The hormonal responses of lipoprotein lipase activity and lipolysis in adipose tissue differ depending on the stage of the estrous cycle in female rats.
OBJECTIVE
This study was designed to elucidate whether there were differences in the hormonal responses of the parameters involving triacylglycerol (TG) deposition and mobilization in adipose tissue among the stages of the estrous cycle in female rats.


METHODS
Adipose tissue was obtained from the parametrial region in female rats at each stage of the estrous cycle. Lipoprotein lipase (LPL) activity in the extracts of acetone/ether powders of the tissues was measured as a parameter for TG deposition. Norepinephrine-stimulated lipolysis in isolated fat cells was measured as a parameter for TG mobilization.


RESULTS
LPL activity changed periodically during the estrous cycle; the activity level was highest at diestrus, began to decrease at proestrus, reached a minimum at estrus, began to increase again at metestrus-1, and increased further at metestrus-2. At diestrus and proestrus, LPL activity was increased with an increase in plasma insulin levels, suggesting that plasma insulin was the predominant up-regulator of LPL. But at estrus, metestrus-1 and metestrus-2, LPL activity remained low even when plasma insulin levels were high, indicating that it was not up-regulated by plasma insulin. Norepinephrine-stimulated lipolysis in fat cells was high at estrus and metestrus-1 and low at diestrus.


CONCLUSIONS
The hormonal responses of LPL activity and lipolysis in adipose tissue differed depending on the stage of the estrous cycle.
Yamaguchi
M
M
Second Department of Medical Biochemistry, School of Medicine, Ehime University, Shigenobu, Onsen-gun, Ehime, Japan. yamaguti@sahs.med.osaka-u.ac.jp
Katoh
S
S
Morimoto
C
C
Sakayama
K
K
Shiosaka
T
T
Masuno
H
H
Okuda
H
H
D000273:Adipose Tissue / Q000201:enzymology* / Q000378:metabolism; D000818:Animals; D004958:Estradiol / Q000097:blood; D030762:Estrous Cycle / Q000378:metabolism*; D004971:Estrus / Q000378:metabolism; D005260:Female; D006728:Hormones / Q000097:blood*; D007328:Insulin / Q000097:blood; D008066:Lipolysis / Q000187:drug effects; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008686:Metestrus / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D009752:Nutritional Status; D009929:Organ Size; D011359:Proestrus / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014280:Triglycerides / Q000378:metabolism; D014599:Uterus / Q000033:anatomy & histology
D006728:Hormones; D007328:Insulin; D014280:Triglycerides; D004958:Estradiol; D008071:Lipoprotein Lipase; D009638:Norepinephrine