Ventilatory response to severe acute hypoxia in guinea pigs and rats with low hemoglobin-oxygen affinity induced by phytic acid

Nutritional evaluation of crambe meal as a partial replacement of soybean meal in Nile tilapia diet

A variety of plant protein sources have been evaluated in aquafeeds. Crambe meal (CM) has potential for inclusion in fish diets because of its nutritional composition. This study evaluated the apparent digestibility coefficient (ADC) of crambe meal and its potential to partially replace soybean meal (SM) protein in Nile tilapia Oreochromis niloticus diets. The ADC for dry matter, crude protein, ether extract, energy, amino acids, calcium and phosphorus of CM were assessed in fish (n = 80; 65.30 ± 5.32 g). Subsequently, an 80-day feeding trial was conducted with Nile tilapia (n = 140; 6.04 ± 0.25 g) randomly distributed in 20 experimental cages (70 L; seven fish cage^-1) allocated in five circular tanks (1000 L) in a recirculation water system, to evaluate the effects of replacement of SM by CM (0, 6, 12, 18 and 24% in isonitrogenous and isoenergetic diets) on growth, blood parameters, fillet yield and proximal composition. The CM shows good digestibility of protein (0.824) and amino acids (0.844) by Nile tilapia and its inclusion in the diet does not affect carcass and fillet yield or proximal composition. Fish fed diets with 24.0% of the SM replaced by CM showed the worst weight gain and feed conversion rate. The protein efficiency ratio decreased in fish fed diets with 12.0, 18.0 and 24.0% of the SM replaced by CM. Hemoglobin, mean corpuscular hemoglobin concentration, total plasma protein, glucose and alanine aminotransferase enzyme activity trend to increase at highest levels of CM in the diet. In conclusion, CM has high digestibility of protein and amino acids for Nile tilapia. However, anti-nutritional factors present in untreated CM interfere on the growth and nutrient utilization of Nile tilapia.

Correlation between convection requirement and carotid body responses to hypoxia and hemoglobin affinity: comparison between two rat strains

We tested the hypothesis that differences in ventilatory ([Formula: see text]) or convection requirement ([Formula: see text]/[Formula: see text]O₂₎ response to hypoxia would be correlated with differences in hemoglobin (Hb) oxygen affinity between two strains of rats, as they have been shown to be among several species of mammals, birds and reptiles. Brown Norway (BN) rats reduce metabolism more than they increase ventilation in response to hypoxia and both the ventilatory and convection requirement responses to hypoxia are lower in the BN than the Sprague-Dawley (SD) rat. The lower threshold of the ventilation/convection requirement responses of the BN to hypoxia are associated with a higher affinity Hb than the SD rats, (P₅₀ values of 32.4 (± 0.6) versus 34.4 (± 0.5), respectively (P < 0.05), and P₇₅ values of 46.1 (± 0.5) for BN versus 50.7 (± 0.8) for SD (P < 0.001). This significant difference, particularly near the inflection point of the dissociation curve, supported our hypothesis. A reduced sensitivity of BN compared to SD carotid bodies was found. BN carotid bodies (from 36 20-60-day-olds) had a mean estimated volume of 26.64 ± 1.47 × 10⁶ μm³, significantly (P < 0.0001) smaller than SD carotid bodies (from 46 16-40-day-olds) at 50.66 ± 3.41 × 10⁶ μm³. Both genetic and epigenetic/developmental mechanisms may account for the observed inter-strain differences.

Dissociating the effects of oxygen pressure and content on the control of breathing and acute hypoxic response

