Esmail D. Zanjani

Renal Erythropoietic Factor: Role of Ions and Vasoactive Agents in Erythropoietin Formation

Evidence is provided for the existence of a renal erythropoietic factor, devoid of vasopressor activity, which upon interaction in vitro with normal serum yields erythropoietin. When undialyzed serum is used, erythropoietin inactivation develops in the incubation mixtures, and this inactivation appears to be dependent on an enzymatic component in preparations of the factor and on ions in serum.

Renal mechanisms underlying actions of androgen and hypoxia on erythropoiesis.

Summary The appearance of increased quantities of ESF in the sera of rats following androgen administration or exposure to hy-poxia has been related to increased amounts or activity of the renal erythropoietic factor (REF). Plethora induced in rats by hyper-transfusion results in a marked decrease in REF activity in response to androgen or hypoxia. This is proposed as the mechanism by which plethora inhibits the production of ESF.

The Renal Erythropoietic Factor (REF). III. Enzymatic Role in Erythropoietin Production.

Summary The properties of the renal erythropoietic factor (REF)-serum reaction, in which ESF is generated in vitro, are described. The amount of serum substrate converted to ESF in a given time is proportional to the REF concentration, when the serum level is kept relatively high and constant. Reaction rate is also directly dependent on serum concentration. The production of ESF as a function of time of incubation of the REF with serum, conforms to a first-order reaction. The data support the contention that the REF is an enzyme which acts on a substrate present in normal serum to produce the ESF.

Stimulation of erythropoiesis by cyclic adenosine monophosphate

Abstract CYCLIC AMP stimulated the incorporation of radioiron by the red blood cells in polycythemic mice. This effect was potentiated by prior incubation of cyclic AMP with dialyzed rat serum and was partially abolished in vivo , but not in vitro , by anti-erythropoietin. These experiments suggest both direct and indirect stimulatory effects of cyclic AMP on erythropoiesis.

The Renal Erythropoietic Factor (REF) VII. Relation to Sex Steroid Hormone Effects on Erythropoiesis

Summary Previous observations that testosterone incrases production of the ESF and the REF are confirmed and extended. The combination of testosterone and hypoxia act synergistically in augmenting plasma ESF and REF activities. The depressive effect of estradiol on ESF production is not accompanied by a decrease in REF activity. However, the serum from estradiol-treated rats exhibits a reduced capacity to serve as a substrate for the REF in the generation of the ESF.

The Renal Erythropoietic Factor (REF). IV. Distribution in Mammalian Kidneys.

Summary The REF has been demonstrated in the kidneys of rats, rabbits, dogs, sheep, pigs and humans. In these 6 species, approximately equal quantities of the REF were found in the renal cortical and medullary tissues. Exposure of rats to hypoxia induced an increase in both cortical and medullary REF activity.

The Renal Erythropoietic Factor (REF) X. The Question of Species and Class Specificity

Summary Incubation of hypotonic extracts of the light-mitochondrial fraction of kidneys from mammalian sources with sera of several vertebrate species resulted in the generation of erythropoiesis-stimulating activity only when duck or mammalian serum was used. Similar extracts of kidneys from carp, frogs, and ducks failed upon incubation with sera from the same species or from mammalian sources to generate an ESF active in the mammalian assay system. Incubation studies also revealed that no species specificity with regard to the REF-serum interaction existed among the members of the Class Mammalia tested.

The renal erythropoietic factor (REF). IX. Its subcellular distribution.

Summary The appearance of the REF in the light mitochondrial and microsomal fractions of rat kidney was studied during a continuous 22.5 hr exposure to hypoxia. Within 15 min a depletion of the REF occurred in the microsomal fraction (105,000g) but ESF-generating activity was detectable at this time in the light mitochondrial fraction (21,000g). Beginning with 1 hr of hypoxia, REF activity reappeared in the microsomal but decreased in the light mitochondrial fraction. At 10 hrs, REF activity was again present in the light mitochondrial but not in the microsomal fraction. With further exposure, the REF was again evident in both fractions up to 22.5 hr. Plasma ESF values rose steadily from hours 2 to 10 followed by a decrease at hour 15 and a secondary rise at 22.5 hours. It is suggested that the REF is generated in the microsomal fraction from which the factor is transported to the peroxisomes contained within the light mitochondrial fraction.

Mechanisms of Leukocyte Production and Release IX. Kinetics of Leukocyte Release in Leukocytapheresed Rats

Summary Leukocyte release was studied in normal rats and in rats subjected to massive leukocyte withdrawal via peritoneal lavage (leukocytapheresis, LAP) using 3HT autoradiography. A significant difference in the emergence time of neutrophils in LAP rats, when compared to normal rats, was observed after flash labeling with 3HT. Peak neutrophil labeling in LAP animals occurred on day 2 following isotope injection, whereas in normal (non‐LAP) animals the peak was seen on days 3‐4. Thus, large numbers of neutrophils entered the peripheral circulation of LAP animals 1‐2 days earlier than normal.

Renal Erythropoietic Factor (REF). VIII. Effect of Exogenous Erythropoietin (ESF) on the endogenous production of the ESF and REF

Abstract Large doses of erythropoietin (ESF) injected into rats inhibit the rise in endogenous ESF induced by hypoxia. No significant alterations in activity of the renal erythropoietic factor (REF) accompany this depressive action on endogenous ESF. A possibility requiring testing is that the negative feedback action of ESF is exerted on the plasma substrate for the REF.