Delayed appearance of liver growth hormone binding sites and of growth hormone-induced somatomedin production during rat development

Flández, B.; Álvarez, Elvira; Blázquez, Enrique

doi:10.1016/0006-291x(86)90873-9

Cited by 9 publications

(3 citation statements)

References 30 publications

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“…Thus, when the results were expressed per square micrometer, hormone binding was similar in both groups (41). In support of this suggestion, when insulin binding sites were studied in vivo (42,43), specific liver insulin uptake in fetuses and suckling rats was the same or greater than in adult animals. Furthermore, our results suggest that fetal hepatocytes might not generate the assumed chemical mediator of insulin action, even though fetal liver insulin receptor concentrations are significant and the subunit structure, autophosphorylation, and tyrosine kinase activity are similar to those observed in adults (44,45).…”

Section: Discussionsupporting

confidence: 71%

Insulin Does Not Induce the Hydrolysis of a Glycosyl Phosphatidylinositol in Rat Fetal Hepatocytes

Ruiz-Albusac

Zueco²,

Velázquez³

et al. 1993

Diabetes

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An inositol phosphoglycan that is the polar head group of a glycosyl phosphatidylinositol has been considered as a putative mediator of insulin action. To gain insight into the functions of this hormone during development, the relationships between insulin, insulin receptors, glycosyl phosphatidylinositol, and inositol phosphoglycan were studied. Glycosyl phosphatidylinositol was isolated and characterized in fetal liver as early as day 15 of intrauterine life. In isolated hepatocytes from fetal and adult rats labeled with [3H]glucosamine, [3H]galactose, or [3H]myo-inositol, these molecules were incorporated into glycosyl phosphatidylinositol. In hepatocytes labeled with [3H]glucosamine and then allowed to react with [1-14C]IAI, the [3H]glycosyl phosphatidylinositol was purified as the 14C-labeled amidinated lipid. Glycosyl phosphatidylinositol molecules from fetal and adult cells were sensitive to hydrolysis by a phosphatidylinositol-specific phospholipase C from B. cereus. The product of this hydrolysis inhibits the activity of a cAMP-dependent protein kinase, whereas this effect was abolished by nitrous acid deamination. In isolated hepatocytes from adult animals, an inverse correlation between extracellular insulin and the number of insulin receptors and the cellular content of glycosyl phosphatidylinositol was observed. However, in fetal hepatocytes insulin failed to reduce the glycosyl-phosphatidylinositol content when labeled either with [1-14C]isethionyl acetimidate or [3H]glucosamine, whereas insulin-like growth factor I produced a significant hydrolysis of glycosyl phosphatidylinositol. Fetal and adult hepatocytes were incubated with insulin or inositol phosphoglycan after which glycogen phosphorylase activities were determined. Inositol phosphoglycan mimicked the action of insulin on both forms of the enzyme from adult hepatocytes, whereas in fetal cells insulin did not change, and purified inositol phosphoglycan reduced the activities of glycogen phosphorylase. These findings suggest a dissociation between insulin receptor occupancy and the expected hormonal effects in fetal hepatocytes. This could be related to alterations at a postreceptor level.

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Section: Discussionsupporting

confidence: 71%

Insulin Does Not Induce the Hydrolysis of a Glycosyl Phosphatidylinositol in Rat Fetal Hepatocytes

Ruiz-Albusac

Zueco²,

Velázquez³

et al. 1993

Diabetes

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“…The dramatic increase in liver IGF-I mRNA corresponds to the onset of GH responsiveness (23)(24)(25). Those tissues that show postnatal increases in IGF-I mRNA (i.e.…”

