Role of antidiuretic hormone in the attenuated furosemide response observed during indomethacin administration

Recently we demonstrated that increased chloride reabsorption in Henle's loop is a major contributor to the blunted furosemide response observed during prostaglandin synthesis inhibition. Because antidiuretic hormone (ADH) modulates chloride reabsorption in the loop and because prostaglandin synthesis inhibition potentiates ADH-mediated water reabsorption, ADH may be necessary for the attenuated furosemide response observed during prostaglandin synthesis inhibition. If such were the case, then prostaglandin synthesis inhibition should have no effect on furosemide's chloruretic response in the absence of ADH. To test this hypothesis, the effect of indomethacin on furosemide chloruresis was determined in homozygous (ADH-deficient) Brattleboro rats and in homozygous Brattleboro rats receiving ADH (2.4 mU/hr) over a short period of time. Furosemide-induced chloruresis was not different (P was not significant) between indomethacin-treated homozygous Brattleboro rats and homozygous Brattleboro rats receiving the indomethacin vehicle (fractional excretion of chloride: 6.28% +/- 1.08% vs. 6.24% +/- 0.98%). However, in ADH-infused Brattleboro rats, furosemide chloruresis was lower in indomethacin-treated rat groups than in vehicle-treated rat groups (fractional excretion of chloride: 3.09% +/- 0.62% vs. 6.61% +/- 0.88%; P less than 0.02) and lower than in indomethacin-treated ADH-deficient Brattleboro rats as well (P less than 0.05). Mean arterial pressure, inulin clearance, and renal blood flow were not different between any groups. Urinary prostaglandin excretion rates were not different between ADH-deficient Brattleboro rats and ADH-treated Brattleboro rats during furosemide administration and were markedly reduced by indomethacin in both circumstances. Thus, ADH is necessary for the blunted furosemide response observed during prostaglandin synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calcium-dependent stimulation of renal medullary prostaglandin synthesis by furosemide

The present study examined the actions of furosemide and other "loop" diuretics on immunoreactive prostaglandin E (iPGE) and [14C]arachidonate (AA) release in vitro in incubates of slices from rat and dog outer or inner medulla. The loop diuretics furosemide, ethacrynic acid, bumetanide and 3-benzylamino-4-phenylthio-5-sulfamoylbenzoic acid all significantly increased [14C]AA and iPGE release (1.5- to 4-fold) into the media of rat outer and inner medulla and dog outer medullary slice incubates. By contrast, equimolar concentrations of chlorothiazide and hydrochlorothiazide were without effects on these parameters. Stimulation of [14C]AA or iPGE by furosemide was abolished by exclusion of Ca++ from the incubation media or by addition of verapamil to complete media, but was not altered by exclusion of Na+. Ca++-free media or verapamil also abolished the increases in [14C]AA and iPGE induced by ionophore A23187. By contrast, these incubation conditions did not influence the iPGE responses to hypertonic mannitol or exogenous AA. The presence of Ca++-responsive acyl hydrolase activity was demonstrated in the microsomal fraction from rat outer medulla. However, this activity was not altered by addition of furosemide to the subcellular fraction in the presence or absence of Ca++. Thus, furosemide and other loop diuretics stimulate renal medullary iPGE synthesis in vitro, and may do so through Ca++-mediated or dependent enhancement of the release of AA.     

Caffeine potentiates the renin response to furosemide in rats. Evidence for a regulatory role of endogenous adenosine

Adenosine is a potent inhibitor of renin release. It has therefore been suggested that endogenous adenosine may play a role in the regulation of renin release. Sodium-chloride transport at the level of the macula densa has been proposed as the primary source of endogenous adenosine. Evidence to support a modulatory role of adenosine on renin release in vivo is, however, limited. We therefore wanted to determine if: 1) adenosine modulates furosemide-induced renin release and 2) sodium-chloride reabsorption at the macula densa is essential for adenosine actions. To test these hypotheses, three groups of rats were pretreated either with saline or the adenosine receptor antagonists caffeine or 1,3-dipropyl-8-(p-sulfophenyl)xanthine (both at a dose of 30 mg/kg followed by 450 micrograms/kg/min). Rats then received furosemide (50 mg/kg i.v.). In the vehicle group, furosemide increased urinary volume, sodium and potassium excretion and increased plasma renin activity from 6 +/- 1 to 45 +/- 11 ngAl/ml/hr. Caffeine and 1,3-dipropyl-8-(p-sulfophenyl)xanthine potentiated the increase in plasma renin activity produced by furosemide (to 120 +/- 15 and 147 +/- 21 ng Al/ml/hr, respectively), whereas having no significant effects on urinary volume, sodium excretion or blood pressure. These results suggest that furosemide-induced renin release in vivo is restrained by endogenous adenosine. In as much as furosemide blocks sodium-chloride transport in the thick ascending limb of Henle's loop and the macula densa cells, it appears that under the conditions of this study sodium transport across these segments is not essential to initiate adenosine-mediated mechanisms.     

