Increase in tumor oxygenation and radiosensitivity caused by pentoxifylline.

The effects of pentoxifylline (PTX), a drug commonly used for vascular disorders in humans, on the pO2 in SCK tumors of A/J mice and FSa-II tumors of C3Heb/FeJ mice as well as on the radioresponse of SCK tumors were investigated. When the host mice were injected intraperitoneally (ip) with 5 mg/kg PTX, the tumor pO2 increased slowly, peaked 20-50 min postinjection, and returned to its original level in 70-90 min. The magnitude of the increase in tumor pO2 varied markedly depending on the site and tumors. The magnitude of the changes in tumor pO2 after an ip injection of 25 or 50 mg/kg PTX was similar to that caused by 5 mg/kg PTX, but the pO2 tended to remain elevated longer with the higher dose of PTX. When the A/J mice bearing SCK tumors in the legs were injected ip with 50 mg/kg PTX and the tumors were X-irradiated 20 min later, the radiation-induced growth delay of the tumors was greater than that caused by X irradiation alone. The present study demonstrated that PTX is potentially useful for increasing the pO2 and the radioresponse of human tumors.     

5-Hydroxytryptophan activates colonic myenteric neurons and propulsive motor function through 5-HT4 receptors in conscious mice

Serotonin [5-hydroxytryptamine (5-HT)] acts as a modulator of colonic motility and secretion. We characterized the action of the 5-HT precursor 5-hydroxytryptophan (5-HTP) on colonic myenteric neurons and propulsive motor activity in conscious mice. Fos immunoreactivity (IR), used as a marker of neuronal activation, was monitored in longitudinal muscle/myenteric plexus whole mount preparations of the distal colon 90 min after an intraperitoneal injection of 5-HTP. Double staining of Fos IR with peripheral choline acetyltransferase (pChAT) IR or NADPH-diaphorase activity was performed. The injection of 5-HTP (0.5, 1, 5, or 10 mg/kg ip) increased fecal pellet output and fluid content in a dose-related manner, with a peak response observed within the first 15 min postinjection. 5-HTP (0.5-10 mg/kg) dose dependently increased Fos expression in myenteric neurons, with a maximal response of 9.9 +/- 1.0 cells/ganglion [P < 0.05 vs. vehicle-treated mice (2.3 +/- 0.6 cells/ganglion)]. There was a positive correlation between Fos expression and fecal output. Of Fos-positive ganglionic cells, 40 +/- 4% were also pChAT positive and 21 +/- 5% were NADPH-diaphorase positive in response to 5-HTP, respectively. 5-HTP-induced defecation and Fos expression were completely prevented by pretreatment with the selective 5-HT4 antagonist RS-39604. These results show that 5-HTP injected peripherally increases Fos expression in different populations of cholinergic and nitrergic myenteric neurons in the distal colon and stimulates propulsive colonic motor function through 5-HT4 receptors in conscious mice. These findings suggest an important role of activation of colonic myenteric neurons in the 5-HT4 receptor-mediated colonic propulsive motor response.     

Skin radioprotection by 5-thio-D-glucose

The radioprotective effect of 5-thio-D-glucose on mouse skin was studied. Intraperitoneal injection of A/J mice with 1.5 g/kg of 5-thio-D-glucose 2 hr prior to X irradiation of the foot reduced early foot skin damage through Day 40 postirradiation by a dose modification factor of 1.3 +/- 0.1. Similarly, late foot deformity during Days 60-90 postirradiation was reduced by a factor of 1.2 +/- 0.1. The radioprotective effect of 5-thio-D-glucose was also compared with that of WR-2721, an aminothiol radioprotector, in CDF1 mice. An intraperitoneal injection of 1.5 g/kg of 5-thio-D-glucose reduced early radiation-induced skin damage by a dose modification factor of 1.2 +/- 0.1 as compared to that of 1.5 +/- 0.2 by 0.65 g/kg of WR-2721 in this strain of mice. 5-Thio-D-glucose is also known to specifically kill and radiosensitize hypoxic tumor cells. Consequently, this drug may be a useful radiotherapy adjuvant, reducing normal tissue damage and enhancing tumor control by minimizing hypoxic protection.     

