Table 3.
Physiological measurements
| Factor | Control/Control | SCFA/Control | Control/Stress | SCFA/Stress |
|---|---|---|---|---|
| Plasma lipopolysaccharide‐binding protein | ||||
| LBP (μg mL−1) | 7.6 ± 0.3 | 8.0 ± 0.2 | 8.5 ± 0.2 | 7.8 ± 0.3 |
| Body weight change | ||||
| Day 3 of stress (Δg) | 0.24 ± 0.13 | 0.15 ± 0.05 | −0.54 ± 0.20** | −0.48 ± 0.21$ |
| Day 9 of stress (Δg) | 0.41 ± 0.16 | 0.39 ± 0.11 | −0.25 ± 0.17* | 0.18 ± 0.25 |
| Day 16 of stress (Δg) | 0.21 ± 0.25 | 0.28 ± 0.16 | 1.82 ± 0.28** | 1.85 ± 0.31$$ |
| 6 weeks post stress (Δg) | 0.39 ± 0.42 | 0.90 ± 0.17 | 1.63 ± 0.30* | 2.26 ± 0.27$$ |
| End of study (Δg) | 1.48 ± 0.29 | 1.44 ± 0.25 | 1.91 ± 0.40 | 2.61 ± 0.29 |
| Daily water intake at end of the study | ||||
| Drinking water consumed (mL) | 5.4 ± 0.2 | 4.8 ± 0.4 | 5.0 ± 0.2 | 4.7 ± 0.3 |
| Organ measurements | ||||
| Left adrenal (mg g−1 BW) | 0.052 ± 0.006 | 0.060 ± 0.006 | 0.067 ± 0.006 | 0.066 ± 0.005 |
| Right adrenal (mg g−1 BW) | 0.037 ± 0.006 | 0.047 ± 0.006 | 0.041 ± 0.006 | 0.043 ± 0.007 |
| Spleen (mg g−1 BW) | 2.48 ± 0.09 | 2.44 ± 0.05 | 2.60 ± 0.08 | 2.60 ± 0.07 |
| Thymus (mg g−1 BW) | 1.52 ± 0.08 | 1.64 ± 0.05 | 1.61 ± 0.08 | 1.67 ± 0.06 |
| Caecum (mg g−1 BW) | 17.2 ± 0.5 | 16.7 ± 0.7 | 17.2 ± 1.0 | 15.9 ± 0.4 |
| Colon (cm) | 7.3 ± 0.2 | 7.5 ± 0.2 | 7.3 ± 0.18 | 7.7 ± 0.3 |
| Faecal SCFAs and BCFAs | ||||
| Acetate (μmol g−1 wet mass) | 32.2 ± 5.6 | 35.0 ± 5.7 | 64.8 ± 11.4** | 54.1 ± 9.0 |
| Propionate (μmol g−1 wet mass) | 2.5 ± 0.3 | 3.2 ± 0.4 | 4.4 ± 0.8 | 4.0 ± 0.6 |
| Butyrate (μmol g−1 wet mass) | 2.0 ± 0.4 | 1.7 ± 0.2 | 2.3 ± 0.6 | 1.7 ± 0.2 |
| Valerate (μmol g−1 wet mass) | 0.85 ± 0.17 | 0.91 ± 0.21 | 1.00 ± 0.18 | 0.84 ± 0.14 |
| Total SCFAs (μmol g−1 wet mass) | 38.3 ± 5.7 | 42.0 ± 5.8 | 74.0 ± 12.6** | 62.2 ± 8.8 |
| Isobutyrate (μmol g−1 wet mass) | 0.53 ± 0.14 | 0.49 ± 0.10 | 0.85 ± 0.26 | 0.95 ± 0.19 |
| Isovalerate (μmol g−1 wet mass) | 0.52 ± 0.09 | 0.52 ± 0.07 | 0.58 ± 0.07 | 0.62 ± 0.08 |
| Total BCFAs (μmol g−1 wet mass) | 1.05 ± 0.18 | 0.99 ± 0.09 | 1.43 ± 0.29 | 1.57 ± 0.24 |
| SCFA GPCR expression | ||||
| FFAR2 (fold change) | 1.00 ± 0.17 | 0.89 ± 0.10 | 1.79 ± 0.23* | 1.89 ± 0.30$ |
| FFAR3 (fold change) | 1.00 ± 0.09 | 0.92 ± 0.04 | 1.14 ± 0.14 | 1.36 ± 0.12$ |
Lipopolysaccharide‐binding protein (LBP) was quantified from plasma obtained at the end of the experiment from trunk blood. Body weights and drinking water consumed were assessed throughout the study and normalised to the starting body weight to calculate body weight change (Δ body weight). Organs were collected at the end of the study and weighted. Thymus, adrenals, spleen and caecum weights were normalised to body weight, whereas the colon is expressed in total colon length. Faecal pellets were collected 6 weeks post psychosocial stress and analysed for SCFA and BCFA levels. Colonic gene expression analysis for SCFA GPCRs was carried out for free fatty acid receptors 2 and 3 (FFAR2 and FFAR3, respectively). Body weight data and gene expression data were non‐parametrically distributed and analysed using the Kruskal‐Wallis test, followed by the Mann‐Whitney test. Data from SCFA levels were normally distributed and analysed using a two‐way ANOVA, followed by an LSD post hoc test. Significant differences are depicted as: * P < 0.05 and ** P < 0.01; Control/Control compared to Control/Stress, $ P < 0.05 and $$ P < 0.01; SCFA/Control compared to SCFA/Stress. Data are expressed as means ± SEM (n = 8–10).