Inhibition by decamethrin and resmethrin of hormone release from the isolated rat neurohypophysis—A model mammalian neurosecretory system

The isolated rat neurophypophysis, which shows a calcium-dependent hormone release when depolarized in vitro was used as a model system to investigate the effects of the pyrethroids decamethrin and resmethrin on mammalian nervous tissue. Both compounds inhibited neurohypophysial hormone release in response to electrical stimulation, decamethrin being more potent than resmethrin. Decamethrin reduced the hormone content of the neurohypophysis. Resmethrin did not reduce stored hormone significantly and its effects on release were dose dependent. They could be mimicked by raising the Na⁺] of the medium but not by lowering the Ca²⁺]. Resmethrin had no effect on the release of hormone following depolarization of the tissue with a raised K⁺]. The results are consistent with the suggestion that the compounds do not act on the potential-dependent secretion process but rather on the mechanism linking depolarization of the secretory terminals with the arrival of action potentials possibly by interfering with sodium-channel activation and inactivation.