Glucocorticoid effects on IGF-1/somatomedin-C and somatomedin inhibitor in streptozotocin-diabetic rats

Prevention of mouse skin tumor promotion by dietary energy restriction requires an intact adrenal gland and glucocorticoid supplementation restores inhibition

Our laboratory has demonstrated in the previous studies that dietary energy restriction (DER) inhibited the promotion of skin tumorigenesis and others have found that adrenalectomy may reverse that inhibition. The purpose of the research reported here was to determine if circulating corticosterone (CCS) may be the adrenal hormone responsible for DER prevention of skin carcinogenesis. Female SENCAR mice were initiated with 7,12-dimethylbenzanthracene (DMBA) and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) in either sham-operated or adrenalectomized (ADX) mice fed ad libitum (AL) or energy restricted diets. DER was 60% of the AL calorie intake with the removal of energy from fat and carbohydrate. CCS, the main glucocorticoid hormone secreted by the murine adrenal gland, was added to the drinking water of AL/ADX and DER/ADX groups to determine the role of CCS in the DER inhibition of tumor development. In sham-operated groups, DER compared with AL-fed mice experienced significantly decreased papilloma incidence and multiplicity (P < 0.0001). ADX did not alter papilloma incidence or multiplicity in AL-fed mice but ADX partially reversed the inhibition of papilloma multiplicity and incidence in DER mice. CCS supplementation to both DER/ADX and AL/ADX mice resulted in reduced papilloma incidence and multiplicity. In DER/ADX mice, CCS dramatically reduced papilloma rates while in AL/ADX mice CCS reduced the papilloma rates to those seen in the DER sham group. DER significantly reduced carcinoma multiplicity mean counts per effective animal (P < 0.0001) compared with AL-fed groups in sham and ADX/CCS groups. DER/ADX mice lost the carcinoma multiplicity protection seen in sham/DER mice. CCS treatment of ADX mice significantly decreased total carcinoma (in situ and invasive) incidence rates per effective animal (P < 0.0003). ADX followed by CCS treatment in the DER mice resulted in the lowest carcinoma incidence and multiplicity. Thus, DER-inhibition of skin tumorigenesis was mediated at least in part through CCS. However, CCS was more effective in preventing papillomas and carcinomas in DER/ADX mice than in AL/ADX mice, suggesting that other factors may also be involved in the DER prevention of tumor formation.

Serum levels of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in children with insulin-dependent diabetes mellitus

Pubertal development has recently been evaluated from the standpoint of changes in insulin-like growth factor (IGF)-I and IGF-binding protein-3 (IGFBP-3) levels in healthy children. We studied puberty related changes in serum IGF-I and IGFBP-3 levels in 24 patients (11 prepubertal) with insulin dependent diabetes mellitus (IDDM) and 26 healthy subjects (14 prepubertal). Serum IGF-I and IGFBP-3 levels were assayed using immunoradiometric assays and radioimmunoassays, respectively. Serum IGF-I and IGFBP-3 levels in diabetics did not increase during puberty, as opposed to those in healthy children. Serum IGF-I and IGFBP-3 levels of diabetic patients were found to be lower than those of control subjects during puberty (p < 0.0001 and p < 0.05, respectively). Proteolysis is believed to be a general mechanism to increase IGF bioavailability in the presence of IGFBPs. Increased IGFBP-3 protease activity has been shown in sera of children with IDDM as well as a decrease in this activity in response to insulin therapy. Our data displaying low IGFBP-3 levels in diabetic children may be due to increased proteolysis, which also causes a shift in IGF-I to its lower molecular weight forms. Higher rate of clearance of the latter may be the reason for the low IGF-I levels we observed in children with IDDM. The moderate correlation between insulin dose and IGFBP-3 levels (r = 0.5, p < 0.01) may suggest insulin to be a contributing factor in the regulation of IGFBP-3 levels. We conclude that regulation of IGF-I and IGFBP-3 concentrations is disturbed in children with IDDM, in particular during adolescence.

