Adrenalectomy decreases vasoactive intestinal peptide mRNA levels in the rat suprachiasmatic nucleus.

Vasoactive intestinal peptide (VIP) concentrations were shown to be regulated by adrenal steroids. Therefore, we investigated whether adrenal steroids affect VIP mRNA levels, which would suggest an effect on VIP mRNA expression. Adrenalectomy performed on adult male rats resulted in a significant decrease in VIP mRNA in the hypothalamus (from 10.6 +/- 0.3 to 3.5 +/- 0.2 arbitrary units). In situ hybridization experiments revealed that a major site of VIP mRNA expression in the hypothalamus is the suprachiasmatic nucleus. Indeed, adrenalectomy resulted in an approximate decrease by half in VIP transcripts in this nucleus. However, this decrease was not reversed by replacement treatment with corticosterone or the glucocorticoid agonist, RU28362. Thus, VIP mRNA may be regulated by indirect mechanisms, influenced by the adrenal gland.