To study the influence of 5 alpha-reductase on the concentration of dihydrotestosterone in prostatic tissue, we measured the activity of this enzyme in stroma and epithelium from 15 normal, 50 hyperplastic, and 20 carcinomatous prostates. Maximum velocity (Vmax) and Km parameters based on the Lineweaver-Burk and Eadie-Hofstee transformations of the Michaelis-Menten equation were related to the stromal and epithelial concentrations of dihydrotestosterone. On the basis of relative Vmax values, there was 6-15 times more 5 alpha-reductase activity in stroma than in epithelium regardless of the histology of the prostate. Stromal enzyme activity also was unique in having a 2- to 5-fold larger mean Km value and greater resistance to competitive and noncompetitive inhibition. Despite the enrichment of 5 alpha-reductase activity in stroma, the dihydrotestosterone concentrations in the stromal and epithelial fractions were very similar. In addition, similar concentrations were found in the stromal fractions of hyperplastic and carcinomatous tissues, notwithstanding a 4-fold difference in the mean Vmax values. This anomaly occurred in association with a large disparity in mean Km values, i.e. 68.3 +/- 1.6 (+/- SE) nmol/L in hyperplasia vs. 23.0 +/- 2.9 nmol/L in carcinoma. The dissociation between parameters of 5 alpha-reductase activity and tissue dihydrotestosterone concentrations was apparent to some extent in benign prostatic hyperplasia, in which the lowest stromal androgen concentrations were found in prostates with the largest Vmax and Km values; also, a rise in stromal Km was almost invariably associated with a proportional increase in Vmax (correlation coefficient = 0.95). These data strongly suggest that the stromal and epithelial forms of 5 alpha-reductase are separate isoenzymes, and that the excess of 5 alpha-reductase in stroma does not promote accumulation of an abnormal amount of dihydrotestosterone. They also imply that both the augmentation of 5 alpha-reductase activity in hyperplastic stroma and the condition of benign hyperplasia of the prostate are mutual consequences of a primary increase in Km.

Collecting duct carcinoma of the kidney is unique and rarely reported. The histological and ultrastructural characteristics of this tumor are well described in the pathological literature. However, there are few reports documenting the clinical presentation and long-term prognosis in patients with this unusual malignancy. Collecting duct carcinoma arises from the epithelium of the collecting tubules within the medulla and secondarily invades the renal cortex. The tumor occurs in a younger age group than is typical for renal cell carcinoma and most patients appear to have metastatic disease at presentation. We describe a case of this uncommon tumor and review the literature.

The true incidence and natural history of ureteral obstruction following reconstructive vascular surgery have not been determined previously. A series of 101 patients undergoing aortofemoral and aortoiliac reconstructive surgery were studied prospectively to determine the frequency of hydronephrosis in the first postoperative year. Serial real-time ultrasound examinations were performed preoperatively as well as at 1 week, 3 months and 1 year postoperatively. Ninety-three patients completed the study, with a total of 181 kidneys at risk. Hydronephrosis of mild to moderate degree developed in 15 kidneys (8 per cent) in 11 patients (12 per cent). All patients were asymptomatic, and the obstruction resolved spontaneously in 10 of 11 patients, including 9 within 3 months of onset. Only a single case persisted at 1 year. This study confirms that the hydronephrosis that occurs within the first year after aortic bifurcation graft surgery is not uncommon but it is rarely of clinical significance in the asymptomatic patient.