Studies on Hypothalamic CRHmRNA

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Corticotropin Releasing hormone (CRH) and Arginine Vaso-Pressin (AVP) are the most important physiological ACTH releasing factors. Gene expression of CRHmRNA and AVPmRNA were investigated. Levels of AVPmRNA in the hypothalamic Supra-Optic Nucleus (SON) and the Para-Ventricular Nucleus (PVN) were determined by semiquantitative in situ hybridization histochemistry. However, we failed to detect CRHmRNA levels by in situ hybridization technique in spite of great efforts.In bilaterally adrenalectomized rats, plasma ACTH levels increased significantly, CRH levels in the Median Eminence (ME) decreased and AVP levels in the ME increased one week after surgery. AVPmRNA in the PVN and SON increased significantly.In the rats given hypertonic saline (2%) for 3 days, CRH levels in the PVN and ME did not differ from those in the control rats. Plasma corticosterone, and AVP increased significantly. AVP contents in the posterior pituitary decreased and AVPmRNA in the PVN and SON increased significantly.Water deprivation increased AVPmRNA in the PVN and SON. Plasma levels of ACTH, corticosterone, AVP and osmolality were significantly elevated. The concentration in the posterior pituitary, ME and the remaining hypothalamic tissue did not differ significantly.Food deprivation decreased AVPmRNA in the PVN and SON. Plasma levels of ACTH and corticosterone were greatly elevated, while plasma AVP and osmolality did not differ significantly. The results indicated that food deprivation stimulated the pituitaryadrenal axis and that a reduction in AVPmRNA levels in food deprived rats was caused by food deprivation per se.According to these observations, AVP may be at least partly responsible for ACTH elevation in adrenal insufficiency, hypertonic saline administration and water deprivation but not in food deprivation.