CONTROL OF POSTERIOR PITUITARY VASOPRESSIN CONTENT - IMPLICATIONS FORTHE REGULATION OF THE VASOPRESSIN GENE

Axon terminals in the posterior pituitary store large quantities of th e hormone vasopressin (AVP), buffering the synthesizing neurons in the hypothalamus against acute changes in physiological demand for hormon e release. The dynamics of pituitary AVP content reflect the competing processes of release and synthesis. This report demonstrates substant ial increases in pituitary AVP content in the maturing rat. Between 7- 10 weeks of age, the total pituitary AVP content in the rat increases from 957 +/- 72 to 1667 +/- 160 ng. Cross-sectional data indicate a pa rallel relationship between body weight and pituitary AVP content. Nev ertheless, weight maintenance does not affect age-related increases in AVP content. Decreasing demand for hormone release and synthesis by i nducing hyponatremia blocks subsequent pituitary accumulation. After w ithdrawing the hyponatremic experimental conditions, animals resume ac cumulation of pituitary AVP, but do not catch up to age-matched contro ls. This indicates that increases in pituitary AVP content do not resu lt from a feedback signal from the neural lobe, but rather, pituitary AVP levels passively reflect changes in hormone release and compensato ry synthesis.