The cellular physiology of glandular kallikrein

Renal (tissue) kallikrein-kinin system in the kidney and novel potential drugs for salt-sensitive hypertension

A large variety of antihypertensive drugs, such as angiotensin converting enzyme inhibitors, diuretics, and others, are prescribed to hypertensive patients, with good control of the condition. In addition, all individuals are generally believed to be salt sensitive and, thus, severe restriction of salt intake is recommended to all. Nevertheless, the physiological defense mechanisms in the kidney against excess salt intake have not been well clarified. The present review article demonstrated that the renal (tissue) kallikrein-kinin system (KKS) is ideally situated within the nephrons of the kidney, where it functions to inhibit the reabsorption of NaCl through the activation of bradykinin (BK)-B2 receptors localized along the epithelial cells of the collecting ducts (CD). Kinins generated in the CD are immediately inactivated by two kidney-specific kinin-inactivating enzymes (kininases), carboxypeptidase Y-like exopeptidase (CPY), and neutral endopeptidase (NEP). Our work demonstrated that ebelactone B and poststatin are selective inhibitors of these kininases. The reduced secretion of the urinary kallikrein is linked to the development of salt-sensitive hypertension, whereas potassium ions and ATP-sensitive potassium channel blockers ameliorate salt-sensitive hypertension by accelerating the release of renal kallikrein. On the other hand, ebelactone B and poststatin prolong the life of kinins in the CD after excess salt intake, thereby leading to the augmentation of natriuresis and diuresis, and the ensuing suppression of salt-sensitive hypertension. In conclusion, accelerators of the renal kallikrein release and selective renal kininase inhibitors are both novel types of antihypertensive agents that may be useful for treatment of salt-sensitive hypertension.

Serine proteases of small intestine mucosa--localization, functional properties, and physiological role

In this review we present data about small intestine serine proteases, which are a considerable part of the proteolytic apparatus in this major part of the gastrointestinal tract. Serine proteases of intestinal epitheliocytes, their structural-functional features, cellular localization, physiological substrates, and mechanisms of activity regulation are examined. Information about biochemical and functional properties of serine proteases is presented in a common context with morphological and physiological data, this being the basis for understanding the functional processes taking place in upper part of the intestine. Serine proteases play a key role in the physiology of the small intestine and provide the normal functioning of this organ as part of the digestive system in which hydrolysis and suction of food substances occur. They participate in renewal and remodeling of tissues, retractive activity of smooth musculature, hormonal regulation, and defense mechanisms of the intestine.

Expression of angiotensin I-converting enzymes and bradykinin B2 receptors in mouse inner medullary-collecting duct cells

We described in mouse inner medullary-collecting duct cells (mIMCD-3) the somatic and the N-domain ACE synthesis and its interaction with the kallikrein-kinin system co-localized in the same cells. We purified two ACE forms from culture medium, M1 (130 kDa) and M2 (N-domain, 60 kDa), and cellular lysate, C1 (130 kDa) and C2 (N-domain, 60 kDa). Captopril and enalaprilat inhibited the purified enzymes. The immunofluorescence studies indicated that ACE is present in the membrane, cytoplasm and in the cell nucleus. Kinin B1 and B2 receptors were detected by immunofluorescence and showed to be activated by BK and DesR9 BK, increasing the acidification rate which was enhanced in the presence of enalaprilat. The presence of secreted and intracellular ACE in mIMCD-3 confirmed the hypothesis previously proposed by our group for a new site of ACE secretion in the collecting duct.

Mineralocorticoid receptor binding, structure and function

The isolation of aldosterone 50 years ago was a critical first step in elucidating the mechanism by which corticosteroids regulate electrolyte homeostasis. The broad principles of this mechanism involving an intracellular receptor acting on specific genes to induce the expression/repression of aldosterone-induced proteins (AIP) were established 30 years ago. The cloning of the mineralocorticoid receptor (MR) has enabled studies of the subcellular mechanisms of aldosterone action, including the molecular dissection of structure-function relationships in the receptor. We have exploited the close structural and functional similarity of the MR with the glucocorticoid receptor to identify the regions in the MR that confer ligand-binding specificity. The critical region is located, not as might be expected in the ligand-binding pocket but rather on the surface of the molecule. These studies have been extended to an analysis of the interactions between the N-terminal and ligand-binding domains of the MR. In the last decade, AIP have been identified; the regulation of the genes encoding these AIP are discussed.

