Molecular and cellular endocrinology
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Mol. Cell. Endocrinol. · May 1994
Growth hormone (GH) and insulin-like growth factor-I (IGF-I) treatment of the GH-deficient dwarf rat: differential effects on IGF-I transcription start site expression in hepatic and extrahepatic tissues and lack of effect on type I IGF receptor mRNA expression.
The rat IGF-I gene consists of six exons, with exons 3 and 4 forming a 'core' mature IGF-I coding region to which alternate 5' and 3' regions are spliced. Transcription occurs from four dispersed start sites (ss) approximately 382 (ss 1), approximately 343 (ss 2), approximately 245 (ss 3) and approximately 30-40 (ss 4) basepairs (bp) from the 3' end of exon 1, and from a region 50-70 bp from the 3' end of exon 2. The expression of ss mRNAs displays tissue-specific and ontogenic regulation. ⋯ In summary, start site-specific regulation by GH was observed in kidney. GH increased IGF-I mRNA expression in muscle, kidney and liver, but had no effect in heart or spleen in the dw/dw rat. Our data suggest that systemic IGF-I can feedback on hepatic and renal IGF-I mRNA expression in the GH-deficient state.
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Mol. Cell. Endocrinol. · Mar 1991
Evidence against a role for insulin-like growth factor II in the autonomous growth of rat 18,54-SF cells.
The 18,54-SF rat cell line multiplies in serum-free medium and has been reported to produce insulin-like growth factor II (IGF-II) and to possess IGF-II/mannose 6-phosphate (Man-6-P) receptors, raising the possibility of autocrine growth stimulation by IGF-II acting through this receptor. When serum-free medium was changed every 24 h the 18,54-SF cells multiplied at the same rate as when the medium was not changed. An antibody (No. 3637) which blocks the binding of IGF-II to the IGF-II/Man-6-P receptor did not decrease or increase the growth rate of the 18,54-SF cells when medium was changed every 24 h. ⋯ When the medium was replaced every 12 h, cells in the periphery of the cultures gradually became nonviable as assessed by trypan blue uptake. However, the percentage of cells synthesizing DNA in the center of the cultures (approximately 50% during a 3 h pulse with tritiated thymidine) was the same whether the medium was changed every 12 h or left unchanged. Addition of IGF-I or IGF-II to the fresh medium change every 12 h did not increase the percentage of cells synthesizing DNA.
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Mol. Cell. Endocrinol. · Sep 1990
Acetylcholine stimulates cortisol secretion through the M3 muscarinic receptor linked to a polyphosphoinositide-specific phospholipase C in bovine adrenal fasciculata/reticularis cells.
Zona fasciculata/reticularis (ZFR) cells, isolated from the bovine adrenal cortex, secreted cortisol in response to acetylcholine (AcCh). The response was present in freshly isolated cells and in cells maintained in primary culture, reaching a maximum after 48-72 h and thereafter declining. Cells maintained in primary culture for 72 h secreted cortisol with an ED50 at 1.2 x 10(-6) M. ⋯ These observations indicate that AcCh promotes rapid activation of a Ca2(+)-independent and polyphosphoinositide-specific phospholipase C, and that the Ins(1,4,5)P3 formed releases Ca2+ from an intracellular pool. The stimulation by AcCh of this signal transduction mechanism is consistent with our conclusion, based on the effects of the selective muscarinic agonist and antagonist on cortisol secretion, that the AcCh receptor is of the M3 subtype. We conclude that AcCh, acting through an M3 receptor coupled to phospholipase C, regulates cortisol secretion at the cellular level in bovine adrenal ZFR cells.