An investigation into the relationship between small intestinal fluid secretion and systemic arterial blood pressure in the anesthetized rat

Abstract

The effects of changes in the steady level of diastolic blood pressure on fluid flux across the jejunum has been investigated in the anesthetized rat during perfusion with a nutrient-free and Na+-free solution. Diastolic blood pressure was manipulated by intravenous infusions, during the jejunal perfusions, of vasodilators (vasoactive intestinal polypeptide, acetyl-β-methylcholine, and phentolamine) and a vasoconstrictor (arginine vasopressin), each of which acts through a different cellular mechanism. The outcome was that fluid flux was related by a parabolic relationship with diastolic blood pressure in which net secretion occurred over the range 40–100 mmHg, whereas net absorption was recorded at diastolic pressures exceeding 100 mmHg and below 40 mmHg. Against a background of normal absorption promoted by perfusion with 145 mmol L−1 Na+/5 mmol L−1 glucose solution, reductions in diastolic blood pressure markedly reduced the mean rate of fluid absorption by 58% overall, whereas the rate of glucose absorption remained unchanged. Our results were explained on the basis that vasodilatation led to increased capillary pressure and then to net filtration of fluid from the mesenteric capillary bed. Experiments in which Escherichia coli heat-stable toxin was added to the jejunal perfusate confirmed the absence of a secretory response, which was consistent with the absence of effect of the toxin on diastolic blood pressure.

The Arteriolar Vasodilatation Model of Vibrio cholerae Induced Diarrhoeal Disease

“…Preliminary studies on the relationship between arterial and therefore capillary pressure and fluid secretion [63] have demonstrated an excellent correlation between these variables, exactly as predicted by a consideration of the Starling forces across the intestinal capillaries.…”

Paracellular Filtration Secretion Driven by Mechanical Force Contributes to Small Intestinal Fluid Dynamics

“…The present findings suggest that this force contributes to fluid secretion [ 15 ]. Increased perfusion of the intestinal vasculature is another driving force for filtration secretion of fluid into the intestine [ 10 , 48 ] and would be concomitant with increased motility. Although present in vivo, it was absent in the cell and intact intestinal tissue preparations we used.…”

Comparison of the Effects of E. coli STa with E. coli LT, Clostridium difficile Toxin A and Osmotic Burdens on Small Intestinal Fluid Transport: Additional Proof that STa is Not a Secretory Enterotoxin

“…Pithing es spinal nerve control and it is likely that sympathetic vasoconstriction is absent. This makes it likelier that pithing and theophylline are secretory in their own right since they are associated with reduced arterial blood pressure and hence increased capillary pressure, making the jejunum secretory because of altered Starling forces [17]. Secretion under these circumstances would be opposed by normal absorption but would become very evident when fluid absorption was inhibited by STa.…”

“…An attempt at reconciliation is that STa is indeed not secretory but is an aberrant enterotoxin for reasons that are unclear; the lack of secretion is a distracting, minor feature of intestinal pathophysiology, potentially eventually explicable within the present enterocyte based paradigm. A more robust defence of the paradigm is that contradictory findings originate from one laboratory only [12,[14][15][16][17][18] and could represent merely the failure in one laboratory to demonstrate the known fact of secretion. The error must arise through inadequate maintenance of blood pressure, a poor perfusion regime that prevents secretion from manifesting itself or a combination of these and other unrealised factors.…”