Modulation of receptors and adenylate cyclase activity during sucrose feeding, food deprivation, and cold exposure.
Thermogenesis in brown adipose tissue (BAT) serves as a regulator of body temperature and weight maintenance. Thermogenesis can be stimulated by catecholamine activation of adenylate cyclase through the beta-adrenergic receptor. To investigate the effects of sucrose feeding, food deprivation, and cold exposure on the beta-adrenergic pathway, adenylate cyclase activity and beta-adrenergic receptors were assessed in rat BAT after 2 wk of sucrose feeding, 2 days of food deprivation, or 2 days of cold exposure. beta-Adrenergic receptors were identified in BAT using [125I]iodocyanopindolol. Binding sites had the characteristics of mixed beta 1- and beta 2-type adrenergic receptors at a ratio of 60/40. After sucrose feeding or cold exposure, there was the expected increase in BAT mitochondrial mass as measured by total cytochrome-c oxidase activity but a decrease in beta-adrenergic receptor density due to a loss of the beta 1-adrenergic subtype. This BAT beta-adrenergic receptor downregulation was tissue specific, since myocardial beta-adrenergic receptors were unchanged with either sucrose feeding or cold exposure. In contrast, food deprivation did not alter BAT beta-adrenergic receptor density. Forskolin-stimulated adenylate cyclase activity increased in BAT after sucrose feeding or cold exposure but not after food deprivation. The ratio of isoproterenol-stimulated to forskolin-stimulated adenylate cyclase activity decreased in the sucrose-fed and cold-exposed rats but not in the food-deprived rats. These data suggest that in BAT, sucrose feeding or cold exposure result in downregulation of beta-adrenergic receptors and that isoproterenol-stimulated adenylate cyclase activity was limited by receptor availability.
Scarpace
P J
PJ
Geriatric Research Education and Clinical Center, Veterans Administration Medical Center, Sepulveda, California 91343.
Baresi
L A
LA
Morley
J E
JE
D000262:Adenylyl Cyclases / Q000378:metabolism*; D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D001835:Body Weight; D003080:Cold Temperature; D005576:Colforsin / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000378:metabolism; D005508:Food Deprivation; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism*
D011506:Proteins; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D013395:Sucrose; D003576:Electron Transport Complex IV; D000262:Adenylyl Cyclases