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Biological Research

versión impresa ISSN 0716-9760

Biol. Res. v.35 n.1 Santiago  2002

http://dx.doi.org/10.4067/S0716-97602002000100005 

Hemoglobin affinity in Andean rodents

HRVOJ OSTOJIC1, VERONICA CIFUENTES2, CARLOS MONGE3


1 Clinicum Laboratorio Automatizado, Iquique, Chile
2 Universidad Arturo Prat, Iquique, Chile
3 Laboratorio de Transporte de Oxígeno. Departamento de Ciencias Fisiológicas
Universidad Peruana Cayetano Heredia, Lima, Perú

Corresponding author: Hrvoj Ostojic P. Clinicum Laboratorio Automatizado. Casilla 169, Iquique, Chile. Telephone: 56-57-420599. Fax: 56-57-427683. e-mail: clinicum@chilesat.net

Received: April 11, 2001. In revised form : December 26, 2001. Accepted : December 27, 2001

ABSTRACT

Blood hemoglobin oxygen affinity (P50) was measured in three Andean species and in the laboratory rat (control), all raised near sea level. Chinchilla lanigera (Molina, 1792) has an altitudinal habitat range from low Andean slopes up to 3000 m., while Chinchilla brevicaudata (Waterhouse, 1848) has an altitudinal range from 3000 to 5000 m. The laboratory type guinea pig, wild type guinea pig (Cavia porcellus), (Waterhouse, 1748), and laboratory rat (Rattus norvegicus) were also raised at sea level.

The Andean species had high hemoglobin oxygen affinities (low P50) compared with the rat. Chinchilla brevicaudata had a higher affinity than Chinchilla lanigera. The wild type guinea pig had a higher affinity than the laboratory type. As has been shown in other species, this is another example of an inverse correlation between the altitude level and the P50 values. This is the first hemoglobin oxygen affinity study in Chinchilla brevicaudata.


Key terms: hemoglobin affinity, rodents, high altitude adaptation.

INTRODUCTION


High hemoglobin oxygen affinity is a blood property that can be considered a genetic mark for high altitude adaptation in mammals, birds (Monge and León-Velarde, 1991) and even amphibians (Ostojic et al, 2000), since hypoxic environments appear to exert strong selective pressure on this property. Since Hall et al (1936) found high hemoglobin oxygen affinity in mammals and birds native to the high Andes, several publications have confirmed these early descriptions.

The guinea pig, an Andean rodent, was introduced in Europe in the sixteenth century (Muñoz-Pedreros and Yañez-Valenzuela, 2000), and despite the fact that its reproduction has been controlled under domestic and laboratory conditions since that time, it still has high hemoglobin affinity ( Hall et al, 1966; Bartels, 1967; Rivera et al 1994; Rivera et al 1995; Turek 1980). Another Andean rodent, the Chinchilla lanigera, also has a high hemoglobin affinity (Hall, 1966). In this publication, we report high hemoglobin oxygen affinity in Chinchilla brevicaudata for the first time.

MATERIALS AND METHODS

Materials

Animals: Chinchilla lanigera, whose natural habit extends from 300 m to 3,000 m (Grau, 1994). Chinchilla brevicaudata, whose natural habit extends from 3,000 to 5,000 m (Muñoz-Pedreros and Yañez-Valenzuela, 2000). The animals were raised in captivity at 2,250 m. Wild guinea pigs (Cavia porcellus) were raised at sea level in captivity at 1,585 m. Laboratory guinea pigs (Cavia porcellus) were raised at 850 m. The laboratory rats (Rattus nornorvegicus) were raised at 850 m.

The `n' used is not a sample. It involves our entire population.

Methods

The TCS HEMOX ANALYZER is an automatic system for recording the oxygen equilibrium curve of blood. It uses spectrophotometric measurements and the continuous monitoring of the oxygen partial pressure with a Clark oxygen electrode. The equipment requires only a few drops of blood (50µl) for a complete plotting of the curve and it provides reliable P50 values. The instrument continuously records the association curve from 0 to 100% saturation as a function of PO2 on a graph recorder.

Four ml of a buffer solution was bubbled with nitrogen into a HEMOX ANALYZER MODEL B set to zero and then with air to raise saturation to 100%. A drop of blood was collected from an ear blood vessel in the Andean species and from a rat femoral vein. 50 µl of blood was diluted in 4 ml of buffer solution, then 20 µl of an additive provided by the instrument company and 10 µl of antifoam solution were then added (buffer pH = 7.4; temperature = 37ºC). The statistical significance was determined by variance analysis with Bonferroni adjustment with software SYSTAT 7.0 for Windows.

