LOCALIZATION OF VASOPRESSIN MESSENGER-RNA AND IMMUNOREACTIVITY IN PITUICYTES OF PITUITARY STALK-TRANSECTED RATS AFTER OSMOTIC STIMULATION

The presence of [arginine] vasopressin (AVP) mRNA and AVP immunoreacti vity in pituicytes of the neural lobe (NL) of intact and pituitary sta lk-transected rats, with and without osmotic stimulation, was examined , AVP mRNA was analyzed by Northern blotting, as well as by in situ hy bridization in combination with immunocytochemistry using anti-glial f ibrillary acidic protein (GFAP) as a marker for pituicytes, In intact rats, a poly(A) tail-truncated 0.62-kb AVP mRNA was detected in the NL and was found to increase 10-fold with 7 days of continuous salt load ing. Morphological analysis of the NL of 7-day salt-loaded rats reveal ed the presence of AVP mRNA in a significant number of GFAP-positive p ituicytes in the NL and in areas most probably containing nerve fibers , Eight days after pituitary stalk transection the NL AVP mRNA diminis hed in animals given water to drink, whereas in those given 2% saline for 18 h followed by 6 h of water, a treatment repeated on 6 successiv e days beginning 2 days after surgery, the 0.62-kb AVP mRNA was presen t, The AW mRNA in the pituitary stalk-transected, salt-loaded rats sho wed an exclusive cellular distribution in the NL, indicative of locali zation in pituicytes, Immunoelectron microscopy showed the presence of AW immunoreactivity in a subpopulation of pituicytes 7 and 10 days af ter pituitary stalk transection in salt-loaded animals, when almost al l AVP fibers had disappeared from the NL. These data show that a subse t of pituicytes in the NL is activated to synthesize AVP mRNA and AVP in response to osmotic stimulation.