Byung L. Roh

Localization of erythropoietin in the glomerulus of the hypoxic dog kidney using a fluorescent antibody technique.

Intense fluorescent staining of cells in the glomerular tuft has been demonstrated in a hypoxic dog kidney with an antibody to erythropoietin (ESF) using the indirect fluorescent antibody technique. The fluorescent staining in the glomeruli was blocked by a highly purified preparation of ESF. This fluorescence appears to be localized in the visceral epithelial cells of the giomerulus. Kidney sections of a normal dog and a dog injected with hypoxic dog plasma ESF to maintain a prolonged elevation in plasma ESF titers failed to show positive fluorescent staining following treatment with the antibody to ESF. The present studies suggest that the epithelial cells of the glomerular tuft are the site of ESF production.

The Cytological Localization of Erythropoietin in the Human Kidney Using the Fluorescent Antibody Technique

Summary Intense fluorescent staining of cells in the glomerular tuft has been demonstrated in an anemic human kidney following application of an antibody to erythropoietin using the indirect fluorescent antibody technique. The fluorescence was more localized in the cytoplasm of epithelial cells in the periphery of the glomerular tuft. A slight amount of fluorescent staining in the glomeruli was blocked by a highly purified preparation of human urinary erythropoietin. The present studies suggest that the visceral epithelial cell of the glomerular tuft is the most likely source of erythropoietin.

Plasma Disappearance of 125I-Labeled Erythropoietin in Anesthetized Rabbits

Summary The rate of plasma disappearance of 125I-labeled highly purified human urinary erythropoietin (ESF) was compared with that of unlabeled partially purified human urinary ESF in anesthetized rabbits. Plasma T1/2 values for both the labeled and unlabeled ESF were essentially biphasic. The mean half-time disappearance of 125I-labeled ESF was 35.87 min for the rapid phase and 10.25 hr for the slow phase. The half-time disappearances of the unlabeled ESF for the rapid and slow phases were 32.39 min and 7.98 hr, respectively. The T1/2 values of the 125I-labeled ESF and the unlabeled ESF are not significantly different.

Erythropoietic Effects of Bilirubin in Rats

Summary Bilirubin was found to increase 59Fe incorporation in red blood cells of fasted rats. A significant increase in 59Fe incorporation in red blood cells of exhypoxic polycythemic mice was also seen following the injection of serum from normal rats treated with bilirubin. This effect was completely blocked by antiserum to erythropoietin, indicating that the effects of bilirubin is erythropoietin dependent. Nephrectomy was also shown to markedly antagonize but not completely block the erythropoietic effects of bilirubin in rats.

Effects of Posterior Hypothalamic Stimulation on Reticulocyte Release and Bone Marrow Microcirculation

Summary Posterior hypothalamic stimulation in rabbits was found to produce a significant increase in blood reticulocytes as well as a slight increase in hematocrit. The increase in reticulocytes and hematocrit following hypothalamic stimulation were not seen during the control or sham-operated periods. Atropine was found to block the reticulocyte response to hypothalamic stimulation. During 24 hr continuous posterior hypothalamic stimulation vasoconstriction and a reduced number of vessels with blood flow in the bone marrow microvasculature were seen during the first hour of stimulation, while by 24 hr vasodilatation and an increase in the number of vessels with blood flow was observed. These changes in the bone marrow circulation were associated with a significant increase in blood reticulocytes during hypothalamic stimulation. These studies suggest the existence of a neurovascular mechanism for the rapid release of stored reticulocytes from marrow sinusoids of the bone marrow.

Enhancement of the erythropoietic response of cats to hypoxia following removal of the carotid body.

Summary Plasma erythropoietin levels in carotid body-ablated cats exposed to hypoxia (0.50 atm for 18 hr) 48 hr after removal of the carotid bodies were significantly higher than that of sham-operated controls exposed to the same degree of hypoxia. The mean plasma ESF levels in the carotid body-ablated group (1.29 ± 0.16 units/ml of plasma) were significantly (p < 0.05) higher than that of sham-operated controls (0.74 ± 0.11 units/ml of plasma). However, plasma ESF levels in cats exposed to hypoxia 2 wk after carotid body ablation or sham-operation were not significantly different. The present studies indicate that removal of the carotid bodies in cats enhances the erythropoietic response to hypoxia.

Antagonism of erythropoietin production in rabbits by atropine.

Summary Atropine was found to inhibit the elevation in plasma ESF levels in rabbits following exposure to hypoxia. The effects of ESF on radioactive iron incorporation in red cells of polycythemic mice was not modified by atropine. The dosage of atropine used in these studies was sufficient to antagonize the muscarinic effects of acetylcholine but not the ganglionic stimulating properties of DMPP on arterial blood pressure in rabbits. The present studies suggest a cholinergic mechanism in the erythropoietic response to hypoxia.