The distribution of interrenal stimulating activity in the brain of Xenopus laevis

The stimulation of corticosteroid release by the interrenal tissue of Xenopus laevis was investigated using an in vitro preparation of the interrenals and a radioimmunoassay for determinations of corticosterone and aldosterone in the perifusate. The stimulatory activity of four different areas was tested, the pars distalis, the post- and preoptic hypothalamus, and the cerebrum. It was found that besides the pars distalis, the post- and preoptic hypothalamus exhibit stimulatory activity on the interrenals. No such activity was found in the cerebrum. There was a decrease of activity found from the pars distalis to the postoptic and then to the preoptic part of the hypothalamus. The release of both steroids had different sensitivity. Aldosterone release was significantly elevated by all three different tissues, while the increase of the release of corticosterone was only found significant in the case of stimulation by the pars distalis. The results also make clear that the increase of the release of corticosterone is less than that of aldosterone. The ratio of corticosterone to aldosterone decreased significantly after stimulation. This points to the fact that the rate of conversion of corticosterone to aldosterone (18-hydroxylation) is stimulated more than the production of corticosterone from progesterone.