Effect of cimetidine on the histamine and dimaprit induced responses on the guinea pig ileum during development

1. In ileal segments obtained from 1, 15, 30, 45 and 60-day-old guinea pigs, histamine produced a dose-dependent significant contractile response from a threshold concentration of 3.2 x 10(-8) M. 2. The mean contractile responses (at 10(-5) M) of the ileum from the 1, 15, 30 and 45-day-old guinea pigs compared to that from the 60-day-old ones were 73.79, 92.30, 94.07 and 94.41% respectively. 3. Dimaprit (at 10(-5) M) had no effect on the ileum of the 1-day-old guinea pigs, while it produced a significant contractile response on the ileum of the guinea pigs at all other ages. 4. The mean contractile responses of the ileum from the 15, 30 and 45-day-old guinea pigs compared to that from the 60-day-old ones were 74.44, 66.66 and 76.94% respectively. 5. Cimetidine (at 10(-5), 3.2 x 10(-5) and 10(-4) M) significantly potentiated the histamine-induced contraction on the ileum of the 1-day (from 10(-7) to 3.2 x 10(-6) M) and the 15-day-old guinea pigs (at 10(-8) M). 6. On the contrary, cimetidine (at 3.2 x 10(-5) M) significantly inhibited the contractile response of the ileum to dimaprit. 7. In conclusion, the guinea pig ileum appears increasingly sensitive to histamine from the newborn to the 60-day-old ones, but its sensitivity to dimaprit, not detectable in the newborn, fluctuates during development. 8. Cimetidine produces a potentiating effect, which declines with age, on the on the histamine-induced contraction, while it inhibits the dimaprit contractile response on the ileum.