Central sensibility of human cases with different body mass during oral glucose tolerance test using functional magnetic resonance imaging

Abstract

Background Because of the limitation of technique, there are few researches on regulating function of central hypothalamus by metabolism, especially the researches on real-time function. Objective To evaluate the response of hypothalamus to oral glucose tolerance test (OGTT) in different body-weighted subjects by using functional magnetic resonance imaging (fMRI) so as to investigate the relationship between the sensitivity of hypothalamus in glycoregulation and disturbance of carbohydrate metabolism. Design Paired design. Setting Department of Radiology and Beijing Geriatrics Institute, Beijing Hospital, National Public Health Bureau. Participants A total of twenty healthy volunteers were selected from Beijing Geriatrics Institute, National Public Health Bureau, including 10 subjects with obesity (5 males and 5 females; body mass > 28.0 kg/m 2) and 10 subjects with normal body mass (5 males and 5 females; body mass from 18.5 to 23.9 kg/m 2). All subjects gave written informed consent before participating in the study. Methods fMRI study was performed on GE 1.5 T Signa Twinspeed Infinity with Excite. Each volunteer was ingested of glucose during the fMRI scan. T2* images were acquired using a single-shot gradient echo (EPI) technique. The parameters of EPI included: TR 3 000 ms, TE 40 ms, Flip angle 90°, field of view (FOV) 24 cm × 24 cm, thickness 5 mm, gap 0 mm, matrix 64 × 64, number of excitation 1. All 10 subjects with normal body mass underwent a repeat fMRI scan after consuming an equivalent amount of water without glucose on a separate day. The procedure for the fMRI scan with water intake was the same as for glucose ingestion. fMRI data were processed with Intensity Averaging Method. Main outcome measures The central response of hypothalamus and feedback orientation during OGTT in different body-weighted subjects. Results An acute transient decrease of fMRI intensity in posterior inferior and anterior inferior of hypothalamus was observed in all subjects within 2 minutes after oral glucose intake. This decrease was followed by a recovery to the baseline. However, obese subjects had a delayed intensity decrease [(1.96±1.06) minutes vs. (1.04±0.71) minutes, t =2.14, P < 0.05] and longer recovery time [(26.62±7.35) minutes vs. (16.29±6.42) minutes, t =3.67, P < 0.01] as compared with normal body-weight subjects. Furthermore, decreased fMRI intensity was significant different from baseline intensity [(5.7±2.5)% vs. (14.3±5.5)%, t =2.56, P < 0.05] in obese subjects, but not in normal body-weight subjects. The area of hypothalamus in normal body-weight volunteers demonstrated no significant signal change before and after oral water ingestion ( P > 0.05). Conclusion Hypothalamus response to glucose loading is different in normal body-weighted and obese subjects. This suggests that fMRI is a useful tool to evaluate the central regulation of glucose metabolism.