The liver is a major site of production of circulating levels of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBPs). We have used primary cultured rat hepatocytes maintained under serum free conditions to explore the regulatory role of various hormones on hepatic IGF-I and IGFBP-1 mRNA levels. / IGF-I mRNA levels were stimulated 2.0 to 2.5 fold by bovine growth hormone (bGH) and 1.8 to 2.0 fold by glucagon but on combining bGH and glucagon, a synergistic effect was observed and IGF-I mRNA level was augmented 10 to 12 fold. Octreotide blocked the hGH induced stimulation of IGF-I production in serum and hepatic IGF-I mRNA levels in hypophysectomized rats. This effect could have been partly due to the low levels of glucagon in serum when hypophysectomized rats were treated with hGH and octreotide. Octreotide was also found to inhibit GH stimulated IGF-I mRNA levels in rat hepatocytes. / The unique synergy observed with glucagon and bGH on IGF-I mRNA levels in hepatocytes was not reproduced by T$ sb3$, oPRL, dexamethasone, EGF or insulin when each was added in combination with bGH or glucagon. Like glucagon, the addition of IBMX or (Bu)$ sb2$cAMP stimulated IGF-I mRNA levels 1.8 to 2.0 fold, but in the presence of bGH, IGF-I mRNA levels were stimulated 10 to 12 fold. PMA stimulated IGF-I mRNA levels 1.2 to 1.4 fold but displayed no synergism when added with bGH. The stimulatory effect of bGH plus glucagon on IGF-I mRNA levels was inhibited in PKC depleted cells, in the presence of inhibitors of PKC and in the presence of cycloheximide. bGH had no posttranscriptional effect on IGF-I mRNA stability whereas glucagon or (Bu)$ sb2$cAMP stabilized IGF-I mRNA at a posttranscriptional level. / In summary, the major hormonal regulators of hepatic IGF-I mRNA levels appear to be GH and glucagon. Hepatic IGF-I mRNA levels are regulated by pathways involving protein kinase C and, protein kinase A as well as by synthesis of one or more protein(s). / Glucagon and dexamethasone each stimulated IGFBP-1 mRNA levels 3 to 4 fold whereas bGH and T$ sb3$ each inhibited IGFBP-1 mRNA levels 45 to 70%. Insulin, which inhibited IGFBP-1 mRNA levels 95%, was the most powerful inhibitor and was also found to inhibit IGFBP-1 mRNA levels in the presence of dexamethasone. IBMX and (Bu)$ sb2$cAMP stimulated IGFBP-1 mRNA levels 6 to 8 fold whereas PMA inhibited IGFBP-1 mRNA levels 40 to 50%. The inhibitory effect of bGH on IGFBP-1 mRNA levels was abolished in PKC depleted cells and also in the presence of inhibitors of PKC. In the presence of cycloheximide, IGFBP-1 mRNA was superinduced by bGH. bGH had no posttranscriptional effect on IGFBP-1 mRNA whereas glucagon and (Bu)$ sb2$cAMP stabilized IGFBP-1 mRNA at a postranscriptional level. / In summary, bGH, T$ sb3$ and insulin inhibited whereas dexamethasone and glucagon stimulated IGFBP-1 mRNA levels in hepatocytes. Effect of glucagon may be via elevation of cAMP levels, whereas the effect of bGH may be via activation of PKC levels. The inhibitory effect of bGH appears to require synthesis of one or more protein(s) besides stimulation of PKC levels.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41300 |
| Date | January 1993 |
| Creators | Kachra, Zarin |
| Contributors | Posner, Barry I. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001351439, proquestno: NN91836, Theses scanned by UMI/ProQuest. |
Page generated in 0.0016 seconds