Changes in blood pressure, urinary kallikrein, and urinary prostaglandin E2 in rats with streptozotocin-induced diabetes

Reduced GABAergic inhibition of kidney-related PVN neurons in streptozotocin-treated type 1 diabetic mouse

Activity of presympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus is known to play an important role in the regulation of sympathetic outflow. Sympathetic overactivity is associated with many pathophysiological conditions such as diabetes mellitus and hypertension; however, the underlying synaptic mechanisms are poorly understood. In this study, we examined the GABAergic inhibitory synaptic control of kidney-related presympathetic PVN neurons in the streptozotocin-treated type 1 diabetic mouse model, using patch-clamp slice electrophysiology in combination with retrograde labeling. Type 1 diabetes resulted in decreased frequency of miniature inhibitory postsynaptic currents (mIPSCs). Our data also demonstrated a reduction of mIPSC amplitude and mean inhibitory current without alteration of input resistance. Furthermore, our data revealed decreased tonic GABAergic inhibition of kidney-related PVN neurons in diabetic conditions, which was consistent with the observed increased excitability of the presympathetic PVN neurons. In summary, our data demonstrated decreased phasic and tonic inhibitory control of kidney-related presympathetic PVN neurons that suggest altered sympathetic circuitry in type 1 diabetes.

Involvement of (pro)renin receptor in the glomerular filtration barrier

(Pro)renin receptor-bound prorenin not only causes the generation of angiotensin II via the nonproteolytic activation of prorenin, it also activates the receptor’s own intracellular signaling pathways independent of the generated angiotensin II. Within the kidneys, the (pro)renin receptor is not only present in the glomerular mesangium, it is also abundant in podocytes, which play an important role in the maintenance of the glomerular filtration barrier. Recent in vivo studies have demonstrated that the overexpression of the (pro)renin receptor to a degree similar to that observed in hypertensive rat kidneys leads to slowly progressive nephropathy with proteinuria. In addition, the handle region peptide, which acts as a decoy peptide and competitively inhibits the binding of prorenin to the receptor, is more beneficial than an angiotensin-converting enzyme inhibitor with regard to alleviating proteinuria and glomerulosclerosis in experimental animal models of diabetes and essential hypertension. Thus, the (pro)renin receptor may be upregulated in podocytes under hypertensive conditions and may contribute to the breakdown of the glomerular filtration barrier.

Inhibition of diabetic nephropathy by a decoy peptide corresponding to the "handle" region for nonproteolytic activation of prorenin

We found that when a site-specific binding protein interacts with the "handle" region of the prorenin prosegment, the prorenin molecule undergoes a conformational change to its enzymatically active state. This nonproteolytic activation is completely blocked by a decoy peptide with the handle region structure, which competitively binds to such a binding protein. Given increased plasma prorenin in diabetes, we examined the hypothesis that the nonproteolytic activation of prorenin plays a significant role in diabetic organ damage. Streptozotocin-induced diabetic rats were treated with subcutaneous administration of handle region peptide. Metabolic and renal histological changes and the renin-Ang system components in the plasma and kidneys were determined at 8, 16, and 24 weeks following streptozotocin treatment. Kidneys of diabetic rats contained increased Ang I and II without any changes in renin, Ang-converting enzyme, or angiotensinogen synthesis. Treatment with the handle region peptide decreased the renal content of Ang I and II, however, and completely inhibited the development of diabetic nephropathy without affecting hyperglycemia. We propose that the nonproteolytic activation of prorenin may be a significant mechanism of diabetic nephropathy. The mechanism and substances causing nonproteolytic activation of prorenin may serve as important therapeutic targets for the prevention of diabetic organ damage.

