Mechanisms of dysregulation of 11β-hydroxysteroid dehydrogenase type I in obese zucker rats

Abstract

Obesity has been associated with alterations in glucocorticoid metabolism in both man and rodents, but the underlying mechanisms remain undefined. We have previously reported tissue-specific alterations in 11β- hydroxysteroid dehydrogenase type 1 (11β-HSD1) in obese Zucker rats predicting that reactivation of corticosterone is decreased in liver but increased in omental fat. The mechanisms of dysregulation of 11β-HSD1 in obesity are not known, and in this study we have investigated the potential role of glucocorticoids and insulin. In one experiment lean and obese Zucker rats were adrenalectomised, and in a second experiment they were sensitised to insulin by treatment with either metformin or rosiglitazone. Adrenalectomy (ADX) of obese animals attenuated weight gain, normalised hepatic 11β-HSD1 kinetics by an effect on Vmax (Vmax in sham-operated animals, 6·6 ± 1·1 nmol/min per mg in lean vs 3·4 ± 0·6 in obese, P<0·01; in ADX animals 5·9 ± 1·1 in lean vs 6·9 ± 1·8 in obese, NS), and reversed the difference in omental fat 11β-HSD1 activity (18·9 ± 4.2% in lean ADX vs 8·2 ± 2·3 in obese ADX, P= 0·03). Both metformin and rosiglitazone improved insulin sensitivity in obese, but not lean animals, and had no effect on 11β-HSD1 activity in either liver or fat. However, both treatments normalised adrenal hypertrophy in obese animals (48 ± 29 mg in obese vehicle vs 37 ±1·2 in metformin and 38 ± 1·8 in rosiglitazone treated, both P<0·01), and rosiglitazone tended to attenuate hypercorticosteronaemia in obese rats. Neither treatment attenuated weight gain; in fact, weight gain was enhanced by rosiglitazone in obese rats. In summary, altered 11β-HSD1 activity in obese Zucker rats is reversible following adrenalectomy, but the mechanism is unclear since adrenalectomy also normalises many other metabolic abnormalities. The current study suggests that hyperinsulinaemia is not responsible for tissue-specific dysregulation of 11β-HSD1. However, insulin sensitisation did reverse adrenal hypertrophy, suggesting that hyperinsulinaemia may be a key factor contributing to activation of the hypothalamic- pituitary-adrenal (HPA) axis in obesity independently of tissue-specific changes in 11β-HSD1.