Corticosterone-induced insulin resistance is not associated with alterations of insulin receptor number and kinase activity in chicken kidney

Insulin's impact on renal sodium transport and blood pressure in health, obesity, and diabetes

Insulin has been shown to have antinatriuretic actions in humans and animal models. Moreover, endogenous hyperinsulinemia and insulin infusion have been correlated to increased blood pressure in some models. In this review, we present the current state of understanding with regard to the regulation of the major renal sodium transporters by insulin in the kidney. Several groups, using primarily cell culture, have demonstrated that insulin can directly increase activity of the epithelial sodium channel, the sodium-phosphate cotransporter, the sodium-hydrogen exchanger type III, and Na-K-ATPase. We and others have demonstrated alterations in the expression at the protein level of many of these same proteins with insulin infusion or in hyperinsulinemic models. We also discuss how this regulation is perturbed in type I and type II diabetes mellitus. Finally, we discuss a potential role for regulation of insulin receptor signaling in the kidney in contributing to sodium balance and blood pressure.

Pharmacological approaches for the treatment of obesity

The high incidence of obesity, its multifactorial nature, the complexity and lack of knowledge of the bodyweight control system, and the scarcity of adequate therapeutics have fuelled anti-obesity drug development during a considerable number of years. Irrespective of the efforts invested by researchers and companies, few products have reached a minimum level of effectiveness, and even fewer are available in medical practice. As a consequence of anti-obesity research, our knowledge of the bodyweight control system increased but, despite this, the pharmacological approaches to the treatment of obesity have not resulted yet in effective drugs. This review provides a panoramic of the multiple different approaches developed to obtain workable drugs. These approaches, however, rely in only four main lines of action: control of energy intake, mainly through modification of appetite;control of energy expenditure, essentially through the increase of thermogenesis;control of the availability of substrates to cells and tissues through hormonal and other metabolic factors controlling the fate of the available energy substrates; andcontrol of fat reserves through modulation of lipogenesis and lipolysis in white adipose tissue. A large proportion of current research is centred on neuropeptidic control of appetite, followed by the development of drugs controlling thermogenic mechanisms and analysis of the factors controlling adipocyte growth and fat storage. The adipocyte is also a fundamental source of metabolic signals, signals that can be intercepted, modulated and used to force the brain to adjust the mass of fat with the physiological means available. The large variety of different approaches used in the search for effective anti-obesity drugs show both the deep involvement of researchers on this field and the large amount of resources devoted to this problem by pharmaceutical companies. Future trends in anti-obesity drug research follow closely the approaches outlined; however, the increasing mass of information on the molecular basis of bodyweight control and obesity will in the end prevail in our search for effective and harmless anti-obesity drugs.

Apoptosis signals in atopy and asthma measured with cDNA arrays

A variety of studies have stressed the importance of the control of inflammatory cell longevity and the balance of pro-survival and pro-apoptotic signalling. Recently, asthma was found to be associated with reduced apoptosis of inflammatory cells in lung tissue. The aim of the study was to investigate the systemic activation of apoptosis pathways using cDNA array technology in atopy and asthma. Eighteen atopic asthmatics (AA), eight atopic non-asthmatic (AN) and 14 healthy control subjects (C) were included in the study. Peripheral blood mononuclear cells were separated with gradient centrifugation, mRNA purified and the reverse-transcribed probes hybridized to cDNA arrays. The signals were compared by standardizing to the 100 most expressed genes and group differences assessed with the Mann-Whitney U-test. We found a concerted up-regulation of several pro-survival cytokines and growth factors in AN and AA. FAS and FASL were not differentially expressed, but FAST kinase was over-expressed in AN and AA. The tumour necrosis factor pathway was activated in AN and AA with increased cytokine and receptor levels and increased TRAF2, an intracellular signalling product. There were indications of a down-regulated p53 system. In contrast, the Bcl-2 family of genes showed a net pro-apoptotic profile in AN and AA. The group of caspases showed a constant gene expression pattern in all groups. In conclusion, significant differences in the expression of apoptosis-related genes were found in peripheral blood of atopic individuals with and without asthma. cDNA array technology proved to be useful and may be complementary to DNA-based studies in order to analyse interactive and multidimensional pathways as shown here for apoptosis.

