Hippocampal levels of dynorphin A (1-8) in neonatal and 16-week-old spontaneously hypertensive rats: comparisons with DOCA-salt hypertension.

In this study the possible role of hippocampal dynorphin in the development of hypertension in spontaneously hypertensive rats (SHR) was investigated by determining dynorphin A (1-8) (DN A (1-8] levels in hippocampus in 16 week old SRH, Wistar Kyoto (WKY) controls and SHR treated with antihypertensive drugs as well as DOCA-salt hypertensive Sprague Dawley (SD) rats, using radioimmunoassay (RIA). We found that DN A (1-8) was decreased significantly in both dorsal (-68%) and ventral (-58%) hippocampus in SHR compared with WKY rats. Treatment with hydralazine and guanethidine (25 mg/kg/24 hr of each drug in drinking water) for 8 weeks to prevent the development of hypertension in young SHR had no effect on this low hippocampal dynorphin level. We failed to find significant changes in hippocampal DN A (1-8) level in DOCA-salt hypertensive rats. The low level of hippocampal dynorphin existed before the development of hypertension in 6 day neonatal SHR (-73%). Hippocampal Met-enkephalin was unchanged in all experimental groups except for a slight decrease in neonatal SHR. The results establish a genetic difference in the hippocampal dynorphin system of SHR compared with WKY, the significance of which, for the development of hypertension, remains to be investigated.