Interleukin-2 enhances the release of endothelin-1 from the rat mesenteric artery

We measured the ET-1 concentration in plasma and in the perfusate of the mesenteric arteries of rats treated with a therapeutic dose of IL-2 for 7 days (100000 U/Kg, iv.). The plasma ET-1 concentration in rats given IL-2 was 14.2 +/- 3.2 pg/ml which was significantly greater than that in the controls (2.5 +/- 0.4 pg/ml, P less than 0.05). The mesenteric arteries also released a significantly greater amount of ET-1 (29.5 +/- 1.6 pg/h) than that in controls (16.8 +/- 2.3 pg/h, P less than 0.01). The arterial blood pressure was significantly lower after IL-2 treatment than the pre-dosing level (P less than 0.05). It is concluded that IL-2 induces ET-1 release from the vascular wall, possibly as a result of reversible endothelial dysfunction caused by IL-2.     

Use of a novel peptide leukotriene receptor antagonist, Ly-163443, in splanchnic artery occlusion shock

We studied the effects of LY-163443, a novel selective receptor antagonist of LTD4 and LTE4, in splanchic artery occlusion (SAO) shock. LY-163443 antagonized the bronchoconstrictor effect of LTD4 given intravenously to anesthetized rats. Anesthetized rats subjected to total occlusion of the superior mesenteric and the celiac arteries for 40 minutes developed a severe shock state usually resulting in a fatal outcome within two hours after release of the occlusion. SAO shock rats pre-treated with LY-163443 before the occlusion of the splanchnic arteries maintained post-release MABP at significantly higher values compared to rats receiving either the vehicle or LY-163443 as a post-treatment 15 min after occlusion (final MABP 96 +/- 8 vs 51 +/- 1, p less than 0.01 and 53 +/- 3, p less than 0.01, respectively). Pre-treatment with LY-163443 attenuated the release of the lysosomal hydrolase, cathepsin D (p less than 0.01 from vehicle and p less than 0.05 from post-treatment groups), and the plasma accumulation of free amino-nitrogen compounds (p less than 0.05 from vehicle). Furthermore, the plasma activity of a myocardial depressant factor (MDF) was significantly lower in the pre-treatment group than in the vehicle group (27 +/- 3 vs 51 +/- 6 U/ml, p less than 0.01). SAO shock rats pretreated with LY-163443 also exhibited significantly higher survival rates (p less than 0.01 from vehicle and post-treatment groups), and prolonged survival times (p less than 0.01 from vehicle and post-treatment groups).(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma and atrial levels of atrial natriuretic peptide (ANP) in pulmonary hypertensive rats

Immunoreactive atrial natriuretic peptide (IR-ANP) was measured in plasma and atrium of normal and monocrotaline induced pulmonary hypertensive rats (PH rats). In these animals, there was right ventricular hypertrophy and right ventricular systolic pressure was elevated. Fourteen days after a single dose of monocrotaline (40 mg/kg), plasma IR-ANP concentrations were significantly elevated (964.3 +/- 63.0 pg/ml vs. 521.0 +/- 81.9 pg/ml in controls, p less than 0.001). Tissue levels of IR-ANP in the right atrium in PH rats was significantly lower than those in the controls (45.1 +/- 3.9 ng/mg vs. 240.5 +/- 10.4 ng/mg, p less than 0.001), while there was no significant difference in tissue levels of atrial IR-ANP in the left atrium between the two groups. Thus, development of pulmonary hypertension led to an increase in release of ANP from the right atrium.     

Thromboxane A2 from Kupffer cells contributes to the hyperresponsiveness of hepatic portal circulation to endothelin-1 in endotoxemic rats