Radiosensitization by nicotinamide in vivo: a greater enhancement of tumor damage compared to that of normal tissues

In this report we describe various aspects of tumor and normal tissue radiosensitization by nicotinamide. The LD50 for a single injection of nicotinamide in C3H mice was found to be 2050 mg/kg. When a large nonlethal dose (1000 mg/kg) was injected into tumor-bearing mice, peak plasma and tumor levels were reached 30-60 min after injection and decayed with a half-life of about 3 h. This dose of nicotinamide enhanced radiation-induced cell killing in three different tumor models (EMT6, Lewis Lung, and RIF-1) when injected at least 1 h before irradiation and produced enhancement ratios (ERs) of between 1.2 and 1.7. The ER in the EMT6 tumor was dependent on the dose of nicotinamide injected, but even at doses as low as 25% of the LD50 value an ER greater than 1.5 could still be observed. In two normal tissue assays (jejunum crypt cell survival and mean skin reaction) ERs of less than 1.2 were obtained. These results, and the fact that high levels can be tolerated in humans, suggest that nicotinamide, or a structurally related compound, could be a likely candidate for development in clinical trials.     

Effect of hypoxia on bronchial circulation

We studied the effect of systemic hypoxia on the bronchial vascular pressure-flow relationship in anesthetized ventilated sheep. The bronchial artery, a branch of the bronchoesophageal artery, was cannulated and perfused with a pump with blood from a femoral artery. Bronchial blood flow was set so bronchial arterial pressure approximated systemic arterial pressure. For the group of 25 sheep, control bronchial blood flow was 22 ml/min or 0.7 ml.min-1.kg-1. During the hypoxic exposure, animals were ventilated with a mixture of N2 and air to achieve an arterial PO2 (PaO2) of 30 or 45 Torr. For the more severe hypoxic challenge, bronchial vascular resistance (BVR), as determined by the slope of the linearized pressure-flow curve, decreased acutely from 3.8 +/- 0.4 mmHg.ml-1.min to 2.9 +/- 0.3 mmHg.ml-1.min after 5 min of hypoxia. However, this vasodilation was not sustained, and BVR measured at 30 min of hypoxia was 4.2 +/- 0.8 mmHg.ml-1.min. The zero flow intercept, an index of downstream pressure, remained unaltered during the hypoxic exposure. Under conditions of moderate hypoxia (PaO2 = 45 Torr), BVR decreased from 4.6 +/- 0.3 to 3.8 +/- 0.4 mmHg.ml-1.min at 5 min and remained dilated at 30 min (3.6 +/- 0.5 mmHg.ml-1.min). To determine whether dilator prostaglandins were responsible for the initial bronchial vascular dilation under conditions of severe hypoxia (PaO2 approximately equal to 30 Torr), we studied an additional group of animals with pretreatment with the cyclooxygenase inhibitors indomethacin (2 mg/kg) and ibuprofen (12.5 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Short-term immobilization of mice by methohexitone

The feasibility of short-term immobilization for <5 min of female mice by methohexitone sodium was studied. In C3H/Neu mice, methohexitone at a dose <40 mg/kg did not result in chemical restraint, doses >50 mg/kg caused considerable lethality. A dose of 44 mg/kg, applied intraperitoneally at a concentration of 6.46 mg/ml, is suitable for immobilization without complications. This concentration was chosen in order to achieve an injection volume of about 0.15 ml for a mouse with an average body weight of 22 g, corresponding to about 1 mg/mouse. Complete immobilization, defined as absence of the righting reflex, was observed within 3.3 +/- 0.8 min (mean +/- SD, n = 10) after the injection and lasted for 1.5 +/- 0.7 min. Recovery of the animals was complete after a total period of 10 to 15 min post-injection. No gross pathomorphological changes were induced when intraperitoneal injections of methohexitone were repeated 10 times within 10 days. In the present study, complete immobilization of the mice was safely achieved after 87 out of 90 injections. In conclusion, immobilization by intraperitoneal injection of methohexitone is a feasible and reliable method in the experimental studies of female mice.     

Inducible nitric oxide synthase is involved in acid-induced gastric hyperemia in rats and mice

