membrane components and contractile filament assemblies. These hypotheses have been limited, however, by the lack of information about the detailed structural organisation of the motile regions of the cytoplasm. As one approach to this problem we have developed procedures for the direct observation of the filamentous components of the lamella regions of cultured cells in the electron microscope8,9. The method, similar to that adopted by Brown et al.10, consists of the negative-staining of cells grown directly on electron microscope grids after removal of the cell membranes with Triton X-100. By this means, we demonstrate here a single polarity of actin at the leading edge of cultured cells, and consider its implications with regard to cell motility.

An improved Timm sulphide silver method for light and electron microscopic localization of heavy metals in biological tissues.

Abstract: Modifications of the Timm sulphide silver method for the demonstration of heavy metals are described. To improve the structural preservation of the tissues perfusion with a glutaraldehyde fixative is employed before perfusion with the sodium sulphide solution. For the subsequent staining for light and electron microscopy, procedures for plastic embedding, paraffin embedding and cryostat sectioning are presented. Examples from several tissues are shown, including the pituitary, pancreas, intestine, tongue, kidney, testis and brain. The staining of autolytic, postmortal human brain tissue is demonstrated.

Lithium intoxication. (Report of 23 cases and review of 100 cases from the literature).

Abstract: Twenty-three patients were studied, 21 of whom developed intoxication during maintenance therapy with a lithium dosage which had been unchanged for months to years Toxic effects on brain, heart and kidneys were found and the severity of lithium intoxication seemed to depend on at least three factors: the height of the serum lithium concentration (SLi), the duration of lithium intoxication and individual tolerance Disorders of water and electrolyte metabolism preceded lithium intoxication in the majority of the patients Water loss due to impaired renal concentrating ability seemed to be a major predisposing factor Renal insufficiency was apparent in 17 of the patients on admission and five of these did not regain normal renal function In seven patients, renal biopsy showed abnormalities which suggest that a chronic nephropathy, possibly caused by lithium, might be another predisposing factor Treatment with sodium chloride infusion had no specific effect on lithium excretion and led to hypernatraemia in some patients and is therefore not recommended Hemodialysis is the most effective method available for removing the lithium ion from intoxicated patients Hemodialysis should be carried out long enough to secure a SLi of less than 1 mmol/l after redistribution of lithium in the body Treatment by peritoneal dialysis is appropriate only if hemodialysis facilities are unavailable Lithium intoxication is a serious condition Of the 23 patients reported, two died and two developed persisting neurological sequelae The best way to prevent lithium intoxication is to control the serum concentration and to assess renal function and renal concentrating ability regularly during therapy

Raman scattering, superconductivity, and phonon density of states of stoichiometric and nonstoichiometric TiN

Abstract: Raman scattering and superconductivity of titanium nitride with various N deficiencies have been investigated. While in stoichiometric superconducting TiN second-order Raman scattering is predominant, first-order Raman scattering increases with increasing N deficiency. The first-order Raman spectrum which agrees well with the phonon density of states shifts to higher frequencies when the N deficiency grows. This frequency shift is particularly strong at small N deficiencies (\ensuremath{\sim}5%) and is coupled with a drastic drop of ${T}_{c}$. The shift of the phonon density of states indicates phonon anomalies in stoichiometric TiN at 200 ${\mathrm{cm}}^{\ensuremath{-}1}$ in close agreement with just performed neutron studies. In almost stoichiometric TiN the mean-square frequencies $〈{\ensuremath{\omega}}^{2}〉$ from the Raman spectra are in good agreement with corresponding specific-heat data. The similarities between the nonstoichiometric Ti${\mathrm{N}}_{0.55}$ and TiC are discussed.

