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Faculty of the Division of Endocrinology & Metabolism

Karen L. Herbst, Ph.D., M.D.

Associate Clinical Professor of Medicine

Associate Director, Fellowship Training Program

Keywords: obesity, adipose tissue, testosterone, lipomatosis

Research Interests

I am interested in adipose tissue and examine two different populations to study obesity from different perspectives. 

First, as men become obese, their abdominal fat increases and free testosterone (T) declines in a linear manner.  I hypothesize that T administration to these young, obese insulin resistant men will improve insulin sensitivity.  Testosterone is metabolized to estradiol and dihydrotestosterone (DHT) and when administered exogenously to men, the levels of these two metabolites can rise dramatically.  I therefore have asked whether inhibition of T metabolism to estradiol or DHT will alter T effects on insulin sensitivity.  In this ongoing clinical study, the gonadal axis is clamped off with acyline, a gonadotropin releasing-hormone antagonist to allow comparison among groups with similar T levels but different estradiol or DHT levels.  Fat and muscle biopsies are examined before and after T administration for glucose uptake, and in muscle, fat oxidation.  Examination of insulin signaling pathways in the fat and muscle might provide information on how T affects insulin sensitivity apart from changes in body composition.


Secondly, I am examining individuals with lipomatosis or non-encapsulated fatty growths.  These individuals have either Madelung’s disease, familial multiple lipomatosis or Dercum’s disease, all rare forms of abnormal fat accumulation.  In Dercum’s disease, individuals can gain a large amount of fat in a short period of time in addition to the lipomatosis.  Understanding the lipomatosis might provide new insights or pathways in the study of obesity.





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