Angiotensin I conversion to angiotensin II stimulates cortical collecting duct sodium transport

Angiotensin (Ang) II directly stimulates epithelial sodium channel activity in the rabbit cortical collecting duct. Because Ang I and converting enzyme analogues might be present in the distal nephron, this raises the possibility of intraluminal generation of Ang II. Conversion of Ang I to Ang II was monitored by Ang II-dependent changes in intracellular sodium concentration as a reflection of sodium transport across the apical membrane. This involved imaging-based fluorescence microscopy with sodium-binding benzofuran isophthalate in isolated, perfused, cortical collecting-duct segments from rabbit kidney. Principal and intercalated cells were differentiated by rhodamine-conjugated peanut lectin. Control principal cell intracellular sodium concentration, during perfusion with 25 mmol/L NaCl and zero sodium in the bath plus monensin (10(-5) mol/L) averaged 5.8+/-0.14 mmol/L (n=156). The increase in intracellular sodium concentration, when luminal NaCl was increased from 25 to 150 mmol/L, was elevated by 3.5-fold in the presence of intraluminal Ang I (10(-6) mol/L). Also, the effects of Ang I on sodium transport were not significantly different from the effects of Ang II (10(-9) mol/L). Ang I was used in micromolar concentrations to ensure that there was sufficient substrate available for conversion to Ang II. Inhibition of the angiotensin-converting enzyme with captopril reduced the stimulatory effect of Ang I. These results suggest that intraluminal conversion of Ang I to Ang II can occur in the cortical collecting duct, resulting in enhanced apical sodium entry.

Mineralocorticoid action

The physiology of mineralocorticoid action, particularly with respect to epithelial sodium transport, is well defined. A full understanding of the molecular basis of mineralocorticoid action has however proven to be more elusive. In the last decade insights into structural and functional aspects of the mineralocorticoid receptor combined with emerging details of the components of the mediators of the sodium flux has resulted in a clearer picture. This review focuses on two aspects of these new developments; the mineralocorticoid receptor and putative aldosterone induced proteins.

Cyclic and linear bradykinin analogues: implications for B2 antagonist design

Bradykinin (BK, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) antagonists are potentially useful for treating inflammation, pain and severe trauma. To identify what chemical features might promote effective antagonism, we replaced Arg1 and Pro7 with structurally constrained and proteolytic-resistant residues, such as Bip (biphenylalanine), Dip (diphenylalanine) or 2Ind (indane amino acid). To determine which BK folding might lead to favourable interactions with receptors, the effects of cyclo(3,8) vs. cyclo(5,8) analogues were compared. The resulting BK analogues were examined for their agonistic and antagonistic activities in guinea pig ileum, rat uterus and depressor assays. The results suggest that co-planarity of the residue-7 side chain with its backbone NH is important for potent agonism as well as antagonism, and a D-directed side chain is crucial for antagonism. For residue-1 an L-orientation is important, and Dip1 may mimic a folded Arg1 side chain to elicit agonistic activities, with Bip1 mimicking an extended Arg1 side chain to elicit inhibitory activities. However, ileal and uterine receptors appear to prefer differently folded BK. For ileum, a BK conformation in which residues-3 and -8 are proximal to each other, but apart from residue-5, led to improved pA2.

