The effect of compound 48/80, substance P and pentagastrin on the isolated guinea pig atrium

It has been shown that histamine is present in guinea pig hearts. In the present work, the effect of some substances, known to liberate mast cell histamine, on the isolated guinea pig atria was studied. Compound 48/80 (100 micrograms/ml), pentagastrin (10(-6) M) and substance P (10(-5) M) were added 2-3 times to the isolated organs and the frequency of contractions was measured. At the end of experiments, the atria were examined histologically for mast cell degranulation. Compound 48/80 and pentagastrin increased the frequency of contractions of isolated atria. Substance P provoked a dose-dependent decrease of contraction frequency; this effect was diminished by atropine (10(-5) M). All three substances provoked pronounced degranulation of mast cells present in the atrium, the effect of substance P being significantly greater than the effects of the other two substances. It can be concluded that mast cells, present in guinea pig atrium, are sensitive to the histamine liberators used; histamine is released in quantities high enough to produce an effect.