Nutritional state regulates insulin receptor and IRS-1 phosphorylation and expression in chicken

After insulin binding, insulin receptors (IR) phosphorylate the insulin receptor substrate 1 (IRS-1) on specific motifs and thereby initiate insulin action. The interaction between IR and IRS-1 and their expression were studied in vivo in two target tissues (muscle and liver) in chickens, a species that is insulin resistant. To induce extreme changes in plasma insulin levels, chickens were subjected to three different nutritional states (ad libitum fed, fasted for 48 h, and refed for 30 min after 48-h fast). Liver membrane IR number was significantly increased in fasted compared with fed chickens. This upregulation of IR number was concomitant with the an enhanced expression of IR mRNA as determined by reverse transcription-polymerase chain reaction. In leg muscle, IR mRNA was not altered by the nutritional state. Using specific antibodies directed toward human IR, anti-phosphotyrosines, or mouse IRS-1, we demonstrated that IR and IRS-1 are associated in vivo in liver and muscles. Tyrosine phosphorylation of liver IR and IRS-1 were significantly decreased by prolonged fasting and restored by 30-min refeeding. These alterations were not observed in muscle. Fasting increased IRS-1 mRNA expression in liver but not in muscle. These results are the first evidence showing that chicken liver and muscle express IRS-1. Therefore, the chicken insulin resistance is not accounted for by the lack of IRS-1. The differences observed for the regulation of IR and IRS-1 messengers and phosphorylation between liver and muscle in response to alterations of the nutritional state remain to be explained.

Naloxone attenuates serum corticosterone and augments serum glucose concentrations in broilers stimulated with adrenocorticotropin

The effects of exogenous naloxone and adrenocorticotropin (ACTH) on circulating concentrations of corticosterone and glucose in broilers were determined. Birds were injected i.m. at 0 and 2 h with either saline or naloxone, then i.v. at 2.5 h with either saline or ACTH. Control birds received saline at each injection. Blood samples were taken before the experiment started (0 min) and 30, 60, and 90 min after the last injection. Intramuscular injections of naloxone significantly reduced subsequent ACTH-stimulated increases in serum corticosterone; however, when followed by saline, naloxone elevated corticosterone by 90 min after the final injection of saline. Glucose levels were significantly elevated at 60 min in birds receiving ACTH i.v., but remained elevated through 90 min in birds pretreated with naloxone. Naloxone pretreatment attenuated serum corticosterone but augmented serum glucose concentrations in ACTH-stimulated broilers.

Continuous infusion of adrenocorticotropin elevates circulating lipoprotein cholesterol and corticosterone concentrations in chickens

The purpose of the present study was to investigate the effects of elevated corticosterone (CORT) on circulating lipoprotein cholesterol during a 1-wk period. For this study, 15 commercial broilers were randomly assigned to one of three treatment groups. Group 1 served as the control (CON) and received no treatment, whereas Groups 2 and 3 received subcutaneous mini-osmotic pumps containing either physiological saline (PS) or adrenocorticotropin (ACTH), respectively. The ACTH was delivered at a rate of 8 IU/kg of BW/d. Blood samples were taken at Time 0 (before implants) and on Days 2, 4, and 7 postimplantation. Continuous infusion of ACTH increased plasma glucose, cholesterol, triglycerides, very low density lipoprotein cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, and CORT during the postimplantation period. The group treated with ACTH also exhibited a decrease in BW during the last 2 sampling d. There were no differences in any of the serum constituents measured between CON and PS birds, which suggest that CON birds can serve as useful controls. These data suggest that birds given a continuous infusion of ACTH at 8 IU/kg of BW/d can experience changes in plasma lipoprotein cholesterol concentrations along with changes in other blood parameters and may serve as a useful model in accelerated lipoprotein production.