Phenotypic drift in osmotic fragility of Sahel goat erythrocytes associated with variability of median fragility
A typical mammalian erythrocyte fragility phenotype (EFP) exhibits a sigmoidal curve of the dependence of fragilities (% haemolysis) on hypotonic saline concentrations, but the goat EFP tends to be hyperbolic. Physiological variation in median erythrocyte fragility (MEF) and the associated EFP of Sahel goats was investigated. Erythrocyte osmotic fragility (EOF) was determined in hypotonic saline using heparinized venous blood from 47 goats (23 males and 24 non-pregnant dry females) aged 1-4 years and weighing 18.87 ± 6.32 (9-30) kg. Packed cell volume (PCV), erythrocyte count and mean corpuscular volume (MCV) were also estimated. Low, medium and high EFP were based on MEF of < 7, 7-8 and > 8 g/L, respectively. MEF of all the goats was 7.5 ± 0.6 (5.9-8.4) g/L. Phenotypic drift from sigmoidal to hyperbolic EOF curve was observed at the lower and upper limits of the phenotypic variation. Frequencies of occurrence of low, medium and high EFP were not different (p > 0.05) between males and females. Fragiligrams of low, medium and high EFP separated at erythrocyte fragilities of 10-70% and saline tonicity of 7-8 g/L. The saline concentrations causing fragilities of 10-70% differed (p < 0.05) among the phenotypes. There was no correlation (r = -0.28, -0.30; p > 0.05) between MEF and MCV or PCV, and between PCV and MCV. In conclusion, phenotypic drift in EOF occurred in Sahel goats without influence by erythrocyte parameters and represented the physiological variability of EOF endpoint estimates that would serve as reference limits in evaluation of erythrocyte membrane defects.
Keywords: Erythrocyte size, Median fragility, Osmotic fragility, Phenotypic drift, Sahel goat