Distribution of tissue kallikreins in lower vertebrates: potential physiological roles for fish kallikreins

Fish skeletal muscle prokallikrein was purified from black sea bass, Centropritis striata, and used for the production of polyclonal antiserum. Tissue proteins from primitive fish and teleosts, an alligator, and an insectivore were resolved by sodium dodecylsulfate-polyacrylamide gel electrophoresis, Western blotted, and probed with fish muscle prokallikrein antiserum. A recurring theme was the presence of approximately 36 and 72 kDa kallikrein-like proteins in skeletal muscle, heart, gill, kidney, and spleen of higher teleosts and in selected tissues of sturgeon, shark, alligator, and mole. The presence of immunoreactive kallikreins in osmoregulatory organs such as the gills of teleosts and the rectal gland of sharks signifies a potential role for these proteins in osmoregulation. Black sea bass, rock bass, and sturgeon contained many immunoreactive kallikreins in their swimbladders, which implicates a role for kallikreins in the regulation of blood flow and vascular permeability to facilitate gas exchange within the bladder. Kallikreins were consistently identified in skeletal muscle and heart of all the species evaluated and may regulate local blood flow, muscle contraction or relaxation, or participate in various transport processes. The antiserum to fish prokallikrein recognized immunoreactive kallikreins from pancreatic tissues from fish and lower vertebrates, but not from the pyloric caecum of sea bass. The wide distribution of tissue kallikrein in lower vertebrates suggests that it may participate in a variety of physiological functions.

Localisation of tissue kallikrein in the kidney of black African women with early onset pre-eclampsia: a pilot study

Increased renal production of vasodilator mediators like kinins would counteract the vasospasm of pre-eclampsia. This study examines the cellular localisation of tissue kallikrein (TK), the potent kinin forming enzyme within the nephron of patients with early onset pre-eclampsia. Using the peroxidase-antiperoxidase immunoenzyme complex, TK was immunolocalised in the principal cells of the distal connecting tubule and the cortical collecting duct cells of the distal nephron of control tissue. Moderate reactivity was observed in the epithelial cells lining the Bowmans capsule. In early onset pre-eclampsia, TK was additionally localised in the proximal tubule cells, however, the intensity of reactivity was reduced when compared to that of the distal tubule cells. In patients with hypertension of pregnancy, the occurrence of TK in the proximal tubule suggests either gene induction or emiocytosis of TK.

Kallikrein and kallikrein-like proteinases: purification and determination by chromatographic and electrophoretic methods

Kallikreins and kallikrein-like enzymes make up a family of serine proteinases present in tissues and body fluids of mammals and in some snake venoms. This review deals with the procedures of purification, detection and determination of these enzymes by chromatographic and electrophoretic methods. The procedures are reported in tables, described and discussed with the aim of illustrating the state-of-the-art of research in the field.

Effects of a single dose and short-term captopril treatment on some pressor and depressor humoral factors in healthy subjects

14 healthy subjects (8 males and 6 females), aged 25-40 years, were studied before and after oral administration of a single dose of 50 mg captopril as well as after 3 d treatment with 100 mg captopril daily per os. We found that in addition to the well-known effects on the renin-angiotensin-aldosterone system, captopril, after 3 d treatment, significantly increases plasma and urinary kallikrein activity, plasma vasopressin and urinary prostaglandin (PG) E2. Atrial natriuretic peptide did not change significantly after either the single dose or the short-term treatment. We conclude that the blood pressure lowering effect of captopril could be mediated by increasing activity of the kallikrein-kinin system and of PGE2 without any participation of atrial natriuretic peptide.

Modulation of phospholipase A2 activity and sodium transport by angiotensin-(1-7)

Angiotensin II (Ang II) receptors are coupled to a variety of signal transduction mechanisms. In the kidney, Ang II at nanomolar concentration binds to proximal tubular cells and stimulates phospholipase A2 (PLA2), which in turn catalyzes the hydrolysis of phosphatidylcholine into lysophosphatidylcholine (LPC) and fatty acid. This signal transduction pathway has been shown to be an important modulator of sodium transport. The kidney cortex possesses the enzyme necessary to convert angiotensin I (Ang I) directly to Ang-(1-7) bypassing Ang II as an intermediate. The present investigation was undertaken to determine whether Ang-(1-7) influences epithelial cell function by comparing this heptapeptide with Ang II as a modulator of PLA2 activity and sodium transport. Proximal tubular cells were labeled in tissue culture with 3H-choline and PLA2 activity was measured by quantitation of LPC. We found that Ang II (10(-9) M to 10(-6) M) significantly increased PLA2 activity (154 +/- 36% to 209 +/- 94%). Similar results were obtained with Ang-(1-7) (240 +/- 130% to 353 +/- 40%). The bioactivity of the peptides was assayed by its ability to regulate transcellular 22Na flux. Ang II (10(-9) M) inhibited 22Na flux by 12 +/- 2% while Ang-(1-7) (10(-9) M) inhibited 22Na flux by 20 +/- 5%. These results suggest that one potential role of Ang-(1-7) in the regulation of kidney epithelial electrolyte transport may involve activation of PLA2.

