Diazepam-binding inhibitor (DBI) was initially isolated from the rat brain as a result of its ability to compete with benzodiazepines for their receptors. Immunohistochemical studies have recently shown the presence of peripheral-type benzodiazepine receptor (PBR)- and DBI-like immunoreactivity in the frog adrenal gland. The aim of the present study was to investigate the effect of two biologically active DBI-derived peptides, the triakontatetraneuropeptide [TTN; DBI(17-50)] and the octadecaneuropeptide [ODN; DBI(33-50)], on corticosteroid secretion by frog adrenocortical cells. Exposure of frog adrenal explants to graded concentrations of TTN (3.16 x 10(-8) to 3.16 x 10(-6) M) induced a dose-related increase in corticosterone and aldosterone secretion. In contrast, ODN did not modify corticosteroid output. When repeated pulses of TTN (10(-6) M) were administered at 2-h intervals, the response of the adrenal explants to the second dose of TTN was markedly reduced, suggesting the existence of a desensitization phenomenon. Exposure of dispersed adrenal cells to TTN also induced a marked stimulation of corticosteroid secretion, indicating that TTN acts directly on adrenocortical cells. The central-type benzodiazepine receptor (CBR) agonist, clonazepam, did not stimulate corticosteroid secretion and the CBR antagonist, flumazenil, did not block the stimulatory action of TTN. Similarly, the PBR agonist, Ro5-4864, did not mimic the stimulatory effect of TTN and the PBR antagonist, flunitrazepam, did not affect the stimulatory action of TTN. The present study provides the first evidence for a stimulatory effect of TTN on intact adrenocortical cells. The receptor mediating the corticotropic action of TTN is not related to central- or peripheral-type benzodiazepine receptors. Our data suggest that TTN, released by chromaffin cells, may act as a paracrine factor regulating the activity of adrenocortical cells.
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- Author: M. Feuilloley x
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O Lesouhaitier, M Feuilloley, and H Vaudry
P. Netchitailo, A. Larcher, F. Leboulenger, M. Feuilloley, D. Philibert, and H. Vaudry
ABSTRACT
To investigate a possible direct action of glucocorticoids on adrenal steroidogenesis, the effect of corticosterone on the conversion of pregnenolone into various metabolites by frog adrenal tissue was examined. Frog interrenal slices were incubated with [3H]pregnenolone (1 mCi/ml) and the various labelled metabolites analysed by reverse-phase high-performance liquid chromatography. With the methanol gradient used, five identified steroids were resolved: progesterone, 11-deoxycorticosterone, corticosterone, 18-hydroxycorticosterone and aldosterone. Corticosterone (10 μg/ml) induced a 45–80% decrease in all steroids synthesized from [3H]pregnenolone. In contrast, the glucocorticoid agonist dexamethasone did not reduce the rate of conversion of pregnenolone into its metabolites. In addition, the inhibitory effect of corticosterone was not reversed by the specific glucocorticoid antagonist RU 43044. These results show that corticosterone exerts a direct inhibitory effect on adrenal steroid secretion. In addition, our data indicate that the ultra-short regulation induced by corticosterone is not mediated through glucocorticoid receptors.
