DISSOCIATION BETWEEN VASOPRESSIN AND OXYTOCIN MESSENGER-RNA AND PEPTIDE SECRETION AFTER AV3V LESIONS

The effect of hypertonic NaCl consumption on vasopressin (VP) and oxyt ocin (OT) mRNA levels and plasma and pituitary peptides was evaluated in rats with sham or anterior ventral third ventricular (AV3V) lesions . Rats were given tap water or 2% NaCl for 4 days. Because the rats wi th lesions drank significantly less salt solution than the controls (7 8.8 +/- 17.4 vs. 205.5 +/- 37.8 ml/4 days), a second control group was included in which saline intake was matched to the lesioned group. AV 3V rats showed a deficit in the peptide response to the osmotic stimul us. There was no increase in plasma VP or OT or decrease in posterior pituitary peptide content in the face of an extreme hypernatremia: pla sma sodium of 180.1 +/- 4.2 meq/l. Evaluation of mRNA changes by means of in situ hybridization showed that animals with lesions responded t o the salt challenge with increases in hypothalamic VP and OT mRNA lev els. There were significant increases in paraventricular and supraopti c OT mRNA and paraventricular VP mRNA in the lesioned group. The salt- matched control group showed no changes in peptide mRNA levels. These results demonstrate that AV3V lesions produce an impairment of the sal t-neuroendocrine reflex but a persistence of the peptide mRNA response . Differences in control mechanisms must account for this dissociation between peptide mRNA expression and peptide secretion.