Attenuated arterial and venous constriction in conscious rats with streptozotocin-induced diabetes

We examined if arterial or venous constriction is impaired in early diabetes. Dose-pressor and mean circulatory filling pressure (index of venous tone) response curves to noradrenaline and angiotensin II were constructed in four groups of conscious, instrumented, Wistar rats pretreated with streptozotocin (60 mg/kg i.v.) or vehicle at 2 weeks prior to the study. Rats with diabetes, relative to controls, had increased ED(50) (reduced potency) for the pressor (2.5-fold of control) and mean circulatory filling pressure (4.3-fold of control) response to noradrenaline, as well as reduced maximum pressor response (efficacy) to noradrenaline (diabetic, 74+/-8 mm Hg; control, 96+/-5 mm Hg). Diabetic rats also had reduced potency (ED(50), 5-fold of control) of the pressor response to angiotensin II; however, maximum pressor response and dose-mean circulatory filling pressure curve to angiotensin II were similar in both groups. Therefore, arterial and venous constrictions are impaired at an early phase of type I diabetes.

Effects of spironolactone on systolic blood pressure in experimental diabetic rats

BACKGROUND

Mineralocorticoid hormones, which maintain electrolyte balance and blood pressure, are thought to be associated not only with the expression of renal 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), but also with that of intracellular mineralocorticoid receptors (MRs). The present study was designed to test whether the mineralocorticoid action of glucocorticoid corticosterone on renal MR is involved in the development of diabetes-associated hypertension by measuring the alterations of renal 11beta-HSD2.

METHOD

We measured the mean systolic blood pressure, renal 11beta-HSD1, and mRNA levels in streptozotocin (STZ)-induced diabetic rats that received spironolactone, insulin, or no treatment, and in nondiabetic controls that received spironolactone.

RESULTS

Four weeks after an injection of STZ, the renal 11beta-HSD2 and mRNA levels were significantly lower in diabetic rats than in control rats, and the mean systolic blood pressure was 14.8% higher in diabetic rats than in controls. Subcutaneous injections of spironolactone into diabetic rats for three weeks partially reversed the decrease in renal 11beta-HSD2 activity and gene expression, and prevented the mean systolic blood pressure elevation. Spironolactone treatment for one week also resulted in a significant reduction in mean systolic blood pressure during the development of diabetic hypertension. However, treatment with STZ did not significantly decrease the renal 11beta-HSD1 activity and mRNA expression, and spironolactone treatment did not exert a significant effect on this enzyme in STZ-induced diabetic rats.

CONCLUSION

In the development of diabetes-induced hypertension, the effect of spironolactone on mean systolic blood pressure may be associated with the mineralocorticoid effects of corticosterone on renal MR, as well as an alteration of renal 11beta-HSD2 activity and its mRNA expression in insulin-dependent diabetic rats.

Altered cardiac tissue and plasma kininogen levels in hypertensive and diabetic rats

The present investigation was aimed at evaluating the cardiac and total plasma kininogen levels, as well as LVWT in hypertensive and diabetic rats. STZ-induced diabetes produced a significant (P < 0.001) rise in mean arterial blood pressure (BP). The LVWT increased (P < 0.001) in SHR with and without diabetes) and diabetic WKYR. The cardiac tissue, as well as total plasma kininogen levels fell significantly (P < 0.001) in diabetic WKYR and SHR with and without diabetes compared to the control WKYR. These findings suggest that reduced kininogen levels may indicate a deficiency in kinin generation in the heart and in the peripheral circulation in diabetic and hypertensive rats. This effect may contribute to the development of LVH.

Time-course of the alterations in prostanoid production and in contractile responses of mesenteric beds isolated from streptozotocin diabetic rats

The prostanoid production and the effect of indomethacin on the noradrenaline-induced contractions were studied in the mesenteric bed of rats at different times (1-8 weeks) after the administration of streptozotocin (STZ). The production of prostacyclin (measured as 6-keto-PGF1alpha) and prostaglandin (PG) E2 was unchanged one week after STZ, but it was reduced to 50% of control values 4 weeks after STZ without further changes 8 weeks after the treatment. The release of thromboxane (TX) A2 (measured as TXB2) and PGF2alpha, increased by 100% one week after STZ and returned to basal values at 3 weeks. TX release was below control values 8 weeks after STZ. The ratio 6-keto-PGF1alpha/TXB2 was reduced one week after STZ, recovered to control values at 4 weeks and augmented at 8 weeks. Indomethacin (10 microM) reduced the contractile responses to noradrenaline in the controls, whereas in STZ-treated rats this effect was observed solely 8 weeks after the treatment. Since this recovery coincided with an increase of the vasodilator/vasoconstrictor prostanoid ratio, a time-dependent compensation of the vascular alterations caused by STZ can be proposed from the present results.