Section: Discussionmentioning

confidence: 99%

Insulin-Like Growth Factor I Messenger Ribonucleic Acids with Alternative 5'-Untranslated Regions Are Differentially Expressed during Development of the Rat

et al. 1989

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Solution hybridization/RNase protection assays were used to study the developmental expression of insulin-like growth factor I (IGF-I) mRNA levels in rats. In liver, heart, and kidney, total IGF-I mRNA levels were low at birth and increased during the 50-day postnatal period, with liver levels increasing by over 100-fold. In contrast, stomach, muscle, and testicular IGF-I mRNA levels were highest at the earliest stages examined (late fetal or early neonatal) and declined thereafter to the levels observed in 50-day-old rats. In brain, IGF-I mRNA levels rose 2-fold during the first week of life and declined over the next 6-7 weeks. Lung IGF-I mRNA levels were highest in 20-day-old fetuses and exhibited some fluctuation during the postnatal period. Alternative splicing in the 5'-untranslated region of the primary rat IGF-I transcript gives rise to three transcripts, classes A, B, and C, which have divergent 5'-untranslated region sequences associated with a common region that encodes the mature IGF-I peptide. These sequences contain upstream in-frame translation initiation codons and may, therefore, encode alternate IGF-I prepropeptides. The class C variant was the predominant mRNA species at all stages of development studied and was the only IGF-I transcript in brain, heart, and muscle. In tissues where multiple 5'-untranslated region splicing variants occurred, therefore, changes in total IGF-I mRNA primarily reflected changes in this splicing variant. However, the class C and class A (as well as class B in liver) transcripts exhibited temporally divergent changes over some developmental intervals. Class A transcripts in the liver, stomach, testes, and lung as well as class B transcripts in liver, exhibited sustained increases from 15 or 22 postnatal days to maximal levels at 50 postnatal days. In kidney, class A transcripts also increased steadily, but beginning at an earlier stage, i.e. at 8-15 days of postnatal life. These results demonstrate that the temporal expression of total IGF-I mRNA in the developing rat occurs in a tissue-specific manner, and additionally, that IGF-I mRNA variants are differentially expressed during development.

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“…In the last days of pregnancy, the fetal pituitary gland releases greater amounts of growth hormone than in other periods of intra-and extrauterine life [4], even though the contribution of this hormone to fetal growth seems to be minimal [9]. However, growth hormone plays an important role in the maturity and growth of pancreatic islets during development by increasing DNA replication and insulin release [24].…”

Section: Discussionmentioning

confidence: 98%

Effects of triiodothyronine and bovine growth hormone on glucose transporter isoform-2 (GLUT-2) and glucokinase (GK) gene expression in pancreatic islets of fetal and adult rats

García-Flores

Blázquez

Zueco

2001

Pfl�gers Archiv European Journal of Physiology

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This study was conducted to determine the effects of triiodothyronine (T3) and bovine growth hormone (bGH) on the expression of glucose transporter-2 (GLUT-2) and of glucokinase (GK) from pancreatic islets of fetal and adult rats. Incubation of both sets of pancreatic islets with T3 did not modify GLUT-2 mRNA levels, but did reduce the content of GLUT-2 protein, while it reduced the expression of GK mRNAs in fetal and adult pancreatic islets. Treatment of fetal and adult pancreatic islets with 1 microg/ml bGH did not alter the expression of GLUT-2 mRNAs, but significantly increased GLUT-2 protein levels in adult islets by 50%. Also, bGH had no effect on the GK mRNA content of fetal and adult pancreatic islets whereas, in contrast, there was a significant reduction in the amount of GK protein in fetal islets cultured with that hormone but not in those corresponding to adult rats. These findings suggest that T3 and bGH are able to modulate the expression of GLUT-2 and GK mRNAs and proteins in pancreatic islets in a manner different from that in the liver, as previously reported by others. In addition, both hormones produced different responses in fetal and in adult pancreatic islets.

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Delayed appearance of liver growth hormone binding sites and of growth hormone-induced somatomedin production during rat development

Cited by 9 publications

References 30 publications

Insulin Does Not Induce the Hydrolysis of a Glycosyl Phosphatidylinositol in Rat Fetal Hepatocytes

Insulin Does Not Induce the Hydrolysis of a Glycosyl Phosphatidylinositol in Rat Fetal Hepatocytes

Insulin-Like Growth Factor I Messenger Ribonucleic Acids with Alternative 5'-Untranslated Regions Are Differentially Expressed during Development of the Rat

Effects of triiodothyronine and bovine growth hormone on glucose transporter isoform-2 (GLUT-2) and glucokinase (GK) gene expression in pancreatic islets of fetal and adult rats

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