This study examined exercise-induced hypoxaemia (EIH) and plasma volume contraction as modulators of serum erythropoietin (Epo) production. Five athletes cycled for 3 min at supra-maximal power outputs, at each of two different elevations (1,000 m and 2,100 m). Five subjects were exposed to normobaric hypoxia (F(I)O(2)=0.159), seven subjects underwent plasmapheresis to reduce plasma volume and eight subjects were time controls for Epo levels. Oxyhaemoglobin saturation was significantly reduced during exercise and during normobaric hypoxia. The time period of haemoglobin oxygen saturation <91% was 24+/-29 s (mean+/-S.D., n=5) for exercise at 1000 m, 136+/-77 s (mean+/-S.D., n=5) for exercise at 2100 m and 178+/-255 s (mean+/-S.D., n=5) with resting hypoxic exposure. However, significantly increased serum Epo levels were observed only following exercise (24+/-3%; mean+/-S.D., n=5 at 1,000 m and 36+/-5%; mean+/-S.D., n=5 at 2,100 m). Volume contraction also resulted in increased serum Epo (35+/-6%; mean+/-S.D., n=7) in spite of a significant rise in haematocrit of 2.2%. Despite similar degrees of arterial desaturation, only the hypoxaemia induced by exercise was associated with an increase in serum Epo. This finding indicates that other factors, in addition to hypoxaemia, are important in modulating the production of Epo in response to exercise. Volume depletion in the absence of exercise resulted in increases in Epo levels that were comparable with those observed in response to exercise. The paradoxical responses of the increased haematocrit and the increase in Epo in subjects undergoing plasmapheresis suggests that plasma volume may also modulate the production of Epo.

Congestive heart failure was produced in nine dogs following surgical removal of the tricuspid valve. Six dogs developed ascites with or without peripheral edema, and four dogs remained ascites-free for 5, 6, and 11 weeks (one dog in this latter group did later develop ascites 14 weeks following operation; it was therefore studied twice and included in both groups). Systolic aortic pressure, sodium balance, right atrial pressure, glomerular filtration rate, sodium para-aminohippurate clearance, plasma aldosterone, norepinephrine, renin activity, and antidiuretic hormone levels were measured in each dog before surgery and during the experimental period of the steady state of edema in the dogs of group A, and at 5, 6, and 11 weeks in the four dogs of group B. Right atrial pressure increased considerably and glomerular filtration rate and sodium para-aminohippurate clearance decreased markedly in each dog. The most significant and important findings were (1) normal sodium balance in the dogs of group B without ascites, whereas four of the six dogs with ascites had a markedly positive sodium balance; (2) increased antidiuretic hormone activity levels in all dogs with congestive heart failure and ascites in contrast with the absence of any change in the dogs without ascites. The changes in plasma aldosterone, norepinephrine, and renin activity levels were not consistent. It is suggested that the antidiuretic hormone may play a role in the formation of ascites and edema in dogs with congestive heart failure following total removal of the tricuspid valve.

Norepinephrine and renin contents in arterial tissues from different vascular territories in mongrel dogs were measured simultaneously. A significantly greater concentration of these two substances was found in the branches of the superior and inferior mesenteric arteries in contrast to arterial tissue taken from the aorta and from carotid, renal, femoral, and hind limb arteries of similar diameter. Norepinephrine and renin were undetectable in the rectus abdominis artery. There was no significant difference in the norepinephrine content of branches of mesenteric vein when compared with similar branches of mesenteric artery.

1970. Renin activity and norepinephrine, cation, rind water contents sf cardiovascular tissue of dogs with congestive heart failure and ascites. Can. J. Physiol. Pharnaacol. 48, 463468. Six dogs with congestive heart failure and ascites were studied for ( a ) renin, norepinephrine, water, sodium, potassium, calcium. and lrnagnesium contents in cardiovascular tissues; ( h ) plasma renin activity and renin substrate; ( c ) renal renin activity, juxtaglomerular index, and glucose-6-phosphate dehydrogenase activity in macula densa cells, and a-glycero-6-phosphate dehydrogenase activity in inacula densa cells and juxtaglonaerular bodies. The most important findings were: (a) a cignificant decrease in renal renin activity and in the juxtaglomcrular index coinciding with increased activities of glucose-6-phosphate and a-glycero-6-phosphate dehydrogenases in nnacula dens2 cells when compared with normal renal hissue: ( b ) a highly significant increase in norepinephrine content in branches of mesenteric veins combined with a decrease in norepinephrine content in most arteries studied; ( c ) a significant increase in the sodium content of most arteries studied, without any change h water content.

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