Role of L-carnitine in the modulation of immune response in aged rats

BACKGROUND: The immune system undergoes alterations in functions with aging which results in progressive deterioration in the ability to respond to infection. The importance of nutrients in regulating immune responses has widened attempts on interventions that improve immune functions with aging. L-carnitine serves as a vital factor in the mitochondrial transport of fatty acids, a process essential for fatty acid oxidation and energy release. L-carnitine is categorized as a conditionally essential nutrient factor and its concentrations are reported to be decreased with aging. METHODS: The immunomodulatory role of L-carnitine was assessed in aged rats after administration of L-carnitine (300 mg/kg body weight/day) for 7, 14 and 21 days by evaluating neutrophil functions, delayed-type hypersensitivity (DTH) responses and immunoglobulin concentrations. RESULTS: Aged animals exhibited decreased non-specific immune functions, delayed-type hypersensitivity responses and immunoglobulin concentrations compared to younger controls. Treatment with L-carnitine improved neutrophil functions, delayed-type hypersensitivity responses and the concentrations of immunoglobulins A and G in aged animals in a significant manner. However L-carnitine treatment did not have any impact on IgM concentration and type responses. CONCLUSIONS: This study demonstrated that aging is associated with a decline in immune functions and supplementing L-carnitine had a positive effect in improving immune responses in aged animals.     

Role of adenosine in the gastric blood flow response to pentagastrin in the rat

We tested the hypothesis that the increase in gastric mucosal blood flow during pentagastrin-stimulated acid secretion in the rat is mediated partly by endogenously generated adenosine. In in vivo microscopic studies, topical 10(-5) to 10(-3) M adenosine dose-dependently dilated the submucosal arterioles, the vessels that control mucosal blood flow. The adenosine receptor antagonist 8-phenyltheophylline, significantly reduced adenosine's vasodilatory response. An adenosine analog with a high A2 receptor affinity was 100 times more potent as a vasodilator than one with a high A1 receptor affinity but lower A2 receptor affinity. We then examined the effect of i.v. 8-phenyltheophylline, 10 mg/kg, on the pentagastrin-stimulated increase in gastric blood flow and gastric acid secretion. Mucosal blood flow was estimated by the hydrogen clearance technique. Pentagastrin increased mucosal blood flow from 26.6 +/- 2.6 to 42.7 +/- 4.9 ml/min/100 g and this was reduced to 31.9 +/- 3.1 ml/min/100 g upon the addition of 8-phenyltheophylline. Gastric acid secretion upon the addition of 8-phenyltheophylline. Gastric acid secretion was stimulated by pentagastrin and stimulated further by the addition of 8-phenyltheophylline from 2.06 +/- 0.34 mEq of H+ per min to 2.84 +/- 0.49 mEq/min. 8-Phenyltheophylline had no effect on basal mucosal blood flow or gastric acid secretion. In contrast, the nonmethylxanthine phosphodiesterase inhibitor RO 20-1724 stimulated acid secretion and increased gastric mucosal blood flow during pentagastrin administration. The data suggest that gastric submucosal arterioles contain adenosine receptors of the A2 subtype that vasodilate when activated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of MK-196 and furosemide on rat medullary thick ascending limbs of Henle in vitro

The effects of the diuretic agents, MK-196 (6,7-dichloro-2-methyl-1-oxo-2-phenyl-5-indanyloxy acetic acid) and furosemide on function of medullary thick ascending limb (tALH) isolated from the rat kidney were studied. tALH were dissected from whole kidneys of male Sprague-Dawley rats which were first perfused in vitro in a recirculating system for 10 to 15 min with a solution containing collagenase. Standard techniques for dissection and perfusion of tALH were followed. Control transepithelial voltage averaged +5.5 +/- 0.5 mV (n = 25). Drug concentration causing 50% inhibition of the voltage (EC50) was determined. EC50 for both MK-196 and furosemide in rat tALH was 8 X 10(-6) M (EC50 for MK-196 in rabbit tALH ws 7 X 10(-5) M). In other experiments, net chloride transport (JCl) in rat tALH averaged 142 +/- 19 pmol.mm-1.min-1 (n = 12), a value nearly twice that reported for the rabbit. In the rat, MK-196 (2 X 10(-4) M) reduced the voltage by 79 +/- 2% and JCl by 76 +/- 13% (n = 6). The same concentration of furosemide inhibited the voltage by 78 +/- 8% and the JCl by 104 +/- 4%(n = 5). Results indicate that: 1) rat tALHs dissected from collagenase-treated kidneys have functional characteristics similar to those reported for the rabbit tALH; and 2) the rat tALH is equally sensitive to MK-196 and furosemide, drugs which act to selectively inhibit active chloride transport.     

