Effects of vasopressin and isoprenaline infusions on the distribution of blood flow in the intestine; criteria for the validity of microsphere studies

Abstract

Summary1. The distribution of superior mesenteric arterial flow was investigated by radioactive microspheres. The small intestine received 83% of the flow ((85 ml/min)/100 g intestine) and flow was uniform along the length of the small intestine. 2. The intestinal wall was separated into 3 layers-muscle, submucosa and mucosa. The muscle received (8 ml/min)/100 g intestine and the combined submucosa and mucosa (77 ml/min)/100 g intestine.3. The distribution of microspheres between the mucosa and submucosa depended on the size of the microspheres; the smaller the spheres, the more were found in the mucosa. It also depended on the state of the vascular bed; if microspheres were given during an infusion of vasopressin, a subsequent infusion of isoprenaline resulted in movement of some of the spheres from the submucosa into the mucosa. 4. Histological studies after India ink injection showed few capillary-sized vessels but many large vessels in the submucosa. Capillary-sized vessels arose close to the junction with the mucosa and passed into the mucosa. 5. These and other data suggest that the intestine consists of two parallelcoupled sections, one to the muscle and the other through the submucosa to the mucosa. The vessels in the submucosa are in series with those in the mucosa and submucosal shunts do not exist. Redistributions of flow between mucosa and submucosa cannot therefore occur during stimulation of the sympathetic nerves or infusions of drugs such as noradrenaline or adrenaline. 6. When microspheres are used in pharmacological investigations on distribution of blood flow in organs, controls to validate the method for the particular areas being studied are essential. If the vessels in the areas studied are in series rather than in parallel, the method is invalid.

Microsphere Measurement of Regional Intestinal Blood Supply and Cardiac Output in the Rat

“…However, as the heart values were unreliable, the cardiac output was calculated after subtraction of the activity in the heart and therefore in fact comprises cardiac output minus coronary blood flow. Our cardiac output values are thus slightly underestimated, but they compare favourably with other results obtained with different techniques (7,14,3,6). The coronary blood flow in the rat has been estimated at 2.9% (11) and 6.4% (12) of the cardiac output.…”

Arteriolar, capillary, and shunt flow gradients along the intestine in relation to the weight distribution of the mucosa, submucosa, and muscularis—a microsphere study

“…Furthemore, in a recent study Shepherd et d. (1984) have demonstrated that during isoproterenol-induced vasodilation the changes in mucosal, submucosal, and muscularis blood flow measured by laser-Doppler velocimetfy were similar to those measured by 15-pm spheres. In contrast, Greenway and Murthy (1972) found that 12-and 17-pm microspheres (these sizes are close to the size range of the 15 * 2.5 )am microspheres used in the present study), which became entrapped in the submucosa during vasoconstriction, migrated to the mucosa during subsequent vasodilation. No such migration was found to occur to or from the muscularis.…”

The measurement of colonic mucosal‐submucosal blood flow in man.

“…However, despite carrying the principal vascular plexus of arteriolar supply to the mucosa and inner part of the muscularis externa, Svanvik & Lundgren (1977) have stated that the submucosa is a small compartment of connective tissue with a scarse nutritional vascularization of its own. Greenway & Murthy (1972) confirmed that the submucosa showed an almost complete absence of capillary-sized vessels. Since the radioactive tracer diffuses into and is subsequently washed away from such nutritional exchange vessels, most of the tracer will be taken up in the abundant capillaries of the mucosa and its clearance from the area will largely be an index of mucosal blood flow.…”