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We have studied rat vascular smooth muscle (VSM) cells in culture for the presence of key elements of the glandular kallikrein-kinin system. Direct radioimmunoassay (RIA) using antiserum against rat urinary kallikrein detected a glandular kallikrein-like enzyme (GKLE) in VSM cells and in media. VSM homogenates and culture media had kininogenase activity, generating kinins from dog kininogen. About half of the GKLE was enzymatically inactive which could be activated with trypsin. Kininogenase activity was inhibited completely by aprotinin but only 20% by soybean trypsin inhibitor (SBTI). Trypsin liberated kinins from homogenates and media, demonstrating that VSM cells contain kininogen. Homogenates and media rapidly degrade bradykinin. GKLE, kininogen, and bradykininase activity were all present in VSM cells grown in defined media that contain no serum, thus eliminating any contamination or artefacts from fetal calf serum in standard culture media.Blood vessels of the rat have been reported to contain GKLE. Our observations indicate that GKLE is synthesized by VSM cells, not deposited from plasma. Furthermore, VSM cells synthesize kininogen and bradykininse(s), the other key elements of the glandular kallikrein-kinin system. Thus it is possible that the system functions as an autocoid mechanism that regulates local vascular tone. (J. Clin. Invest. 1990.

The arcades are long, branched renal tubules which connect deep and mid-cortical nephrons to cortical collecting ducts in the renal cortex. Because they are inaccessible by standard physiological techniques, their functions are poorly understood. In this paper, we demonstrate that the arcades are a site of expression of two proteins, aquaporin-2 (the vasopressin-regulated water channel) and the V 2 vasopressin receptor, that are important to regulated water transport in the kidney. Using a peptide-derived polyclonal antibody to aquaporin-2, quantitative ELISA in microdissected segments showed that aquaporin-2 is highly expressed in arcades and that the expression is increased in response to restriction of fluid intake. Immunocytochemistry revealed abundant aquaporin-2 labeling of structures in the cortical labyrinth in a pattern similar to that of the Na ϩ -Ca

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Correction of renal hypertension in the rat by prolonged infusion of angiotensin inhibitors. SUMMARY Inactive plasma renin (a prorenlp-like substance) can be activated by trypsin. There are also endogenous neutral serine proteases in plasma that can activate inactive renin in vitro, but only after protease inhibitors are either destroyed by acidification (the alkaline phase of acid activation) or inactivated by cold (cryoactivation). In the present study we have shown that cold also facilitates trypsin activation. But even at -4°C, as much as 1 rag/ral of trypsin was required to overcome endogenous inhibitors and reproducibly activate inactive plasma renin during a 1-hour incubation at pH 7.4. After partial destruction of plasma protease inhibitors by acidification to pH 33., less trypsin was required for complete activation at pH 7.4:200 Mg/ml at 25°C and 100 Mg/ml at -4°C. In contrast, 10 fig/ml of the renal enzyme urinary kallikrein completely activated inactive renin in previously acidified plasma at 25°C. Maximum activation of inactive plasma renin by either trypsin or renal kallikrein was almost identical. Both enzymes caused activation in plasmas deficient in Hageman factor or Fletcher factor (prekallikrein), suggesting that their ability to activate inactive renin is not mediated by these neutral serine proteases of the intrinsic coagulation system.Using maximum trypsin activation to define "total" renin, we found that among 22 normal subjects and hypertensive patients there was a direct relationship between the proportion of active renin in plasma (active/total) and the concurrent urinary kallikrein excretion (r = 0.46, p < 0.05). Normotensive white subjects had a higher proportion of active plasma renin than blacks, in whom urinary kallikrein is reported to be low. Altogether, these data suggest that there might be a link between prorenin and renal kallikrein in vivo. Further studies are required to evaluate this possibility and to determine whether prior hydrolysis of inactive renin, for example, by acidification, is required for renal kallikrein to activate inactive renin. 4 which seem to be completely inhibited.