We examined the role of thromboxane A2 (TXA2) in LPS-induced hyperresponsiveness of hepatic portal circulation to endothelins (ETs) and whether Kupffer cells are the primary source of TXA2 release in response to ET-1 in endotoxemia. After 6 h of LPS (1 mg/kg body wt ip) or saline (control), liver was isolated and perfused with recirculating Krebs-Henseleit bicarbonate buffer at a constant flow rate (100 ml.min(-1).kg body wt(-1)). ET-1 (10 pmol/min) was infused for 10 min. Portal pressure (PP) was continuously monitored during perfusion. Perfusate was sampled for enzyme immunoassay of thromboxane B2 (TXB2; the stable metabolite of TXA2) and lactate dehydrogenase (LDH) assay. ET-1 infusion resulted in a significantly greater increase of PP in the LPS group than in controls. Both TXA2 synthase inhibitor furegrelate (Fureg) and TXA2 receptor antagonist SQ-29548 (SQ) substantially blocked enhanced increase of PP in the LPS group (4.9 +/- 0.4 vs. 3.6 +/- 0.5 vs. 2.6 +/- 0.6 mmHg for LPS alone, LPS + Fureg, and LPS + SQ, respectively; P < 0.05) while having no significant effect on controls. GdCl3 for inhibition of Kupffer cells had similar effects (4.9 +/- 0.4 mmHg vs. 2.9 +/- 0.4 mmHg for LPS alone and GdCl3 + LPS, respectively; P < 0.05). In addition, the attenuated PP after ET-1 was found concomitantly with significantly decreased releases of TXB2 and LDH in LPS rats treated with Fureg, SQ, and GdCl3 (886.6 +/- 73.4 vs. 110.8 +/- 0.8 vs. 114.8 +/- 54.7 vs. 135.2 +/- 45.2 pg/ml, respectively; P < 0.05). After 6 h of LPS, Kupffer cells in isolated cell preparations released a significant amount of TXA2 in response to ET-1. These results clearly indicate that hyperresponsiveness of hepatic portal circulation to ET-1 in endotoxemia is mediated at least in part by TXA2-induced receptor activation, and Kupffer cells are likely the primary source of increased TXA2 release.     

Microvascular versus macrovascular dysfunction in type 2 diabetes: differences in contractile responses to endothelin-1

Vascular dysfunction characterized by a hyperreactivity to vasoconstrictors and/or impaired vascular relaxation contributes to increased incidence of cardiovascular disease in diabetes. Endothelin (ET)-1, a potent vasoconstrictor, is chronically elevated in diabetes. However, the role of ET-1 in resistance versus larger vessel function in mild diabetes remains unknown. Accordingly, this study investigated vascular function of third-order mesenteric arteries and basilar arteries in control Wistar and Goto-Kakizaki (GK) rats, a model of mild Type 2 diabetes. Six weeks after the onset of diabetes, contractile responses to 0.1-100 nM ET-1 and relaxation responses to 1 nM-10 microM acetylcholine (ACh) in vessels preconstricted (baseline + 60%) with serotonin (5-HT) were assessed by myograph studies in the presence or absence of a nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine (L-NNA). Maximum contractile response to ET-1 was augmented in mesenteric vessels (155 +/- 18% in GK vs. 81 +/- 6% in control; n = 5-7) but not in the basilar artery (134 +/- 29% in GK vs. 107 +/- 17% in control; n = 4 per group). However, vascular relaxation was impaired in the basilar arteries (22 +/- 4% in GK vs. 53 +/- 7% in control; n = 4 per group) but not in mesenteric arteries of GK rats. Inhibition of NOS decreased the relaxation response of basilar arteries to 15 +/- 8% and 42 +/- 5% in GK and control rats, respectively; whereas, in resistance vessels, corresponding values were 56 +/- 7% and 89 +/- 3% (vs. 109 +/- 2% and 112 +/- 3% without NOS blockade), indicating the involvement of different vasorelaxation-promoting pathways in these vascular beds. These findings provide evidence that the ET system is activated even under mild hyperglycemia and that it contributes to the hyperreactivity of resistance vessels, therefore, the ET system may play an important role in elevated blood pressure in Type 2 diabetes.     

