The isolation of a hypertensin

A similar decrease appears to take place during embryonic development, as shown in Figs. Work on the early embryo has demonstrated neither changes during development nor local differences in the oxygen uptake if this is calculated per unit of nitrogen or dry weight (see In the present study on older embryos, however, the reduction in Q2 with age or with increasing body weight during embryonic life was definite and characteristic. Such a reduction might conceivably be due to developmental changes in the respiratory-enzyme systems. Stained sections of embryonic arteries, however, suggested that it might be associated with an increase of relatively inert material such as reticulin, collagen and elastic tissue. The attempt to put this on a quantitative basis by means of densitometer readings gave a surprising degree of correlation between the curves for Qo, and for reciprocals of densitometer readings of Mallory-stained sections. Such reciprocals may be taken to represent the degree of cellularity of the sections. Whatever other influenices may be at work, therefore, the accumulation of connective tissue is likely to be a dominant factor in deter- mining the reduction in respiratory activity of the artery with advancing development. SUMMARY 1. The Qo, of artery slices from the rat, rabbit, sheep, pig and ox have been determined with the Warburg manometer.