RESULTS


Table I
contains mean values, standard deviations and variation coefficient of hemoglobin oxygen affinity for Andean species and rat. Small variation coefficients indicate reduced data variability. Figure 1 summarizes results and shows that rat has a higher P50 value than all Andean species in this study.

Statistical comparison between pairs of P50 values was done by variance analysis with Bonferroni adjustment (Table II).

Chinchilla lanigera (27.3 mmHg) differs from Chinchilla brevicaudata (23.3 mmHg). Wild type Cavia porcellus (23.7 mmHg) differs from laboratory type Cavia porcellus (26.1 mmHg). The rat differs from all other species. Chinchilla brevicaudata does not differ from wild type guinea pig, nor does Chinchilla lanigera differ from laboratory type guinea pig (Table II).

DISCUSSION


Methodology developed by TCS Scientific Corp (Hemox-Analyzer Model B) allowed the use of micro blood samples to measure P50 at pH of 7.4 without Bohr factor determination, which would have otherwise required large blood samples for blood equilibration at different pH values. Equilibration with N2 and O2 containing CO2 was also unnecessary. Since Chinchillas are an endangered species, minimal amounts of blood were taken. Very small variation coefficients obtained for each group of animals indicate the accuracy of the technique used.

TABLE I

P50 values mean


species
n
sex
average
weight (kg)
P50 (mean)
mmHg
standard
deviations

variation
coefficient


Rattus
norvegicus

5
m
0.35
38.3
1.4
0.04

Chinchilla
lanigera

6
m
0.6
27.2
0.9
0.03

Chinchilla
brevicaudata

5
m
0.55
23.3
1.3
0.06

Cavia
porcellus

(wild type)

5
m
0.95
23.7
0.5
0.02

Cavia
porcellus

(laboratory
guinea pig)

5
m
0.75
26.1
1.1
0.04

 

TABLE II

Statistical Analysis (P<0.05)

Bonferroni Adjustment.
Matrix of pairwise comparison probabilities:


Chinchilla
lanigera
Chinchilla
brevicaudata
C. porcellus
(wild type)
C. porcellus
(laboratory)
Rattus
norvegicus

C. lanigera
-
-
-
-
C. brevicaudata
0.00
-
-
-
-
C. porcellus (wild type)
0.00
1.00
-
-
-
C. porcellus (laboratory)
1.00
0.006
0.023
-
-
R. norvegicus
0.00
0.00
0.00
0.00
-

Hemoglobin affinity has long been considered a genetic marker of high altitude adaptation, regardless of altitude level. Hemoglobin affinity was then found to correlate with habitat altitude so that the higher the habitat, the higher the affinity (Snyder et al, 1982, Snyder 1985). This presented the need to extend these studies to other species. Later works therefore showed that larger mammals of the same species, such as the puma and the wild cat, who occupy high and low altitude niches also show higher affinities in higher habitats (León-Velarde et al, 1996).

The study of both chinchillas show low P50. This is the first report of a high affinity in the Chinchilla brevicaudata. The habitat of Chinchilla brevicaudata is also higher than that of Chinchilla lanigera (see Material and Methods). This finding is the third report showing an inverse correlation between altitude levels and P50 values. This work confirms that the laboratory type guinea pig (Cavia porcellus) has low P50 (26 mmHg). This value is similar to others reported. The wild type guinea pig (23.7) has lower P50 values than the laboratory type. It is difficult to interpret this difference because the wild type may be from high altitude or may even include hybrid individuals from other close species (Muñoz-Pedreros and Yáñez-Valenzuela, 2000). The rat has a much higher P50 (38.3 mmHg) than any of the Andean species in this study. This value supports previous reports. Figure 1 summarizes the results. We have failed to differentiate the two chinchillas using respiratory responses to hypoxia and cold (work in preparation) but the hemoglobin affinity shows clear differences.

One important result of this work is to show that the laboratory rat considered a standard model for environmental hypoxic studies is of limited value because it is very sensitive to cold and hypoxia, which characterize the high altitude environment. The guinea pig, originating from the Andes, has a high affinity hemoglobin, is very tolerant to the hypoxic environment, and has a high reproduction rate in laboratory conditions, both at sea level and at high altitude. We recommend the guinea pig as a standard animal model for environmental respiratory studies.

Figure 1: P50 values in all species used.

ACKNOWLEDGEMENTS

This work was supported by a grant from FONDEF D-9711068.

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