Alterations in atrial and plasma atrial natriuretic factor (ANF) content during development of hypoxia-induced pulmonary hypertension in the rat

Distension of the atrial wall has been proposed as a signal for the increased release of atrial natriuretic factor (ANF) from atrial myocytes in response to perceived volume overload. To determine whether pressure changes resulting from hypertension in the pulmonary circulation may stimulate release of ANF, rats were exposed to chronic hypobaric hypoxia for 3 or 21 days and the ANF concentration in the atria and plasma were determined by specific radioimmunoassay. Exposure to chronic hypoxia resulted in significant increases in hematocrit at both 3 (p less than 0.025) and 21 days (p less than 0.005) and in the development of right ventricular hypertrophy (RVH) expressed as the ratio of the weight of the right ventricle to the weight of the left ventricle and septum (RV/LV+S) at both 3 (RV/LV+S = 0.278 +/- 0.005) and 21 days (RV/LV+S = 0.536 +/- 0.021). After 21 days, left atrial (LA) ANF content was significantly increased in hypoxic rats compared to controls (508 +/- 70 ng/mg tissue vs 302 +/- 37 ng/mg), while right atrial (RA) ANF content was significantly reduced (440 +/- 45 vs 601 +/- 58 ng/mg). At this time, plasma ANF concentration was significantly elevated compared to controls (238 +/- 107 pg/ml vs 101 +/- 10 pg/ml). These results suggest that the development of pulmonary hypertension following chronic hypobaric exposure induces altered atrial ANF content and increased plasma ANF concentration as a result of altered distension of the atrial wall.     

Endothelin-1 and endothelin-3 stimulate prostaglandin E2 secretion from the rat median eminence.

The in vitro effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) on the release of prostaglandin (PG)E2 from the rat median eminence were investigated. The addition of ET-1 from 10(-9) M to 10(-6) M stimulated PGE2 release in a dose-dependent manner (from 10.5 +/- 2.1 to 54.4 +/- 5.6 pg/ME fragment/30 min; mean +/- SEM, p less than 0.001). ET-3 also stimulated the release of PGE2 from 10(-7) M to 10(-5) M dose dependently (from 18.1 +/- 0.7 to 60.9 +/- 17.4 pg/ME fragment/30 min p less than 0.05). The time course effect of ET-3 (10(-6) M) showed that PGE2 release was stimulated within five minutes (control, 1.5 +/- 0.5; ET-3, 15.8 +/- 3.0 pg/ME fragment/5 min, p less than 0.01). These results suggest that ET-1 and ET-3 have some physiological effects on the rat median eminence.     

Effects of hyperbaric oxygen in circulatory shock induced by splanchnic artery occlusion and reperfusion in rats

We studied the effects of hyperbaric oxygen in a severe model of circulatory shock induced by occlusion and reperfusion of major splanchnic arteries (splanchnic artery occlusion (SAO) shock). Pentobarbital-anesthetized rats subjected to total occlusion of the superior mesenteric and the celiac arteries for 40 min developed a severe shock state, resulting in a uniformly fatal outcome after release of the occlusion. Exposure to hyperbaric oxygen at 2 ATA (atmosphere absolute) (1 ATA = 0.1 MPa) was initiated immediately after reperfusion. SAO shock rats exposed to hyperbaric oxygen maintained mean arterial blood pressure at significantly higher values throughout the postreperfusion period compared with untreated SAO shock rats (p less than 0.01), with final mean arterial blood pressures of 88 +/- 9 and 51 +/- 4 mmHg, respectively. Treatment with hyperbaric oxygen attenuated the increase in plasma activities of the lysosomal hydrolase cathepsin D (p less than 0.05), and diminished the increase of hematocrit (p less than 0.01 from untreated shock rats). Splanchnic occlusion shock rats treated with hyperbaric oxygen also exhibited a significantly higher survival rate than the untreated shock group (77 vs. 0%, respectively; p less than 0.01). Our results suggest that the beneficial effects of exposure to hyperbaric oxygen immediately after reperfusion of the splanchnic region outweigh its possible deleterious effect.     