Effect of cyclooxygenase inhibition on the pulmonary vasodilator response to furosemide

Furosemide is a potent vasodilator of the systemic arterial and venous systems. The mechanism of vasodilatation, however, remains unclear. We investigated the vasodilatory effect of furosemide and its relation to endogenous prostaglandins (PGs). In the isolated canine lung lobe, furosemide significantly decreased mean pulmonary artery pressure. This effect was inhibited by indomethacin. Furosemide also attenuated the pulmonary vasoconstrictor response to the endoperoxide analog U46619 and PGF2 alpha. The pulmonary pressor response to a submaximal constrictor dose of arachidonic acid was significantly enhanced by furosemide, however, the pressor response to a maximal constrictor dose of arachidonic acid was attenuated, although not significantly. In animals pretreated with indomethacin, furosemide had no effect on the vascular response to PGF2 alpha, but the response to U46619 was significantly increased. Prostacyclin reduced pulmonary perfusion pressure and inhibited the pressor response to PGF2 alpha and U46619. Furosemide failed to alter inactivation of PGE2 on pulmonary lobe transit. We conclude that: 1) the vasodilatory activity of furosemide is mediated by increased production and not decreased metabolism of an endogenous cyclooxygenase product; 2) the effect of prostacyclin on vascular reactivity is similar to that of furosemide; and 3) local formation of prostacyclin by vascular tissue most likely mediates the vascular activity of furosemide.     

Role of autonomic nervous system in the response of plasma pancreatic polypeptide to glycopenia in dogs

The effect of cholinergic and adrenergic influences on pancreatic polypeptide (PP) release was studied in dogs. Administration of acetylcholine resulted in an elevation of plasma PP, whereas epinephrine induced no increase. Insulin-induced hypoglycemia increased plasma PP in a conscious state but not in anesthetized dogs. The infusion of phentolamine or propranolol did not affect the response of plasma PP to insulin-induced hypoglycemia, whereas atropine markedly inhibited the increase in plasma PP. Likewise, atropine reduced the rise of plasma PP during the intravenous administration of 2-deoxy-D-glucose (2-DG). We conclude from the present experiments that cholinergic mechanisms are of major importance in the response of PP to insulin- and 2-DG-induced glucoprivation, while the major role of the adrenergic mechanism was not proved.     

Tubular sites of furosemide natriuresis in volume-replaced and volume-depleted conscious rats

There is accumulating evidence that the renal Li clearance reflects the delivery of Na and volume out of the proximal tubules. In the present study we used the Li clearance technique to evaluate the effects of submaximal furosemide (Fur) infusion (7.5 mg/kg/hr) on proximal and distal Na reabsorption in conscious rats with and without volume replacement with saline. Li was given as an p.o. test dose (0.5 mmol/kg) and [3H]inulin was infused in saline to measure the glomerular filtration rate (GFR). In control rats not infused with F, fractional Na excretion was about 1% and fractional Li excretion was about 30 to 35%. Infusion of F with constant rate and volume replacement increased fractional Na excretion to 22% and fractional Li excretion to 57% associated with a small decrease of the GFR. Without volume replacement F infusion caused a smaller and temporary diuretic and natriuretic response (maximum fractional Na excretion = 7.5%) followed by a decrease of urine flow and Na excretion almost to control levels, despite continued high excretion rates of F. The GFR decreased by 25% and fractional Li excretion showed an initial increase followed by return to baseline levels. The results suggest that in conscious rats submaximal doses of F cause major inhibition of proximal tubular Na reabsorption, which effect contributes substantially to the initial natriuresis. Along with diuretic-induced volume contraction, the natriuretic response is abolished due to a fall in GFR and particularly due to a secondary increase in fractional Na reabsorption, which occurs both in proximal distal tubular nephron segments.     

