Alpha-2 Adrenergic Antilipolytic Effect in Dog Fat Cells: Incidence of Obesity and Adipose Tissue Localization

Summary

The main intention of this study was to characterize the α-adrenoceptor responsible for the inhibition of lipolysis in dog fat cell and to define circumstances that may be associated to a modification of the α-mediated antilipolytic effect.

Isolated fat cells from omental and subcutaneous adipose tissue from normal and obese dogs were used. Basal and theophylline stimulated lipolysis was studied in the presence of selected alpha-adrenergic agonists and antagonists.

The antilipolytic effect of catecholamines is mediated by α₂-type adrenoceptors in dog fat cell. The α-adrenergic responsiveness is enhanced (or unmasked) in large fat cells of obese dogs and depends on the site from which the adipose tissue sample is taken. The α-response is stronger in subcutaneous than in omental adipocytes.

In conclusion, the weakened lipolytic responsiveness to epinephrine of obese dog fat cells seems related to an increased α-adrenergic response rather than a decreased β-lipolytic effect. Obesity is a circumstance characterized in the dog fat cell by a modification of the balance between alpha-2 and beta receptors.

Key-Words:

Lipolysis - Obesity - Fat Cell Size - Alpha 2 Adrenoceptors - Beta-Adrenoceptors - Epinephrine - Clonidine - Adipocytes