Identification of vasopressin and determination of its corticomedullary levels in rat kidney tissue.

To investigate the kidney tissue level of arginine vasopressin (AVP), tissue AVP was extracted, identified and assayed. Rat kidney tissue was separated into the papilla (P), medulla (M), and cortex (C). After homogenization, AVP was extracted with acetone and determined by radioimmunoassay. Fractionation of the tissue extract by Sephadex G25 column chromatography showed that the peak of immunoreactive AVP was identical to that of synthetic AVP. There was good correlation between bioassayable and immunoassayable AVP for the tissue extracts. Tissue AVP concentrations (pg/g wet weight) after 36 hr of dehydration were: P, 164.3 +/- 13.0; M, 93.8 +/- 8.4; and C, 28.9 +/- 3.9 with a plasma AVP (pg/ml) of 11.7 +/- 1.0 (mean +/- SE, N = 18). Thus, the papilla/plasma AVP concentration ratio was high. When 125I-AVP was administered, the papilla/plasma ratio was very low. Under water diuresis, the tissue AVP level was very low. The kidney tissue level of dDAVP, which was administered exogenously, was much higher than that of AVP when compared at similar plasma levels. Thus, the present study demonstrated the existence of a corticomedullary concentration gradient of AVP with a medullary level much higher than the plasma level. The accumulation of AVP seemed to result from receptor-mediated processes, since 125I-AVP, which is biologically inactive and does not bind to hormone receptors, showed only a slight accumulation. The higher tissue level of dDAVP suggested that the tissue level was determined by the balance between accumulation and inactivation, since dDAVP is known to be scarcely inactivated in the kidney.