Blood corpuscles and blood hemoglobins: a possible example of coevolution.

A model which equates oxygen transport to hemoglobin concentration and molecular weight is used to demonstrate that high concentrations of hemoglobin will augment oxygen transport only if the molecular weight of the hemoglobin is low. The evolution of corpuscles is a necessary counterpart to having high concentrations of the low molecular weight hemoglobins. corpuscles prevent loss of the small molecules by way of excretory filters and prevent the development of exceedingly high plasma osmotic pressures.

Estimating diffusion distances in muscle.

Models of fibers and capillaries in cross sections of muscle were used to quantify the relationships between diffusion distances and tissue capillarity. The fibers were constructed as square and hexagonal arrays, and the placement of capillaries around the perimeters of the fibers ordered them in similar arrays. Diffusion distances were measured as the percent cumulative frequency of fiber area within a given distance of a capillary when capillary-to-fiber ratio was increased from 0.5 to 4.0. Equations fitted to the data make it possible to estimate diffusion distances in muscle and to correlate changes in diffusion distances with fiber growth, capillary growth, and the geometrical arrangement of capillaries in the muscle bed.

Model analyses of capillary growth and tissue oxygenation during hypoxia.

Theoretical analyses were used to determine whether capillary growth is an adaptive response to hypoxia. Parameter values were obtained from models of transverse sections of muscles in which individual fibers were distributed in square-ordered arrays and capillaries were added to the perimeters of individual fibers in the arrays. Increasing the number of capillaries up to 2.0 per fiber increased hypoxic tolerance by 157% above that expected for a Krogh cylinder. However, increasing the number of capillaries from 2.0 to 4.0 per fiber increased hypoxic tolerance by only 18% and, assuming the entire perimeter of each fiber was perfused with blood, increased hypoxic tolerance by only 11% over the value obtained when capillary-to-fiber ratio was 4.0. Capillary growth during normal maturation may result in capillary-to-fiber ratios around 2.0, near the upper limit for producing marked changes in hypoxic tolerance. Therefore, capillary growth may not be an adaptive response to ambient hypoxia because there is little or no gas transport benefit derived from the additional capillaries.

An improved method for studying microvascular geometry using fluorescent dyes: preventing dye extravasation, preserving dye integrity and enhancing tissue morphometry.

A procedure for stabilizing fluorescent markers used to study the microvascular geometry and morphometry of muscle tissue is described. The procedure involves fluorescent labeling of plasma, fixation of muscle tissue in 10% buffered formalin, and quick freezing. This procedure prevents extravasation of the fluorescent dyes out of the capillaries as frequently seen in other muscle microvascular techniques, thereby greatly increasing the time that capillaries are visible. We found that formalin may actually increase the rate of fluorochrome bleaching by photo-oxidation, but the increased rate of bleaching is more than offset by the greater concentration of dye trapped in the capillaries. Further, formalin fixation results in little distortion of the muscle fibers themselves, making this approach ideal for morphometric studies.

Capillarity in rat skeletal muscle: effects of rapid freezing versus perfusion fixation.

We determined the effects of rapid freezing and perfusion fixation on fiber geometry and capillarity in rat skeletal muscle. Fiber areas were significantly decreased, and capillary densities significantly increased, in perfusion-fixed versus quick-frozen muscle. Significant differences in capillary-to-fiber ratios were not observed, suggesting that differences in fiber geometry, not the methods of quantifying capillaries, accounted for the differences in capillary density. We conclude that estimates of fiber geometry, capillarity, and diffusive gas conductances obtained from perfusion-fixed muscles are subject to significant error due to shrinkage.

Capillary growth in chick skeletal muscle with normal maturation and hypertrophy.

Tissue capillarity and tissue enzyme activity (citrate synthase and lactate dehydrogenase) were determined for two red muscles and two white muscles from the domestic chicken during normal maturation and, for one red muscle, during muscle hypertrophy. Muscle fiber cross sectional area increased with muscle mass during normal maturation and with the additional increase in muscle mass following hypertrophy. Normal maturation and hypertrophy did not affect lactate dehydrogenase activity or citrate synthase activity for the muscles with anaerobic fiber types. Citrate synthase activity per unit muscle mass was positively correlated with muscle capillary density for the muscles with aerobic fiber types. Capillary to fiber ratios increased with fiber size and were significantly higher in muscles with aerobic fibers than in muscles with nonaerobic fibers. However, capillary densities decreased with maturation and with fiber hypertrophy. For each of the muscles sampled, the number of capillaries per unit linear distance of muscle fiber perimeter was independent of muscle fiber growth during normal maturation and during hypertrophy. The results from the present work are consistent with the hypothesis that muscle fiber type and muscle fiber surface area may be the primary determinants of capillary growth during normal maturation and during fiber hypertrophy.