Opioid inhibition of formalin-induced changes in plasma extravasation and local blood flow in rats

Hindpaw injection of dilute formalin produces brief (Phase 1) and persistent (Phase 2) nociceptive responses in the rat. We recently showed that systemically-administered remifentanil during Phase 1 interacted with peripheral opioid receptors to delay the onset and termination of Phase 2 (Taylor et al., 1997b). To test the hypothesis that opioid inhibition of proinflammatory events during Phase 1 contributed to this delay, we evaluated the effects of remifentanil on the time course of formalin-induced inflammation. We found that formalin increased paw thickness (edema), plasma extravasation and local blood flow within minutes of its injection, i.e. during Phase 1. Each of these responses was blocked during remifentanil administration (30 microg/kg i.v. bolus, followed 90 s later with a 15 microg/kg/min infusion for 13.5 min), indicating that opioids inhibit Phase 1 inflammation. Opioid blockade of the blood flow response could be reversed with a peripherally-acting opioid antagonist, naloxone methiodide, indicating that remifentanil acted upon peripheral opioid receptors. Although the administration of remifentanil during Phase 1 did not reduce the magnitude of inflammatory responses during Phase 2, it did delay the onset and termination of edema during Phase 2. As this corresponds to the effects of remifentanil on nociceptive responses during Phase 2, we suggest that opioid analgesics act upon peripheral sites to inhibit inflammation during Phase 1, leading to a delay in the temporal profile of inflammatory (and likely nociceptive) responses during Phase 2.     

Tissue specific modulation of beta-adrenoceptor number in rats with chronic hypoxia with an attenuated response to down-regulation by salbutamol

The number of beta-adrenoceptors and their affinity for the radioligand 125I-labelled cyanopindolol (125I-CYP) were measured in crude membrane preparations of left ventricle, spleen and lung from Wistar rats exposed to 28 days continuous hypoxia. beta-Adrenoceptor density in the left ventricle was not significantly altered after exposure to chronic hypoxia (binding site maxima, Bmax.: normoxic control 36 SEM 5, hypoxic 24.8 SEM 2 fmol/mg of protein). There was no change in beta-adrenoceptor number in the spleen in response to chronic hypoxia (Bmax.: normoxic control 76 SEM 19 fmol/mg of protein, hypoxic 80 SEM 15 fmol/mg of protein). Chronic hypoxia resulted in a significant increase in beta-adrenoceptor number in lung tissue (binding site maxima, Bmax.: normoxic control 406 (SEM 31) fmol/mg of protein; hypoxic 535 (SEM 30) fmol/mg of protein, P less than 0.01 without change in the dissociation constant (KD) of the radioligand. beta-Adrenoceptor subtypes in lung homogenates were studied by establishing displacement curves for 125I-CYP by ICI 118551 (a selective beta 2-antagonist). A significant difference was seen in the proportion of beta 1-/beta 2-adrenoceptor subtypes after hypoxia (normoxic control 66 SEM 2.5%, hypoxic 79 SEM 2.4% beta 2-adrenoceptors, P less than 0.01). alpha 1-Adrenoceptor number in lung membranes was measured with 125I-labelled 2-[beta-(4-hydroxyphenyl)ethylaminomethyl]tetralone (125I-HEAT). No difference was seen in the number of alpha 1-receptors in normoxia and in chronic hypoxia [Bmax.: normoxic control 48 (SEM 3), hypoxic 48 (SEM 5) fmol/mg of protein].(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of furosemide on plasma concentration and beta-blockade by propranolol.

Although propranolol and furosemide are used together for hypertension, the effects of furosemide on plasma levels and beta-blocking action of propranolol are not known. Ten healthy subjects received propranolol 40 mg orally; the mean plasma propranolol levels in 60, 90, 180, and 300 min were 85 +/- 16, 90 +/- 7, 82 +/- 8, and 58 +/- 8 ng/ml. Propranolol was then given together with furosemide (25 mg orally) and the propranolol blood level was measured. Mean propranolol plasma levels were 106 +/- 11 ng/ml at 60 min, 120 +/- 12 ng/ml at 90 min (p less than 0.01), 102 +/- 8 ng/ml at 180 min (p less than 0.05), and 78 +/- 8 ng/ml at 300 min (p less than 0.01). Six additional subjects were given an infusion of 1 microgram/min isoproterenol increased by 0.5 microgram/min every 2 min until the heart rate rose by 25% after oral administration of furosemide 25 mg. This procedure was repeated after propranolol (40 mg orally) and propranolol with furosemide (25 mg orally). The amount of isoproterenol which raised the heart rate by 25% was 2.6 +/- 0.3 micrograms after furosemide alone and 17.7 +/- 2 micrograms after propranolol (p less than 0.01). After propranolol with furosemide the dose of isoproterenol required to elevate heart rate by 25% was 109 +/- 15 micrograms (p less than 0.001).     

