Alterations of heart dynorphin-A in the development of spontaneously hypertensive rats

In order to investigate the pathophysiological role of heart dynorphin-A (Dyn-A) in genetic hypertension, immunoreactive (ir)-Dyn-A was measured in heart extracts of spontaneously hypertensive rats (SHR) and compared with that of age matched Wistar (WR) and Wistar Kyoto (WKY) rats. Heart ir-Dyn-A contents in 8 week-old WK (84 fmol/g tissue) were not significantly different from those of age matched WKY (109 fmol/g tissue). In control WKY, the levels of ir-Dyn-A did not significantly vary with the age (from 109 to 117 fmol/g) except in 16 week-old animals which displayed a significant increase (238 fmol/g tissue) compared to younger animals. In SHR, the heart content of ir-Dyn-A displayed a 6.5 fold increase at 8 weeks compared to age matched WKY. Older SHR showed a return of their heart ir-Dyn-A content to control (12 week-old) or below control values (16 week-old; 121 compared with 238 fmol/g tissue in WKY). Heart ir-Dyn-A in WKY and SHR eluted as a single peak on mu-Bondapak HPLC, corresponding with the retention time of synthetic Dyn-A. A local function for cardiac ir-Dyn-A is suggested by the presence in heart membrane preparations of a high affinity binding site for the kappa selective opioid ligand, [3H]U-69593, with KD of 6.4 (WKY) and 8.5 (SHR) nM and Bmax of 3.7 (WKY) and 3.6 (SHR) pmol/g protein. The alterations in the levels of cardiac ir-Dyn-A during the development of hypertension in SHR were analyzed in regard with the reported effects of Dyn-related peptides on heart natriuretic and sympathetic functions.