Hyperinsulinemia and insulin resistance in hypertension: differential effects of antihypertensive agents

Both hypertension and diabetes mellitus are multifaceted dynamic expressions of pathophysiological disequilibrium that are closely related with and even intermingled by a number of common factors. Hyperinsulinaemia and insulin resistance may be possible links between hypertension and diabetes mellitus. While working on the effect of different antihypertensive agents in several animal models of simultaneously occurring diabetes-mellitus and hypertension it was found that most antihypertensives prevented streptozotocin (STZ)-induced hypertension in rats. Hydralazine, angiotensin converting enzyme (ACE) inhibitors, calcium channel blockers (CCB) and clonidine prevented STZ-induced cardiomyopathy, hyperlipidaemia and glucose tolerance. It was further demonstrated that atenolol produced many unfavourable effects like hyperlipidaemia and decreased cardiac functions. We also used other animal models of simultaneously occurring diabetes-mellitus and hypertension such as genetically hypertensive or spontaneously hypertensive (SH), Deoxycorticosterone acetate (DOCA)-hypertensive and neonatal streptozotocin-induced NIDDM rats. Results of our studies suggest that SH, neonatal STZ-induced NIDDM, and fructose hypertensive rat models may be considered as models for insulin resistance - the concept that has come into limelight in recent years. DOCA may have some influence on glucose homeostasis and insulin sensitivity and some sort of counteraction to STZ-induced cardiovascular and metabolic changes occur with DOCA. Hence, it may not be considered as an ideal model to study the metabolic and cardiovascular complications of hypertension associated with diabetes-mellitus. Among ACE inhibitors, perindopril, spirapril, and among calcium channel blockers (CCB) used in our study amlodipine and nifedipine were found to produce an increase in insulin sensitivity. Enalapril, ramipril, lisinopril and nitrendipine failed to alter insulin sensitivity as far as the glycaemic control is concerned. Extension of the results of these experiments to the clinical practice substantiated many of the findings and a good correlation between results obtained from experimental studies and clinical data was found.

Left ventricular hypertrophy and its relation to the cardiac kinin-forming system in hypertensive and diabetic rats

We investigated the cardiac tissue kallikrein and kininogen levels, left ventricular wall thickness and mean arterial blood pressure of Wistar Kyoto and spontaneously hypertensive rats with and without streptozotocin-induced diabetes. The mean arterial blood pressure was highly elevated (P<0.001) in Wistar Kyoto diabetic and spontaneously hypertensive diabetic rats as compared with their respective controls. The cardiac tissue kallikrein and kininogen levels were reduced significantly (P<0.001) in diabetic Wistar Kyoto, spontaneously hypertensive and diabetic spontaneously hypertensive compared with Wistar Kyoto control rats. In addition, the left ventricular thickness was found to be increased (P<0.001) in diabetic Wistar Kyoto and spontaneously hypertensive rats in the presence and in the absence of diabetes. Our results indicate that reduced activity of the kinin-forming system may be responsible for inducing left ventricular hypertrophy in the presence of raised mean arterial blood pressure in diabetic and hypertensive rats. Thus, the kinin-forming components might have a protective role against the development of left ventricular hypertrophy. The possible significance of these findings is discussed.

Renal expression of two rat kallikrein genes under diabetic conditions

OBJECTIVE

We have reported that bradykinin (BK) excretion is increased in severely diabetic rats, independent of the activity of the main renal kinin-forming enzyme, true kallikrein (KLK). To further investigate the relationship between renal BK excretion and renal KLK in diabetes we studied the regulation of the renal kallikrein-like gene, rat kallikrein 7 (rKLK7), as well as of the KLK encoding gene, rKLK1, in streptozotocin-induced (STZ) diabetic rats.