Eel calcitonin suppresses plasma human calcitonin levels in medullary carcinoma of the thyroid

The effects of synthetic [Asu1,7]-eel calcitonin (0.5 MRC unit/kg body weight intravenously for 30 min) on circulating levels of human calcitonin, calcium and gastrin were investigated in five patients with medullary carcinoma of the thyroid. Blood samples were obtained before and 15, 30, 60, 90, 120 and 180 min after commencement of infusion of [Asu1,7]-eel calcitonin. Plasma levels of human calcitonin were measured by radioimmunoassay. Cross-reactivity with [Asu1,7]-eel calcitonin in this assay was negligible. On infusion of [Asu1,7]-eel calcitonin, the mean plasma level of human calcitonin decreased significantly to 71.0 +/- 8.7% of the basal level (mean +/- SEM, P less than 0.05) after 30 min and 68.4 +/- 25.4% of the basal level (P less than 0.05) after 60 min. The serum calcium level also decreased significantly, but lagged behind the decrease of human calcitonin, being 95.1 +/- 0.7% of the basal level (P less than 0.01) at 120 min and 94.8 +/- 0.6% of the basal level (P less than 0.02) at 180 min. The mean plasma gastrin level did not change significantly on infusion of [Asu1,7]-eel calcitonin. In pooled data for all times, the percentage change in human calcitonin was not significantly correlated with either the percentage change in calcium (r = -0.25, P greater than 0.1) or the percentage change in gastrin (r = -0.38, P greater than 0.1).     

Role of thromboxane in impaired renal vasodilatation response to acetylcholine in hypercholesterolemic rats.

Short-term cholesterol feeding has been shown to cause impaired vasodilatation in response to acetylcholine. The present study of renal hemodynamics was carried out to examine the role of thromboxane/PGH2 in mediating this abnormal response. In normal rats (ND), infusion of acetylcholine into the suprarenal aorta caused marked increases in renal blood flow, GFR, single nephron glomerular filtration rate, single nephron afferent plasma flow, and ultrafiltration coefficient, accompanied by a fall in preglomerular resistance. In cholesterol fed rats (CSD), the response to acetylcholine was markedly blunted. Infusion of L-arginine, the precursor to nitric oxide (NO), caused comparable renal vasodilatation in ND and CSD rats, implying that the ability to synthesize NO from its precursor was not severely impaired in the CSD animals. The observations do not exclude, however, the possibility of impaired synthesis of NO from endogenous precursor. In additional experiments, we infused a TxA2/PGH2 receptor antagonist in CSD rats and then administered acetylcholine. Renal vasodilatation occurred to a degree indistinguishable from that in ND rats given acetylcholine alone. When ND rats were infused with the same combination of the TxA2/PGH2 receptor antagonist and acetylcholine, renal vasodilatation was also significantly greater than with acetylcholine alone. This suggests that acetylcholine initiates release of vasoconstrictor prostanoids as well as NO from vascular endothelium. This was observed in ND as well as in CSD animals. Because LDL increases the supply of arachidonic acid for prostaglandin synthesis, we postulate that greater amounts of PGH2/TxA2 are synthesized via calcium activation of phospholipase A2 when acetylcholine is administered to CSD animals. This may account in large measure for the blunted vasodilatation to acetylcholine.     

延髓头端腹外侧区在大鼠外侧下丘脑/穹窿周围区升压反应中的作用

目的 探讨延髓头端腹外侧区（RVL）对大鼠外侧下丘脑/穹窿周围区（LH/PF）升压反应的影响和作用机制.方法 30只健康Wistar大鼠随机分成4组：酚妥拉明组;心得安组;阿托品组和谷氨酸二乙酯组,每组均用生理盐水作对照.谷氨酸钠微量注入大鼠LH/PF后,观察血压升高和心率加快反应;然后分别将酚妥拉明、心得安、阿托品和谷氨酸二乙酯微量注射到RVL,再观测注射谷氨酸钠后的血压和心率变化.结果 谷氨酸钠微量注入LH/PF后大鼠的动脉血压明显升高,心率加快;RVL内分别微量注射酚妥拉明、心得安、甲基阿托品和谷氨酸二乙酯后再注射谷氨酸钠,各组大鼠的升压反应明显降低,与生理盐水对照组之间有非常显著性差异（ P〈0.01）.结论 RVL内的α-、β-、M-和谷氨酸（Glu-）受体介导LH/PF的升压反应.