Secretory activity of the subcommissural organ in Rana temporaria under osmotic stimulation.

The secretory activity of the subcommissural organ (SCO) in the frog Rana temporaria was studied under conditions of dehydration. After injection of a radioactive precursor the amount and concentration of radioactively labelled material in the SCO are smaller in dehydrated than in control animals. Concomitantly, the growth rate of the CSF-fibre (Reissner's fibre) increases in dehydrated animals. It follows that water deprivation enhances the secretory activity of the SCO. To investigate whether the SCO may be responsible for the secretion of an aldosteronotropic factor as suggested in the literature, brains were incubated in vitro with a radioactive precursor and with or without aldosterone. The SCO of the aldosterone-treated brains contains more radioactively labelled material than the SCO of the control brains. It is argued that this is indicative of a lower secretory activity It means that aldosterone inhibits the secretory activity of the SCO, possibly by a process of negative feed-back regulation. The results of the present experiments can be interpreted in favour of an involvement of the SCO-Reissner's fibre complex in osmoregulation.