To evaluate the pathophysiological significance of renal NAD-dependent 15 hydroxyprostaglandin dehydrogenase (PGDH) in young spontaneously hypertensive rats (SHR), the intranephron distribution of PGDH was compared with age-matched Wistar Kyoto rats (WKY). With supernatants of kidney homogenates, PGDH activities in 3 week-old SHR were significantly lower than those in WKY, and no difference in PGDH activities was found between male and female in both WKY and SHR. By using microdissected nephron segments of 3 week-old WKY and SHR, PGDH activities in both groups were found to be exclusively distributed in the proximal tubules, within which the activity of the straight portion (PST) was several fold higher than that of the convoluted one (PCT). In 3 week-old SHR, a significant decrease of PGDH activity was observed only in PST, possibly indicating a decrease of enzyme content in PST because of similar Km values in both groups. These results may suggest that intraproximal PG concentration could be regulated by the change of PGDH in PST of young SHR.