METHODS

Experiments were performed in STZ-induced diabetic male Wistar rats and their non-diabetic controls (n = 7 each group). Twelve weeks after STZ injection, urinary KLK activity, glomerular filtration rate and total protein excretion were determined. After extraction of total renal cortical RNA, specific oligonucleotides were used to generate a reverse transcription-polymerase chain reaction (RT-PCR) products of renal cortical rKLK1 and rKLK7 messenger (m)RNA. Southern blot analysis of these RT-PCR products were hybridized with appropriate gene-specific oligonucleotide probes.

RESULTS

After 12 weeks, the rats showed hyperglycemia, proteinuria and a reduced glomerular filtration rate. Renal kininogenase was reduced, as indicated by a reduction in the expression of rKLK1, as well as of the KLK-related gene, rKLK7.

CONCLUSIONS

Our data show that the expression of the two principal renal KLK genes is downregulated in the renal cortex of STZ-diabetic rats. We suggest that under severe diabetic conditions the rise in urinary BK excretion is not related to activation of the renal kinin-forming enzyme system.

Blood pressure regulation by the kallikrein-kinin system

1. The kallikrein-kinin system has a significant role in regulating arterial blood pressure. 2. Reduced formation of the kinin compontents may cause hypertensive diseases. This is because of the fact that this system is responsible for vasodilatation, reduction in total peripheral resistance, natriuresis, diuresis, increasing renal blood flow and releasing various vasodilator agents. 3. Reduced kinin-kallikrein generation in hypertensive subjects may also be associated with genetic and environmental defects. 4. The kallikrein-kinin system when administered to hypertensive patients can lower their raised blood pressure to normotensive levels. 5. The mode of action of angiotensin-converting enzyme inhibitors principally may be dependent on the kinin system protection.

Effects of diabetes, insulin treatment, and osmolality on contractility of isolated rat resistance arteries

The effects of osmolality, diabetes, and insulin-treatment on microvascular contractility were examined in mesenteric resistance arteries (internal diameter approximately 250 microns) isolated from streptozotocin-induced diabetic rats, streptozotocin-induced diabetic rats treated with 1-3 U insulin/day during the week before being killed, and age- and sex-matched control rats. Vessels were mounted in a microvascular myograph for isometric tension recording and responses were generated in physiological salt solutions with varying amounts of glucose or mannitol added. The passive response (expressed as the diameter the vessels would maintain if relaxed and exposed to a transmural pressure of 100 mmHg), the maximal response to noradrenaline, and the response produced by partial depolarization with 50 mmol/l potassium were not dependent on glucose or mannitol concentrations of the bathing medium; also, these responses were not dissimilar in vessels from the three groups of rats tested. The sensitivity to noradrenaline, however, was inversely related to the concentration of glucose (P < 0.01) and mannitol (P < 0.01) of the bathing medium without significant differences in slopes of regression lines between rat groups. Moreover, vessels from streptozotocin-induced diabetic rats were less sensitive to noradrenaline than were vessels from control rats; vessels from insulin-treated streptozotocin-induced diabetic animals had the lowest sensitivity to noradrenaline. These data suggest that osmolality, diabetes, and insulin-treatment independently affect microvascular sensitivity to the endogenous neurotransmitter, noradrenaline.

High sensitivity to salt in kininogen-deficient brown Norway Katholiek rats

Brown Norway Katholiek rats, which have very low levels of plasma kininogens, excreted a much smaller amount of kinin in the urine than normal rats of the same strain. The systolic blood pressure of 7-week-old kininogen-deficient rats fed low (0.3%) NaCl diets (131 +/- 4 mm Hg, n = 12) was not different from that in normal rats. Two percent NaCl diets given from 7 weeks of age for 4 weeks caused rapid increases in blood pressure (167 +/- 4 mm Hg, n = 12, 9 weeks old) in deficient rats, although the same diets induced no blood pressure increase in normal rats. Urinary excretion of active kallikrein and prokallikrein remained constant in both rat groups throughout NaCl loading. During this period, the deficient rats secreted less urine (9 weeks old, P < .05) and less urinary sodium (11 weeks old, P < .05). Serum levels of sodium in deficient rats were higher (P < .05) than in normal rats at 9 weeks of age. Intracellular concentrations of sodium in the erythrocytes of deficient rats were higher (P < .05) than in normal rats throughout NaCl loading. Subcutaneous infusion of bovine low molecular weight kininogen with an osmotic pump in NaCl-loaded deficient rats induced a reduction (P < .01) in blood pressure and increases (P < .05) in urine volume and urinary sodium and kinin levels. By contrast, subcutaneous infusion of the bradykinin antagonist Hoe 140 or of aprotinin in NaCl-loaded normal rats induced a hypertensive response. This antagonist treatment reduced urine volume and urinary sodium. These results indicate that the lack of kinin generation observed in the kininogen-deficient rats was related through sodium retention to the hypertensive response to NaCl loading.