Localisation of gastrins to neuro- and adenohypophysis

Abstract: SEVERAL peptides including substance P1,2, somatostatin3,4, the enkephalins5,6 and cholecystokinin (CCK)7–10 have been found both in nerve cells of the brain and in endocrine cells of the gut. CCK was first demonstrated in brain tissue by a gastrin radioimmunoassay as a peptide different from and smaller than heptadecapeptide gastrin7. Using six different gastrin antisera, Dockray provided strong evidence that the reported gastrin immunoreactivity7 corresponded to the COOH-terminal octa-peptide of CCK8, which reacts with certain gastrin antisera because of the identical COOH-terminal pentapeptide sequences of gastrin and CCK. Studies using antisera specific for CCK without cross-reaction with gastrin have now confirmed that CCK is present in large quantities in the brain9,10 and that the peptide originally demonstrated by gastrin antisera7 indeed corresponded to the COOH-terminal octapeptide of CCK. In contrast, no peptides similar to any of the known molecular forms of gastrin have so far been found in brain tissue. We have used various sequence-specific antisera to distinguish between gastrin and CCK, and we report here that true gastrin also is present in the central nervous system. The only region of the brain containing significant amounts of gastrin was the hypophysis cerebri. Both pituitary lobes contained molecular forms of gastrin closely resembling those found in antrum11.

Organization of the mossy fiber system of the rat studied in extended hippocampi. I. Terminal area related to number of granule and pyramidal cells

Abstract: A quantitative and qualitative study of the septotemporal organization of the hippocampal mossy fiber system has been carried out in the rat. Transverse sections of isolated and extended hippocampi were stained according to Nisel's or Timm's method. At 12 equidistant levels covering the entire length of the hippocampus the following parameters were measured: the length of the granule cell layer and the mossy fiber layer, the area of the fields containing mossy fiber boutons, the number of granule cells, and the number of pyramidal cells in the hilus and in the regio inferior. Septally the pyramidal layer of the regio inferior is broad and the cells within the layer are relatively widely spaced. Here the mossy fiber boutons intrude deep into the layer. At more temporal levels the cells are tightly packed, the cell-layer is narrower, and the boutons predominantly terminate suprapyramidally. The length of the granular layer is greatest septally, while the length of the mossy fiber layer is greatest temporally. The area of the hilus, occupied by the mossy fiber boutons, is large at most of the temporal levels and small at the septal levels, whereas in CA3 the reverse is true. The greatest number of granule cells was found at the more septal levels. Conversely, the majority of the pyramidal cells in the hilus and in the regio inferior is situated temporally. The ratio of granule cells to pyramidal cells (hilus and regio inferior together) declines linearly from approximately ten at septal levels to approximately one at temporal levels. Because the mossy fibers are distributed fairly transverse to the long axis of the hippocampus, the variation in the ratio of granule cells to pyramidal cells reflects a corresponding variation in the number of innervating to innervated cells within the mossy fiber system.

A comparison of methods for the quantification of bacterial sulfate reduction in coastal marine sediments: II. Calculation from mathematical models

Abstract: A mathematical model describing vertical sulfate gradients as a function of diffusion, bacterial reduction, and sedimentation is applied to calculate the steady‐state rates of sulfate reduction in coastal sediments. Diffusion coefficients of sulfate are determined experimentally in different sediment types and depths. The rate of sulfate reduction is also determined directly on sediment cores by a radiotracer technique. Experimentally determined rates are compared with those calculated from the model. The results of the model are shown to depend strongly on its assumptions about the kinetics of bacterial sulfate reduction.

Laminar differentiation of the hippocampus, fascia dentata and subiculum in developing rats, observed with the Timm sulphide silver method.