The role of different isoforms of nitric oxide synthase (NOS) in the gastric mucosal hyperemia, induced by 155 mM luminal hydrochloric acid (pH approximately 0.8) without a barrier breaker, was investigated. Rats were anesthetized with Inactin (120 mg/kg ip), and mice were anesthetized with Forene (2.2% in 40% oxygen gas at 150 ml/min); the gastric mucosa was exteriorized. Gastric mucosal blood flow was measured with laser-Doppler flowmetry (LDF) in rats treated with Nomega-nitro-l-arginine (l-NNA; unspecific NOS inhibitor), l-N6-(1-iminoethyl)lysine [l-NIL; inducible (i) NOS inhibitor], or S-methyl-l-thiocitrulline [SMTC; neuronal (n) NOS inhibitor], 10 mg/kg, followed by 3 mg. kg-1. h-1 iv, in iNOS-deficient (-/-) and nNOS(-/-) mice. mRNA was isolated from the gastric mucosa in iNOS(-/-) and wild-type (wt) mice, and real-time RT-PCR was performed. The effect of 155 mM acid on gastric mucosal permeability was determined by measuring the clearance of 51Cr-EDTA from blood to lumen. LDF increased by 48 +/- 13% during 155 mM HCl luminally, an increase that was abolished by l-NNA, SMTC, or l-NIL. In iNOS wt mice, LDF increased by 33 +/- 8% during luminal acid. The blood flow increase was attenuated substantially in iNOS(-/-) mice. RT-PCR revealed iNOS mRNA expression in the gastric mucosa in the iNOS wt groups. The blood flow increase in response to acid was not abolished in nNOS(-/-) mice (nNOS-sufficient mice, 39 +/- 18%; heterozygous mice, 25 +/- 19%; -/- mice, 19 +/- 7%). Mucosal permeability was transiently increased during 155 mM HCl. The results suggest that iNOS is constitutively expressed in the gastric mucosa and is involved in acid-induced hyperemia, suggesting a novel role for iNOS in gastric mucosal protection.     

Opioid action on luteinizing hormone secretion in newborn pigs: paradoxical effect of naloxone

German Landrace piglets, 6-7 days of age, received either saline (9 males, 8 females), 0.5 mg naloxone/kg body weight (7 males, 7 females), 2.0 mg naloxone/kg (7 males, 8 females) or 0.5 mg DADLE (potent leu-enkephalin analog)/kg (7 males, 7 females) through a catheter inserted into the jugular vein 2-4 days previously. Male or female piglets were allocated randomly, within litter, to the different experimental groups. Blood samples were withdrawn for a period of 240 min at 10-min intervals for the first 60 min following injection and at 20-min intervals for the rest of the test period. Piglets were separated from their mother via a detachable wall and were allowed to suckle every 50 min. DADLE failed to alter plasma levels of LH in both males and females. Naloxone induced a significant (P less than 0.01) decrease in LH concentrations in females 10 to 60 min after injection (saline: 2.3 +/- 0.2 ng/ml plasma (SEM); 0.5 mg naloxone/kg: 1.0 +/- 0.2 ng/ml plasma and 2 mg naloxone/kg 1.2 +/- 0.4 ng/ml plasma). In males low doses of naloxone reduced plasma LH levels 10 to 40 min after injection (saline: 2.0 +/- 0.3 ng/ml plasma and 0.5 ng naloxone/kg: 1.1 +/- 0.3 ng/ml), whereas a decrease in plasma LH levels occurred 80 to 140 min after injection of high doses of naloxone (saline: 2.1 +/- 0.2 ng/ml and 2 mg naloxone/kg: 1.0 +/- 0.2 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

原发性高血压患者红细胞抗高血压因子对高血压...

The effects of antihypertensive factor (AHF) from erythrocytes of essential hypertensive human subjects on the systolic blood pressure (SBP) and diastolic blood pressure (DBP) in spontaneously hypertensive rats (SHR), renal hypertensive rats (RHR), Wistar-Kyoto rats (WKY) and Wistar rats were examined. Single intraperitoneal injection of AHF (1.6 mg/kg body weight) resulted in a significant decrease in SBP of SHR and RHR. At 10 min postinjection, AHF lowered the SBP in SHR by 34.0 mmHg. SBP recovered to the original level at 3 h. The maximal decrease of SBP in RHR by 92.5 mmHg was at 24h postadministration and the SBP did not recover until the 9th day. When AHF was administered via femoral vein (0.8 mg/kg body weight), the maximal decrease values of the SBP and the DBP were 42.8 and 48.2 mmHg in SHR at 12 min and 38.3 and 42.5 mmHg in RHR at 25 min postinjection respectively. The DBP in Wistar rats decreased considerably (from 96.7 +/- 12.9 to 83.3 +/- 11.7 mmHg) at 5 min postadministration of AHF, but no effect on DBP in WKY rats was observed. The depressor effect of AHF on SBP in RHR was dose-dependent. AHF could also antagonize the pressor effect of norepinephrine in Wistar rats.     

