1. The effects of spermine in the concentration range 0–10 mmol/l on (a) the fluid absorption, (b) the polyethylene glycol permeability, (c) the release of collagenase activity activity into the lumen and (d) the histological appearance of rat descending colon were examined.
2. Spermine (5 mmol/l) decreased fluid absorption from 48.83 ± 2.98 (n = 7) to 23.98 ± 2.32 (n = 6) μl h−1 cm−2 (P<0.01); polyethylene glycol 4000 permeability was increased from 0.030 ± 0.001 (n = 7) to 0.047 ± 0.003 (n = 6) cm/h (P<0.01) and luminal collagenase activity increased from a negligible control value to 250 ± 39 (n = 6) units/ml (P<0.001). Spermine also caused oedema formation within the mucosal interstitial fluid, without inducing an overt breakdown of the mucosa at the luminal surface.
3. Polyamine-free dialysed seminal plasma had no effect on polyethylene glycol 4000 permeability, although it still caused a significant decrease in colonic fluid absorption from 48.83 ± 2.98 (n = 7) (control) to 31.41 ± 2.08 (n = 5) μl h−1 cm−2 (P<0.01).
4. Low-molecular-mass heparin (600 units/ml) prevented the spermine (5 mmol/l)- and whole-semen-induced increase in colonic polyethylene glycol 4000 permeability and reduced the effect of semen on fluid absorption by 63% (P<0.001) and that of spermine by 56% (P<0.01).
5. The Zn2+ chelator and collagenase inhibitor o-phenanthroline reduced the effect of spermine on fluid absorption and polyethylene glycol 4000 permeability by 100% (P<0.001) and on interstitial oedema formation. o-Phenanthroline also reduced the effects of whole semen on fluid absorption (by 70%, P<0.01) and on polyethylene glycol 4000 permeability by 95%, P<0.01).
6. A synthetic peptide inhibitor of mammalian collagenase activity with high affinity reduced the effects of whole semen on polyethylene glycol 4000 permeability (P<0.01) and on fluid absorption (P<0.01) in a dose-dependent manner. The inhibitor (2 mmol/l) also reduced the effects of spermine (5 mmol/l) on fluid absorption and polyethylene glycol 4000 permeability.
7. These results indicate that polyamines that are present within semen in the concentration range 5–15 mmol/l act co-operatively with seminal collagenases to disrupt the colonic barrier. Cationic polyamines may activate collagenases by binding to and neutralizing the anionic charge of heparins within the interstitial matrix.