Weight loss reduces plasma endothelin-1 concentration in obese men

Obesity is associated with endothelial dysfunction that may contribute to the development of diabetes, hypertension, and atherosclerosis. Endothelin-1 (ET-1), which is produced mostly by vascular endothelial cells, has potent vasoconstrictor and proliferative activity in vascular smooth muscle cells and, therefore, has been implicated in regulation of vascular tonus and the progression of atherosclerosis, suggesting that ET-1 may be important in endothelial dysfunction. We studied whether diet-induced weight loss (i.e., lifestyle modification) affects plasma ET-1 concentration in obese individuals. We measured plasma ET-1 concentration in seven obese men (age: 48 +/- 4 years old, body mass index: 27.7 +/- 0.5 kg/m2) before and after a 3-month, diet-induced weight reduction program (i.e., lifestyle modification program). Caloric restriction reduced body weight from 78 +/- 3 to 68 +/- 2 kg (P < 0.001) and resulted in 12.1 +/- 1.2% reduction in body mass index (24.3 +/- 0.3 kg/m(2), P < 0.0001). After the weight reduction program, systolic and diastolic blood pressure significantly decreased (128 +/- 7 vs. 115 +/- 4 mm Hg, P < 0.05 and 88 +/- 4 vs. 77 +/- 2 mm Hg, P < 0.01, respectively). The plasma level of ET-1 significantly decreased after the program (5.1 +/- 0.4 vs. 4.0 +/- 0.3 pg/ml, P < 0.05). The percentage systolic blood pressure reduction and percentage plasma ET-1 concentration reduction was in a linear relationship (r = 0.86, P < 0.05). Furthermore, the relationship between percentage weight reduction and percentage plasma ET-1 concentration reduction was linear (r = 0.87, P < 0.05). We conclude that weight loss by low-calorie diet (i.e., lifestyle modification) reduces plasma ET-1 concentration in obese individuals. This reduction may contribute to the improvement of obesity-induced endothelial dysfunction.     

Central endothelin: effects on vasopressin and the arterial baroreflex in doxorubicin heart failure rats

Endothelin 1 (ET-1) is increased in heart failure, both in plasma and within the central nervous system. Centrally, ET-1 induces sympathetic hyperactivity and arginine vasopressin (AVP) secretion. Both sympathetic activity and AVP secretion are regulated by the arterial baroreflex, which is typically impaired in heart failure. We hypothesized that central blockade of ETA receptors (ETAR) alters the baroreflex response of heart rate, renal sympathetic nerve activity (RSNA), and plasma AVP levels in a cardiomyopathic model of heart failure. Female Sprague-Dawley rats received weekly intraperitoneal injections of doxorubicin 2.5 mg x kg(-1) (doxorubicin heart failure, doxo-HF) or saline vehicle (control). After 8 weeks, they were instrumented, conditioned to the study environment, and then studied in the awake, non-restrained state. Baseline mean arterial pressure (MAP), RSNA, and plasma osmolality were similar in both groups, but heart rate (p<0.02), left ventricular pressure (p<0.001), and plasma AVP (p<0.01) were higher in the doxo-HF group. ET-1 dose dependently increased MAP, but the rise was significantly attenuated in doxo-HF rats at all doses. Baseline baroreflex control of heart rate and RSNA was similar in both groups. ETAR blockade with 4 nmol BQ123 i.c.v. significantly decreased both the upper plateau (p<0.05) and the range (p<0.05) of the baroreflex response of both heart rate and RSNA in doxo-HF but not in control rats. Despite higher basal plasma levels of AVP, ET-1 evoked a rise in plasma AVP of 13.6+/-3.2 pg x mL(-1) in doxo-HF compared with 0.4+/-0.4 pg x mL(-1) in control rats (p<0.001). To account for the blunted pressor response to ET-1 in the doxo-HF rats, gain of AVP release was calculated as DeltaAVP/DeltaMAP and was also found to be significantly greater in the doxo-HF rats (p<0.001). BQ123 prevented the rise in AVP and restored the gain in doxo-HF rats to that seen in controls. Thus, central ETAR contribute to the sympathoexcitation and AVP responses observed in heart failure due to doxorubicin cardiomyopathy.     

