Figure 1.
Hyperglucagonemia is involved in the hyperglycemia of DEX rats.
A: Blood glucose, B: plasma insulin, C: plasma glucagon, and D: plasma insulin to glucagon ratio in fasted (12–14 h) and fed DEX and CTL rats. E: HOMA index, F: TyG index and G: ipGTT in fasted (12–14 h) DEX and CTL rats. H: Fasted and I: fed blood glucose in rats receiving 1 µmol/l.kg−1 of des-His1-(Glu9]-glucagon (1–29) amide from the third day to the last day of dexamethasone administration. Data are the mean ± SEM. n = 10 in A to G. n = 7 in H and I. * p<0.05, ** p<0.01, *** p<0.001 vs. CTL. † p<0.05, ††† p<0.001 vs. fasted in A, B, C and D. # p<0.05 vs. DEX. HOMA, homeostatic model assessment; ipGTT, intraperitoneal glucose tolerance test.
Figure 2.
The inhibition of glucagon secretion by pancreatic α-cells in response to glucose is impaired in DEX rats.
A: Glucagon secretion in response to 0.5 mmol/l or 11.1 mmol/l glucose in isolated islets from DEX and CTL rats (n = 10 wells). B: Total islet glucagon content (n = 10). C: In vitro glucagon secretion in response to 0.5 mmol/l or 11.1 mmol/l glucose in isolated islets that were pre-incubated for 3 h with 8.3 mmol glucose with or without 1 µmol/l dexamethasone (n = 10 wells). D: Total islet glucagon content (n = 10). Data are the mean ± SEM. * p<0.05 vs. CTL. † p<0.05 vs. 0.5 mmol/l glucose. G, glucose.
Table 1.
Glucagon secretion (ng/l) per islet in response to low or high glucose in isolated islets.
Figure 3.
The pancreatic α-cell mass in DEX rats.
A: Panoramic and detailed view of DEX and CTL pancreas sections that were immunostained for glucagon. B: Relative, C: absolute, and D: normalized α-cell mass in DEX and CTL rats. Data are the mean ± SEM (n = 6). Scale bars = 200, 50, 20 and 10 µm from the top to bottom images in A.
Figure 4.
The number of docked glucagon granules is increased in the α-cells of DEX rats.
A: Electron micrographs of α-cells from CTL and DEX rats. The images demonstrate an enlargement of the Golgi complex (GC) and the increase in glucagon granules docked to the plasma membrane in the DEX α-cells (*). N, Nucleus; Mi, mitochondria. B: Profile of glucagon granules per median section of α-cells. C: Proportion of granules docked to the plasma membrane of α-cells. Data are the mean ± SEM (n = 16 cells in each condition). ** p<0.01 vs. CTL.
Figure 5.
Glucagon stimulates insulin secretion in islets isolated from DEX rats.
A: Insulin secretion in response to incubation with 5.6 mmol/l glucose with or without glucagon or forskolin in islets isolated from DEX and CTL rats (n = 10 wells). B: Representative immunoblots for the glucagon receptor (GR) and β-actin and their quantification (bar graphs) for DEX and CTL islet lysates (n = 6 independent samples). Data are the mean ± SEM. * p<0.05, *** p<0.001 vs. CTL. ††† p<0.001 vs. 5.6 m glucose. ‡‡‡ p<0.001 vs. 5.6 mmol/l glucose plus 1 µmol/l glucagon in A. C: Immunostaining of pancreas sections from DEX and CTL rats for the GR (green) and insulin or glucagon (red). Merged in orange. DAPI was used for nuclei staining (n = 3 pancreases). Scale bars = 7.5 µm.
Table 2.
Insulin secretion ratio in isolated islets from CTL and DEX rats.
Figure 6.
11-Dehydrocorticosterone [11-DHC) stimulates insulin secretion under basal glucose conditions in islets isolated from DEX rats.
A: Insulin secretion in response to incubation with 5.6 mmol/l glucose with or without 11-DHC or carbenoxolone in islets isolated from DEX and CTL rats (n = 10 wells). B: Insulin secretion in response to incubation with 16.7 mmol/l glucose with or without 11-DHC or carbenoxolone in islets isolated from DEX and CTL rats (n = 10 wells). Data are the mean ± SEM. *** p<0.001 vs. CTL. † p<0.05 vs. 5.6 mmol/l glucose. ‡ p<0.05 vs. 5.6 mmol/l glucose plus 100 nmol/l 11-DHC.
Figure 7.
11β Hydroxysteroid dehydrogenase type 1 [11βHSD-1) content and cellular distribution in the pancreas in DEX rats.
A: Representative immunoblots for 11βHSD-1 and β-actin and their quantification (bar graphs) in DEX and CTL islet lysates (n = 6 independent samples). Data are the mean ± SEM. C: Immunostaining of pancreas sections from DEX and CTL rats for glucagon (red) and 11βHSD-1 (green). Merged in orange. n = 3 pancreases. Scale bars = 7.5 µm.