1. 1.

    A semi-isolated caterpillar heart bioassay was used to detect the presence of endogenous cardioactive material in the CNS of Manduca sexta larvae.

  2. 2.

    Cardioactivity was detected in all nervous tissue examined. Most activity (about 70% of the total in the CNS) was in the ganglia of the abdominal nerve cord (ANC). Cardioactivity was also detected in the abdominal transverse nerves, the proctodeal nerves and the corpora cardiaca/corpora allata. The source with the highest specific activity was the frontal ganglion.

  3. 3.

    Two factors, separable by Sephadex gel filtration, were distinguished in extracts of ANC: CAF 1, which has an estimated relative molecular mass (Mr) of about 4000, and CAF2 for which Mr is probably less than 1000. Both factors are apparently peptides. Neither is similar to any known insect cardioaccelerator.

  4. 4.

    Both CAF 1 and CAF 2 are able to cause cardioacceleration when injected into tetrodotoxin-paralysed caterpillars.

  5. 5.

    CAF 2 is present in both larvae and in adults. CAF 1 is present only in the caterpillar. The larval heart responds to both factors; the adult heart responds only to CAF 2.

  6. 6.

    Partial purification of CAF 1 and CAF 2 by reverse-phase HPLC gives a single peak of bioactivity in each case.

  7. 7.

    The biological activity of CAF 1 is destroyed by α-chymotrypsin, but not by trypsin. CAF 2 is not attacked by trypsin or by α-chymotrypsin. Treatment with performic acid or cyanogen bromide destroys the activity of both CAF 1 and CAF 2.

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