Effect of millimeter wave irradiation on tumor metastasis

One of the major side effects of chemotherapy in cancer treatment is that it can enhance tumor metastasis due to suppression of natural killer (NK) cell activity. The present study was undertaken to examine whether millimeter electromagnetic waves (MMWs) irradiation (42.2 GHz) can inhibit tumor metastasis enhanced by cyclophosphamide (CPA), an anticancer drug. MMWs were produced with a Russian-made YAV-1 generator. Peak SAR and incident power density were measured as 730 +/- 100 W/kg and 36.5 +/- 5 mW/cm(2), respectively. Tumor metastasis was evaluated in C57BL/6 mice, an experimental murine model commonly used for metastatic melanoma. The animals were divided into 5 groups, 10 animals per group. The first group was not given any treatment. The second group was irradiated on the nasal area with MMWs for 30 min. The third group served as a sham control for group 2. The fourth group was given CPA (150 mg/kg body weight, ip) before irradiation. The fifth group served as a sham control for group 4. On day 2, all animals were injected, through a tail vein, with B16F10 melanoma cells, a tumor cell line syngeneic to C57BL/6 mice. Tumor colonies in lungs were counted 2 weeks following inoculation. CPA caused a marked enhancement in tumor metastases (fivefold), which was significantly reduced when CPA-treated animals were irradiated with MMWs. Millimeter waves also increased NK cell activity suppressed by CPA, suggesting that a reduction in tumor metastasis by MMWs is mediated through activation of NK cells.     

Insulin secretion and acetylcholinesterase activity in monosodium l-glutamate-induced obese mice.

OBJECTIVE: Pancreatic islets isolated from mice treated neonatally with monosodium L-glutamate (MSG) were used to study insulin secretion. MATERIALS AND METHODS: Total acetylcholinesterase (AchE) activity of tissue extract was measured as a cholinergic activity marker. Obesity recorded in 90-day-old MSG mice (OM) by Lee index reached 366.40 +/- 1.70, compared to control mice (CM) 324.40 +/- 1.10 (p < 0.0001). Glucose 5.6 mM induced insulin secretion of 36 +/- 5 pg/15 min from islets of CM and 86 +/- 13 from OM (p < 0.001). When glucose was raised to 16.7 mM, islets from OM secreted 1,271 +/- 215 and 1,017 +/- 112 pg/30 min to CM. AchE activity of pancreas from OM was 0.64 +/- 0.02 nmol of substrate hydrolyzed/min/mg of tissue and 0.52 +/- 0.01 to CM (p < 0.0001). Liver of obese animals also presented increase of AchE activity. RESULTS: These indicate that OM insulin oversecretion in low glucose may be attributed, at least in part, to an enhancement of parasympathetic tonus.     

Dopamine D(2) receptors mediate amylin's acute satiety effect

The anorectic effect of the pancreatic peptide amylin has been established in numerous studies. Here, we investigated the influence of a pretreatment with dopamine (DA) D(1)- and D(2)-receptor antagonists on the anorectic effect of intraperitoneally injected amylin in rats fed a medium-fat (18% fat) diet. In 24-h food-deprived rats, pretreatment with the DA D(2)-receptor antagonist raclopride [100 microg/kg (0.2 micromol/kg) ip] significantly attenuated amylin's (5 microg/kg ip) anorectic effect, whereas raclopride alone had no effect on food intake [i.e., food intakes 1 h after injection were (n = 12): NaCl/NaCl 7.3 +/- 0.5 g; NaCl/amylin 3.9 +/- 0.6; raclopride/NaCl 7.7 +/- 0.7; raclopride/amylin 5.6 +/- 0.7]. Pretreatment with another DA D(2) receptor antagonist, sulpiride [50 mg/kg (154 micromol/kg) ip], similarly reduced amylin's satiety effect, whereas pretreatment with the DA D(1)-receptor antagonist SCH-23390 [10 microg/kg (0.03 micromol/kg) ip] did not influence amylin's effect. SCH-23390, however, completely blocked the anorexia induced by D-amphetamine (0.3 mg/kg ip). These results suggest that, under the present feeding conditions, the dopaminergic system mediates part of amylin's inhibitory effect on feeding in rats when administered intraperitoneally. This seems to involve DA D(2) receptors but not D(1) receptors.     

Anti-hypoxic effect of glutathione depletors

The effect of various reduced glutathione (GSH) depletors on the survival time under normobaric and hypobaric hypoxia was examined in mice. The survival time was markedly prolonged in mice treated with glutathione S-transferase substrate, 2-cyclohexene-1-one (50-100 mg/kg, ip) and phorone (100-250 mg/kg, ip). The anti-hypoxic effect lasted for at least 3 hr and the maximum effect was found 0.5 hr after injection. Further, both compounds significantly elevated blood glucose levels 0.5-1 hr after treatment. The extent of the elevated blood glucose was nearly comparable to that of the mice treated with glucose (1-2 g/kg, ip), which was found to possess an anti-hypoxic effect. However, a GSH synthesis inhibitor, buthionine sulfoximine, could cause neither a prolongation of survival time of hypoxic mice nor an elevation of blood glucose. Moreover, unlike the depletion of hepatic GSH, brain GSH was markedly decreased by 2-cyclohexene-1-one and phorone, but not by buthionine sulfoximine. These findings suggest that the elevated blood glucose may involve in one of the mechanisms of the anti-hypoxic effect of 2-cyclohexene-1-one and phorone. A relationship between the anti-hypoxic effect and the depletion of brain GSH was also discussed.     

