Vasopressin RNA in the neural lobe of the pituitary: dramatic accumulation in response to salt loading.

The peptides vasopressin (VP) and oxytocin are derived from preprohormone precursers encoded by highly homologous linked genes that are expressed in discrete groups of hypothalamic neurons. The mature hormones are released into the peripheral circulation from the neural (posterior) lobe of the pituitary and have also been implicated in the regulation of anterior lobe. We have used Northern blotting and in situ hybridization to RNA in tissue sections to describe the presence, anatomical localization, and regulation of VP and oxytocin RNAs in the pituitary gland itself. We were unable to detect VP transcripts in the anterior and intermediate lobes of the pituitary. Rather we found low levels of VP RNA in the neural lobe. Furthermore, the osmotic stimulation of a 2% (wt/vol) NaCl drinking diet resulted in a marked accumulation of VP RNA in the neural lobe. We suggest that VP, locally synthesized in pituicytes, may have paracrine effects on VP receptors in the neural lobe.