Abstract: The laminar staining of the rat hippocampal region with the Timm sulphide silver method is from studies on adult rats known to depend on the various fibersystems terminating in these laminae. In order to illustrate the development of these fibersystems the laminar differentiation of the Timm staining of fascia dentata, hippocampus and subiculum is presented for rats between 1 and 31 days old. Corresponding changes in cytoarchitectonics as revealed by thionin staining are briefly demonstrated. Even on the first postnatal day there are indications of the mature, laminar staining pattern, and between three and nine days all the laminae corresponding to the terminal fields of the major afferent and intrinsic systems appear. After 12 days only minor additions to the laminar pattern develop, but there are adjustments of absolute and relative dimensions of layers and fields, and also the staining densities of individual laminae change. These observations are in good correlation with the available information on both hippocampal neurogenesis and cytodifferentiation, and the few fiber tracing studies performed on the developing hippocampal region. Compared to the latter, which ideally marks only one system or one lamina per animal, the Timm method provides an excellent means for getting an overview of the general developmental situation at the different ages. Thus developmental gradients along septotemporal, medio-lateral and basal-apical axes are found; which should be heeded in future studies on hippocampal synaptogenesis. The observations are discussed in relation to current models for neuronal growth and formation of nervous connections.

Respiratory adaptations in carp blood influences of hypoxia, red cell organic phosphates, divalent cations and CO2 on hemoglobin-oxygen affinity

Abstract: This study concerns the adaptation of oxygen transporting function of carp blood to environment hypoxia, tracing the roles played by erythrocytic cofactors, inorganic cations, carbon dioxide and hemoglobin multiplicity. Carp acclimated to hypoxia ( $$P_{O_2 }$$ ∼30 mmHg) display striking increases in blood oxygen affinity compared to normoxic ( $$P_{O_2 }$$ =120–150 mm) specimens (P 50's are 3.0 and 7.0 mm, respectively, at pH 7.9 and 20°C). This correlates with a marked decrease in erythrocytic concentrations of NTP (nucleoside triphosphates) (Figs. 1, 2, Table 1), permitting investigation of the time-course of the response (Fig. 3). That GTP (guanosine triphosphate) plays a greater role than ATP in the allosteric regulation of blood oxygen affinity, follows from greater decreases in its concentration during hypoxia, and its greater effect on oxygen affinity of the hemoglobin (Figs. 1, 5). It is furthermore shown that divalent cations (which complex with NTP) inhibit the regulatory role of GTP on O2 affinity to a lesser extent than that of ATP (Fig. 7). However, the divalent cation, Mg2+, occurs in similarly high concentrations in the erythrocytes of hypoxic and normoxic fish (Table 1). CO2 specifically depresses the O2 affinity of carp hemoglobin, but below pH 8.3, its effect is obliterated by ATP and GTP suggesting that the β chains are the main sites for CO 2 − binding. Four carp hemoglobin components are isolated and their oxygen-binding properties compared with those of the cofactor-free hemolysate (Figs. 4, 8, 9). The results are discussed comparatively with special reference to hemoglobin function in fish and mammals.

Acute and chronic effects of nifedipine in arterial hypertension.

Abstract: Sublingual administration of nifedipine 10 mg to 11 patients and 20 mg to 6 patients with arterial hypertension caused a rapid and significant decrease in blood pressure in both groups. The average maximal reductions in the two groups were 21/16 mm Hg and 27/21 mm Hg. A concomitant rise in heart rate was found. Forearm blood flow showed a significant increase and the calculated vascular resistance a significant decrease 15–60 min after administration of both the 10 mg and the 20 mg doses. There was a negative correlation between basal vascular resistance and the maximal change of this parameter (r=−0.72, p<0.01). Plasma concentrations of nifedipine showed considerable individual variation, with slow absorption in some patients, which indicated failure of sublingual absorption in them. The difference between the mean plasma concentration in the two dose groups was statistically significant after 45 min. A negative correlation was present between the plasma concentration of nifedipine and the observed change in calculated vascular resistance (r=−0.74 at t=30 min). Treatment of 10 hypertensive patients with nifedipine 30–60 mg daily for 6 weeks reduced mean blood pressure from 175/115 mm Hg to 151/96 mm Hg (p<0.001). Heart rate and forearm blood flow rose, whereas the forearm vascular resistance showed a significant decrease. Side effects of a sensation of heat and reddening of face were noted in some patients. It is suggested that nifedipine may be useful both in the acute and chronic treatment of arterial hypertension.

