Regulatory mechanism of hypothalamo-pituitary-adrenal (HPA) axis and neuronal changes after adrenalectomy in type 2 diabetes.
Diabetes, especially type 2, is closely associated with hypothalamo-pituitary-adrenal (HPA) axis regulation. Short-term effects of adrenalectomy (ADX) in type 2 diabetes are well characterized; however, there have been few reports on the long-term effects of ADX in genetically engineered type 2 diabetes and the neuroendocrine system. We performed bilateral ADX in Zucker Lean Control rats (ZLC; ADX-ZLC), Zucker Diabetic Fatty rats (ZDF; ADX-ZDF), and sham control rats to evaluate how the HPA axis would be regulated in long-term corticosterone deficient type 2 diabetic animals. We evaluated arginine vasopressin (AVP), glucocorticoid receptor (GR), and corticotropin-releasing hormone (CRH) expression with immunohistochemistry (IHC), immunofluorescence, real-time PCR, and Western blot analysis in each treatment group 7 weeks post ADX to assess HPA axis regulatory patterns in connection with type 2 diabetes. Additionally, mRNA expression of AVP and CRH receptors (V1aR, V1bR, CRHR1, and CRHR2) was also measured and adrenocorticotropin hormone (ACTH) immunoreactivity was surveyed by IHC to add to data regarding the regulatory mechanism. AVP and CRH protein expression levels increased after ADX in the hypothalamus of diabetic rats based on IHC results; however, we found that the subtypes of each receptor may be regulated differently in ADX groups compared to sham groups. Immunoreactivity of ACTH in the pituitary gland was enhanced in ADX groups and GR expression levels in the hypothalamic paraventricular nuclei (PVN) remained high, as determined by IHC as well as Western blot analysis. Without the negative feedback system of corticosterone, CRH is highly enhanced and may primarily combine with CRHR1 to stimulate negative feedback through ACTH in the pituitary gland in type 2 diabetic rats with long-term ADX. Although the negative feedback signal was not transmitted appropriately following long-term ADX with type 2 diabetes, a high GR protein level was maintained as in type 2 diabetes. The long-termed lack of corticosterone in the blood stream is a very important factor for normal regulation of the HPA axis even in diabetic animals. From the data, we can conclude that the stimulated HPA axis regulation in the developing type 2 diabetic animals following long-term adrenalectomy has remained elevated rather than diminished. Therefore, the current study may provide useful information to better understand patients suffering from both type 2 diabetes and Addison's disease.
Yi
Sun Shin
SS
Department of Anatomy and Cell Biology, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 151-742, South Korea.
Hwang
In Koo
IK
Shin
Jae Hoon
JH
Choi
Jung Hoon
JH
Lee
Choong Hyun
CH
Kim
Il Yong
IY
Kim
Yo Na
YN
Won
Moo-Ho
MH
Park
In-Sun
IS
Seong
Je Kyung
JK
Yoon
Yeo Sung
YS
D000315:Adrenalectomy; D000704:Analysis of Variance; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism; D001786:Blood Glucose; D015153:Blotting, Western; D003345:Corticosterone / Q000097:blood; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism* / Q000601:surgery; D005260:Female; D005951:Glucose Tolerance Test; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D009474:Neurons / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D010913:Pituitary-Adrenal System / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011924:Rats, Zucker; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D001786:Blood Glucose; D011965:Receptors, Glucocorticoid; D001127:Arginine Vasopressin; D003346:Corticotropin-Releasing Hormone; D003345:Corticosterone