The changes in the types of erythroid cells produced during embryogenesis of the chick have been correlated with the changes in the types of haemoglobins found in the embryo. Primitive erythroid cells constitute the only red blood cells of 2- to 5-day embryos. The first recognizable immature definitive erythroid cells appear in the embryonic circulation at 5 to 6 days and progressively replace the primitive cells, such that by 14 to 16 days the primitive cells constitute less than 1% of the circulating erythroid cells. Primitive erythropoiesis is strikingly different from definitive erythropoiesis. At any one time point between 2 and 16 days, all of the isolated primitive cells appear, by morphological criteria, to be at the same stage of maturation, and, although variation in cell size is observed, for an individual maturation stage, the small cells are not more mature than the medium-size cells, nor are the large cells less mature than the medium or small cells. Maturing primitive erythroid cells undergo the progressive changes in cell structure characteristic of erythroid maturation in mammalian erythropoietic systems, but do so as a uniform cell population. Haemoglobin, isolated from primitive erythroid cells of 2- to 5-day embryos, shows two components on polyacrylamide gel electrophoresis, haemoglobin E and haemoglobin P. The haemoglobin E/P ratio is constant in lysates from 2- to 5-day embryos. At 6 to 7 days when the first haemoglobinized immature definitive erythroid cells appear in the embryonic circulation, two new haemoglobin components are observed in lysates of erythroid cells. These two new haemoglobin components are electrophoretically and immunologically identical to the two haemoglobin components of adult chickens, haemoglobins A and D. As the definitive erythroid cells replace the primitive erythrocytes in the embryonic circulation, the haemoglobins A and D increase in amount and replace haemoglobin P. Haemoglobin P cannot be detected immunologically in erythroid cell lysates from 16-day embryos which contain less than 1% primitive cells. In erythroid cell lysates from late embryos, which contained few, if any, primitive erythrocytes, a minor haemoglobin, electrophoretically similar to haemoglobin E on pH 10.3 polyacrylamide gels, is consistently observed. This component differs from haemoglobin E on pH 8.9 polyacrylmide gels, on Sephadex G-100 columns, on polyacrylamide gels of different porosities, and shows a reaction of only partial identity with haemoglobin E by two-dimensional immunodiffusion. This haemoglobin component, haemoglobin H, is detectable electrophoretically in lysates from 12-day embryos and immunologically in lysates from 8-day embryos. Haemoglobin H has not been observed in adult chickens. The switch from the production of primitive to definitive erythroid cells during development of the chick embryo is associated with the initiation of synthesis of three new haemoglobins, the two adult haemoglobins and haemoglobin H. The haemoglobin D/A ratio of adult chicken haemoglobin, determined from the ratio of gel scan peak masses, is 0.30. When haemoglobins D and A first appear in erythroid cell lysates from 6- to 7-day embryos, the haemoglobin D/A ratio is about 0.9. The D/A ratio of lysates falls to 0.5 by 16 to 18 days, a time when 99% of the erythroid cells of the embryo are mature definitive erythrocytes. However, the haemoglobin D/A ratio of lysates from late embryos and young chicks of 0.5 to 20 days of age is consistently greater than that of adult chicken haemoglobin. Definitive erythrocytes of chick embryos and young chicks appear to differ from definitive cells of adult chickens in at least two ways: the presence of haemoglobin H and the higher haemoglobin D/A ratio.

The erythroid cells and haemoglobins of the chick embryo.

Although the liver is the major site of erythropoietin (Ep) production in the fetus, this function is assumed by kidneys in the adult. The mechanisms underlying the liver to kidney switch of Ep formation are not understood. We studied the natural progression of this transition in sheep by measuring Ep production in response to anemia in normal and bilaterally nephrectomized fetal and newborn sheep beginning at about 80 d gestation (normal gestation: 140 d). Removal of both kidneys before induction of anemia did not affect Ep formation up to about 120 d of gestation. A significant reduction (29%, P < 0.02) in Ep synthesis was first noted at about 130 d of gestation (initiation of switch). This level of nephrectomy-induced reduction of Ep formation persisted until about 15 d after birth. Thereafter, bilateral nephrectomy caused further significant decreases (P < 0.05) in Ep production, gradually resulting in near total absence of Ep production at about day 40 postpartum (completion of switch). Chronic administration of testosterone (12 mg/wk) or estradiole benzoate (1.5 mg/d, 5 d/wk) to the fetus/newborn beginning at 85-90 d of gestation enhanced or suppressed erythropoiesis, respectively, but failed to affect the time at which the liver to kidney switch was initiated and/or completed. By contrast, a significant delay (P < 0.001) in the onset, but not completion of the switch occurred in animals that were either thyroidectomized or rendered chronically anemic beginning in the second third of the gestation period. Administration of thyroxin (1.2 mg/d, 5 d/wk) to thyroidectomized fetus/newborns not only prevented the delay in the initiation of the switch, but also accelerated the rate at which the switch was completed. These results demonstrate that in sheep (a) the liver to kidney switch of Ep production is initiated in utero during the last third of the gestation period, but is completed after birth, (b) this transition occurs gradually; the assumption of Ep producing capacity by the kidney is not preceded by an abrupt loss of hepatic Ep formation; and (c) the switch is not affected by changes in sex hormone levels during the prenatal-postnatal growth periods, but is profoundly influenced by alterations in thyroid hormone and oxygen supply-demand levels.

/pdf/studies-on-the-liver-to-kidney-switch-of-erythropoietin-435l3q1xwg.pdf

Studies on the Liver to Kidney Switch of Erythropoietin Production

Vertebrate red Blood cells : , Vertebrate red Blood cells : , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Vertebrate red blood cells

Renal erythropoietin: Properties and production

Day time somnolence or excessive snoring, or both, occurred in five out of 11 patients with acromegaly. All five had episodes of sleep apnoea, and three had the sleep apnoea syndrome. Growth hormone concentrations were higher (p less than 0.025) in these patients than in the six patients without these symptoms. One patient with daytime somnolence and one asymptomatic patient had flow loop evidence of upper airways obstruction. Two of the patients with the sleep apnoea syndrome had cardiomegaly. Sleep apnoea appears to be common and clinically important in acromegaly, and it may be central, obstructive, or mixed. Polygraphic nocturnal monitoring is indicated to assess these patients properly.

https://www.bmj.com/content/bmj/280/6218/894.full.pdf

Sleep apnoea in acromegaly.

The regulation of red cell production in the adult animal has been shown to be governed, at least in part, by oxygen-dependent erythropoietin production by the ‘kidney. In rodents the degree of dependency on renally produced erythropoietin approaches the absolute.’ Thus the nephrectomized rat or mouse has almost complete suppression of red cell production. Changes in the oxygen supplydemand relationship have been shown to have a profound effect upon the rate of erythropoiesis. It is to be noted, however, that such perturbations in high order mammal^^,^ do not produce as marked a change in red cell production as that in the rodent. The question has been raised as to whether regulation of erythropoiesis in fetal and neonatal life is the same as that for the “ a d ~ l t ” ~ TO answer this question, the evolution of the erythron and its regulation have been studied in the fetal and neonatal rat, which is a relatively immature animal in comparison with human beings at birth, and in the guinea pig, an animrl.1 in which the degree of maturity at birth approaches that of the human being. These data will be briefly summarized and are reviewed extensively e l~ewhere .~

A. Porcellini

Papers

Fetal and neonatal erythropoiesis.