Distribution of membrane thickness determined by lineal analysis.

Abstract: SUMMARY The expected statistical distributions of intercept length are derived in terms of geometrical probability density functions pertaining to plates with known thickness penetrated by lines with random orientation. These expressions provide arithmetic and graphical solutions for obtaining distributions of membrane thickness and reciprocal membrane thickness from empirical distributions of intercept lengths. Furthermore, general relationships between probability density functions of distributions of intercept length and membrane thickness are derived as well as those between their moments. Examples of the application of the method to biological samples are given, and estimated distributions of glomerular basement membrane thickness are compared to those obtained by an independent, direct method. Various sources of bias, which in practice may occur due to departures from the sample model, are discussed and the influence of some of them is estimated. The knowledge of the probability density function of reciprocal intercepts makes it possible to perform a correction of the distributions of measured intercept length, which to some extent eliminates bias.

Functional mRNA half lives in E. coli.

Abstract: Analysis of the synthetic rate of individual protein species at various times after complete inhibition of transcription with either streptolygidin or rifampicin was carried out by two-dimensional polyacrylamide electrophoresis of total Escherichia coli cell extracts The decay rate of the potential to synthesize different proteins was assumed to be equal to the functional decay rate of the corresponding mRNA We conclude the following: (a) The tufA and tufB messengers have different half lives (30 and 24 min, recpectively) (b) Different genes within the same transcriptional unit can have different half lives (S7, EFG and EFTuA — 25, 38 and 30 min, respectively) (c) There is at least a twenty-fold variation in individual mRNA half lives in E coli; ribosomal protein Sl mRNA was observed to have the shortest half life in the cell (40 sec), while the longest observed half life was approximately 20 min (all values at 30°C) (d) addition of rifampicin increases the absolute rate of RNA polymerase subunit α and β synthesis twofold (e) The induction of the synthesis of α subunit of RNA polymerase takes palce without a concomitant induction of ribosomal protein S4 and L17, which are reported to be on either side of α in the same transcriptional unit

Organization of the mossy fiber system of the rat studied in extended hippocampi. II. Experimental analysis of fiber distribution with silver impregnation methods.

Abstract: The mossy fibers, a major intrinsic hippocampal pathway connecting the dentate granule cells with the pyramidal cells in CA4 and CA3, have been reexamined in rats using mainly Fink-Heimer silver impregnation methods for demonstration of degenerating axons. By extending isolated hippocampi and cutting sections normal to the long axis, simple two-dimensional reconstructions of both the lesions and the resultant degeneration could be made. In the hilus, the zone with the greatest concentration of degenerating boutons was found between the lesioned granule cells and the CA3 pyramidal cells abuting on the hilus; outside this zone the concentration declines rather rapidly. Degenerating boutons were also observed in low concentration up to 200-300 microgram septal and temporal to the lesion. The mossy fibers in CA3 nearest the hilus have an intrapyramidal course and display a lamellar organization with fibers from the granule cells of the medial blade lying deep to those from the dentate crest. These in turn lie deep to those from the graule cells of the lateral blade. A mediolateral difference in the projection of the graule cells on the CA3 pyramidal cells was discovered: fibers from the medial granule cells descend about 600 micrometer in the temporal direction, whereas fibers from the lateral granule cells descend about 1,200 micrometer. This causes a divergence of the fibers from one single level, especially of the part of the fibers, being farthest away from the hilus. The degree of descent of the fibers from each mediolateral position of the granule cells was constant at all septotemporal levels examined.

The Aarhus County vagotomy trial. II. An interim report on reduction in acid secretion and ulcer recurrence rate following parietal cell vagotomy and selective gastric vagotomy.

