Dexamethasone action on rat thymic atrial natriuretic peptide.

The rat thymus gland expresses the ANP gene and synthesizes the ANP-precursor, suggesting a role for this peptide within the immune system. This study provides further evidence for this notion, as expression of ANP mRNA in the thymus is altered in response to administration of the glucocorticoid dexamethasone to rats (1.5 mg/kg). This drug causes involution of the thymic gland and at day 4 after steroid exposure a striking increase (up to 30 fold) in mRNA coding for ANP was observed. The increase of the ANP precursor was found to be 4-fold as compared to saline treated controls. During regeneration of the thymus the mRNA and precursor levels normalize, reaching control values the day 18 after dexamethasone. The strong stimulation of the thymus ANP system subsequent to the glucocorticoid may suggest a critical function of this peptide in mechanisms leading to cellular depletion or during the regeneration of the gland after exposure to the steroid.