Involvement of capsaicin-sensitive primary afferent fibers in regulation of jejunal alanine absorption

Abstract

Capsaicin-sensitive primary afferent fibers (CSPA) in the small intestine regulate many functions through the release of peptides and neurotransmitters. This study was undertaken to assess the role of CSPA in the regulation of jejunal alanine absorption in the rat. In a series of in vivo experiments, the effects of the sensory neurotoxin capsaicin on small intestinal alanine absorption were evaluated. In vitro experiments were also done to study its effects on alanine uptake by isolated jejunal strips and mucosal scrapings. Jejunal alanine absorption was reduced by 27% when capsaicin (160 and 800 microM) was perfused intraluminally and by 21% when it was applied topically to the cervical vagi. On the other hand, bilateral cervical vagotomy and reversible block of vagal CSPA increased alanine absorption by 29 and 41%, respectively. In vitro, capsaicin reduced alanine uptake by intestinal strips in a dose-dependent manner. Maximal inhibition (36.5%) occurred at 400 microM with the mean ineffective concentration at 87 microM. Alanine uptake by jejunal mucosal scrapings, however, was decreased only by 6.7% when incubated with 1,600 microM capsaicin. These data suggest that vagal CSPA exerts a tonic inhibitory effect on alanine absorption and that capsaicin's inhibitory effect on alanine absorption is mediated largely by the capsaicin-sensitive afferent fibers.

Capsaicin-sensitive vagal afferents modulate posttranscriptional regulation of the rat Na+/glucose cotransporter SGLT1

“…Studies have shown that intraluminal capsaicin infusion (which is acutely excitatory on vagal afferents) in the short term suppresses alanine transport and expression of the PepT1 peptide transporter (2,18). In contrast, vagal deafferentation leads to upregulation of alanine transport (25). Functional studies (using brush-border membrane vesicle uptake of glucose) have demonstrated that vagal deafferentation prevents upregulation of glucose transport after switching to a highcarbohydrate diet in guinea pigs (3).…”

Inhibitory effect of experimental colitis on fluid absorption in rat jejunum: role of the enteric nervous system, VIP, and nitric oxide

“…The ENS, one of the major parts of the autonomic nervous system, is involved in the regulation of gastrointestinal transport of fluid (19,29) and amino acids (5,41). Changes in the ENS and extrinsic innervation in colitis have been described, as evidenced by an increase in c-Fos in myenteric neurons, enteric glia, brain stem, and spinal cord in formalin-induced colitis in rats (31,33) and by an increase in ileal myoelectric activity in TNBS-treated rats (3).…”

Amino acids in the rat intestinal lumen regulate their own absorption from a distant intestinal site

“…Aliquots of the initial and effluent solutions were assayed for phenol red concentration and radioactivity content. Absorption was calculated from the rate of disappearance of labeled amino acid from the perfusate solution, taking into account water transport as measured by the change of phenol red concentrations (9,40,41).…”

“…1 filter paper, its wet weight was determined, and then the strip was extracted in 2 ml of 0.1 M HNO 3 for at least 4 h. Aliquots of the tissue extracts and incubation media were counted for their [ 14 C]Ala content in a liquid scintillation counter. From the data obtained, intracellular concentration of Ala was calculated after correction for the extracellular space by using a trace amount of [ 3 H]inulin as an extracellular marker (41). Values of intracellular Ala concentration were plotted against Ala concentration in the incubation medium.…”