Neural and hormonal stimulation of DNA and protein synthesis in cultured regeneration blastemata in the newt Notophthalmus viridescens

Distal portions of cone-stage newt forelimb blastemata were cultured transfilter to spinal ganglia for 36 or 72 hr. Addition of insulin to the medium consistently resulted in a significant increase (250% in ganglionated and 238% in nonganglionated blastemata) in the incorporation of ³H]thymidine into DNA, as compared to nontreated controls. When blastemata were cultured without ganglia for 36 or 72 hr, DNA synthesis decreased to 73 and 71%, respectively, of that achieved by ganglionated explants. When insulin was excluded from the medium, DNA synthesis decreased to 40% of insulin-treated explants, and, in the absence of both nerves and insulin, it declined to 31% of insulin-treated, innervated explants. The presence of insulin in the medium also resulted in an augmentation of (¹⁴C)-labeled amino acid incorporation into proteins; the average increase was 168%, as compared to untreated controls. l-thyroxine, growth hormone and hydrocortisone in combination with insulin, did not enhance the effects on DNA or protein synthesis of insulin alone. Also, exogenous cyclic nucleotides (cAMP, cGMP) and alterations of their endogenous levels with acetylcholine, sodium azide, theophylline or prostaglandins failed to elicit significant changes in DNA or protein synthesis. The existence of a synergistic action on DNA synthesis between nerves and insulin is suggested.