[Circadian rhythm changes of the levels of endogenous insulin in growing rat condylar cartilage after functional mandibular protrusion].
OBJECTIVE
In order to determine which time of the day is best to wear functional appliances in clinic, the author investigates the circadian rhythm of the level of endogenous Insulin in growing rat condylar cartilages and the changes after functional mandibular protrusion in daytime (8:00-20:00) or nighttime (20:00-8:00).


METHODS
72 4-week-old SD rats were divided equally and randomly into experimental and control groups, and the rats in experimental groups were put on the functional appliance in daytime (8:00-20:00) or nighttime (20:00-8:00). After 7 days, all rats were sacrificed at 0:00, 4:00, 8:00, 12:00, 16:00, 20:00 in a day. Radioimmunoassay methods were used to detect the levels of endogenous insulin in growing rat condylar cartilages.


RESULTS
1. The levels of endogenous insulin in the growing rat condylar cartilage displayed a significant circadian rhythm. The acrophase was about 12:13. 2. The circadian rhythm still existed after the rats had been put on the functional appliance. Both mesor and amplitude were significantly higher in the experimental groups than in the control group 3. The levels (both mesor and amplitude) of endogenous insulin in the condylar cartilage were significantly higher in the daytime-forced group than in the nighttime-forced group.


CONCLUSIONS
1. The growth and remodeling of the condylar cartilage in the growing rats shows significant circadian rhythm. The most active period of chordrocyte proliferation may occur during the daytime. 2. The circadian rhythm still exists after the rats have been put on the functional appliances. 3. Compared with nighttime appliance wearing, daytime appliance wearing may be more conductive to cell proliferation, so it may be more effective to stimulate the growth and remodeling of condylar cartilage in the growing rat. 4. Related to human beings, these data suggest that the best period for patients to wear the functional appliances might be from 20:00 pm to 8:00 am of the next day.
Lou
X
X
College of Stomatology, West China University of Medical Sciences.
Chen
Y
Y
Luo
S
S
Chen
G
G
D000818:Animals; D002356:Cartilage / Q000254:growth & development / Q000378:metabolism*; D002940:Circadian Rhythm; D007328:Insulin / Q000378:metabolism*; D008297:Male; D008335:Mandibular Condyle / Q000254:growth & development / Q000378:metabolism*; D017289:Orthodontic Appliances, Functional; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley
D007328:Insulin