Abstract: In a prospective clinical trial, vagotomy for duodenal ulcer (DU) and prepyloric ulcer (PPU) was performed in 748 patients, 353 of whom were randomly allocated to selective gastric vagotomy and drainage (SGV + D), 54 to SGV + antrectomy (A), 273 to parietal cell vagotomy (PCV), and 68 to PCV + D. By 3 months postoperatively, basal acid secretion (BAO) had not stabilized. During the following year patients with SGV + A showed a decrease, while those with the other operations showed a rise in BAO, significant for SGV + D. One year after operation the level of BAO was the same after the 3 operations that did not remove the antrum. Peak acid output after pentagastrin stimulation (PAOPg) continued to decrease from 3 months to 1 year after SGV + A, while the other operations were followed by an increase, statistically significant for PCV. After 1 year the postoperative reduction in PAOPg was 90% for SGV + A, 45% for PCV, and approximately 60% for SGV + D and PCV + D. Overall clinical grading showed more failures following PCV than after SGV. Since failures after PCV were mainly ulcer recurrences, the final grading (after treatment of the failures) showed an equal number of failures for the 2 operations. Calculation of the probability of ulcer recurrence suggested a 6% rate after SGV + D and an 11% rate after PCV. However, when calculations took into account the location of the primary ulcer, the recurrence rate was the same after SGV + D for DU and PPU, while PCV showed a similar rate when used for DU but an incidence of 22% when used for PPU. The risk of recurrence was found to be constant from month to month during the first 2 1/2 years, after which no new recurrent ulcers were observed. It is suggested that for DU, PCV is preferable to SGV + D because the recurrence rate is the same but the incidence of sequelae is lower. When PCV is used for PPU, a higher ulcer recurrence rate may be expected.

Geographic variation, niche breadth and genetic differentiation at different geographic scales in the mussels Mytilus californianus and M. edulis

Abstract: Genetic differentiation was investigated in the marine mussels Mytilus californianus Conrad and M. edulis Linn. from the west coast of North America. In allopatry with M. californianus, M. edulis occurs throughout the intertidal zone; however, in microgeographic sympatry its ecological range is restricted to above the M. californianus mussel bed and to patches of substratum opened by natural disturbances within the bed. Over the same geographic scale, the broader-niched M. edulis shows greater among-locality genetic difference and greater levels of polymorphism than M. californianus at two enzyme loci. Genetic differentiation on a geographic basis was investigated in M. californianus at a single rock (on a scale of meters), on an island (on a scale of kilometers), throughout a strait (on a scale of 102 kilometers), and along the west coast of North America (on a scale of 103 km). Differentiation was minimal over the west coast, and could be explained by microhabitat differences in a local area. The minimal differentiation in west coast mussels relative to strong geographic differentiation of M. edulis on the east coast of North America may be related to the steeper latitudinal thermal gradient on the east coast. Local ecologically related microgeographic variation can result in biased and misleading estimates of genetic heterogeneity but microgeographic variation at enzyme loci may not be due to selection at the loci investigated or may even be due to the breeding structure of the mussel populations, as suggested by Tracey et al. (1975).

Phonon anomalies in transition-metal nitrides: ZrN

Abstract: For the first time we have observed soft-mode behavior in a superconducting transition-metal nitride. The phonon dispersion curves measured by inelastic neutron scattering exhibit sharp minima for the longitudinal-acoustic branches in the high-symmetry directions. The experimental results are well reproduced by calculations based on a double-shell model. The dispersion curves of TiN are similar to those of NbC except for significant difference in the anomalous region.

Development of the hippocampus and fascia dentata: morphological and histochemical aspects.

