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The effects of glucocorticoids on insulin-stimulated lipogenesis in primary cultures of rat hepatocytes.

ABSTRACT: We used primary cultures of rat hepatocytes to evaluate the effects of glucocorticoids on insulin-responsive hepatic lipogenesis. The data indicate that hepatocytes incubated for 20 h with dexamethasone (0.1 microM) alone are profoundly resistant to the ability of insulin to stimulate lipogenesis acutely. In contrast, primary cultures of hepatocytes incubated with dexamethasone plus insulin are hyper-responsive to the ability of insulin to stimulate lipogenesis chronically. This potentiation of insulin action by a glucocorticoid occurs at physiological concentrations of the two hormones. Exposure to dexamethasone plus insulin for more than 4 h is required for the two hormones to enhance insulin action either by overcoming the insulin resistance induced by dexamethasone alone or by stimulating insulin action induced by insulin alone. Despite the marked potentiation of insulin action, hepatocytes exposed to dexamethasone plus insulin are less sensitive to insulin, as demonstrated by a shift to the right in the dose-response curve for insulin-stimulated lipogenesis. The resistance of hepatocytes to the acute effects of insulin after exposure to dexamethasone alone and the potentiation of insulin action and decreased sensitivity to insulin after exposure to insulin plus dexamethasone are all mediated by post-insulin-binding events. These studies demonstrate potentiation of insulin action in the liver by physiological concentrations of glucocorticoids and may have physiological significance for the regulation of normal hepatic lipogenesis, for the hyperlipidaemia observed with the pharmacological use of glucocorticoids, and for disease states in man associated with hyperinsulinaemia and hypercortisolism.

SUBMITTER: Amatruda JM

PROVIDER: S-EPMC1152020 | biostudies-other | 1983 Apr

REPOSITORIES: biostudies-other

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Project description:AIM:To investigate the effects of electroporation on primary rat hepatocyte and to optimize the electroporation conditions introducing foreign genes into primary hepatocytes. METHODS:A single-pulse procedure was performed at low voltage (220-400 V) but with high capacitance (500-950 microF). Hepatocytes were divided into 4 groups according to the electroporation conditions: group I, 220 V and 500 microF; group II, 220 V and 950 microF; group III, 400 V and 950 microF,and group IV. The control group was freshly isolated hepatocytes and directly cultured under the same conditions as those of electroporation groups. The effects of electroporation on primary rat hepatocytes were detected by trypan blue exclusion (TBE) and MTT analysis. Besides, albumin (Alb), alanine transaminase (ALT) and lactate dehydrogenase (LDH) in the supernatants of cultured hepatocytes were measured by biochemical assay. RESULTS:Between day 1 and day 15 after incubation, primary rat hepatocytes of each electroporation group appeared normal, being the same with those of control group. TBE staining showed that slight hepatocyte damage and high survival rate were found in the electroporation groups and the control group. Cultured for 3, 7, 11 and 15 days, hepatocyte viability was approximately 92.6+/-2.5 %, 89.5+/-3.3 %, 82.0+/-3.5 % and 74.3+/-1.2 %, respectively. MTT analysis indicated that the viabilities of hepatocytes had no significant difference between each electroporation group, and those were similar to that of control group. At the 36th hour after electroporation, Alb, ALT and LDH in the supernatants of control group were 5.3+/-0.1 g x L(-1), 183.7+/-8.4 nkat x L(-1) and 896.8+/-58.5 nkat x L(-1); those of group II were 5.7+/-0.1 g x L(-1), 215.4+/-16.7 nkat x L(-1) and 1063.8+/-51.8 nkat x L(-1); and those of group III were 5.8+/-0.2 g x L(-1), 217.1+/-8.4 nkat x L(-1) and 1063.8+/-10.0 nkat x L(-1). Statistically, the proteins of group II and group III were significantly higher than those of control group (P<0.05), whereas the protein production of group I, Alb, ALT and LDH were 5.3+/-0.2 g x L(-1), 205.4+/-3.3 nkat x L(-1) and 1035.4+/-116.9 nkat x L(-1), were similar to those of control group. At the same time, TBE and MTT analysis indicated that there was no significant cell viability difference between electroporation groups and control group. CONCLUSION:This single-pulse electroporation procedure performed at low voltage (220-400 V) but with high capacitance (950 microF) is one of the optimal choices to introduce foreign genes into primary rat hepatocyte.

Project description:The present studies were undertaken to determine whether the interaction between cAMP-dependent and insulin-dependent pathways in primary cultures of rat hepatocytes affects biological functions and tyrosine phosphorylation. Quiescent hepatocytes were pretreated with dibutyryl cAMP or cAMP-generating agents such as glucagon, and then treated or not with insulin. Preincubation for 6 h with dibutyryl cAMP or glucagon enhanced the effect of insulin on DNA synthesis, but not the effect of insulin on amino acid transport or glycogen and protein synthesis. Tyrosine phosphorylation of intracellular proteins was determined by immunoblot analysis using an anti-phosphotyrosine antibody. Maximum tyrosine phosphorylation of a 195 kDa protein, which may be a substrate of insulin receptor kinase, of 175-180 kDa proteins, including insulin receptor substrate (IRS)-1, and of 90-95 kDa proteins, including the insulin receptor beta-subunit, was reached within 30 s of incubation with insulin. Pretreatment for about 3 h with dibutyryl cAMP or cAMP-generating agents clearly increased insulin-dependent tyrosine phosphorylation of the 195 kDa protein, but not IRS-1, IRS-2 or the insulin receptor beta-subunit. Because dibutyryl cAMP and cAMP-generating agents did not increase insulin receptor number or its kinase activity, the effect of cAMP on this potentiation of tyrosine phosphorylation is assumed to be exerted at a step distal to insulin receptor kinase activation. The potentiation by cAMP pretreatment of insulin-stimulated tyrosine phosphorylation may in part be secondary to inhibition of phosphotyrosine phosphatase activity, because cAMP pretreatment blunted the effect of Na3VO4 on the net tyrosine phosphorylation of the 195 kDa protein as compared with cells pretreated with no additive. In summary, the interactions between cAMP-dependent and insulin-dependent pathways that lead to augmentation of DNA synthesis appear to parallel the changes in tyrosine phosphorylation. Further studies will be required to determine whether there is a causal relationship between these phenomena.

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The effects of glucocorticoids on insulin-stimulated lipogenesis in primary cultures of rat hepatocytes.

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