Biomedical subjects
Publications and source records attributed to M Comer.
The case is reported of a man with Felty's syndrome in whom digital cutaneous vasculitis developed after a splenectomy. This may be a coincidental occurrence but a possible mechanism is suggested by which the splenectomy may have modified the immunopathology of the disease.
Temporary remission of scleroderma during the successful treatment of an associated malignant lymphoma by chemotherapy is reported in a patient with systemic sclerosis and mixed connective tissue disease. There is a well established relation between malignant disease and polymyositis/dermatomyositis but no overall association with systemic sclerosis or mixed connective tissue disease. Reports of the coexistence of malignancy and systemic sclerosis, however, emphasise a close temporal relation in their occurrence. A review of published work has identified several postulated mechanisms for this relation which may explain the response to chemotherapy.
To clarify the roles of glucose and insulin in the regulation of the PL receptor in fetal and maternal sheep liver, we administered iv glucose to pregnant ewes during a 72-h fast. The binding of ovine PL (oPL) to hepatic membranes from glucose-infused ewes and their fetuses was compared with the binding of oPL to tissues of fasted, saline-infused sheep and sheep fed normally ad libitum. Fasting of pregnant ewes caused a 58-70% reduction in the number of PL receptors in fetal and maternal liver. Intravenous administration of glucose during fasting increased the number of PL receptors in fetal liver by 137.4%. In contrast, glucose administration during fasting had no effect on the number of PL receptors in maternal liver. The number of PL binding sites in fetal liver correlated positively with fetal weight (r = 0.59) and length (r = 0.54) and with fetal plasma glucose (r = 0.69) and insulin (r = 0.55) concentrations. In contrast, PL binding was inversely related to fetal plasma oPL concentrations (r = -0.70). These findings suggested that glucose, insulin, and/or oPL may regulate PL binding in the ovine fetus. To determine whether glucose or insulin exert direct effects on the PL receptor in ovine fetal tissues, we examined the binding of radiolabeled oPL to ovine fetal hepatocytes and fibroblasts in culture. The specific binding of oPL to fetal hepatocytes was low and variable (1.0 +/- 0.5%) and it was not possible to assess reliably the effects of glucose or insulin supplementation. The specific binding of oPL to fetal fibroblasts (5.4 +/- 0.6%/mg) was unaffected by variations in media glucose concentrations (5.5-16.5 mM) or by pretreatment with insulin (10-1000 ng/ml). The results of these studies demonstrate that glucose and other nutritional factors regulate the expression of the PL receptor in fetal and maternal sheep liver. Alterations in PL binding play roles in the metabolic adaptation of the mother and fetus to nutritional deprivation and stress.
In a recent study we demonstrated that fasting of the pregnant ewe reduces the number of placental lactogen (PL) receptors in fetal sheep liver. In the present study we examined the effects of a 72-h fast on the number and affinity of PL receptors in maternal sheep liver. Fasting caused a 57% reduction in the number of hepatic ovine PL receptors; this effect was reversed by refeeding. There were no changes in the affinity of the PL receptor, the subunit structure of the receptor, or the extent of occupancy of the receptor by endogenous circulating maternal hormones. The number of hepatic PL receptors was correlated positively with the maternal plasma concentrations of glucose and insulin, suggesting that these factors may regulate PL binding to maternal tissues during pregnancy. In addition, PL receptor number was correlated positively with maternal plasma insulin-like growth factor I (IGF-I) concentrations, suggesting that a reduction in hepatic ovine PL binding may contribute to the reduction in maternal IGF-I during fasting. Fasting produced a 72% reduction in the number of ovine growth hormone receptors in maternal liver and an 83% increase in hepatic insulin binding. These findings indicate that fasting of the pregnant ewe reduces the number of PL receptors in maternal and fetal liver. The reduction in PL binding may contribute to maternal and fetal hyposomatomedinemia and may play a role in the pathogenesis of the intrauterine growth retardation that accompanies maternal nutritional deprivation.
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Recent findings from this laboratory suggest that the biological actions of placental lactogen (PL) in mammalian fetal tissues are mediated through binding of the hormone to a distinct and unique PL receptor. We have now purified this receptor from fetal and maternal sheep liver, characterized its binding to PL, growth hormone (GH), and prolactin (PRL), and determined its molecular weight by SDS-PAGE and by affinity cross-linking techniques. Soluble extracts containing specific, high-affinity (Kd 0.5 nM) PL binding activity were prepared by incubating ovine fetal and maternal liver microsomes with 1% Triton X-100. The detergent solubilized PL receptor was purified two- to threefold by ion-exchange chromatography and an additional twofold by gel exclusion chromatography on Sepharose 6B. The PL receptor was then purified 75,000- to 125,000-fold by affinity chromatography using a column of ovine PL (oPL) coupled to Affi-Gel 10. The molecular weight of the oPL receptor as determined by SDS-PAGE and by cross-linking techniques was 44,000 +/- 2,000 (range 40,000-48,000). The purified receptor bound 125I-oPL specifically and with high affinity (Kd 0.5 nM) but did not bind either radiolabeled ovine GH or ovine PRL. In addition, in competition studies using 125I-oPL as the radioligand, the purified PL receptor bound unlabeled oPL with a potency 30-50 times greater than that of ovine GH and 500-1,000 times greater than that of ovine PRL. These findings demonstrate the presence of a specific PL receptor in fetal and maternal sheep liver. The PL receptor, together with the GH and PRL receptors, constitute a family of distinct but related hormone receptors that differ in their relative affinities for PL, GH, and PRL. Changes in the expression of the three receptors may mediate changes in the hormonal control of growth during the transition from fetal to postnatal life.
