The action of enterostatin as a potential relaxing factor for intestin
al smooth muscles has been investigated. Motor responses of muscle str
ips obtained from the duodenum, Jejunum and ileum of the pig were foll
owed in isometric conditions. Enterostatin in concentrations of 0.05,
0.5, 5.0 and 50 mu g/ml did not influence either the muscle tension or
the motility index of duodenal and ileal sections. The jejunal sectio
ns responded in a significant manner only to the highest dose (50 mu g
/ml) of the pentapeptide with relaxation to about 65% of the mean basa
l tension, while its motility index remained unchanged. Those findings
indicate that enterostatin does nos not act directly on intestinal mu
scle contractile activity in vitro. The effect of the dose of 50 mu g/
ml of enterostatin on jejunal motility is rather of pharmacological re
levance and thus should not be considered physiologically important.