Effects of thyroid hormones on urinary and renal kallikreins

The effects of thyroid hormones on the urinary excretion of kallikrein and on renal kallikrein were studied in rats. Total and active urinary kallikrein was decreased after thyroidectomy, but renal kallikrein content remained unchanged. Diuresis increased, and kidney weight and plasma aldosterone concentration decreased. Treatment with 3,5,3'-triiodo-L-thyronine restored the urinary kallikrein in thyroidectomized rats to normal and increased it in intact rats. It also produced increases in kidney weight and plasma aldosterone and a decrease in diuresis. The effect of thyroid hormones on the urinary kallikrein response to mineralocorticoids was also tested. Deoxycorticosterone acetate increased urinary kallikrein more in normal than in thyroidectomized rats. These results suggest that thyroidectomy decreases renal kallikrein synthesis and lowers the turnover rate of the enzyme, changes not detectable by a single measurement of the renal kallikrein content but reflected by an alteration in the urinary excretion of the enzyme. Thyroid hormones participate in the control of urinary kallikrein. This effect, however, is probably indirect and may be mediated by mineralocorticoids since thyroid function affects both the plasma level of aldosterone, which is known to influence renal kallikrein, and the kallikrein response to exogenous mineralocorticoids.

Is yohimbine-induced increase in salivary secretion a kinin-dependent mechanism?

We have previously reported that the alpha 2-adrenoceptor antagonist yohimbine induced a significant increase in both salivary flow rate and kallikrein output. In order to assess the possible role of the kinin-kallikrein system in the increase in salivary secretion elicited by yohimbine, the effects of aprotinin, an inhibitor of kallikrein activity, were investigated in yohimbine-treated conscious dogs. Aprotinin (at a dose, 5000 IU/kg iv, which reduced both resting and yohimbine-induced increase in kininogenase and amidolytic activities of saliva) which remained inactive alone, failed to modify the increase in salivary volume elicited by yohimbine (0.5 mg/kg iv). These results show that the rise in salivary flow rate observed under alpha 2-adrenoceptor antagonist is not induced by the kinin-kallikrein system. The release of kallikrein into saliva observed after yohimbine is rather the consequence than the cause of the increase in salivary secretion.

Sites of synthesis of urokinase and tissue-type plasminogen activators in the murine kidney

Kidneys have long been recognized as a major source of plasminogen activators (PAs). However, neither the sites of synthesis of the enzymes nor their role in renal function have been elucidated. By the combined use of zymographies on tissue sections and in situ hybridizations, we have explored the cellular distribution of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators and of their mRNAs in developing and adult mouse kidneys. In 17.5-d old embryos, renal tubules synthesize u-PA, while S-shaped bodies produce t-PA. In the adult kidney, u-PA is synthesized and released in urine by the epithelial cells lining the straight parts of both proximal and distal tubules. In contrast, t-PA is produced by glomerular cells and by epithelial cells lining the distal part of collecting ducts. The precise segmental distribution of PAs suggests that both enzymes may be implicated in the maintenance of tubular patency, by catalyzing extracellular proteolysis to prevent or circumvent protein precipitation.

