Insulin-like receptors and carbohydrate metabolism in gills of the euryhaline crab Neohelice granulata: Effects of osmotic stress

The present study determined the effect of osmotic stress on the insulin-like receptor binding characteristics and on glucose metabolism in the anterior (AG) and posterior (PG) gills of the crab Neohelice granulata. Bovine insulin increased the capacity of the PG cell membrane to phosphorylate exogenous substrate poly (Glu:Tyr 4:1) and the glucose uptake in the control crab group. The crabs were submitted to three periods of hyperosmotic (HR) and hyposmotic (HO) stress, for 24, 72 and 144 h, to investigate the insulin-like receptor phosphorylation capacity of gills. Acclimation to HO for 24 h or HR for 144 h of stress inhibited the effects of insulin in the PG, decreasing the capacity of insulin to phosphorylate exogenous substrate poly (Glu:Tyr 4:1) and decreasing the glucose uptake. Hyperosmotic stress for the same period of 144 h significantly affected ¹²⁵I-insulin binding in the AG and PG. However, HO stress for 24 h significantly reduced ¹²⁵I-insulin-specific uptake only in the PG. Therefore, osmotic stress induces alterations in the gill insulin-like receptors that decrease insulin binding in the PG. These findings indicate that osmotic stress induced a pattern of insulin resistance in the PG. The free-glucose concentration in the PG decreased during acclimation to 144 h of HR stress and 24 h of HO stress. This decrease in the cell free-glucose concentration was not accompanied by a significant change in hemolymph glucose levels. In AG from the control group, neither the capacity of bovine insulin to phosphorylate exogenous substrate poly (Glu:Tyr 4:1) nor the glucose uptake changed; however, genistein decreased tyrosine-kinase activity, confirming that this receptor belongs to the tyrosine-kinase family. Acclimation to HO (24 h) or HR (144 h) stress decreased tyrosine-kinase activity in the AG. This study provided new information on the mechanisms involved in the osmoregulation process in crustaceans, demonstrating for the first time in an estuarine crab that osmotic challenge inhibited insulin-like signaling and the effect of insulin on glucose uptake in the PG.

Insulin binding characteristics in canine muscle tissue: effects of the estrous cycle phases

Abstract: Hormonal fluctuations during the different estrous cycle are a well-recognized cause of insulin resistance in bitches, and little is known about insulin receptor binding or post-binding defects associated with insulin resistance in dogs. To evaluate insulin binding characteristics in muscle tissue of bitches during the estrous cycle, 17 owned bitches were used in the study (six in anestrus, five in estrus, and six in diestrus). An intravenous glucose tolerance test (IVGTT) was performed in all patients by means of injection of 1mL/kg of a glucose 50% solution (500mg/kg), with blood sample collection for glucose determination at 0, 3, 5, 7, 15, 30, 45 and 60 minutes after glucose infusion. Muscle samples, taken after spaying surgery, were immediately frozen in liquid nitrogen and then stored at -80 ºC until the membranes were prepared by sequential centrifugation after being homogenized. For binding studies, membranes were incubated in the presence of 20,000cpm of human 125I-insulin and in increasing concentrations of unlabeled human regular insulin for cold saturation. The IVGTT showed no differences among bitches during the estrous cycle regarding baseline glycemia or glycemic response after glucose infusion. Two insulin binding sites - high-affinity and low-affinity ones - were detected by Scatchard analysis, and significant statistical differences were observed in the dissociation constant (Kd1) and maximum binding capacity (Bmax1) of the high-affinity binding sites. The Kd1 for the anestrus group (6.54±2.77nM/mg of protein) was smaller (P<0.001) than for the estrus (28.54±6.94nM/mg of protein) and diestrus (15.56±3.88nM/mg of protein) groups. Bmax1 in the estrus (0.83±0.42nM/mg of protein) and diestrus (1.24±0.24nM/mg of protein) groups were also higher (P<0.001) than the values observed in anestrus (0.35±0.06nM/mg of protein). These results indicate modulation of insulin binding characteristics during different phases of the estrous cycle in dogs, showing that muscle insulin binding affinity for its receptor is reduced during estrus and diestrus. However, this poor hormone-receptor affinity is compensated for by a greater total binding capacity, once there is no difference in patients' glycemic response after an intravenous glucose load.

Effect of insulin/IGF-I like peptides on glucose metabolism in the white shrimp Penaeus vannamei

The insulin-like hormone superfamily encompasses insulin, relaxin, and insulin-like growth factors I (IGF1) and II (IGF2). Insulin hormones regulate cell growth, metabolism, and tissue-specific functions. The presence of insulin has been demonstrated in various invertebrates, and their function as growth promoting or controlling factors has been established in molluscs and insects. In crustaceans, the presence of insulin/insulin-like growth factor (IGF)-like peptides has also been suggested and functional studies have been associated with metabolic control. The general aim of the current study was to elucidate the functional significance of insulin-like peptides in the white shrimp Penaeus vannamei. Because the primary structure of Penaeus insulin is yet unknown, we examined the effect of mammalian insulin/IGF-I on glucose metabolism in P. vannamei. Juvenile shrimps were injected with a single dose of recombinant human (rh) IGF-I or bovine insulin in intermolt stage. Glucose/glycogen levels in shrimp hemolymph and tissues (muscle, hepatopancreas and gills) were determined over a 5h period by means of an enzymatic analysis. We showed that an injection of rhIGF-I induced a significant (P<0.01) increase in glucose levels in hemolymph, 1h after injection and followed by a decrease (P<0.05) 5h post-injection. In the hepatopancreas, an increase (P<0.05) in the glycogen content was observed 3h after insulin treatment. Finally, a significant elevation (P<0.01) of glycogen content in the gills throughout the entire sampling period was detected. Our study suggests the presence of endogenous Penaeus insulin(s) that, just like its vertebrate counterparts, is likely to be involved in the regulation of carbohydrate metabolism in crustaceans.

In vitro insulin stimulatory effect on glucose uptake and glycogen synthesis in the gills of the estuarine crab Chasmagnathus granulata

The aim of the present study was to examine the effects of insulin on glucose uptake and glycogen synthesis in crab Chasmagnathus granulata gills. We observed an increased glucose uptake and incorporation of d-[(14)C]glucose into glycogen when posterior C. granulata gills were incubated in the presence of insulin; however, this was not observed in anterior gills, despite the presence of similar insulin receptors. In posterior gills, basal glucose uptake in the summer was significantly higher than in the winter. Moreover, in the summer, the insulin dose required to stimulate glucose uptake was twice as high as in the winter. However, there was no significant difference in terms of basal glycogen synthesis in summer and winter. In crustaceans, the endogenous insulin/IGFI substance might be involved in the rapid restoration of glycogen levels in the gills, increasing glucose uptake and glycogen synthesis. Bovine insulin seems to have a stimulatory effect on glycogen metabolism only in posterior gills.