Reactive oxygen species contribute to sleep apnea-induced hypertension in rats

In clinical studies, sleep apnea is associated with hypertension, oxidative stress, and increased circulating endothelin-1 (ET-1). We previously developed a model of sleep apnea by exposing rats to eucapnic intermittent hypoxia (IH-C) during sleep, which increases both blood pressure and plasma levels of ET-1. Because similar protocols in mice increase tissue and plasma markers of oxidative stress, we hypothesized that IH-C generation of reactive oxygen species (ROS) contributes to the development of ET-1-dependent hypertension in IH-C rats. To test this, male Sprague-Dawley rats were instrumented with indwelling blood pressure telemeters and drank either plain water or water containing the superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 1 mM). Mean arterial pressure (MAP) and heart rate (HR) were recorded for 3 control days and 14 treatment days with rats exposed 7 h/day to IH-C or air/air cycling (Sham). On day 14, MAP in IH-C rats treated with Tempol (107 +/- 2.29 mmHg) was significantly lower than in untreated IH-C rats (118 +/- 9 mmHg, P < 0.05). Tempol did not affect blood pressure in sham-operated rats (Tempol = 101 +/- 3, water = 101 +/- 2 mmHg). Immunoreactive ET-1 was greater in plasma from IH-C rats compared with plasma from sham-operated rats but was not different from Sham in Tempol-treated IH-C rats. Small mesenteric arteries from IH-C rats but not Tempol-treated IH-C rats had increased superoxide levels as measured by ferric cytochrome c reduction, lucigenin signaling, and dihydroethidium fluorescence. The data show that IH-C increases ET-1 production and vascular ROS levels and that scavenging superoxide prevents both. Thus oxidative stress appears to contribute to increases in ET-1 production and elevated arterial pressure in this rat model of sleep apnea-induced hypertension.     

Vascular reactivity to norepinephrine in rats with cirrhosis of the liver

Vascular reactivity to norepinephrine was studied in rats with early cirrhosis of the liver and in control rats. Cirrhotic rats showed water and sodium retention but not ascites. Studies were performed in whole animals, isolated hindquarters, and isolated femoral arteries. Plasma catecholamine levels were measured by radioenzymoassay and their urinary metabolites by gas-liquid chromatography. Plasma norepinephrine was 331 +/- 49 pg/mL (mean +/- SEM) in control rats and 371 +/- 66 pg/mL in cirrhotic animals (p greater than 0.05). No differences in plasma epinephrine or dopamine were observed. Urinary excretion of catecholamine metabolites was increased in cirrhotic rats. These data suggest a moderate activation of the sympathetic nervous system. In basal conditions, cirrhotic rats showed lower mean arterial pressure than controls (101 +/- 4 vs. 116 +/- 4 mmHg (1 mmHg = 133.3 Pa); p less than 0.01). However, perfused hindlimb resistance was similar in cirrhotic and in control animals. In the whole animal and in the perfused hindquarter, the contractile response to norepinephrine was similar for control and for cirrhotic rats. The contractile response to norepinephrine exhibited by isolated femoral arteries was similar in those from cirrhotic and control rats. This indicates that the peripheral vascular bed has a well-maintained ability to constrict in response to norepinephrine, suggesting that circulatory abnormalities in early experimental cirrhosis are not caused by refractoriness of the vascular smooth muscle to norepinephrine.     

Angiotensin II generation in mesenteric arteries in rats: effects of nephrectomy, deoxycorticosterone and dexamethasone

Angiotensin II (ANG II) generation in the mesenteric arteries was studied in four groups of rats: deoxycorticosterone (DOCA)/salt treated, glucocorticoid treated, nephrectomized and control rats. Basal plasma renin activity (PRA) was undetectable in the nephrectomized group and suppressed in the DOCA/salt treated rats, but was increased in the rats treated with glucocorticoid. The Basal plasma ANG II concentration changed comparably with PRA in all four groups of rats. In the control rats, ANG II was released from the mesenteric arteries at a rate of 43.0 +/- 12.0 pg/h, and it was not decreased by nephrectomy. In DOCA/salt rats and glucocorticoid rats, ANG II release significantly decreased to 12.8 +/- 7.1 and 6.9 +/- 1.5 pg/h, respectively. Captopril treatment significantly reduced ANG II release from the mesenteric arteries in both controls and nephrectomized rats, but did not influence ANG II output in DOCA/salt rats or in glucocorticoid treated rats. In nephrectomized rats, captopril lowered blood pressure in association with a significant reduction in the mesenteric ANG II formation. These results indicate that the renal and vascular renin-angiotensin system (RAS) may be independently regulated, and in nephrectomized animals the vascular RAS contributes in part to the maintenance of blood pressure. The present results also suggest that volume expansion per se and/or pharmacological intervention by DOCA and glucocorticoid could modulate vascular ANG II generation.     

