Action of crude and fractioned homogenates of the midgut gland of the sea hare Aplysia brasiliana rang, 1828 on some cholinoceptive structures

Abstract

1. Crude and fractioned homogenates of the midgut gland of Aplysia brasiliana were tested on the heart of the toad Bufo ictericus ictericus and cholinoceptive structures of some invertebrates. 2. In the in situ heart of the toad the fractions, with increasing concentrations, first decreased both the frequency and the amplitude and then stopped the organ in diastole. 3. On recovery from the effect of the fractions, the toad heart could not be stopped by vagus stimulation. This result is admitted as due to the urocanylcholine present in the fractions. 4. The application of acetylcholine on an isolated toad heart previously treated by the active fractions was also ineffective. Atropine blocked the action of the active fractions in the isolated heart. 5. The tonus and the frequency of beating of the isolated heart of A. brasiliana are enhanced by the active fractions. This action can be blocked by atropine but not by B.O.L. The quiescent isolated heart of this gastropod resumes its beating on the application of the active fractions. 6. In the isolated heart of the bivalve Perna perna the active fractions also rise the amplitude of the beating. 7. Crude homogenates and the active fractions of the midgut gland strongly contract the protractor muscle of the sea urchin lantern and the longitudinal muscle of the sea cucumber. In both cases this action can be blocked by atropine. 8. Column muscle preparations of the sea anemone Bunodosoma caissarum are also sensitive to the active fractions. 9. The present results confirm and extend to A. brasiliana the existence of cholinergic principles in the midgut gland, probably acetylcholine and urocanylcholine, as found by Blankenship et al. (1975) in another sea here.