Abstract
Extracts of 10 identified neurosecretory cells in the pars intercerebralis exhibit myotropic activity when added to the medium bathing an isolated ovary of Rhodnius. The myotropic activity of the preparation, expressed as the power in joules per second, increases linearly over a 100-fold range of concentrations but is not further affected by higher concentrations. The activity in the extracts is stable after heating to 90 °C for 5 min, and is reduced by incubation with trypsin. Comparison with the effects of proctolin demonstrates that the neurosecretory myotropin is not proctolin.