Dexamethasone does not increase IGF-I and IGFBP-3 levels in man in the absence of endogenous GH

The impact of glucocorticoid replacement regimens on metabolic outcome and comorbidity in hypopituitary patients

BACKGROUND

Hypopituitary patients with untreated GH deficiency and patients on inappropriately high doses of glucocorticoid (GC) share certain clinical features.

OBJECTIVE

The aim of the study was to examine the influence of GC substitution on clinical characteristics in hypopituitary patients before and after GH replacement therapy.

METHOD

A total of 2424 hypopituitary patients within the KIMS (Pfizer International Metabolic Database) were grouped according to ACTH status. Comparisons were performed between subjects on hydrocortisone (HC) (n = 1186), cortisone acetate (CA) (n = 487), and prednisolone/dexamethasone (n = 52), and ACTH-sufficient patients (AS) (n = 717) before and after 1 yr of GH treatment in terms of body mass index, waist and hip circumference, blood pressure, glucose, glycosylated hemoglobin (HbA1c), serum lipids, IGF-I, and comorbidity. Hydrocortisone equivalent (HCeq) doses were calculated, and measurements were adjusted for sex and age.

RESULTS

At baseline, the HC group had increased total cholesterol, triglycerides, waist circumference, and HbA1c, and the prednisolone/dexamethasone group had increased waist/hip ratio as compared with AS. After HCeq dose adjustment, the HC group retained higher HbA1c than the CA group. GC-treated patients showed a dose-related increase in serum IGF-I, body mass index, triglycerides, low-density lipoprotein cholesterol and total cholesterol levels. Subjects with HCeq doses less than 20 mg/d (n = 328) at baseline did not differ from AS in metabolic endpoints. The 1-yr metabolic response to GH was similar in all GC groups and dose categories. All new cases of diabetes (n = 12), stroke (n = 8), and myocardial infarction (n = 3) during GH treatment occurred in GC-treated subjects.

CONCLUSION

HCeq doses of at least 20 mg/d in adults with hypopituitarism are associated with an unfavorable metabolic profile. CA replacement may have metabolic advantages compared with other GCs.

Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review

The growth hormone-insulin-like growth factor (GH-IGF) axis has gained considerable focus over recent years. One cause of this increased interest is due to a correlation of age-related decline in plasma GH/IGF levels with age-related degenerative processes, and it has led to the prescribing of GH replacement therapy by some practitioners. On the other hand, however, research has also focused on the pro-carcinogenic effects of high GH-IGF levels, providing strong impetus for finding regimes that reduce its activity. Whereas the effects of GH/IGF activity on the action of xenobiotic-metabolizing enzyme systems is reasonably well appreciated, the effects of xenobiotic exposure on the GH-IGF axis has not received substantial review. Relevant xenobiotics are derived from pharmaceutical, nutraceutical and environmental exposure, and many of the mechanisms involved are highly complex in nature, not easily predictable from existing in vitro tests and do not always predict well from in vivo animal models. After a review of the human and animal in vivo and in vitro literature, a framework for considering the different levels of direct and indirect modulation by xenobiotics is developed herein, and areas that still require further investigation are highlighted, i.e. the actions of common endocrine disruptors such as pesticides and phytoestrogens, as well as the role of xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. It is anticipated that a fuller appreciation of the existing human paradigms for GH-IGF axis modulation gained through this review may help explain some of the variation in levels of plasma IGF-1 and its binding proteins in the population, aid in the prescription of particular dietary regimens to certain individuals such as those with particular medical conditions, guide the direction of long-term drug/nutraceutical safety trials, and stimulate ideas for future research. It also serves to warn athletes that using compounds touted as performance enhancing because they promote short-term GH release could in fact be detrimental to performance in the long-run.