Mobilization of colonic kallikrein following pelvic nerve stimulation in the atropinized cat

Abstract

1. Pelvic nerve stimulation (p.n.s.) in cats induces atropine-resistant colonic vasodilatation and colonic contraction. The effects of this on cat colon are mimicked by synthetic bradykinin infusions. The present study examines the effect of p.n.s. on the activation of kallikrein, the kinin-forming enzyme present in colonic tissue and its effects on the plasma kinin system in the atropinized cat.2. Mean level (+/- S.D.) of mucosal kallikrein was found to be about 37 times higher in unstimulated colonic mucosa (300 +/- 100 ng bradykinin equivalents min(-1)g(-1)) than in the underlying muscle (8.2 +/- 6.3 ng bradykinin equiv min(-1)g(-1)).3. After a p.n.s. of 5 min, mean kallikrein level in colonic muscle was 7.3 +/- 3.5 ng bradykinin equiv min(-1)g(-1), which was not significantly different from the control muscle kallikrein. However, there was an 86% fall in mucosal kallikrein to 41.3 +/- 34.7 ng bradykinin equiv min(-1)g(-1) after 5 min p.n.s., indicating a rapid activation and secretion of mucosal kallikrein.4. Secretion of mucosal kallikrein was paralleled by specific depletion of plasma kininogen, the precursor of active kinin in blood draining the colon. The mean plasma kininogen level fell to 79 and 68% of the prestimulated value (3.1 +/- 1.1 S.D. mug bradykinin equiv per ml. plasma) after 5 and 10 min p.n.s. respectively. Total plasma protein and haematocrit remained unaltered excluding non-specific changes due to protein extravasation or haemodilution and indicating utilization of the plasma kinin precursor.5. Following 2 hr p.n.s., raised levels of kallikrein were detected in both colonic muscle (28 +/- 2.0 bradykinin equiv min(-1)g(-1)) and mucosa 434 +/- 118 ng bradykinin equiv min(-1)g(-1)). Preliminary studies using a kallikrein inhibitor indicated that the increased kallikrein levels originated from plasma.6. Direct stimulation of the parasympathetic pelvic nerve in the atropinized cat thus produced activation of the plasma kinin system in the colon and formation of free kinins may be responsible for the mucosal vasodilatation and strong motor contraction which is not blocked by large doses of atropine. The observation that prolonged stimulation causes extravasation of plasma kallikrein, a potential inflammatory mediator, into the tissues may be of clinical significance.