We have recently identified and purified from fetal liver a distinct receptor that mediates the effects of placental lactogen (PL) on amino acid transport, glycogen synthesis, and somatomedin production in fetal tissues. At present, the factors that regulate the number and affinity of PL receptors in the fetus are unknown. Since maternal nutrition plays a critical role in fetal metabolism and growth, we have examined the role of nutrition in the regulation of the PL receptor in fetal lambs. Pregnant ewes at 123-126 days gestation were fed ad libitum (FED), fasted for 3 days (FASTED), or fasted for 3 days and then refed for an additional 3 days (REFED). The ewes were then killed, and the binding of [125I]ovine (o) PL to hepatic microsomes from the fetal lambs was examined. Maternal fasting caused a 60-75% reduction in the specific binding of oPL to fetal liver; the effect of fasting was reversed in part by refeeding [specific binding per mg protein: FED, 11.8 +/- 2.2% (n = 8); FASTED, 2.8 +/- 0.4% (n = 7); REFED, 7.2 +/- 2.6% (n = 3)]. The decrease in oPL binding resulted from an 80% reduction in the number of fetal oPL-binding sites (Scatchard analysis); there were no changes in the affinity of the oPL receptor (Kd, 0.6 nM), the subunit structure of the receptor, or the degree of occupancy of the receptor in vivo by endogenous fetal hormones. The specific bindings of GH (0.6%), PRL (0.3%), and insulin (35%) to fetal liver were not affected by maternal fasting, indicating that caloric restriction exerted a specific effect on oPL binding in the fetus. The number of fetal oPL-binding sites was positively correlated with the fetal liver glycogen content (r = 0.69; P less than 0.01) and the fetal plasma concentrations of glucose (r = 0.68; P less than 0.01) and insulin-like growth factor-I (r = 0.74; P less than 0.001), suggesting a role for the PL receptor in the regulation of fetal carbohydrate metabolism and growth. The number of fetal PL receptors was inversely correlated with the fetal plasma oPL concentration (r = 0.47; P less than 0.05). These studies demonstrate that fasting of the pregnant ewe reduces the number of PL receptors in ovine fetal liver. The reduction in fetal hepatic PL receptors may contribute to the mobilization and depletion of fetal liver glycogen stores and may play a role in the pathogenesis of the fetal growth retardation that accompanies maternal caloric deprivation.
Previous studies from this laboratory provided evidence for the existence of a specific placental lactogen (PL) receptor in tissues of fetal lambs and pregnant sheep. The PL receptor is structurally and functionally distinct from somatotropic (GH) and lactogenic (PRL) receptors, and there are conspicuous differences in the expression of the three receptors during ontogeny. The results of the present study indicate striking differences in the solubilization of PL- and GH-binding sites in maternal and fetal sheep liver. Radiolabeled ovine PL (oPL) bound specifically and with high affinity (Kd, 0.97 nM) to soluble detergent extracts of ovine fetal liver, but there was no specific binding of radiolabeled ovine GH (oGH) or oPRL to soluble extracts or insoluble fractions of fetal liver. When liver microsomes of pregnant sheep were extracted with Triton X-100, 80% of the [125I]oPL-binding sites were recovered in the soluble fraction, but 76% of the [125I]oGH binding sites were recovered in the insoluble pellet. Soluble extracts of maternal liver had high affinity for oPL (Kd, 1.45 nM), but low affinity for oGH (Kd 33 nM) and oPRL (Kd, 1-2 microM). On the other hand, Triton-insoluble fractions of maternal liver had high affinity for oGH (Kd, 0.95 nM) as well as oPL (Kd, 0.91 nM), but low affinity for oPRL (Kd, 1-2 microM). The subunit structure of the [125I]oPL-binding site in soluble fractions of fetal and maternal liver (mol wt, 38-47K) was distinct from that of the [125I]oGH-binding site in Triton-insoluble fractions of maternal liver (mol wt, 54/118K). These findings indicate that treatment of microsomal fractions of fetal and maternal sheep liver with Triton X-100 solubilizes the oPL receptor but not the oGH receptor. The differential solubilization of PL- and GH-binding sites may facilitate purification of the two distinct receptors and clarification of their respective roles in the regulation of fetal and postnatal growth.
