G. Bassotti et al., NIFEDIPINE AND VERAPAMIL INHIBIT THE SIGMOID COLON MYOELECTRIC RESPONSE TO EATING IN HEALTHY-VOLUNTEERS, Diseases of the colon & rectum, 41(3), 1998, pp. 377-380
BACKGROUND: Constipation is not an infrequent side effect complained o
f by patients taking calcium channel blockers. This effect may reduce
patients' compliance and yield potentially serious consequences. Howev
er, the underlying mechanisms for constipation caused by such compound
s are not known. AIMS: The purpose of the present study was to assess
the effects of nifedipine and verapamil on the sigmoid myoelectric res
ponse to eating, a physiologic test of colonic motor function. SUBJECT
S AND METHODS: Nine healthy male volunteers with no previous abdominal
surgery were recruited for the study and underwent three paired studi
es at two-week intervals. Myoelectric sigmoid activity was recorded by
means of two clip electrodes introduced within the viscus without pre
paration for 30 minutes basally and 90 minutes postprandially. Each st
udy was preceded by placebo, nifedipine (20 mg), or verapamil (120 mg)
. RESULTS: Analysis of the tracings revealed that nifedipine strongly
inhibited the sigmoid myoelectric response to the meal. This response
was also significantly reduced in those taking verapamil compared with
the placebo group, although to a much lesser extent than in those tak
ing nifedipine. CONCLUSIONS: We conclude that constipation as a result
of some calcium channel blockers may be caused by inhibition of colon
ic motor activity by nifedipine and, to a lesser extent, by verapamil.
The latter compound probably displays other mechanisms (reduced colon
ic transit, increased water absorption) also responsible for this side
effect.