THE EFFECT OF SALT-LOADING ON CORTICOTROPIN-RELEASING HORMONE AND ARGININE-VASOPRESSIN MESSENGER-RNA LEVELS IN THE MOUSE HYPOTHALAMUS - A QUANTITATIVE IN-SITU HYBRIDIZATION ANALYSIS

Previously, we showed that during salt-loading in mice there was an ac ute rise in plasma ACTH levels after 2 days followed by a transient de crease after 4 and 9 days. Pro-opiomelanocortin (POMC) mRNA levels in the anterior pituitary increased after 2 days and returned to normal t hereafter. In this study, changes in hypothalamic CRH and AVP mRNA lev els during salt-loading were investigated using quantitative in situ h ybridization histochemistry. CRH mRNA was expressed only in the parave ntricular nucleus (PVN), while AVP mRNA was expressed in both the supr aoptic (SON) and paraventricular nuclei. CRH mRNA levels were unchange d after 2 days salt-loading, but declined to 77% of control levels aft er 9 days. AVP mRNA levels rose to 260% and 634% of control levels in the SON, and to 352% and 522% of control levels in the PVN, after 2 an d 9 days salt-loading, respectively. These data suggest a major role o f AVP in the acute stimulation of ACTH secretion and POMC mRNA levels seen after 2 days salt-loading. Densitization of AVP receptors at the corticotroph level and a centrally mediated inhibition of CRH release may account for the decrease of ACTH secretion and POMC mRNA levels in the anterior pituitary with prolonged salt-loading.