We bring up these points because some of our experiments indicated that ethylene had negative as sell as positive effects on muscle regeneration. Continuous exposure was appreciably less efficient than the discontinuous nighttime regimen. Simple addition would require that the values from continuous experiments be greater than or, at the minimum, equal to the nighttime values. The number of myotubes that developed in response to continuous inhalation, therefore, must contain a negative component, hidden in the overall positive character of the final outcome. It is convenient to regard the results of each schedule as representing plus and minus terms summed algebraically over a range from zero to some positive value.
Different events correspond to the nighttime and daytime inhalation schedules.
The point made in the last paragraph is not that ethylene exerts its net effect on regeneration by enhancing DNA synthesis and suppressing transcription or mitosis, but that these well-characterized initial phases of the regenerative process are, at the minimum, concomitants of whatever it is that ethylene affects pharmacodynamically. Events such as replication, mitosis, etc. can serve as useful guideposts in designing future investigations. Given, for example, a comprehensive knowledge of synchrony in dystrophic muscle, a schedule might be devised to enhance regeneration several orders beyond those we observed. We thank Anson Hobbs, Nuclear and Basic Research Laboratory, The Dow Chemical Company for performing ethylene analyses. Exposure chambers were designed by Dr. Theodore Torkelson of our laboratory.