The effects of lesions in the pars compacta of the substantia nigra of 4-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) were studied on (a) changes in blood pressure during a period of 6 weeks following lesioning, and (b) dopamine and metabolite concentrations in the caudate nucleus and (c) the in vitro release of [3H]dopamine from caudate nucleus slices 6 weeks after the lesioning. We report here that substantia nigra lesions caused a profound attenuation of the development of hypertension in SHR. No effect on heart rate was observed. Whereas the concentrations of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in the caudate nucleus were not different, the amount of homovanillic acid (HVA) and the ratios DOPAC/dopamine and HVA/dopamine were lower in sham-treated SHR than in sham-treated WKY, indicating a lower turnover of dopamine in SHR. Six weeks after lesioning, the concentrations of dopamine, DOPAC and HVA were decreased in the caudate nucleus (46-66%) of both strains, whereas DOPAC/dopamine and HVA/dopamine ratios tended to be increased in both SHR and WKY. Using an in vitro superfusion method, it was found, that the electrically stimulated release of [3H]dopamine from caudate nucleus slices of sham-treated SHR was lower than from slices of sham-treated WKY at the age of 10 weeks. Six weeks after lesioning, the stimulus-evoked release of [3H]dopamine from the remaining terminals was significantly increased in caudate nucleus slices of SHR, whereas the difference did not reach statistical significance in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)