Olfactory stimulation modulates the blood glucose level in rats

Abstract

In both humans and animals, chemosensory stimuli, including odors and tastes, induce a variety of physiologic and mental responses related to energy homeostasis, such as glucose kinetics. The present study examined the importance of olfactory function in glucose kinetics following ingestion behavior in a simplified experimental scenario. We applied a conventional glucose tolerance test to rats with and without olfactory function and analyzed subsequent blood glucose (BG) curves in detail. The loss of olfactory input due to experimental damage to the olfactory mucosa induced a marked decrease in the area under the BG curve. Exposure to grapefruit odor and its main component, limonene, both of which activate the sympathetic nerves, before glucose loading also greatly depressed the BG curve. Pre-loading exposure to lavender odor, a parasympathetic activator, stabilized the BG level. These results suggest that olfactory function is important for proper glucose kinetics after glucose intake and that certain fragrances could be utilized as tools for controlling BG levels.

Keywords: blood glucose; glucose tolerance test; odor; the area under the curve of blood glucose.

Figure 1

Effect of anosmic treatment on the blood glucose curve. A, comparison of the latency to the finding of the cookie before and after the anosmic treatment in the control and anosmic groups. Data are mean ± SEM (n=6, per each group), *P < 0.05 (after vs. before anosmic treatment), Wilcoxon signed-rank test, ^†P < 0.01 (anosmic groups vs. control groups after the anosmic procedure), Mann-Whitney U test. B, the BG curves before and after anosmic treatment in anosmic rats. Data are mean ± SEM (n=6), *P < 0.05 (after vs. before anosmic treatment), two-way repeated-measures ANOVA followed by Tukey-kramer test.

Figure 2

Effect of addition of olfactory stimulus on the blood glucose curve. The effect of odor stimulation on the blood glucose curve is shown under the following conditions: (A) control and sniffing of grapefruit odor for 15 min (n=6), (B) control and sniffing of lavender odor for 15 min (n=6), (C) sniffing grapefruit and limonene odors contained in grapefruit oil for 15 min (n=5), and (D) sniffing grapefruit for 15 min before and after anosmic treatment (n=6). Data are mean ± SEM. *P < 0.05, two-way repeated-measures ANOVA followed by Tukey-kramer test.