Respiratory adaptations in diving mammals.

This report examines the evidence for the presence of oxygen stores in the lungs, blood and systemic musculature of diving mammals, the modifications in the respiratory functions of blood that may be important in utilizing the lung and blood oxygen stores, and the potential importance of the oxygen stores and the respiratory functions of blood in supporting short-duration, aerobic dives. Increasing oxygen stores by increasing lung volume does not occur in diving mammals. The long-duration diving whales have small lung volumes which results in lung collapse during dives and the seals dive following partial expiration which produces the same effect. The short-duration diving dolphins, porpoises and rodents have lung volumes comparable to terrestrial mammals, dive following inspiration and appear to use the lungs as an oxygen store. Adaptations in the oxygen affinity of the blood parallel the modifications in lung volume. Where the lungs do not represent a potential oxygen store the oxygen affinity is low, maximizing the unloading of oxygen while maintaining a high tissue oxygen tension. Where the lungs do represent an oxygen store, the affinity is high, maximizing the uptake of oxygen from the alveolar space. Increases in the concentration of respiratory pigment in the blood and in muscle are important adaptations in diving mammals. The blood oxygen stores in diving mammals vary from near normal to over three times normal for terrestrial mammals while the muscle oxygen stores vary from near normal to nearly ten times normal. The degree to which the blood and muscle oxygen stores are increased can be equated to the duration of the dive and demands for oxygen; longer duration divers and those with higher metabolic demands have greater oxygen stores than divers that remain submersed for shorter periods or have lower rates of oxygen utilization.

Muscle capillarity in chicks following hypoxia.

1. Muscle capillarity was examined in chicks exposed to normobaric hypoxia with and without increased workload. 2. Capillarity was higher in the lateral head of the gastrocnemius, but not in the other muscles examined. Increased workload did not contribute to the effects of hypoxia. 3. Thus, hypoxia served as a stimulus for the development of new capillaries in muscle containing twitch fibers, but not in muscle containing tonic fibers.

Capillary growth and diffusion distances in muscle.

1. Tissue capillarity in muscle was modelled as square-ordered arrays with capillary-to-fiber ratios (C/F) from 0.5 to 'infinity'. 2. C/F up to two had marked effects on diffusion distances, but C/F above had only slight effects on average distances and almost no effect on maximal distances. 3. Capillary growth during normal maturation results in C/F around two. Thus, capillary growth in adult muscle may not be an adaptive mechanism for reducing diffusion distances.

Capillarity and diffusion distances in skeletal muscles in birds.

Tissue capillarity and diffusion distances were determined for red and white skeletal muscles of adult birds ranging in mass from 10.8 to 6200 g. In addition, literature values for capillarity and diffusion distances in skeletal muscles of mammals were incorporated into the data set. Muscle mass was closely coupled to body mass. However, no significant allometric relations were found for any of the other variables measured. Number of capillaries per fiber was not correlated with cross sectional area of individual muscle fibers. Thus, capillary density decreased in a hyperbolic manner against fiber area and diffusion distance decreased in a hyperbolic manner against the number of capillaries per muscle fiber. Red muscles had significantly higher numbers of capillaries per fiber and significantly shorter diffusion distances than did white muscles. The patterns for tissue capillarity and diffusion distances in avian muscle reported here are similar to values reported previously for mammalian muscles. In both taxonomic groups capillarity and diffusion distances are independent of body mass. In addition, diffusion distances are characteristic of capillaries distributed in random arrays through the muscle cross section.

Anatomical organisation of the microvasculature in the anterior and posterior latissimus dorsi muscles of the chicken.

