Interactions of stress hormones on lipid and carbohydrate metabolism in man with partial insulin deficiency

Acute physiological effects of glucocorticoids on fuel metabolism in humans are permissive but not direct

BACKGROUND AND AIMS

The effects of glucocorticoids on fuel metabolism are complex. Acute glucocorticoid excess promotes lipolysis but chronic glucocorticoid excess causes visceral fat accumulation. We hypothesized that interactions between cortisol and insulin and adrenaline account for these conflicting results. We tested the effect of cortisol on lipolysis and glucose production with and without insulin and adrenaline in humans both in vivo and in vitro.

MATERIALS AND METHODS

A total of 20 healthy men were randomized to low and high insulin groups (both n = 10). Subjects attended on 3 occasions and received low (c. 150 nM), medium (c. 400 nM) or high (c. 1400 nM) cortisol infusion in a randomized crossover design. Deuterated glucose and glycerol were infused intravenously along with a pancreatic clamp (somatostatin with replacement of glucagon, insulin and growth hormone) and adrenaline. Subcutaneous adipose tissue was obtained for analysis. In parallel, the effect of cortisol on lipolysis was tested in paired primary cultures of human subcutaneous and visceral adipocytes.

RESULTS

In vivo, high cortisol increased lipolysis only in the presence of high insulin and/or adrenaline but did not alter glucose kinetics. High cortisol increased adipose mRNA levels of ATGL, HSL and CGI-58 and suppressed G0S2. In vitro, high cortisol increased lipolysis in the presence of insulin in subcutaneous, but not visceral, adipocytes.

CONCLUSIONS

The acute lipolytic effects of cortisol require supraphysiological concentrations, are dependent on insulin and adrenaline and are observed only in subcutaneous adipose tissue. The resistance of visceral adipose tissue to cortisol's lipolytic effects may contribute to the central fat accumulation observed with chronic glucocorticoid excess.

Distinct but nonadditive effects of epinephrine and cortisol on determinants of glucose tolerance in dogs

Effects of physiological increments of epinephrine (Epi) and cortisol (F) on glucose metabolism were assessed in dogs just before and during an intravenous glucose tolerance test performed in the last 3 h of an acute (short F + Epi, 4 h F and 3.5 h Epi) or prolonged (long F + Epi, 75 h F and Epi) infusion period. Comparison of the F + Epi effects with those of F and Epi alone enabled us to describe interactions between these hormones. The increase in plasma glucose after long F + Epi [from control (saline, Sal) of 5.2 +/- 0.1 to 5.8 +/- 0.1 mmol/l; n = 8; P less than 0.01] was not greater than the sum of the glucose increments after long F and long Epi individually. Long Epi and long F both reduced glucose tolerance (KGlc) significantly, but the decline during long F + Epi (from Sal 3.6 +/- 0.7 to 2.9 +/- 0.5%/min; P greater than 0.1) was less than during either individual infusion. Minimal model analysis showed that F attenuated the inhibitory effects of long Epi on glucose-mediated glucose disposal (SGlc), so that it was not reduced from 3.8 +/- 0.8 (Sal) during long F + Epi compared with the fall to 1.3 +/- 0.7 x 10(-2) min-1 (n = 6; P less than 0.05) during long Epi alone. F had the dominant influence on insulin sensitivity (SI) during infusion of F + Epi. The reduction of SI from 8.4 +/- 1.1 (Sal) to 6.6 +/- 1.2 (short F + Epi) and 5.1 +/- 1.1 x 10(-4) min-1 per mU/l (long F + Epi; P less than 0.05) paralleled that seen with F alone but contrasted with the acute reduction of SI during short Epi (4.8 +/- 1.5; P less than 0.02 vs. Sal) and its restoration to control values of 9.0 +/- 2.1 x 10(-4) min-1 per mU/l during long Epi. We conclude that Epi and F have distinct but nonadditive effects on determinants of glucose tolerance.