Insulin and glucose sensitivity, insulin secretion and β-cell distribution in endocrine pancreas of the fruit bat Artibeus lituratus

Abstract

The fruit bat Artibeus lituratus absorbs large amounts of glucose in short periods of time and maintains normoglycemia even after a prolonged starvation period. Based on these data, we aimed to investigate various aspects related with glucose homeostasis analyzing: blood glucose and insulin levels, intraperitoneal glucose and insulin tolerance tests (ipGTT and ipITT), glucose-stimulated insulin secretion (2.8, 5.6 or 8.3 mmol/L glucose) in pancreas fragments, cellular distribution of beta cells, and the amount of pAkt/Akt in the pectoral muscle and liver. Blood glucose levels were higher in fed bats (6.88+/-0.5 mmol/L) than fasted bats (4.0+/-0.8 mmol/L), whereas insulin levels were similar in both conditions. The values of the area-under-the curve obtained from ipGTT were significantly higher when bats received 2 (5.5-fold) or 3g/kg glucose (7.5-fold) b.w compared to control (saline). These bats also exhibited a significant decrease of blood glucose values after insulin administration during the ipITT. Insulin secretion from fragments of pancreas under physiological concentrations of glucose (5.6 or 8.3 mmol/L) was similar but higher than in 2.8 mmol/L glucose 1.8- and 2.0-fold, respectively. These bats showed a marked beta-cell distribution along the pancreas, and the pancreatic beta cells are not exclusively located at the central part of the islet. The insulin-induced Akt phosphorylation was more pronounced in the pectoral muscle, compared to liver. The high sensitivity to glucose and insulin, the proper insulin response to glucose, and the presence of an apparent large beta-cell population could represent benefits for the management of high influx of glucose from a carbohydrate-rich meal, which permits appropriate glucose utilization.

Seasonal variation of energy reserves and reproduction in neotropical free-tailed bats Molossus molossus (Chiroptera: Molossidae)

“…Several studies have shown that the diet composition interferes directly with the metabolic pattern displayed by diverse vertebrates (Nagy and Pistole, 1988;Silva and Migliorini, 1990;Sartori et al, 1995), including bats (Freitas et al, 2003;Pinheiro et al, 2006;Freitas et al, 2010;Protzek et al, 2010). Another factor which also interferes with energy metabolism is the species' reproductive patterns, which are directly linked to environmental conditions and food availability (Pirlot, 1967;Dweyr, 1970;Wojciechowski et al, 2007).…”

Physiological Responses to Fasting in Bats

“…Because of their large hepatic glycogen stores, A. lituratus can endure 2-6 days with no food and still maintain normal levels of blood glucose (Pinheiro et al 2006), an ability rarely seen among mammals. This phenomenon is peculiar given that insulin levels remain similar in both fasted and fed A. lituratus (Protzek et al 2010). Although hyperinsulinemia is characteristic of insulin insensitivity (Modan et al 1985), A. lituratus, which possesses a comparatively high number of pancreatic b-cells (Protzek et al 2010), also has high insulin sensitivity and high blood glucose tolerance.…”

“…This phenomenon is peculiar given that insulin levels remain similar in both fasted and fed A. lituratus (Protzek et al 2010). Although hyperinsulinemia is characteristic of insulin insensitivity (Modan et al 1985), A. lituratus, which possesses a comparatively high number of pancreatic b-cells (Protzek et al 2010), also has high insulin sensitivity and high blood glucose tolerance. Consequently, glycogenolysis does not seem to be used as a mechanism of short-term fast resistance in other fruit bat species, as indicated by their limited use of hepatic glycogen during this period (Freitas et al 2010;Pinheiro et al 2006).…”

“…This mechanism allows fruit bats to store relatively large amounts of hepatic glycogen ( Fig. 16.1; Protzek et al 2010).…”

Avaliação fisiológica de morcegos frugívoros neotropicais e estruturação da assembleia causado pela alteração de habitat no cerrado

“…Poucos estudos avaliaram o metabolismo de morcegos frugívoros (Protzek et al, 2010;Pinheiro et al, 2006), mas nenhum relacionou a resposta fisiológica ao habitat.…”