Yohimbine increases submaxillary kallikrein release into the saliva in dogs: evidence for alpha 2-adrenoceptor-mediated inhibition of cholinergic pathways

1. The effects of the alpha 2-adrenoceptor antagonist, yohimbine (0.5 mg kg-1, i.v.) on basal, sympathetic and parasympathetic stimulation-induced submaxillary kallikrein release were investigated in the anaesthetized dog. Kallikrein was measured by its kininogenase activity before and after trypsin activation which also allowed a study of the proportion of active to total enzyme. 2. Yohimbine induced a rapid, three fold increase in basal kallikrein release correlated with an increase in salivary flow rate which lasted for 60 min following injection. 3. Sectioning the chorda tympani did not affect basal kallikrein release but abolished yohimbine-induced rise in salivary kallikrein secretion. 4. Parasympathetic stimulation alone induced a 3 to 4 fold increase in basal kallikrein release correlated with an increase in salivary flow rate. Yohimbine induced a significant additional increase in parasympathetic-stimulated kallikrein release. 5. When the cervical sympathetic nerve was sectioned the basal kallikrein release decreased by 30 to 40%. 6. Sympathetic stimulation alone also induced a 3 to 4 fold increase in basal kallikrein. This was not correlated with the salivary flow and unaffected by yohimbine. 7. The results indicate that yohimbine increases submaxillary kallikrein release into the saliva by inhibition of presynaptic alpha 2-adrenoceptors located on the chorda tympani nerve endings.

Tissue-specific regulation of the expression of rat kallikrein gene family members by thyroid hormone

We have altered the thyroid hormonal status of both male and female rats and examined the expression of six functional members of the rat kallikrein gene family (PS, S1, S2, S3, K1 and P1) in the submandibular gland (SMG), kidney, prostate, testis and anterior pituitary gland (AP) of these animals. On Northern-blot analysis with gene-specific oligonucleotide probes, the steady-state mRNA levels of S1, S2, S3, K1 and P1 were all dramatically altered in the SMG of male and female rats treated with propylthiouracil (PTU; 100 mg/litre of drinking water) or thyroxine (T4; 10 micrograms/100 mg body wt.) for 3 weeks. The SMG mRNA levels of these five genes were all lowered (30-90%) in hypothyroid (PTU-treated) male and female rats and elevated (1.4-4-fold, male; 1.5-11-fold, female) in the hyperthyroid (T4-treated) and PTU/T4-treated animals. In contrast, PS (true kallikrein) mRNA levels in the male or female SMG or kidney were essentially unchanged. K1 mRNA levels in the kidney were considerably less responsive to thyroid status than those in the SMG. Changes in S3 and P1 mRNA levels in the prostate were also variable, but essentially unaffected by these treatments. AP PS mRNA levels were also unaffected by changes in thyroid-hormonal status, as were levels of a novel P1-like mRNA in the testis. In summary, these studies demonstrate that the same kallikrein gene family member(s) may be differentially regulated by thyroid hormones in the rat SMG, kidney, prostate and pituitary, and thus further extend the concept of tissue-specific expression and hormonal regulation of the kallikrein gene family in the rat.

Oestrogen administration and the expression of the kallikrein gene family in the rat submandibular gland

Using a series of oligonucleotide probes (18-21 mers) specific for members of the rat kallikrein/tonin (arginyl-esteropeptidase) gene family (PS, S1, S2, S3, K1, P1), we have shown by Northern blot analysis that all six genes are expressed in the submandibular gland (SMG), with PS (true kallikrein) the most abundant in both male and female rats. Though female levels of PS mRNA are similar to that in the male, levels of mRNA from both the kallikrein-like (S1, K1, P1) and tonin (S2)/tonin-like (S3) genes are all substantially lower in the female than in the male rat. In contrast with the oestrogen dependence of anterior pituitary kallikrein (PS) gene expression, oestrogen administration (6 micrograms/day for 8 days) to castrate male or female rats is without effect on PS or S1, S2, S3, K1, P1 mRNA levels in the SMG. These findings suggest a tissue-specificity in the oestrogen regulation of true kallikrein gene expression in the two tissues. In intact male rats, oestrogen administration lowers SMG levels of S1, S2, S3, K1, and P1 but not PS mRNA to castrate levels, presumably by suppression of the pituitary/gonadal axis, consistent with the previously reported androgen dependence of SMG expression of these genes with the exception of PS.