Abstract: Publisher Summary This chapter discusses the aspects of the development of the hippocampus and the fascia dentata in the rat. The emphasis is placed on the developmental changes that take place during the first postnatal month. To illustrate the different developmental stages, including the laminar differentiation of the afferent fiber systems, results obtained with the Timm sulfide silver method are used. This histochemical method provides an excellent means for monitoring and screening en bloc the development of the afferent systems to the hippocampal region. The chapter presents examples of the experimental approaches, which involve the hippocampus and the fascia dentata and help clarify which factors are important for the formation and laminar segregation of nervous connections. The chapter also presents the preliminary results obtained by transplantation of hippocampal and dentate tissue from neonatal rats into the central nervous system (CNS) of littermates and adult rats.

Distribution of gastrin and CCK cells in the rat gastrointestinal tract. Evidence for the occurrence of three distinct cell types storing COOH-terminal gastrin immunoreactivity.

Abstract: Gastrin and cholecystokinin (CCK) cells of the rat gastrointestinal tract have been studied by immunocytochemistry and radioimmunoanalysis. With antisera directed against the COOH-terminal tetrapeptide sequence, which is common to gastrin and CCK, three distinct endocrine cell types are detected. One of the cell types predominates in the antrum, is scarce in the rest of the gut and corresponds to the gastrin cell. The second cell type is virtually confined to the duodenum and jejunum and corresponds to the CCK cell. The third cell type occurs disseminated in the small intestines, predominates in the ileum, and reacts with COOH-terminus-specific antisera only following diethylpyrocarbonate and not following formaldehyde fixation. It is possible that the third cell type stores a third member of the gastrin-CCK family of gut hormones.

A determination of the volumes of the layers of the rat hippocampal region.

Abstract: The absolute volumes of the hippocampal and subicular cortical layers in the rat were determined. The boundaries of the various layers were defined on series of sections made through the entire hippocampal region of five rats and stained according to the Timm sulfide silver technique. Coordinates representing the boundaries of the layers on selected sections were fed into a mini-computer programmed to calculate the volume of the layers from the areas of the profiles and the distances between the sections. The distribution of the layers indicates that they constitute the same proportion of the volume of the dorsal and ventral divisions of the hippocampal region, with the exception of the structures lying in regio inferior and regio superior. Although the combined regio superior and regio inferior components of the layers of Ammon's horn occupy the same percentage of the volume of the dorsal and ventral hippocampal regions, the regio superior components occupy a larger percentage of Ammon's horn in the dorsal region than they do in the ventral region. The inter-animal variations in the volumes of the various layers indicate that it is possible to describe quantitatively the subdivisions of the hippocampal region with a precision that is compatible with comparative studies.

Changes in the respiratory properties of the blood in the carp, Cyprinus carpio , induced by diurnal variation in ambient oxygen tension

Abstract: Effects of diurnal variation in ambient oxygen tension on acid-base balance and blood respiratory properties were investigated in carp (Cyprinus carpio). The carp were subjected to two cycles in ambient $$P_{O_2 }$$ between about 130 mm Hg and about 12 mm Hg at 17°C (cf. Figs. 1 and 2). The first period of hypoxia was characterized by a non-compensated respiratory alkalosis, i.e. whole blood showed an increase in pH from 7.92 to 8.14. During the second hypoxic period, 24 h later, a significantly smaller respiratory alkalosis was present, whole blood pH changed from 7.95 (the value found during the intermediate return to normoxia) to 8.08. The latter increase was associated with a significant increase of 25% in plasma bicarbonate concentration compared with the first period of hypoxia (Fig. 1, Table 1). The erythrocytic concentrations of hemoglobin and ATP were lowered by about 10%, compared with the normoxic values, during the two episodes of hypoxia, and this was due to a swelling of the erythrocytes during hypoxia. The red cell GTP concentration showed an altogether different change during the O2 cycling: the absolute concentration of red cell GTP changed to a steady level, 50% below that present at the onset of the experiment and the major part of this change took place between the two hypoxic periods (Fig. 2, Table 2). The results are discussed with reference to the respiratory function of the blood of carps during subjection to cyclic $$P_{O_2 }$$ changes in nature.