Reciprocal relationship between the concentrations of serotonin and the activity of serotonin-N-acetyltransferase in rat pineal glands in culture.

Abstract

Serotonin is a co-substrate for catabolism of acetyl CoA by serotonin N-acetyltransferase (NAT), and acetyl CoA is the most potent known stabilizer of NAT activity against rapid thermal inactivation in pineal homogenate. The possibility that serotonin may modulate NAT activity was considered and subjected to experimentation. Chlorophenylalanine (4 mM) and R04–4602 (100 μM) enhanced the nor- epinephrine (NE)-induced stimulation of NAT activity in rat pineal glands in culture; whereas, 5-hydroxytryptophan (1 mM) attenuated it. Chlorophenylalanine (4 mM) decreased the fall of NAT activity induced by Z-propranolol; whereas, reserpine (50 μM) and serotonin (0.5 mM) had no effect. In contrast, 5-hydroxytryptophan (1 mM) accelerated the fall of NAT activity induced by Z-propranolol. Consequently, a reciprocal relationship appears to exist between the serotonin concentrations and NAT activity in pineal gland. Comparing the kinetics of native and NE-stimulated NAT, there occurred changes in Vmax with regard to bot...