Anterior and posterior latissimus dorsi muscles of twelve chickens were injected with India ink to visualise their microvasculature. Both muscles have multiple feeding arterioles that branch into a meshwork of arcade arterioles. Transverse arterioles arise from the arcade system and these, in turn, give rise to capillaries. The major differences in the microvasculatures of the two muscles are in the numbers of vessels in the arcade meshworks and the dimensions of these vessels. The differences in geometry and topology of the arcade vessels suggest that the microvasculature in the anterior latissimus dorsi may be able to support levels of oxidative metabolism almost 8 times higher than those in the posterior latissimus dorsi.

Intracellular pH in the toad Bufo marinus following hypercapnia.

We investigated the effects of hypercapnia on intracellular acid-base regulation in brain and liver of the toad Bufo marinus L. After 1 h at 5% CO2, arterial PCO2 increased significantly, from 1.6 +/- 0.04 to 5.7 +/- 0.23 kPa, while brain and liver intracellular pH (pHi) decreased significantly. Reductions in pHi of both tissues were partially compensated by increased levels of bicarbonate. Surprisingly, however, compensation was lower than expected in brain and higher than expected in liver. We suggest that compensation in brain may be limited by secondary effects of bicarbonate loading in this tissue.

Hemodynamics of the lesser mouse deer, Tragulus javanicus.

Mouse deer possess the smallest known erythrocytes. In contrast to the usual biconcave shape, mouse deer corpuscles are spherical which results in an appreciable increase in vitro blood viscosity. In the absence of compensation, increased viscosity should produce hemodynamic consequences. However, we find that cardiac output, arterial pressure, and total peripheral resistance are all within normal limits, while packed cell volume is considerably lower than normal. We suggest that reduced packed cell volume represents a compensation for the spherical shape of the corpuscles, serving to maintain blood viscosity and dependent hemodynamic parameters within normal limits. These results contrast markedly with the pattern observed in man where conditions which result in a high in vitro blood viscosity also have significant hemodynamic consequences. Mean values for three mouse deer were: body mass, 1.18 kg; packed cell volume, 29.8%; heart rate, 182 beats/min; cardiac output, 145 ml-(kg-min)-1., mean arterial pressure, 99 Torr; total peripheral resistance, 4.90 X 10(5) dyn-s-cm-5.

Water loss and survival in embryos of the domestic chicken.

In this report we show that the amount of water lost during incubation is an important determinant of hatchability in embryos of the domestic chicken. However, when the loss of water is restricted to the first half versus the second half of the total incubation period, it is the loss of water during the first half that affects hatching success. We propose that regulating the permeability of the egg shell may be important in preventing excessive drying of the inner shell membrane during early development along with limiting the total amount of water lost from the embryo during incubation.

Hematology, viscosity, and respiratory functions of whole blood of the lesser mouse deer, Tragulus javanicus.

Blood samples from the lesser mouse deer were examined for hematology, viscosity, oxygen dissociation curve, and magnitude of the Bohr effect. Red corpuscle dimensions, determined under oil immersion with an ocular micrometer, averaged 2.2 micron while the cell counts averaged 53 million/micronl blood, and the packed cell volume averaged 31.2%. Blood hemoglobin concentration averaged 11.2 g/100 ml and the calculated mean cell hemoglobin concentration was 38 g/100 ml. The relative viscosity of the mouse deer plasma was 1.97 and increased in a nonlinear manner with hematocrit to 100 at 80% packed cell volume. Oxygen-hemoglobin equilibrium curves, determined with a mixing technique at 37 degrees C and 10, 36 and 71 Torr PCO2, have the same configuration observed in blood from mammals in general. The P50 of the mouse deer blood at pH = 7.40 is 34 Torr and the Bohr effect (deltalog P50/deltapH) is -0.483. The mouse deer have blood hematocrits which are well below the hematocrits observed in mammals with larger erythrocytes, but similar to the blood hematocrits observed in other mammals with small erythrocytes. We suggest that the low hematocrit is an adaptation which circumvents the hemodynamic problems associated with a high blood viscosity and that, in the mouse deer, the expected concomitantly low total blood hemoglobin concentration is compensated by a higher than average mean cell hemoglobin concentration.

Relationships between body temperature, thermal conductance, Q10 and energy metabolism during daily torpor and hibernation in rodents.