Insulin infusion induces endothelin-1-dependent hypertension in rats

We previously showed that chronic insulin infusion induces insulin resistance, hyperendothelinemia, and hypertension in rats (C. C. Juan, V. S. Fang, C. F. Kwok, J. C. Perng, Y. C. Chou, and L. T. Ho. Metabolism 48: 465-471, 1999). Endothelin-1 (ET-1), a potent vasoconstrictor, is suggested to play an important role in maintaining vascular tone and regulating blood pressure, and insulin increases ET-1 production in vivo and in vitro. In the present study, BQ-610, a selective endothelin A receptor antagonist, was used to examine the role of ET-1 in insulin-induced hypertension in rats. BQ-610 (0.7 mg/ml; 0.5 ml/kg body wt) or normal saline was given intraperitoneally two times daily for 25 days to groups of rats infused with either saline or insulin (2 U/day via sc-implanted osmotic pumps), and changes in plasma levels of insulin, glucose, and ET-1 and the systolic blood pressure were measured over the experimental period, whereas changes in insulin sensitivity were examined at the end of the experimental period. Plasma insulin and ET-1 levels were measured by RIA, plasma glucose levels using a glucose analyzer, systolic blood pressure by the tail-cuff method, and insulin sensitivity by an oral glucose tolerance test. Our studies showed that insulin infusion caused sustained hyperinsulinemia in both saline- and BQ-610-injected rats over the infusion period. After pump implantation (2 wk), the systolic blood pressure was significantly higher in insulin-infused rats than in saline-infused rats in the saline-injected group (133 +/- 3.1 vs. 113 +/- 1.1 mmHg, P < 0.05) but not in the BQ-610-injected group (117 +/- 1.2 vs. 117 +/- 1.8 mmHg). Plasma ET-1 levels in both sets of insulin-infused rats were higher than in saline-infused controls (2.5 +/- 0.6 and 2.5 +/- 0.8 vs. 1.8 +/- 0.4 and 1.7 +/- 0.3 pmol/l, P < 0.05). Oral glucose tolerance tests showed that BQ-610 treatment did not prevent the insulin resistance caused by chronic insulin infusion. No significant changes were found in insulin sensitivity and blood pressure in saline-infused rats treated with BQ-610. In a separate experiment, insulin infusion induced the increase in arterial ET-1 content, hypertension, and subsequent plasma ET-1 elevation in rats. These results suggest that, in the insulin infusion rat model, ET-1 plays a mediating role in the development of hypertension, but not of insulin resistance.     

Role of glucagon in the splanchnic and systemic hemodynamic changes induced by portal-systemic blood shunting

Portal-systemic blood shunting is often accompanied by hyperglucagonemia and hemodynamic changes. To determine this causal relation, splanchnic and systemic hemodynamics (radioactive microspheres) and plasma glucagon levels (radioimmunoassay) were assessed in conditions of total portal-systemic shunting in portacaval-shunted (PCS) rats and in sham-operated (SO) normal rats. To compare these results, another hemodynamic study was undertaken basally and during glucagon infusion in nonoperated normal rats. PCS rats showed a threefold greater plasma glucagon concentration than SO animals (924 +/- 134 vs. 309 +/- 18 pg/ml, p less than 0.01), and they developed a hyperdynamic splanchnic circulation with higher portal venous inflow than SO rats (8.29 +/- 1.1 vs. 5.09 +/- 0.4 ml/min/100 g, p less than 0.05). Infusion of a pharmacological dose of glucagon in normal rats increased portal venous inflow (from 4.92 +/- 0.33 to 6.24 +/- 0.48 ml/min/100 g, p less than 0.05) so as to imply this hormone in the development of the hyperdynamic splanchnic circulation in conditions of portal-systemic shunting. However, the discrepancies in systemic hemodynamics between PCS and glucagon-infused rats may be a result of the different plasma glucagon levels reached in the two groups.     

