Figure 3.

GLP-1 Secretion from Primary Intestinal Cultures

(A and B) Mixed primary cultures from the upper half of the small intestine (A) or the colon (B) were incubated in bath solution containing the glucose concentrations indicated. The percentage of GLP-1 secretion in each well is expressed relative to the basal secretion measured in parallel on the same day. Dose-response curves were fitted through the entire data set using a logistic equation, giving EC₅₀s of 4 mM and 0.7 mM for the small intestine and colon, respectively (not significantly different). Error bars represent 1 SE, and significance is shown relative to baseline using a single-factor t test. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001.

(C) GLP-1 secretion from primary colonic cultures triggered by forskolin/IBMX (F/I, 10 μM of each), bombesin (Bb, 100 nM), or glucose (Gluc, 10 mM), as indicated, measured and expressed as in (A). Error bars represent 1 SE, and significance is shown relative to baseline using a single-factor t test: ^∗∗∗p < 0.001. The additional effect of glucose was analyzed by regression analysis to compensate for variation in the effectiveness of forskolin/IBMX or bombesin between different experiments: ΔΔΔp < 0.001.

(D and E) GLP-1 secretion from the upper small intestine (D) or colon (E), measured as in (A), following addition of glucose (Gluc, 10 mM), αMG (10 mM), tolbutamide (tolb, 500 μM), sucralose (sucl, 1 or 20 mM), or acesulfame K (AceK, 2 mM). The control bar (Con) and dashed line indicate the basal rate of secretion. Data represent the mean and SE of the number of wells indicated, and significance is shown relative to baseline, tested by a single-factor t test. ^∗p < 0.05, ^∗∗ p < 0.01. n.s., not significant.