Kallikrein-gene expression in the rat gastrointestinal tract

The serine proteinase glandular kallikrein has been demonstrated in the gastrointestinal tract, although there is some doubt as to whether it is synthesized there or derives from exocrine-gland secretions. Using a rat pancreatic kallikrein cRNA probe we have demonstrated kallikrein-like gene expression in the corpus, duodenum, jejunum, ileum, caecum and colon, and compared the pattern of expression with that of the gastrointestinal peptides somatostatin, gastrin and glucagon. In addition, using a panel of oligonucleotide probes specific for various members of the rat kallikrein-gene family, we have shown that the kallikrein-like gene expressed appears to be expressed as true kallikrein.

Sialochemistry in Sjögren's syndrome: a review

Sjögren's syndrome (SS) is an autoimmune exocrinopathy. The salivary glands are the site of activated T- and B-lymphocytes, along with gradual parenchymal destruction, diminished flow and altered composition of the secretory product. At present, sialochemistry has achieved no significance for the evaluation of SS patient. However, the number of sialochemical publications is steadily growing. This study review current sialochemical findings in patients with SS and relate the observations to the present concept of diagnosis, pathogenesis and prognosis of SS. An ideal combination of the collection of low-stimulated pure secretion, measurements of absolute flow-rates, and biopsy from the same glands seem to be unobtainable in SS patients. But two procedures may be appropriate: stimulated parotid secretion combined with parotid biopsies, or absorbance of low-stimulated labila saliva combined with labial gland biopsy. Sufficient data on disease-specific alterations in salivary composition in SS are still lacking. However, detection of specific changes in protein synthesis or in glycosylation as well as the detection of inflammatory cell products should be possible with the use of sensitive biochemical assays.

The expression of the kallikrein gene family in the rat pituitary: oestrogen effects and the expression of an additional family member in the neurointermediate lobe

Abstract Using a series of oligonucleotide probes (18 to 21 mers) specific for members of the rat kallikrein/tonin gene family (PS, S1, S2, S3, K1, P1), we have shown by Northern blot analysis that the oestrogen-dependent kallikrein gene expressed in the male and female rat anterior pituitary is true kallikrein (PS). In addition, we have demonstrated that oestrogen treatment may also induce PS gene expression in the male and female rat neurointermediate lobe. None of the other five rat arginyl-esteropeptidase genes so far described (S1, S2, S3, K1, P1) was found to be expressed in the anterior pituitary or neurointermediate lobe under these conditions. However, the demonstration of an additional hybridization signal in the male neurointermediate lobe using a relatively non-specific PS gene probe suggests the expression of another, as yet uncharacterized, kallikrein gene family member in this tissue.

Direct radioimmunoassay of active and inactive human glandular kallikrein: some physiological and pathological variabilities

We have developed a sensitive and specific radioimmunoassay which allows the detection of human glandular kallikrein in biologic fluids at a level of 40 pg/ml. The antisera did not recognize human plasma kallikrein and glandular kallikrein from other species including marmoset. Furthermore the antibody did not bind pro-kallikrein but was specific for the trypsin activated kallikrein. The antibody inhibited the kininogenase activity of standard kallikrein incubated with human kininogen. However active kallikrein inhibited by inhibitors bound at the active site is still detectable, indicating that the antibody is specific for the structure of the active form but not for the active site. In normotensive subjects, daily urinary kallikrein excretion increased with age until 30, then a decrease was observed. In renal transplanted recipients a progressive increase of the active form was found. A low concentration of immunoreactive active kallikrein was detected in lymphatic fluids of patients suffering from acute pancreatitis treated by lymphatic drainage; although this kallikrein is the active immunoreactive form, a very weak kininogenase activity was measured, suggesting a partial inhibition by anti-proteases. These data provide complementary evidence for the physiological and pathological role of glandular kallikrein.

