Presence of Plasma Erythropoietin in Hypoxic Rats with or without Kidney(s) and/or Spleen

Abstract

The presence of an erythropoietic factor in the plasma of animals subjected to hypoxic hypoxia has been reported recently by Stohlman( 1 ) and Prentice and Mirand( l a ) . Additional data from our laboratory bear out a time-concentration relationship of plasma erythropoietin (EPF) in hypoxic hypoxic rats. Knowing of this time-concentration of EPF, studies were carried out to determine whether this time-concentration relationship of plasma EPF can be altered in absence of the kidney (s) and/or the spleen. Jacobson et aZ. (2) reported recently that bleeding and cobalt chloride administration did not produce circulating erythropoietin in the absence of the kidneys and postulated that the kidney is the site of production of EPF. The purpose of this report is to demonstrate that hypoxic hypoxic rats with or without their kidney(s) and/or spleen can produce erythropoietin.Material and methods. Sprague-Dawley rats were placed in chambers constructed of plexiglass. Into each chamber was directed a mixture of nitrogen and oxygen, the proportions of which, along with ambient pressure, determined the simulated altitude. Flow of nitrogen and oxygen was regulated by a rotameter type of flow-meter and remained quite constant over the experimental period. The chamber 0 2 concentration was checked by reading of the oxygen and nitrogen flowmeters and also by a portable Beckman Oximeter. Random air samples were also taken from the chamber in a Douglas bag and checked with a mass spectrograph for 02, N2 and COS. Good agreement in results was obtained. A flow of approximately 5 liters/minute was maintained through the chamber and soda lime and sulfuric acid were placed in the chamber to minimize C02 and humidity levels.Sprague-Dawley rats, 2 to 3 months old, used as donors, were exposed in a chamber to an atmosphere of approximately 10% 0 2 for the time intervals shown in Table I. Rats of another group, used as donors, were nephrectomized and/or splenectomized and caution was taken during the operation that no bleeding occurred. They were then immediately placed in an atmosphere of 10% 0 2 a t various time intervals (Table 11). Food (Purina Laboratory chow) and H 2 0 were available to rats in the chamber at all times. At the end of the respective intervals the donor rats were withdrawn from the chamber and promptly exsanguinated from the dorsal aorta. A final hematocrit was done on each rat and no animal with hematocrit below 40 was used as a source of plasma. Plasma obtained was frozen and stored until used.Recipient animals were 3-month-old Sprague-Dawley rats which were used as assay animals approximately 15-20 days after hypophysectomy (3,4). They received 2 cc of donor rat plasma to be tested I.V. via the jugular vein on 2 successive days. On day 3 approximately 1 pc FeG9 was given I.V. via femoral vein and on day 4, a 24-hour FeJ9 uptake was done. The results for each group of animals were expressed as the average 24hour Fe59 uptake for the particular group.Results. The time-concen tra tion rela tionship of plasma EPF in hypo...

Decline of erythropoietin formation at continuous hypoxia is not due to feedback inhibition

“…2, top), are in accordance with previous studies employing hypobaric (1,5,17,20,22,24,26,31) or also normobaric hypoxia (22). Although the reported time intervals after which peak serum levels were reached are variable, it appears to be a consistent finding that EPO titers do not remain at the elevated levels that are reached early upon hypoxia, but despite continued hypoxic exposure decline to values that are still above base line, but severalfold below peak concentrations.…”

“…Following acute hypoxic hypoxia, an increase in renal EPO mRNA has been demonstrated after 1 h (27), and circulating EPO increases within 1.5-2 h (27). Interestingly, it has been demonstrated that EPO levels reach maximal values after 6-24 h in rodents (1,5,15,17,20,22,26,31) and within 48 h in humans (1,24) and thereafter decline despite continued hypoxia. This early decrease in EPO levels occurs before red cell mass and therewith blood oxygen content has increased significantly (1,17,20,26).…”

“…In some (l3), but not all of their experiments (14), plasma erythropoietic bioactivity in rats that were both made hypoxic and injected with EPO approximated the sum of that in animals that received EPO only and that in animals made hypoxic without receiving exogenous EPO. However, in these studies EPO was administered for no longer than 3 h before the onset of hypoxia, and animals were then exposed to continuous hypoxia for only 3 h. Because EPO levels have mainly been reported to decline 18 h or later after onset of hypoxia (1,5,17,20,22), this chosen time interval might have been too short to see an effect that could account for the reduction of EPO levels normally occurring under continuous hypoxia. In this study we injected rats with recombinant human EPO (rhEP0) either 12 h, 6 h, or immediately before a hypoxic exposure of 12 h to mimic the early increase in EPO levels and compared the endogenous EPO production following the hypoxia with that in untreated animals.…”

The Role of the Kidney in Erythropoiesis*

“…These results strongly suggest that the kidney produces an erythropoietic factor. In the rat, Jacobson and associates (16) and Goldwasser, Fried and Jacobson (30) have pointed out the lack of erythropoietic factor response to hypoxia after nephrectomy, but other workers did not obtain the same results (31). On the other hand, Erslev (27), working on the rabbit, concluded that the kidney did not play a role in erythropoietic function.…”

Hormonal stimulation of erythropoietin production and erythropoiesis in anephric sheep fetuses.

“…However, in inost species, smnall but detectable amounts of Ep are produced in the absence of both kidneys (3,4,35). The overwhelming evidence suggests that the liver is the major source of this extrarenal Ep (5,36).…”