Abstract
Previously, we showed that during salt-loading in mice there was an acute rise in plasma ACTH levels after 2 days followed by a transient decrease after 4 and 9 days. Pro-opiomelanocortin (POMC) mRNA levels in the anterior pituitary increased after 2 days and returned to normal thereafter. In this study, changes in hypothalamic CRH and AVP mRNA levels during salt-loading were investigated using quantitative in situ hybridization histochemistry. CRH mRNA was expressed only in the paraventricular nucleus (PVN), while AVP mRNA was expressed in both the supraoptic (SON) and paraventricular nuclei. CRH mRNA levels were unchanged after 2 days salt-loading, but declined to 77% of control levels after 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 and 9 days salt-loading, respectively. These data suggest a major role of 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.
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