Hormonal Stimulation of Erythropoietin Production

(Ep) production was studied in control and nephrectomized sheep fetuses beginning at about 100 d of gestation. Fetuises were given injections of either 1.2 mg/d x 13 of L-T4, 12 mg, once every 5 d x 3 of DT or the vehicle alone. Fetal plasma samples for Ep determinations were obtained before and at intervals after the start of the treatment. Retictulocyte and hematocrit levels, and the percent erythrocyte-59Fe uptake values were used to assess erythropoiesis in each fetus. No Ep was detected in plasmas ofcontrol fetuses, while significant amounts of Ep were present in plasmas obtained from DTand L-T4-treated intact fetuses. Bilateral nephrectomy did not diminish the Ep response to DT and L-T4. In both intact and nephrectomized fetuses, treatment with DT resulted in the production of significantly greater amounts of Ep than L-T4. The rise in Ep in all groups was accompanied by increases in reticulocytes (2.2+0.2% vs. L-T4:8.1+0.4% and DT:7.6+0.7%), percent erythrocyte-59Fe uptake (20.5 +2.9% vs. L-T4:36.7+3.8% and DT:39.1+4.0%) and hematocrit (31.2+2% vs. L-T4:41.8+3% and DT:48.6 +4.2%). The enhaniced erythropoiesis in all groups of nephrectomized fetuses was dependent upon the presence of Ep, because the adiministration of anti-Ep to these fetuses resuilted in the suppression of erythropoiesis in all thlee groups. These data demonstrate that (a) DT aind L-T4 are effective promnoters of extrarenal Ep production, thereby enhancing erythropoiesis in intact and nephrectomized fetuses; (b) DT is a stronger stimulus of extrarenal Ep formation than L-T4; and (c) Ep is required for the expression of the erythropoietic effects of L-T4 and DT. This study was presented at the 21st Annual 'Meeting of the American Society of Hematology and has been published in abstract form in 1978. Blood. 52(Suppl. 1): 219. Address reprint requests to Dr. Zanjani. Received for ptublicationt 4 Alail 1979 aind in revised form 13 July 1979. INTRODUCTION Erythropoiesis in the mammalian fetus and the adult is regulated by the hormone erythropoietin (Ep)l (1, 2). Although Ep is produced mainly by the kidneys in the normal adult (3), a numl)er of sttudies have demonstrated the existence of extrarenal sources that, when appropriately stimulated, can produce about 5-10% of the Ep normally evoked in intact adults (4). The most important extrarenal source of Ep in the adult is the liver (5). By contrast, the liver represents the primary source of Ep during fetal and early neonatal periods (6, 7). The production of Ep by the liver in the fetus-newborn is regulated by mechanisms similar to those that control renal Ep production in the adult (6, 7). Thus hypoxia represents the fundamental erythropoietic stimulus for both organs (7). The switch from hepatic to renal production of Ep, which occurs soon after birth, is accompanied by the effective loss of hepatic Ep formation. It is likely that the decline in hepatic Ep production is associated with increased maturity of the liver. However, the possibility that renal Ep exerts a suppressive influence on this aspect of liver function can not be ruled out. The decreased hepatic Ep production is apparent from the observations that an adequiate rate of erythropoiesis is not maintained in renoprival adults (8, 9). Thus anemia is a fairly constant feature of renal dysfunction in man (10, 11). Although erythrocyte abnormalities, chronic blood loss, deficiencies in certaini essential elements re(quired for heme synthesis, and inhibitors of erythropoiesis may be contributing factors, it is generally suspected that the underlying cause of the anemia in this disorder is a decrease in Ep production (11, 12). A recent study employing plasma concentrates (13) has showni the presence of detectable levels of Ep in anephric patients (14). However, the levels were significantly below those found in uiremicnephric patients with comparable degree of anemia. ' Abbreviations used in this paper: DT, testosterone cyclopentyl propionate (depo-testosterone); Ep, erythropoietin; L-T4, L-thyroxin. J. Clin. Invest. (D The American Society for Clinical Itnvestigation, Inc. 0021-9738/79/11/1181107 $1.00 Voluime 64 Novemnber 1979 1181-1187 1181 Reactivation ofhepatic Ep formation can be achieved by exposure of the nephrectomized adult to hypoxiaproducing stimuli (4, 15). However, studies with laboratory animals have shown that the intensity of hypoxia needed to activate the extrarenal site is significantly greater than that required by the kidneys (15). Stimulation of hepatic Ep formation in renoprival adults is of considerable clinical interest because it may provide a more physiological approach to the treatment of the anemia in these individuals; normalization of erythropoiesis in uremic-anemic rats with chronic administration of Ep has been demonstrated (16). Androgens have been employed in the treatment of the anemia in some patients with chronic renal failure (17-20). The therapy has been generally more effective in patients with residual renal tissue (19), but certain of the androgenic compounds have also been effective in some anephric patients receiving adequate hemodialysis (18). In some patients with chronic renal failure (with or without residual renal tissue) the androgeninduced erythropoietic stimulation was accompanied by an increase in circulating Ep levels, whereas increased Ep levels were not demonstrated in others (17-19). It is probable that in the latter group of patients, enhanced erythropoiesis was also associated with increased Ep production, which the relative insensitivity of the bioassay did not detect. It is now firmly established that the erythropoietic effect(s) of androgens is mediated, at least in part, through increased production of Ep (21-23). Studies employing nephrectomized adult animals have shown that this effect is dependent on the presence of kidneys (24). However, the efficacy of androgens in promoting extrarenal Ep formation was not determined in these studies partly because the experimental models used (usually rats) did not allow for adequate evaluation. In the present study, we have employed the sheep fetus as an animal model for the study of factors influencing the production of extrarenal Ep. Chronic fetal sheep preparations have been employed extensively in the study of fetal growth and developmental physiology and have proven particularly suitable for the study of mechanisins regulating fetal erythropoiesis. Specifically, we have examined the effects of two well-established erythropoietic agents (testosterone and thyroxin) on hepatic Ep formation in the presence and absence of the kidneys. Because ofthe unique position ofthe fetus, which permits relatively long-term observations, we have been able to assess the efficacy ofthese two agents in promoting extrarenal Ep formation in anephric fetuses. The results demonstrate that testosterone and thyroxin stimulate hepatic Ep production, thereby enhancing erythropoiesis in the anephric fetus.