The effect of total parenteral nutrition (TPN) on gastrin release in the rat

The effect of short-term (7 days) total parenteral nutrition (TPN) on gastrin release was studied in vivo and in the isolated vascularly perfused rat stomach. The daily plasma gastrin concentration of parenterally fed rats was significantly lower than in ad lib fed control animals (53 +/- 17 pg/ml vs 159 +/- 32 pg/ml, P less than 0.05) as early as day 2 and a similar pattern was observed on days 4 and 6. The fasting plasma gastrin concentration of control animals was 2-fold greater than of the parenterally fed group (P less than 0.05). Following oral peptone, the gastrin response of TPN and control animals doubled although peak gastrin levels were greatly reduced in TPN rats. Basal gastrin release from the perfused stomachs of control rats was 2-fold greater than from TPN rats (P less than 0.05). Electrical stimulation of the vagal trunks resulted in a significantly greater elevation in gastrin secretion from control stomachs compared to TPN animals (4-fold vs. 2.4-fold increase, P less than 0.05). Quantification of the antral G-cell population revealed a significant reduction in the number of G-cell of TPN rats compared to controls (97 +/- 8 cells/mm vs 76 +/- 6 cells/mm, P less than 0.05). These results indicate that luminal nutrient stimulation is necessary for the maintenance of normal G-cell secretory activity in vivo and from the in vitro stomach. G-cell hypoplasia appears to be partially responsible for reduced gastrin output to basal and stimulated conditions after TPN.     

The concentrations of 6-keto-PGF1 alpha and TXB2 in plasma samples from patients with benign and malignant tumours of the breast

Peripheral plasma concentrations of 6-keto-PGF1 alpha and TXB2 were measured in patients with benign and malignant tumours of the breast, in patients with non-gynecological diseases, and in healthy female controls. The values were significantly higher in female patients with malignant tumours of the breast than in healthy controls (146 +/- 28 vs 13 +/- 2.5 pg/ml for 6-keto-PGF1 alpha p less than 0.01 and 78 +/- 17 vs 11 +/- 2 pg/ml for TXB2, p less than 0.01). Benign tumours of the breast were also associated with significantly raised plasma levels of 6-keto-PGF1 alpha and TXB2 compared to normal controls (52 +/- 5 vs 13 +/- 2.5 pg/ml for 6-keto-PGF1 alpha, p less than 0.01 and 26 +/- 5 vs 11 +/- 2 pg/ml for TXB2, p less than 0.05). The high levels of 6-keto-PGF1 alpha and TXB2 were not found to be correlated with clinical and histopathological data. The surgical removal of the primary tumour has apparently no effect on the plasma concentrations of 6-keto-PGF1 alpha and TXB2 over a follow-up period of 9 days after operation. The lack of alterations in the ratio of TXB2:6-keto-PGF1 alpha in the cancer patients and other subjects studied before and after surgery is indicative of the regulatory power of metabolic systems to preserve the homeostatic balance.     

Prevention of endothelin-1-induced increases in blood pressure: role of endogenous CGRP

To determine the role of endothelin-1 (ET-1) and its receptors in the regulation of calcitonin gene-related peptide (CGRP) release, male Wistar rats were divided into six groups and subjected to the following treatments for 1 wk with or without ABT-627 (an ET(A) receptor antagonist, 5 mg.kg(-1).day(-1) in drinking water) or A-192621 (an ET(B)-receptor antagonist, 30 mg.kg(-1).day(-1) by oral gavage): control (Con), ET-1 (5 ng.kg(-1).min(-1) iv), Con + ABT-627, Con + A-192621, ET-1 + ABT-627, and ET-1 + A-192621. Baseline mean arterial pressure (MAP, mmHg) was higher (P < 0.05) in Con + A-192621 (122 +/- 4) and ET-1 + A-192621 (119 +/- 4) groups compared with Con (104 +/- 6), ET1 (106 +/- 3), Con + ABT-627 (104 +/- 3), and ET1 + ABT-627 (100 +/- 3) groups. Intravenous administration of CGRP(8-37) (a CGRP receptor antagonist, 1 mg/kg) increased MAP (P < 0.05) in ET-1 (13 +/- 1), Con + A-192621 (12 +/- 1), and ET-1 + A-192621 (15 +/- 3) groups compared with Con (4 +/- 1), Con-ABT-627 (4 +/- 1), and ET-1 + ABT-627 (5 +/- 1) groups. Plasma CGRP levels (in pg/ml) were increased (P < 0.05) in ET-1 (57.5 +/- 6.1), Con + A-192621 (53.9 +/- 3.4), and ET-1 + A-192621 (60.4 +/- 3.0) groups compared with Con (40.4 +/- 1.6), Con + ABT-627 (40.0 +/- 2.9), and ET-1 + ABT-627 (42.6 +/- 1.9) groups. Plasma ET-1 levels (in pg/ml) were higher (P < 0.05) in ET-1 (2.8 +/- 0.2), ET-1 + ABT-627 (3.2 +/- 0.4), Con + A-192621 (3.3 +/- 0.4), and ET-1 + A-192621 (4.6 +/- 0.3) groups compared with Con (1.1 +/- 0.2) and Con-ABT-627 (1.3 +/- 0.2) groups. Therefore, our data show that ET-1 infusion leads to increased CGRP release via activation of the ET(A) receptor, which plays a compensatory role in preventing ET-1-induced elevation in blood pressure.     