Renal kallikrein mRNA localization by in situ hybridization

Tissue kallikrein gene expression in rat kidney was examined by in situ hybridization histochemistry. A rat tissue kallikrein cDNA probe, 534 bases in length and complementary to the 3' end of kallikrein mRNA was first used in Northern blot analysis to demonstrate the existence of tissue kallikrein mRNA in rat kidney. Then, kallikrein mRNA's localization in rat kidney sections was studied in situ hybridization histochemistry using the same probe. Positive signals were concentrated in the renal cortex at the vascular pole of the glomeruli and to a lesser degree, the distal tubular cells. Prehybridization with the unlabeled probe can abolish the positive signal; the same result can also be achieved by pretreatment of the tissue section with ribonuclease. By using the same technique, tissue kallikrein mRNA was also localized in granular convoluted tubule and striated duct cells of rat submandibular gland. The results suggest a new site of renal kallikrein synthesis at the vascular pole of the glomerulus. These findings, coupled with the previous studies that tissue kallikrein can participate in activation and releasing of renin, raise a potential physiological role of kallikrein in renin release or prorenin processing at juxtaglomerular cells.

A tissue kallikrein in the synovial fluid of patients with rheumatoid arthritis

Tissue kallikrein is an enzyme that forms the vasoactive peptide kallidin from an endogenous substrate L-kininogen. Tissue kallikrein has been identified in joint fluids and in inflammatory infiltrates within synovial membranes. It is suggested that tissue kallikrein and kinins have an important role in synovitis and joint damage. Immunoreactive tissue kallikrein and amidase activity were both measured in the synovial fluid of 24 patients with rheumatoid arthritis (RA) and 12 with osteoarthritis (OA). Active enzyme concentrations were higher in RA than in OA and correlated well with the lysosomal enzymes beta-glucuronidase and lactate dehydrogenase. Both total immunoreactive tissue kallikrein and the proenzyme values were similar in RA and OA. Tissue kallikrein was localised by immunocytochemistry to the polymorphonuclear leucocytes present in the synovial fluid and membranes of patients with RA.

Involvement of the kallikrein-kinin system in the antihypertensive effect of the angiotensin converting enzyme inhibitors

1. Studies were performed in normal subjects and in rats to assess the effect of angiotensin converting enzyme (ACE) inhibition on the kallikrein-kinin system. As ACE is identical to kininase II, one of the enzymes physiologically involved in bradykinin degradation, bradykinin may be expected to accumulate during ACE inhibition. 2. A competitive antagonist of bradykinin was used to explore in unanaesthetized rats the contribution of circulating bradykinin to blood pressure control under ACE inhibition. 3. No evidence was found for a role of this vasodilating peptide in the blood pressure lowering effect of acute ACE inhibition. 4. The plasma activity of carboxypeptidase N (= kininase I), another pathway of bradykinin degradation, remained intact during a 1 week course of treatment with an ACE inhibitor in normal subjects. This therefore indicates that bradykinin formed during ACE inhibition can still be metabolized.

Brain neuropeptides: actions on central cardiovascular control mechanisms

The many peptides we have not considered (e.g. gastrin, motilin, FMRFamide, carnosine, litorin, dermorphin, casomorphin, eledoisin, prolactin, growth hormone, neuromedin U, proctolin, etc.) were omitted due to lack of information as far as any putative central cardiovascular effects are concerned. However, even for some of these peptide pariahs intriguing snippets of information are available now (e.g. ref. 85), although as we write, the list of possible candidates for investigation grows longer. On an optimistic note, it is becoming clear that many brain neuropeptides may have important effects on cardiovascular regulation. It seems feasible that 'chemically coded' pathways in the brain might be the neuroanatomical correlate of a 'viscerotopic' organization of cardiovascular control mechanisms, whereby the activity of the heart and flows through vascular beds are individually controlled, but in an integrated fashion, utilizing particular combinations of neurotransmitters and neuropeptides within the brain. Such possibilities can only be investigated, properly, by measurement of changes in cardiac output and regional haemodynamics in response to appropriate interventions, in conscious, unrestrained animals.

