Catabolism and disposition of exogenous 5-hydroxytryptamine in cockroach, Periplaneta americana, tissues

Abstract

The concentrations of tryptophan, 5-hydroxytryptophan, 5-hydroxytryptamine, N-acetyl 5-hydroxytryptamine and N-acetyl dopamine were determined in the cerebral ganglia, haemolymph and Malpighian tubules of the cockroach Periplaneta americana, using high performance liquid chromatography with electrochemical detection. Injected 5-hydroxytryptamine was rapidly removed from the haemolymph with a concomitant elevation of circulating N-acetyl 5-hydroxytryptamine and little accumulation of 5-hydroxytryptamine in the cerebral ganglia. N-acetyl 5-hydroxytryptamine and N-acetyl dopamine were also rapidly removed from the haemolymph. Incubation of haemolymph from 5-hydroxytryptamine-injected insects and glucosidase or phosphatase, indicated that most of the injected 5-hydroxytryptamine had been converted to a sugar conjugate of N-acetyl 5-hydroxytryptamine. Whole haemolymph did not catabolize 5-hydroxytryptamine or N-acetyl 5-hydroxytryptamine whereas Malpighian tubules N-acetylated both 5-hydroxytryptamine and dopamine and metabolized N-acetyl 5-hydroxytryptamine. Injection of p-chlorophenylalanine (200 and 500 μg/g) had no effect on 5-hydroxytryptamine concentrations in the cockroach cerebral ganglia.