In the present paper we examine the ability of rodents to maintain body temperature (TB) following the marked reductions in metabolic heat production associated with torpor. Previously published values for metabolic rate (M), TB and ambient temperature (TA) were used to calculate thermal conductances (C') during normothermy and torpor in rodents capable of daily torpor (11 species) and hibernation (18 species). Values of C' for torpid animals are uniformly lower than C' in normothermic animals. In addition, C' of normothermic and torpid rodents decreases with increasing body mass (BM). However, the slope of the relationship between C' and BM is almost 4-fold greater for normothermic than for torpid animals. Thus, the ability of torpid rodents to conserve body heat by reducing C' decreases with increasing mass. Rodents that use daily torpor tend to be small and they tend to maintain TB well above TA during torpor. Hibernators tend to be larger and regulate TB relatively close to TA. Thus, the reductions in C' appear to be closely correlated with the level of TB regulation during torpor. We suggest that the changes in C' represent a suite of physiological adaptations that have played a central role in the evolution of torpor, enabling rodents to regulate TB above TA during periods of very low heat production. Based on the approach used here we address the controversy of whether reductions in M during torpor are due entirely to temperature effects or whether metabolic inhibition in addition to temperature effects may be important. We suggest that the controversy has been confused by using Q10 to evaluate the relationship of M and TB in endotherms.(ABSTRACT TRUNCATED AT 250 WORDS)

Microvascular development in chick anterior latissimus dorsi following hypertrophy.

Right (hypertrophied) and left (control) anterior latissimus dorsi muscles (ALD) were injected with India ink to visualise microvascular geometry in these muscles. The ALD muscles have multiple feeding arterioles that branch into meshworks of arcade arterioles. Transverse arterioles arise from the arcade system and give rise to capillaries. Hypertrophy is attended by an increase in the combined length of arterioles in the arcade system due to an increase in the number of arcade segments. Morphometric characteristics of each segment remained constant. Hypertrophy produced a significant increase in the numbers of capillaries per individual muscle fibre due to an increase in number of transverse arterioles and an increase in number of capillaries per transverse arteriole. However, the increased numbers of capillaries per fibre just matched fibre hypertrophy, so that the number of exchange vessels per cross sectional area of muscle remained constant. These results are consistent with the argument that muscle growth is the primary determinant of capillarity.

Effects of maturation on tissue capillarity in chickens.

Tissue capillarity, diffusion distances and myoglobin concentrations in the anterior latissimus dorsi (ALD), consisting entirely of slow tonic fibers, the posterior latissimus dorsi (PLD), consisting entirely of twitch fibers, and the gastrocnemius (GST), consisting of both twitch and tonic fibers, were determined for the domestic chicken throughout maturation. Increases in muscle mass for the three muscles are due to fiber hypertrophy and are quantified as changes in the average cross-sectional area (FCSA) of the fibers. Capillary densities were highest in the newly hatched chicks: ALD = 3967 +/- 888 caps/mm2, PLD = 8360 +/- 1078 caps/mm2, and GST = 8360 +/- 8360 +/- 1283 caps/mm2; and decreased in proportion to the increase in FCSA, to adult values of ALD = 450 +/- 50, PLD = 120 +/- 20 and GST = 267 +/- 33 caps/mm2. In contrast to mammals, the ratio of the numbers of capillaries to the numbers of muscle fibers appears to be fixed at or shortly after hatch; there is not an increase in the numbers of capillaries to offset fiber hypertrophy. Consistent with the observations on capillary densities, the diffusion distances are shortest in the newly hatched chicks where the maximal diffusion distance is 17.9 +/- 1.06 micron in the ALD, 12.5 +/- 1.08 micron in the PLD and 17.4 +/- 0.93 micron in the GST. The maximal diffusion distance increased in proportion to FCSA; to 42.4 +/- 5.75 micron in the ALD, 88.8 +/- 1.33 micron in the PLD and 64.4 micron +/- 8.59 micron in the GST. In the adult the diffusion distances varied with the fiber type of the muscle. Myoglobin concentrations were similar in the ALD and PLD and were lowest at hatch but increased to plateau values of 4.3 +/- 0.51 mg/g for the slow-tonic ALD and 2.2 +/- 0.33 mg/g for the fast-twitch PLD. In contrast, myoglobin concentrations in the GST were highest in the newly hatched chicks and decreased to a low-level plateau of 1.8 +/- 0.83 mg/g in the adult. The very high myoglobin concentrations in the GST of the newly hatched chicks may represent an adaptation to conditions of extreme hypoxia in the hind limb of the developing embryo.