Author ORCID Identifier


Defense Date


Document Type


Degree Name

Doctor of Philosophy


Physiology and Biophysics

First Advisor

John R. Grider

Second Advisor

Srinivasa Murthy Karnam


Isovaleric Acid (IVA) is a 5-carbon branched chain fatty acid present in fermented foods and produced by the fermentation of leucine by colonic bacteria. IVA activates G-protein coupled receptors such as FFAR2, FFAR3, and OR51E1 known to be expressed on enteric neurons and enteroendocrine cells. We previously reported that the shorter, straight chain fatty acids acetate, propionate and butyrate, differentially affect colonic propulsion; however, the effect of branched chain fatty acids on gastrointestinal motility is unknown. We hypothesize that IVA relaxes smooth muscle in a cAMP/PKA dependent manner by direct action on smooth muscle cells. IVA will also decrease peristalsis and encourage retention of luminal contents. This thesis investigates the effect of IVA on smooth muscle tension and peristaltic activity in isolated colon and individual smooth muscle cells.

Colon segments from C57BL/6J mice were placed in a longitudinal orientation in organ baths in Krebs buffer and fastened to force transducers. Segments were contracted with 10 μM acetylcholine (ACh) and the effects of IVA at several concentrations were measured in the absence and presence of Nitric Oxide Synthase inhibitor L-N-nitroarginine (L-NNA), neuronal action potential inhibitor tetrodotoxin (TTX), and adenylate cyclase inhibitor SQ22536. To study individual live cells, mouse smooth muscle was isolated from colon, suspended in smooth muscle buffer, and after contraction with ACh were relaxed with micromolar concentrations of IVA. For peristalsis studies, whole colonic segments isolated from C57BL/6J were catheterized and placed horizontally in organ baths with circulating Krebs buffer. The colon was clamped on the anal end, and a solution (5 μL per mm of colon length) of either Krebs buffer or 50 mM IVA was delivered from the oral end to the lumen. Video of the peristalsis was then analyzed for diameter, changes in diameter, velocity of diameter changes along the length of the colon, normalized to the anatomical changes in the proximal region.

IVA in concentrations of 10 mM to 50 mM relaxed the ACh-induced contraction in a sigmoidal fashion. In separate studies, L-NNA nor TTX affected the ability of IVA to inhibit relaxation. SQ22536 inhibited IVA induced relaxation in longitudinal colon compared to vehicle control. In isolated cells, SQ22536 and PKA inhibitor H-89 inhibited IVA-induced relaxation. In peristalsis studies, 50 mM IVA in Krebs buffer changed the character of the peristaltic action by increasing proximal diameter, inhibiting contractions in the proximal end of the colon, and decreasing overall velocity of peristaltic contractions in the proximal region.

The data indicate that the branched chain fatty acid IVA causes a concentration-dependent relaxation of colonic smooth muscle that is direct to the smooth muscle and independent of neuronal activity. This relaxation is cAMP/PKA dependent. In addition to the direct relaxation of smooth muscle, intraluminal IVA decreased overall colonic propulsive activity and encouraged retention of the luminal contents. We conclude that the ingestion and production of branched chain fatty acids could affect overall GI motility and is an area for study in dietary and therapeutic control of bowel activity.


© Bryan Adam Blakeney

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Available for download on Monday, July 10, 2023