Effects of cilostazol, a phosphodiesterase inhibitor, on urinary excretion of albumin and prostaglandins in non-insulin-dependent diabetic patients

Microalbuminuria is characteristic in diabetic nephropathy and is thought to be influenced by renal hemodynamics, especially by the metabolism of prostaglandins (PGs) in glomruli. To reduce urinary albumin excretion in patients with non-insulin-dependent diabetes mellitus (NIDDM), we administered 100 mg of cilostazol, a phosphodiesterase inhibitor, daily for 3 months. The urinary albumin index (UAI: microgram albumin/mg creatinine) decreased significantly after 3 months of administering cilostazol. Urinary excretions of thromboxane B2 (TXB2), a stable metabolite of thromboxane A2, decreased significantly after treatment. However, it had no effects on urinary excretions of PGE2 and 6-keto PGF1 alpha (6KF), a stable metabolite of prostacyclin. The ratio 6KF/TXB2 has been known to reflect the renal metabolism of PGs. In this study, urinary 6KF/TXB2 ratio increased significantly in parallel with a significant reduction of UAI. Cilostazol had no adverse effects on the control of blood glucose and lipids. In conclusion, cilostazol has a beneficial effect on UAI in patients with NIDDM by reducing renal production of TXB2., which increases 6KF/TXB2 ratio.

Increased renal TXA2 synthesis in diabetes mellitus: simultaneous determination of urinary TXB2 and 2,3-dinor-TXB2

The present study was designed to determine urinary excretion of kallikrein(KAL)-kinin as well as prostaglandin (PG) E2, TXB2 and 2,3-dinor-TXB2, a major urinary metabolite of TXA2 synthesized in platelets, by specific RIAs in patients with diabetes mellitus (DM). KAL or kinin excretion in 26 type II DM did not differ from control values obtained in 18 age-matched healthy subjects (C), although DM with HbA1 greater than 11% excreted less KAL. Urinary PGE2 excretion (7.6 +/- 2.8 ng/mg creatinine, mean +/- SE) was significantly lower in DM compared to C (17.5 +/- 3.9, p less than 0.05), while DM excreted more TXB2 (0.57 +/- 0.09, p less than 0.01) and 2,3-dinor-TXB2 (0.56 +/- 0.12, N.S.) than C (0.19 +/- 0.02 or 0.33 +/- 0.01). DM with or without mild proteinuria demonstrated lower PGE2, but higher TXB2 and 2,3-dinor-TXB2 excretion. A positive correlation of TXB2/2,3-dinor-TXB2 with proteinuria was observed in this group. However, in DM with massive proteinuria over 500 micrograms/mg creatinine, TXB2 and 2,3-dinor-TXB2 excretion decreased to levels almost identical to C. As a whole, a ratio of TXB2 to PGE2 or 2,3-dinor-TXB2 in DM was significantly higher than in C. The results suggest that a relative preponderance of TXB2 to 2,3-dinor-TXB2 may indicate an augmented renal, in addition to platelet, TXA2 synthesis. An excessive vasoconstrictive and proaggregatory TXA2 renal synthesis, concomitant with a decrease in vasodilatory and antiaggregatory PGE2, may have profound effects on renal functions such as protein excretion in DM.

