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SUMMARY1. The release of vasoactive intestinal polypeptide (VIP) into blood from the gastrointestinal tract was studied when eliciting autonomic nervous effects known to be mediated via non-adrenergic, non-cholinergic nerve fibres. All studies were performed on animals given atropine.2. Electrical stimulation of the low threshold vagal fibres to the stomach did not significantly change gastric volume or VIP concentration in the venous effluent from the stomach. Stimulating the high threshold fibres, on the other hand, produced a gastric relaxation concomitant with a significant increase of venous plasma VIP concentration. When eliciting a similar vagal relaxation of the stomach by distending a balloon in the oesophagus a significant increase of venous plasma VIP concentration was also recorded.3. Mechanical stimulation of the mucosa of the small bowel increased intestinal blood flow and a significant increase of venous plasma VIP concentration was observed.4. Stimulation of the pelvic nerves to the colon produced a transient vasodilation and a significant increase of VIP in the venous effluent from the large bowel. A maintained vasodilation in the colon was induced by mechanically stimulating the rectal mucosa. This vascular response was accompanied by a significant raise of venous plasma VIP concentration.5. The results demonstrate that all the studied nervous effects known to be mediated via non-adrenergic, non-cholinergic nerve fibres were accompanied by significant increases of the VIP concentration in the venous effluent. The possible physiological implications of these findings are discussed and it is proposed that VIP may be a neurotransmitter in the gastrointestinal tract.

FOLKOW, B., U. HAGLUND, M. JODAL and 0. LUNDGREN. Blood flow in the calf muscle of man during heavy rhythmic exercise. a c t a physiol. scand. 1971. 81. 157-1 63.133Xenon clearance was recorded during maximal vasodilatation in the calf muscles of trained subjects during rest and during heavy rhythmic exercise (contraction about 0.3 sec, relaxation about 0.7 sec) when the subject was tilted from a supine to a "leg down" position. The k-value for the wash-out curve, divided by the mean arterial blood pressure at heart level (MABP), was considered to reflect the relative levels of maximal flow in the two experimental situations. While a shift to "leg down" position during post-exercise hyperemia did not significantly increase flow through the fully dilated muscle vessels, indicating that they were already maximally distended, the same shift during rhythmic exercise raised the average value of k/MABP approximately 60 per cent above control. This observation is in all probability explained by a marked lowering of mean venous pressure by the "muscle pump" in the dependent legs, despite the huge flow during the heavy rhythmic exercise. This would result in a considerable gain in local perfusion pressure and hence in maximal flow capacity. 157

Intestinal secretion was produced in anesthetized cats and rats by exposing isolated intestinal segments to cholera enterotoxin. Giving, for example, tetrodotoxin, a nerve-conduction-blocking agent, or adding lidocaine, a local anesthetic agent, to the solution in the intestinal segments markedly inhibited the rate of choleraic secretion, and in most experiments a net absorption of fluid was observed. The results suggest that intramural nervous mechanisms are involved in the pathogenesis of choleraic secretion.

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