TY - JOUR
T1 - Nonreceptor-Mediated Responses of Adenylate Cyclase in Membranes from Liver, Muscle, and White and Brown Adipose Tissue of Obese (fa/fa) and Lean (Fa/) Zucker Rats
AU - Naim, Michael
AU - Katz, Yair
AU - Brand, Joseph G.
AU - Kare, Morley R.
PY - 1990/12
Y1 - 1990/12
N2 - Adenylate cyclase activity was determined in membranes of liver, muscle, white adipose tissue, and brown adipose tissue (BAT) of lean (Fa/) and obese (fa/fa) Zucker rats. Responses were monitored following β-adrenergic receptor stimulation and addition of GTP, gtpγs, or forskolin. β-Adrenergic responses in liver, white adipose tissue, and BAT were lower in obese than in lean animals. No such difference was observed in muscle membranes. Production of cAMP after addition of guanine nucleotides was lower in liver and white adipose tissue membranes from obese rats compared with their lean littermates. Synthesis of cAMP in muscle membranes of obese animals after addition of GTP was either not different, or slightly higher, than that observed in muscle membranes from lean animals. Furthermore, production of cAMP after forskolin addition to muscle membranes of obese rats was significantly higher than that observed from lean rats under the same conditions. Interestingly, BAT membranes of obese rats were significantly more sensitive to guanine nucleotide activation than those of lean animals. The results confirm recent findings indicating inferior function of G proteins in liver plasma membranes of obese Zucker rats, and extend this observation to adipose tissue. The present results further suggest that the “nonreceptor” components (e.g., G proteins) responsible for the activation of adenylate cyclase in BAT membranes of obese rats are more responsive to stimulation than those of lean animals. Such sensitivity may be related to and perhaps compensate for the reduced thermogenic activity in the obese Zucker rat during the development of obesity.
AB - Adenylate cyclase activity was determined in membranes of liver, muscle, white adipose tissue, and brown adipose tissue (BAT) of lean (Fa/) and obese (fa/fa) Zucker rats. Responses were monitored following β-adrenergic receptor stimulation and addition of GTP, gtpγs, or forskolin. β-Adrenergic responses in liver, white adipose tissue, and BAT were lower in obese than in lean animals. No such difference was observed in muscle membranes. Production of cAMP after addition of guanine nucleotides was lower in liver and white adipose tissue membranes from obese rats compared with their lean littermates. Synthesis of cAMP in muscle membranes of obese animals after addition of GTP was either not different, or slightly higher, than that observed in muscle membranes from lean animals. Furthermore, production of cAMP after forskolin addition to muscle membranes of obese rats was significantly higher than that observed from lean rats under the same conditions. Interestingly, BAT membranes of obese rats were significantly more sensitive to guanine nucleotide activation than those of lean animals. The results confirm recent findings indicating inferior function of G proteins in liver plasma membranes of obese Zucker rats, and extend this observation to adipose tissue. The present results further suggest that the “nonreceptor” components (e.g., G proteins) responsible for the activation of adenylate cyclase in BAT membranes of obese rats are more responsive to stimulation than those of lean animals. Such sensitivity may be related to and perhaps compensate for the reduced thermogenic activity in the obese Zucker rat during the development of obesity.
UR - http://www.scopus.com/inward/record.url?scp=0025611618&partnerID=8YFLogxK
U2 - 10.3181/00379727-195-43157
DO - 10.3181/00379727-195-43157
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C2 - 2175438
AN - SCOPUS:0025611618
SN - 0037-9727
VL - 195
SP - 369
EP - 374
JO - Experimental Biology and Medicine
JF - Experimental Biology and Medicine
IS - 3
ER -