Nutrition and somatomedin. XXI. Insulin-like growth factor-I and somatomedin inhibitor in streptozotocin-diabetic rats: relation to ketogenesis and gluconeogenesis

Diabetes is associated with a fall in serum insulin-like growth factor-I (IGF-1) and a rise in somatomedin inhibitor, a circulating factor(s) of approximately 30,000 MW that is released by the liver and can antagonize both somatomedin and insulin action. Levels of inhibitor correlate with levels of glucose, beta-hydroxybutyrate, and weight loss. To study pathways that could underlie the fall in IGF-1 and rise in inhibitor, the effects of metabolic inhibitors on circulating metabolic fuels, serum IGF-1, and serum somatomedin inhibitor activity were studied. Rats given streptozotocin exhibited weight loss of 14% +/- 0.1%, glucose 457 +/- 26 mg/dL, and beta-hydroxybutyrate (BOHB) 6.3 +/- 0.5 mmol/L. Somatomedin inhibitor was separated from IGF-1 by size exclusion HPLC at pH 3; IGF-1 was measured by RIA, and somatomedin inhibitor by cartilage bioassay. Diabetic animals exhibited a fall in IGF-1 to 76% of normal (P less than .02) and a rise in inhibitor to 270% of normal (P less than .01). 3-Mercaptopicolinic (3-MPA) acid, an inhibitor of gluconeogenesis, lowered glucose to 68 +/- 2 mg/dL and BOHB to 0.96 +/- 0.09 mmol/L (both P less than .01 v diabetic), but levels of inhibitor did not fall. Nicotinic acid, an inhibitor of lipolysis, did not affect glucose but reduced BOHB to 0.42 +/- 0.02 mmol/L; somatomedin inhibitor fell 19% below diabetic levels (NS) but remained above normal (P less than .01). In contrast, inhibition of fatty acid oxidation with methyl-2-tetradecylglycidate reduced glucose to 191 +/- 18 mg/dL but lowered BOHB to normal, 0.16 +/- 0.02 mmol/L, accompanied by normalization of somatomedin inhibitor levels (152% +/- 33% of normal, NS). Below 1.0 mmol/L BOHB, somatomedin inhibitor and BOHB were strongly correlated (r = .67, P less than .001); no comparable relation was found with glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutrition and somatomedin: nutritionally regulated release of somatomedins and somatomedin inhibitors from perfused livers in rats

Circulating somatomedin activity reflects the presence of both somatomedins and somatomedin inhibitors, factors which antagonize the growth-promoting actions of somatomedins. Although both are regulated by nutrition, somatomedin inhibitors respond more rapidly than somatomedins to refeeding in fasted animals. To explore the role of the liver in such responses, release of somatomedin activity and somatomedin inhibitor activity was assessed during perfusion of livers from normal, fasted, and fasted-refed rats. Size-exclusion high-performance liquid chromatography (HPLC) revealed that liver perfusates contain both somatomedin and somatomedin inhibitor activity of apparent molecular weight (mol wt) comparable to that found in the circulation (approximately 7,000 and approximately 30,000, respectively), as well as activity of apparently higher wt. In subsequent studies, responses to nutrition were evaluated as fluctuations in bioactivity only of mol wt comparable to that found in the circulation. Release of both somatomedin and somatomedin inhibitor activity was progressive over at least two hours of recirculating perfusion. Perfusates of livers from normal fed rats had somatomedin activity (stimulation of cartilage SO4 uptake) 94 +/- 19% above buffer (P less than .01), which fell to undetectable levels after three days of fasting. With refeeding, perfusate somatomedin activity rose within three hours to approximately 25% of levels in fed rats, but did not become significant until after 12 hours (29 +/- 7%, P less than .02). Perfusates of livers of fed rats also contained somatomedin inhibitor activity (42 +/- 10% inhibition of cartilage stimulation by normal serum), which rose after three days of fasting to 114 +/- 22% (P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)