To determine whether epidermal growth factor (EGF) or EGF-like transforming growth factors (TGFs) are present in ovine fetal tissues, we have tested acid-ethanol extracts of ovine fetal kidney for the ability to induce anchorage-independent growth of normal rat kidney fibroblasts in soft agar and to compete with 125I-mouse EGF for binding to receptors in sheep liver. The fetal kidney extract (20-1000 micrograms protein/ml) stimulated a dose-dependent increase in the number of soft agar colonies of normal rat kidney cells. Approximately 70% of these colonies measured greater than or equal to 3100 microM2. The fetal kidney extract was dissolved in 1 M acetic acid and chromatographed on Bio-Gel P 10. Two peaks of TGF-like activity, with approximate MW 14.5K (peak 1) and 9K (peak 2), eluted from the column. Half-maximal effects of pooled peaks 1 and 2 on colony formation were achieved using 100 and 20 micrograms protein/ml, respectively. Peaks 1 and 2 also competed with 125I-mouse EGF for binding to EGF receptors in ovine fetal liver but had no activity in a homologous mouse EGF radioimmunoassay sensitive to 15 pg mouse EGF. Neither TGF activity nor EGF receptor binding activity was detected in Bio-Gel fractions co-eluting with 125I-mouse EGF. Specific 125I-EGF binding sites in fetal liver were detected as early as midgestation, and the number of EGF binding sites increased markedly in late gestation, exceeding the number of EGF binding sites in the livers of pregnant ewes. These findings demonstrate the presence of TGF-like activity in ovine fetal kidney and high affinity EGF receptors in ovine fetal liver.(ABSTRACT TRUNCATED AT 250 WORDS)
To determine whether there are structural differences between the binding sites for placental lactogen (PL) and GH, we have compared the molecular weights of complexes formed by the covalent cross-linking of [125I]ovine (o) PL and [125I]oGH to hepatic membranes from fetal and pregnant sheep in mid- and late gestation and from postnatal nonpregnant sheep at 3 days to 7 months of age. Specific [125I]oPL binding sites in fetal liver were detected as early as midgestation, and cross-linking of [125I]oPL to fetal hepatic membranes yielded a major radiographic band with a mol wt of 60 +/- 5 K (mean +/- SD). Unlabeled oPL at low concentrations (0.9-9 nM) specifically competed with [125I]oPL for binding to the 60 K complex. In contrast, oGH and oPRL competed for binding to the 60 K complex only at much higher concentrations (greater than or equal to 90 nM). In addition, no specific cross-linking of [125I]oGH or [125I]oPRL to fetal hepatic membranes was observed. These findings suggest the presence of a distinct and unique PL binding site in ovine fetal liver. Since the mol wt of oPL is 22 K, the estimated mol wt of the oPL receptor protein is 38 +/- 5 K. During the first week after birth, there was a striking increase in the number of [125I]oGH binding sites. Cross-linking of [125I]oGH to postnatal liver yielded radiographic bands with apparent mol wts of 75 K and 140 K. The relative potencies of oPL, oGH, and oPRL in competing for binding to the 75 K and 140 K complexes were similar to the relative potencies of these hormones in competing for [125I]oGH binding sites in postnatal liver, suggesting that the 75 K and 140 K bands represent subunits of the oGH receptor bound covalently to [125I]oGH. Cross-linking of [125I]oPL to pregnant and postnatal nonpregnant liver yielded three radiographic bands with mol wts of 60 K, 75 K, and 140 K. The intensities of all three bands were reduced by low concentrations (0.9-9 nM) of oPL. Higher concentrations of oGH abolished the 75 K and 140 K bands but reduced the intensity of the 60 K band by only 20-30%. oPRL had minimal effect on band intensities. These observations suggest the presence of two functionally and structurally distinct receptors in pregnant liver: the oPL receptor, which has high affinity for oPL and low affinity for oGH and oPRL.(ABSTRACT TRUNCATED AT 400 WORDS)
To determine whether changes in the relative biological potencies of ovine placental lactogen (oPL) and ovine growth hormone (oGH) during development derive from ontogenetic changes in the binding of these hormones to hepatic receptors, we have compared the binding of 125I-oPL and 125I-oGH to hepatic membranes from fetal lambs and pregnant sheep at mid- and late gestation and from postnatal sheep at 1 day to 7 mo of age. Specific high-affinity 125I-oPL binding sites in ovine fetal liver were detected as early as day 70 of gestation (term = 145 days), and the number of fetal 125I-oPL binding sites increased progressively throughout the latter half of gestation, reaching a maximum (11.2 fmol/mg protein) at 3-7 days before parturition. The potency of oPL (Kd 0.27 nM) in competing for 125I-oPL binding sites was 90 and 1,300 times greater than that of oGH and ovine prolactin, respectively. Although the number of fetal 125I-oPL binding sites increased throughout pregnancy, there was little or no specific binding of 125I-oGH noted in the fetus. Treatment of fetal liver membranes with 4 M MgCl2 did not enhance the subsequent specific binding of 125I-oGH, suggesting that the low specific binding of oGH did not result from occupation of hepatic receptors by endogenous circulating oPL or oGH. In contrast, MgCL2 treatment markedly increased the apparent number of fetal 125I-oPL binding sites, suggesting that oPL receptors in fetal liver are partly saturated in vivo by oPL.(ABSTRACT TRUNCATED AT 250 WORDS)
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