Arterial oxygen tension and oxyhemoglobin saturation (S a O 2 ) decrease in parallel during hypoxia. Distinguishing between changes in oxygen tension and oxygen content as the relevant physiological stimulus for cardiorespiratory alterations remains challenging. To overcome this, we recruited nine individuals with hemoglobinopathy manifesting as high-affinity hemoglobin [HAH; partial pressure at 50% S a O 2 (P50) = 16 ± 0.4 mmHg] causing greater S a O 2 at a given oxygen partial pressure compared with control subjects (n = 12, P50 = 26 ± 0.4 mmHg). We assessed ventilatory and cardiovascular responses to acute isocapnic hypoxia, iso-oxic hypercapnia, and 20 min of isocapnic hypoxia (arterial Po2 = 50 mmHg). Blood gas alterations were achieved with dynamic end-tidal forcing. When expressed as a function of the logarithm of oxygen partial pressure, ventilatory sensitivity to hypoxia was not different between groups. However, there was a significant difference when expressed as a function of S a O 2 . Conversely, the rise in heart rate was blunted in HAH subjects when expressed as a function of partial pressure but similar when expressed as a function of S a O 2 . Ventilatory sensitivity to hypercapnia was not different between groups. During sustained isocapnic hypoxia, the rise in minute ventilation was similar between groups; however, heart rate was significantly greater in the controls during 3 to 9 min of exposure. Our results support the notion that oxygen tension, not content, alters cellular Po2 in the chemosensors and drives the hypoxic ventilatory response. Our study suggests that in addition to oxygen partial pressure, oxygen content may also influence the heart rate response to hypoxia.NEW & NOTEWORTHY We dissociated the effects of oxygen content and pressure of cardiorespiratory regulation studying individuals with high-affinity hemoglobin (HAH). During hypoxia, the ventilatory response, expressed as a function of oxygen tension, was similar between HAH variants and controls; however, the rise in heart rate was blunted in the variants. Our work supports the notion that the hypoxic ventilatory response is regulated by oxygen tension, whereas cardiovascular regulation may be influenced by arterial oxygen content and tension.

Structure of the altitude adapted hemoglobin of guinea pig in the R2-state

BACKGROUND

Guinea pigs are considered to be genetically adapted to a high altitude environment based on the consistent finding of a high oxygen affinity of their blood.

METHODOLOGY/PRINCIPAL FINDINGS

The crystal structure of guinea pig hemoglobin at 1.8 A resolution suggests that the increased oxygen affinity of guinea pig hemoglobin can be explained by two factors, namely a decreased stability of the T-state and an increased stability of the R2-state. The destabilization of the T-state can be related to the substitution of a highly conserved proline (P44) to histidine (H44) in the alpha-subunit, which causes a steric hindrance with H97 of the beta-subunit in the switch region. The stabilization of the R2-state is caused by two additional salt bridges at the beta1/beta2 interface.

CONCLUSIONS/SIGNIFICANCE

Both factors together are supposed to serve to shift the equilibrium between the conformational states towards the high affinity relaxed states resulting in an increased oxygen affinity.

Chronic intermittent hypobaric hypoxia protects the heart against ischemia/reperfusion injury through upregulation of antioxidant enzymes in adult guinea pigs

AIM

To investigate the protection and the anti-oxidative mechanism afforded by chronic intermittent hypobaric hypoxia (CIHH) against ischemia/reperfusion (I/R) injury in guinea pig hearts.

METHODS

Adult male guinea pigs were exposed to CIHH by mimicking a 5000 m high altitude (p(B)=404 mmHg, p(O2)=84 mmHg) in a hypobaric chamber for 6 h/day for 28 days. Langendorff-perfused isolated guinea pig hearts were used to measure variables of left ventricular function during baseline perfusion, ischemia and the reperfusion period. The activity and protein expression of antioxidant enzymes in the left myocardium were evaluated using biochemical methods and Western blotting, respectively. Intracellular reactive oxygen species (ROS) were assessed using ROS-sensitive fluorescence.

RESULTS

After 30 min of global no-flow ischemia followed by 60 min of reperfusion, myocardial function had better recovery rates in CIHH guinea pig hearts than in control hearts. The activity and protein expression of superoxide dismutase (SOD) and catalase (CAT) were significantly increased in the myocardium of CIHH guinea pigs. Pretreatment of control hearts with an antioxidant mixture containing SOD and CAT exerted cardioprotective effects similar to CIHH. The irreversible CAT inhibitor aminotriazole (ATZ) abolished the cardioprotection of CIHH. Cardiac contractile dysfunction and oxidative stress induced by exogenous hydrogen peroxide (H(2)O(2)) were attenuated by CIHH and CAT.

CONCLUSIONS

These data suggest that CIHH protects the heart against I/R injury through upregulation of antioxidant enzymes in guinea pig.Acta Pharmacologica Sinica (2009) 30: 947-955; doi: 10.1038/aps.2009.57; published online 22 June 2009.

Hypothermia and physiological control: the respiratory system

1. Ventilation (VE) in unanaesthetized hypothermic animals remains tightly coupled to oxygen consumption (VO2) such that VE/VO2 remains constant despite changes in body temperature. 2. Ventilatory responses to hypoxia would suggest that, relative to metabolic rate, the gain of the respiratory system is unaltered in hypothermic animals. 3. Future studies should exercise care to ensure that the method applied in inducing hypothermia does not complicate ventilatory control and that the ability of the species to hibernate is taken into consideration.