Papaverine effects on PGI2 and TXA2 release from the canine vascular wall.

Operative manipulation of blood vessels might lead to spasm, thereby destroying the endothelial cell function: the spasm can be prevented by the vasodilator papaverine. To study if this was mediated via the prostanoid pathway the following investigation was undertaken: canine jugular veins and carotid arteries were dissected with or without papaverine. Vessel segments were then perfused with Hank's balanced salt solution for five times 15 min. Prostacyclin was measured as the stable degradation product 6-keto-PGF1 alpha and thromboxane as TXB2, by radioimmunoassay. Control arterial segments' 6-keto-PGF1 alpha release was initially 129.5 + 20.1 pg/mm2/15 min, and 29.7 + 10.4 after 60 min (p less than 0.05 vs initial value) and responded to arachidonic acid (AA) with an increase to 139.2 +/- 23.1 pg/mm2/15 min (p less than 0.05). Segments treated with papaverine had the same release as the controls. In venous segments there was a lower initial release (p less than 0.05) from segments given papaverine than from controls, but this was more likely an effect of papaverine on the assay. There was no difference in release of prostacyclin from segments given papaverine in the perfusate compared to controls when using 125I tracer. When using 3H tracer including absorption of free antigen to dextran coated charcoal, papaverine displaced the free tracer giving artificially low values. There was no effect of papaverine given intraoperatively on the TXB2 release, neither from arteries nor from veins. In another experiment the vessel wall tension was examined and the cyclooxygenase inhibitor diclofenac did not inhibit the vasodilating effect of papaverine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma endothelin-1 levels and albumin excretion rate in normotensive,microalbuminuric type 2 diabetic patients

BACKGROUND: Endothelin-1 (ET-1) is able to determine functional and structural renal alterations and plasma levels of this vasoconstrictor peptide are increased in diabetic patients. In a selected group of type 2 normotensive diabetic patients with microalbuminuria, we investigated circulating ET-1 levels compared to a control group and verified whether there is a relationship between ET-1 levels and albumin excretion rate in diabetics. SUBJECTS AND METHODS: Thirty-two microalbuminuric type 2 diabetic patients (12 males and 20 females; mean age 57 +/- 8 years) without hypertension, renal failure, hypercholesterolemia or atherosclerotic damage were selected. The control group was made up of 28 healthy subjects matched for sex and age. Blood pressure, creatinine clearance, serum cholesterol and plasma ET-1 values were determined in diabetic and control group. In diabetic patients, glycosilated hemoglobin and urinary albumin excretion rate were also assayed. Mean ET-1 values in diabetics and controls were compared using Student's t-test. Linear regression test was done to relate two variables. Statistical significance was set at p<0.05. RESULTS: Mean ET-1 values were significantly higher in the diabetic group than in controls (11.77 +/- 1.16 pg/ml vs 8.9 +/- 2.1 pg/ml; p<0.05). No relationship (p>0.05) was found between circulating ET-1 and blood pressure, creatinine clearance, serum cholesterol and metabolic control in diabetics. There was a significant positive correlation (r=0.403; p=0.03) between plasma ET-1 levels and albumin excretion rate in diabetic patients. CONCLUSIONS: Our results showed that circulating ET-1 values were increased in microalbuminuric, normotensive, type 2 diabetic patients and correlated with albumin excretion rate. These findings confirm that endothelial dysfunction, as expressed by ET-1 levels, occurs early in these patients and support the hypothesis of a potential role for this peptide in development of microalbuminuria in diabetic nephropathy.