Glandular kallikrein, renin and angiotensin converting enzyme of diabetic and hypertensive rats

To clarify the relationship between kallikrein-kinin and renin-angiotensin systems, glandular kallikrein, renin and angiotensin converting enzyme in the submandibular gland, the kidney and plasma were investigated in streptozotocin diabetic and spontaneously hypertensive rats. Kallikrein content in the submandibular gland, the kidney and plasma of diabetic rats was found to be decreased compared with nondiabetic controls. Renin activity in diabetic rats was also reduced in the submandibular gland, but the activity showed no significant changes in the kidney and plasma. The activity of angiotensin converting enzyme (ACE) in plasma significantly increased in diabetic rats. On the other hand, kallikrein content in hypertensive rats was depressed in the kidney, while the content was unchanged in the submandibular gland and plasma. Renin activity in hypertensive rats was found to be higher than that of normotensive rats in the submandibular gland, but the activity showed no remarkable changes in the kidney and plasma. ACE activity in plasma markedly decreased in hypertensive rats in contrast to diabetic rats. In hypertensive-diabetic rats, changes in the levels of these enzymes in tested materials were similar to those of diabetic rats. From these results it is reasonable to assume that (1) reduced kallikrein generation and elevated ACE activity may induce impaired kinin formation and contribute to the development of diabetes mellitus apart from the presence of hypertension and (2) low kallikrein content in the kidney could cause hypertension.

Blood pressure and metabolic effects of streptozotocin in Wistar-Kyoto and spontaneously hypertensive rats

There are conflicting reports regarding the action of streptozotocin (STZ) on blood pressure (BP) in rats. This study investigated the BP, metabolic and hormonal effects of increasing doses of STZ in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR), with consideration to methodological aspects. Indirect tail-cuff systolic BP measured in a conscious state was mildly elevated after 2 to 4 weeks and remained so in severely diabetic, emaciated WKY, whereas there were no changes in the SHR. Four and 20 weeks after STZ administration, systolic, mean and diastolic BPs measured in a conscious state with an arterial catheter were unchanged in the diabetic WKY and were decreased in the diabetic SHR. Thus, the changes in BP depended on the method used. Dose-dependent increases in blood glucose were similarly evident under conscious and ether-anesthetized conditions. Triglycerides were increased, and blood insulin and thyroxine levels were decreased in both strains. Between-strain comparisons revealed that the hypoinsulinemic response was similar, but the hyperglycemic and hypertriglyceridemic responses were greater in the SHR. The findings provide a data base for further investigation on STZ diabetes. In addition, the results suggest a different BP and metabolic susceptivity to STZ treatment in the SHR and WKY.

Interrelationship between the kallikrein-kinin system and hypertension: a review

The evidence presented here suggests strongly that the kallikreins-kininogens-kinins-kininase II system has most significant role in regulation of systemic BP. This system is involved in mediation and modulation of renin-angiotensin-aldosterone, PGS and vasopressin in the regulation of sodium water balance, renal hemodynamic and BP. Therefore, reduction in the kinin-formation due to high production of kininase II, and lower formation of tissue kallikrein might result in an increased release of vasoconstrictor angiotensin II on one side, and on the other side much reduced production of PGE, vasodilator. These changes might lead to deranged vascular smooth muscle structures and cell membrane functions, retention of sodium and water, increased plasma volume, and renovascular constriction. These physiological defects might result in the development of essential hypertension (Fig. 4). Although, it is possible now to treat hypertensive conditions with tissue kallikrein and kininase II inhibitors. These discoveries have opened up new vistas to research on the pharmacological applications of kallikreins-kininogens-kinins-kininases in human diseases.

Abnormal regulation of renal kallikrein in experimental diabetes. Effects of insulin on prokallikrein synthesis and activation

The effects of streptozotocin (STZ) diabetes and insulin on regulation of renal kallikrein were studied in the rat. 1 and 2 wk after STZ injection, diabetic rats had reduced renal levels and urinary excretion of active kallikrein. Tissue and urinary prokallikrein levels were unchanged, but the rate of renal prokallikrein synthesis relative to total protein synthesis was reduced 30-45% in diabetic rats. Treatment of diabetic rats with insulin prevented or reversed the fall in tissue level and excretion rate of active kallikrein and normalized prokallikrein synthesis rate. To further examine insulin's effects, nondiabetic rats were treated with escalating insulin doses to produce hyperinsulinemia. In these rats, renal active kallikrein increased. Although renal prokallikrein was not increased significantly by hyperinsulinemia, its synthesis was increased. As this was accompanied by proportionally increased total protein synthesis, relative kallikrein synthesis rate was not changed. Excretion of active kallikrein was unchanged, but prokallikrein excretion was markedly reduced. Therefore, increased tissue active kallikrein seen with hyperinsulinemia can be explained not only by increased synthesis but also by retention and increased activation of renal prokallikrein. These studies show that STZ diabetes produces an impairment in renal kallikrein synthesis and suggest that this disease state also impairs renal prokallikrein activation. The findings also suggest that insulin modulates renal kallikrein production, activation, and excretion.

