Fenoxycarb and thyroid hormones have JH-like effects on the follicle cells of Locusta migratoria in vitro.

Earlier work had shown that JH acts on the membrane of the follicle cell of Locusta migratoria, bringing about a rapid reduction in volume which can be detected in vitro by measuring the increase in optical path difference using quantitative interference microscopy. The juvenoid fenoxycarb, a phenoxyphenyl derivative, is unrelated in structure to the juvenile hormones (which are derivatives of farnesoic acid), but it also caused a reduction in volume of the cells in vitro as measured by an increase in the optical path difference. The vertebrate hormone thyroxine, and thyronine, the non-iodinated derivative of thyroxine, also phenoxy phenyl compounds, evoked a response like fenoxycarb. The effect of thyroxine was abolished by ouabain, which inhibits Na+/K+ ATPase, the effector molecule for JH, and inhibited by ethoxyzolamide which inhibits the binding of JH to a putative membrane receptor. Triiodothyronine, the effective vertebrate hormone, acted at a lower threshold and optimum concentration, and had a greater magnitude of effect than the other compounds tested. These facts suggest that these phenoxyphenyl compounds are JH agonists and that the membrane receptor for JH may resemble a possible membrane receptor for thyroxine.