Kallikrein gene expression in estrogen-induced pituitary tumors

Anterior pituitary kallikrein-like enzyme activity, immunoreactivity and mRNA levels have previously been shown to be regulated by estrogen, in parallel with prolactin. In this study, we have examined the relationship between kallikrein and prolactin mRNA levels in estrogen-induced pituitary tumors. Treatment of Fischer 344 rats with diethylstilbestrol implants for 3, 5 and 7 weeks produced a dramatic increase in kallikrein mRNA levels and a modest increase in prolactin mRNA levels. These changes were partially reversed by bromocriptine treatment, and completely reversed by bromocriptine plus estrogen withdrawal. Using a panel of oligonucleotide probes specific for various members of the rat kallikrein gene family, we have shown that the kallikrein-like gene expressed appears to be true kallikrein.

Localization and regulation of the renal kallikrein kinin system: possible relations to renal transport functions

The complete renal kallikrein kinin system has recently been localized in defined nephron segments. Kallikrein was found to be formed and secreted by connecting tubule cells in the late distal convoluted tubule, whereas kininogen and a novel kininase were located in collecting tubules. Kinins were shown to act on collecting tubule as well as medullary interstitial cells and the renal vasculature. The literature on interactions of this system with renal sodium transport is conflicting. Renal and urinary kallikrein was found to be increased under sodium restricted conditions, whereas kinin has a diuretic and natriuretic effect in the collecting tubule, when added from the basolateral surface. On the other hand renal kallikrein activity and connecting tubule cell morphology change in parallel with dietary potassium load indicating a coupling to potassium secretion. The possible role of the renal kallikrein kinin system in regulating collecting tubule function by tubular and vascular effects is outlined in spite of many open questions which remain to be answered.

A new direct radioimmunoassay of rat urinary kininogen

A protein-binding radioimmunoassay (RIA) of rat low molecular weight (LMW) kininogen with the following characteristics has been developed: sensitivity, 2.5 ng/tube; inter-assay coefficient of variation, 12.4% (N = 28); and intra-assay coefficient of variation, 9.4% (N = 11). The new assay correlated (r = 1) with the determination of kinin equivalence of kininogen after trypsinization. The cross-reactivity of rabbit anti-rat LMW kininogen antibody was 2.5% with bovine LMW kininogen, 5.8% with rat plasma high molecular weight (HMW) kininogen, and none with kinin. Although the antibody appears to partially recognize des-kinin-kininogen, the low degree of cross-reactivity and the extremely low levels of kinin-free-kininogen allow accurate determination of total LMW kininogen in rat urines. The LMW kininogen formed 20% kinins with salivary kallikrein when compared with trypsin, suggesting that the preparation consists of both K- and T-kininogens (K = kallikrein susceptible; T = trypsin susceptible). The newly developed protein-binding RIA recognizes LMW kininogen of rat urine which consists of both K- and T-kininogens.

Urinary kallikrein excretion in chronic renal failure: relationship to blood pressure and the acute effect of captopril

Previous studies of the renal kallikrein-kinin system in chronic renal failure (CRF) have given conflicting results. We have assessed activity of this vasoactive hormone system in CRF and investigated a possible relationship to hypertension in patients with CRF: 24-hour urinary kallikrein excretion (UKa) was measured in 22 patients with CRF (9 normotensive and 13 hypertensive) and 11 healthy controls. Age, sex, urine volume, and urinary sodium excretion were similar in each group. Compared with controls, UKa was reduced in both normotensive and hypertensive patients with CRF, with no difference between CRF groups. The reduction in UKa in CRF was less than the reduction in glomerular filtration rate (GFR), as assessed by endogenous creatinine clearance (CCr). When UKa was divided by CCr, UKa/mL CCr was therefore increased, to a similar extent, in both normotensive and hypertensive patients with CRF. This suggests that release of renal kallikrein from functioning nephrons is increased in CRF. The results do not support a role for deficient kallikrein release in the genesis of hypertension in CRF, as previously suggested; however, these abnormalities could be relevant to other aspects of renal function in CRF. The converting-enzyme inhibitor, captopril, was given to 5 patients with CRF, hypertension, and low UKa. Introduction of captopril was followed by a further reduction in UKa in all subjects. Captopril is known to inhibit kininase II, the principal enzyme involved in degradation of kinins; this potentiating effect may be counteracted by a reduction in renal kallikrein release and hence in kinin generation.