Growth promoting effect of head activator in cultured chick embryo brain cells.

To investigate the regulatory role of head activator (HA) and its synthetic analogue, (Arg1,Phe5)-HA(AHA) on brain cell growth, we measured serial uptakes of [3H]thymidine, [3H]uridine and [3H]leucine and changes in cyclic AMP content in cultured chick embryo brain cells. HA stimulated all of these uptakes at a concentration of 10(-10) M, while 10(-9) M AHA suppressed them. The stimulatory effect of HA on [3H]thymidine uptake was observed after 4 h of the treatment, reached a maximum of 200% of the initial value at 8 h and declined to the pre-treatment level at 14 h. [3H]uridine uptake began to increase after 6 h of HA treatment, and the effect lasted for 4 h. Increase in [3H]leucine followed after 12 h and sustained for 4 h. Prior to the initiation of HA stimulation, cyclic AMP also began to rise, reaching 170% of the pre-treatment level at 6 h. In contrast, depression of [3H]thymidine uptake by AHA was noted at 6 h and continued for 8 h. Uptake of [3H]uridine and [3H]leucine showed similar tendency. Cyclic AMP in AHA-treated cells at 6 h was significantly lower than that in non-treated cells. These results indicate that HA stimulates DNA, RNA and protein synthesis in an early stage of growing brain cells, in which cAMP may be involved as a regulator of nerve cell growth.