Studies on the cardiovascular response to hypoxia

Fifty-eight adults, nearly all male, aged between 35 and 50, with slight bronchiopneumopathy in a state of functional compensation, were subjected to hypoxia by rerespiration. Heart rate and oxyhaemoglobin saturation were observed. In nearly all cases, hypoxia caused an increase in heart rate that varied considerably from subject to subject, but seemed more marked between the 1st and 2nd minute after start of the trial. Normalization of heart rate, similarly very variable, reflected the increase phase and was complete in periode varying between 30 and 210 seconds. It may be supposed that as regards heart rate the wide variety of responses to the same stimulus is due to individual states of equilibrium of a predominantly vegetative nature. There was no relation between duration of the hypoxia trial, extent of desaturation and time of resaturation in air because the rate of haemoglobin desaturation and resaturation varied from case to case.     

Isolation of globin messenger RNA of Xenopus laevis

The polypeptide chains of Xenopus laevis hemoglobin have been analyzed by sodium dodecyl sulfate (SDS) and acid-urea gel electrophoresis. Four components can be distinguished, each having an approximate molecular weight of 13,000 daltons. Messenger RNA coding for the globin chains has been isolated and characterized. In a denaturing acrylamide gel the mRNA has an approximate molecular weight of 250,000 daltons. The complexity of the RNA is consistent with the presence of four different mRNA molecules, each of this molecular weight. When the mRNA is assayed in a wheat germ in vitro translation system, four polypeptides are synthesized corresponding to the four globin subunits. The relative proportion of the four synthesized polypeptides appears to vary according to the developmental stage of the red blood cells used for mRNA isolation. Hybridization of a complementary DNA (cDNA) copy of the globin mRNA to Xenopus laevis DNA in DNA excess indicates that each of the globin genes is present in one to three copies per haploid genome.