Does so-called streptozocin hypertension exist in rats?

Although the existence of so-called streptozocin hypertension seems well established, some reports have indicated that no rise in blood pressure (BP) occurred after streptozocin treatments. To ascertain the streptozocin-induced BP response, normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were treated with streptozocin, 40 to 45 and 35 mg/kg i.v., respectively, and BP was determined directly and indirectly every week for 3 to 4 weeks. Direct mean BP was determined without anesthesia or restraint through a cannula inserted into the rat's abdominal aorta. Indirect BP was determined at the tail without anesthesia after prewarming the rat in a holder. Compared with control values, indirect BP increased significantly in diabetic WKY 2 weeks after streptozocin treatment. In contrast, direct BP of these rats decreased, compared with control values. Indirect BP of diabetic SHR was as high as that of the controls, whereas direct BP of diabetic SHR decreased significantly 1 week after the treatment and thereafter, compared with control values. These discrepancies between the direct and indirect BP values may be caused by severe emaciation of diabetic rats. Extra pressure in the cuff may be necessary to occlude the bloodstream. These results indicate that under these conditions the value of BP obtained by the direct measurement is more reliable than that by the indirect one; therefore, we concluded that so-called streptozocin hypertension does not exist.

Relevance of plasma, glandular and urinary kallikrein in renal hypertrophy in streptozotocin-diabetic rats

The relevance of plasma, glandular and renal kallikrein as an intrarenal hemodynamic regulator, in renal hypertrophy, in 1-5 weeks streptozotocin diabetic rats has been investigated. The fasting plasma glandular kallikrein level significantly decreased with increasing duration of diabetes (p less than 0.05). Glandular kallikrein correlated negatively with kidney weight (r = 0.76, p = 0.05). The 24 hour urinary kallikrein excretion significantly increased with increasing duration of diabetes (p less than 0.05), but this level was not correlated with glucose level, nor with kidney weight. Aprotinin (a kallikrein inhibitor) injected (10 X 10(3) KIU/kg) twice daily for 2 weeks in diabetic rats, significantly decreased plasma glucose levels by 28%, 24 hour urinary kallikrein by 37% (p less than 0.05) and kidney weight by 6%. These results suggest that plasma, glandular and renal kallikrein did not play an important role in the renal hypertrophy observed in streptozotocin diabetic rats.

Insulin potentiates cholecystokinin (CCK)-induced secretion of pancreatic kallikrein

The effects of insulin on pancreatic kallikrein secretion were studied in streptozotocin diabetic rats and after acute administration of insulin to normal rats. Studies on total protein and amylase secretion were included for comparison. In diabetic rats, the concentration of amylase in pancreatic tissue as well as basal and CCK-stimulated amylase exocrine secretion were significantly reduced. Insulin treatment restored pancreatic tissue concentration and exocrine release of amylase to normal. Insulin deficiency did not induce any change in the concentration of kallikrein or trypsin-like activity in pancreatic tissue. However, basal kallikrein secretion was higher in diabetic rats than in controls. Insulin treatment of diabetics rats did not alter basal kallikrein secretion but potentiated CCK-stimulation of kallikrein release. In normal rats, CCK induced an increase of pancreatic protein, amylase, and kallikrein secretion but not pancreatic juice flow. Additional administration of insulin potentiated the CCK-induced secretory rate of pancreatic juice, protein, and kallikrein but not amylase. A 1.6 times higher concentration of kallikrein was found in the portal vein than in arterial blood, indicating an endocrine release of pancreatic kallikrein. No difference in the concentration of circulating kallikrein was observed between the control and the insulin-treated group.