Isoproterenol Stimulation of Heme Synthesis in Cultures of Human Fetal Liver from Early Gestation Departments of Biochemistry and Experimental Medicine, McGill University and the Royal Victoria Hospital, Montreal, Quebec, Canada H3A 1A1 ABSTRACT. The role of isoproterenol in the synthesis of heme associated with hemoglobin has been studied in primary cultures of human fetal liver. This drug (10~10M) stimulated the incorporation of 59Fe into heme associated with hemoglobin in cell cultures of livers obtained from human fetuses 8 to 10 weeks gestation but was inactive in cell cultures prepared from livers of older fetuses. Isoproterenol has its optimal activity at a much
I
N RECENT years the hormonal control of erythropoiesis in human fetal liver has been the subject of increasing interest among investigators (1-3). One of the most intriguing aspects of the regulation of red cell formation and hemoglobin synthesis in human fetal liver is the time during gestation when the optimal hormonal effects can be demonstrated. Basch (1) studied the erythropoietin-stimulated increase in hemoglobin synthesis in cell cultures from livers of fetuses between 6 and 22 weeks of gestation and found that the optimal response towards this hormone was in cells prepared from 16-18 week old fetuses. Hemoglobin synthesis in human fetal liver is very active before 16 weeks of gestation, which may be explained by the presence of erythropoietinindependent stem cells during early stages of development. An alternative explanation is that the cells during early fetal development are under direct regulation of erythropoietic factors of endodermal origin not as yet fully characterized (4-6), or that the cells may be activated to the stage of erythroid differentiation by hormones other than erythropoietin. This seems to hold true for Received April 29, 1976. Supported by grants from the Medical Research Council of Canada (MT-1658) and the U.S. Public Health Service (HDO-4365). L.F.C. is a Scholar of the Medical Research Council of Canada.
earlier time in gestation than that previously reported for testosterone or erythropoietin. The interpretation of these results is that there is present a cell population in human fetal liver early in gestation with the appropriate isoproterenolreceptors and capable of erythroid differentiation after exposure to the drug. (Endocrinology 100: 1303, 1977)
testosterone, because this steroid hormone is known to stimulate the synthesis of heme associated with hemoglobin in fetal liver cells at 11-13 weeks gestation. The possible explanation for this early action may be the presence of a large population of testosterone-sensitive erythroid cells at 11-13 weeks gestation. Erythropoietin and testosterone have not only different effects during development but also seem to act on erythroid cells by different mechanisms (7). Both hormones act independently of cAMP (8-10). Since dibutyryl cAMP stimulates heme synthesis in erythroid cells (2) it was of interest to know whether a cAMP-dependent differentiation process in liver erythroid cells could be detected at a gestation period different from that where the optimal effects of erythropoietin and testosterone are observed. We did not test the direct action of dibutyryl cAMP because it may enter and activate cells which do not have the membrane receptors for a cAMPdependent hormone or drug. On the other hand, the role of dibutyryl cAMP in erythyroid cell differentiation is not clear because of the observations of Leder et al. (3) who showed that butyric acid stimulates differentiation in erythroleukaemic cells. Because of these considerations we decided to test the action of isoproterenol, one of the most potent hematopoietic-stimulating factors described (11,12). Its actions as a
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L. F. CONGOTE AND SAMUEL SOLOMON
Endo • 1977 Vol 100 • No 5
CONGOTE AND SOLOMON
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TABLE 1.59Fe incorporation into heme associated with hemoglobin in primary cultures of human fetal liver cells after treatment with different concentrations of DL-isoproterenol
(M)
dpm ± SEM
Ratio of treated cells/controls (paired experiments)
0 10-'3 lo -io 10-« io-«
18,700 ± 1,300(10) 19,800 ± 1,300 (8) 23,900 ± 1,800(10) 26,900 ± 3,700 (8) 18,000 ± 1,000 (8)
— 1.06 ±0.07 (8) 1.27 ±0.10(10) P
I
N RECENT years the hormonal control of erythropoiesis in human fetal liver has been the subject of increasing interest among investigators (1-3). One of the most intriguing aspects of the regulation of red cell formation and hemoglobin synthesis in human fetal liver is the time during gestation when the optimal hormonal effects can be demonstrated. Basch (1) studied the erythropoietin-stimulated increase in hemoglobin synthesis in cell cultures from livers of fetuses between 6 and 22 weeks of gestation and found that the optimal response towards this hormone was in cells prepared from 16-18 week old fetuses. Hemoglobin synthesis in human fetal liver is very active before 16 weeks of gestation, which may be explained by the presence of erythropoietinindependent stem cells during early stages of development. An alternative explanation is that the cells during early fetal development are under direct regulation of erythropoietic factors of endodermal origin not as yet fully characterized (4-6), or that the cells may be activated to the stage of erythroid differentiation by hormones other than erythropoietin. This seems to hold true for Received April 29, 1976. Supported by grants from the Medical Research Council of Canada (MT-1658) and the U.S. Public Health Service (HDO-4365). L.F.C. is a Scholar of the Medical Research Council of Canada.
earlier time in gestation than that previously reported for testosterone or erythropoietin. The interpretation of these results is that there is present a cell population in human fetal liver early in gestation with the appropriate isoproterenolreceptors and capable of erythroid differentiation after exposure to the drug. (Endocrinology 100: 1303, 1977)
testosterone, because this steroid hormone is known to stimulate the synthesis of heme associated with hemoglobin in fetal liver cells at 11-13 weeks gestation. The possible explanation for this early action may be the presence of a large population of testosterone-sensitive erythroid cells at 11-13 weeks gestation. Erythropoietin and testosterone have not only different effects during development but also seem to act on erythroid cells by different mechanisms (7). Both hormones act independently of cAMP (8-10). Since dibutyryl cAMP stimulates heme synthesis in erythroid cells (2) it was of interest to know whether a cAMP-dependent differentiation process in liver erythroid cells could be detected at a gestation period different from that where the optimal effects of erythropoietin and testosterone are observed. We did not test the direct action of dibutyryl cAMP because it may enter and activate cells which do not have the membrane receptors for a cAMPdependent hormone or drug. On the other hand, the role of dibutyryl cAMP in erythyroid cell differentiation is not clear because of the observations of Leder et al. (3) who showed that butyric acid stimulates differentiation in erythroleukaemic cells. Because of these considerations we decided to test the action of isoproterenol, one of the most potent hematopoietic-stimulating factors described (11,12). Its actions as a
1303
Downloaded from https://academic.oup.com/endo/article-abstract/100/5/1303/2617746 by Leiden University / LUMC user on 16 January 2019
L. F. CONGOTE AND SAMUEL SOLOMON
Endo • 1977 Vol 100 • No 5
CONGOTE AND SOLOMON
1304
TABLE 1.59Fe incorporation into heme associated with hemoglobin in primary cultures of human fetal liver cells after treatment with different concentrations of DL-isoproterenol
(M)
dpm ± SEM
Ratio of treated cells/controls (paired experiments)
0 10-'3 lo -io 10-« io-«
18,700 ± 1,300(10) 19,800 ± 1,300 (8) 23,900 ± 1,800(10) 26,900 ± 3,700 (8) 18,000 ± 1,000 (8)
— 1.06 ±0.07 (8) 1.27 ±0.10(10) P