Effects of cocaine on plasma catecholamine and muscle glycogen concentrations during exercise in the rat

This study was designed to test the hypothesis that cocaine (C) alters the normal physiological responses to exercise. Male rats were injected with saline (S) or C (12.5 mg/kg) either intravenously (iv) or intraperitoneally (ip). After injection the animals were allowed to rest for 30 min or were run on the treadmill (26 m/min, 10% grade). At rest plasma epinephrine values were 245 +/- 24 pg/ml in the S group and 411 +/- 43 (ip) and 612 +/- 41 (iv) pg/ml in the C groups (P less than 0.05 between S and C). During exercise plasma epinephrine levels were 615 +/- 32 pg/ml in S and 1,316 +/- 58 (ip) and 1,208 +/- 37 (iv) pg/ml in the C groups (P less than 0.05 between S and C). Similar results were obtained for norepinephrine. Glycogen content in the white vastus lateralis muscle was reduced to 31 +/- 2 mumol/g in S after exercise, but after C and exercise the values were 12 +/- 4 (ip) and 16 +/- 3 (iv) mumol/g (P less than 0.05 between S and C). There was no effect of the drug on this parameter at rest. Blood lactate rose to 4.8 +/- 1.0 (ip) and 5.8 +/- 1.3 (iv) mM in the C groups but to only 3.0 +/- 0.2 in the S group after exercise (P less than 0.05 between S and C). These results show that C and exercise combined exert a more dramatic effect on plasma catecholamine, muscle glycogen, and blood lactate concentrations than do C and exercise alone. They provide further insight into explaining the adverse effects of C on exercise endurance observed previously (Bracken et al., J. Appl. Physiol. 66: 377-383, 1989).     

Editorial comment

A single injection of Cyclophosphamide (CY) in a dose of 300 mg of CY/kg of mice resulted in enhanced delayed hypersensitivity (DH) when administered between at least 7 days prior to and 15 days after intracutaneous (ic) immunization of sheep red blood cells in Freund's complete adjuvant. The maximal enhancement occurred when CY was applied 8 hr before the antigen. Using the latter interval, the effect of varying the dose of CY before ic or intraperitoneal (ip) injections of antigen was studied. Combined with ic immunization, increasing doses of CY resulted in increasing DH. The ip route of immunization needed CY in amounts of at least 100 mg/kg to augment DH to a detectable level. The enhancing effect of lower doses of CY was more pronounced when the interval between immunizing and eliciting injections was reduced. Administration of 300 or 200 mg of CY/kg before ip immunization suppressed the antibody formation, when measured S and 7 days later. A dose of 100 mg of CY/kg caused a suppression of antibody formation on Day 5, but an enhancement on Day 7. With this dose, a maximal enhancement of DH was found on both days. The results suggest that CY interferes with more than one regulatory mechanism of the immune response.     

Radioprotection of normal tissues against gamma rays and cyclotron neutrons with WR-2721: LD50 studies and 35S-WR-2721 biodistribution

The ability of WR-2721 to protect mice against two modes of death following whole-body radiation with 137Cs gamma rays or d(22)+Be neutrons was examined. For single fractions, 400 mg/kg WR-2721 was administered prior to irradiation. In two-fraction exposures, the dose was 275 mg/kg given prior to each fraction. Dose modification factors (DMFs) were calculated as ratios of LD50 values. For single fractions of gamma rays, the DMF was 1.74 for the LD50/7 end point and for LD50/30, the DMF for single fractions was 2.25. For two fractions 3 hr apart, it was 1.88. For single fractions of cyclotron neutrons, the DMF was 1.32 for LD50/7. Measured with the LD50/30 end point, the DMF for single neutron doses was 1.41 and for two fractions, 1.19. Substantial radioprotection of bone marrow and intestinal epithelium against cyclotron neutrons was seen in these investigations. Biodistribution studies were done following ip injection of 35S-labeled WR-2721 into C3H mice bearing RIF-1 tumors. Blood levels peaked at 10 min after injection and declined thereafter. Most normal tissues achieved maximum levels of 35S at 30 to 60 min postinjection and high concentrations were retained in most tissues for up to 2 hr. Assuming that all 35S is in parent compound or dephosphorylated radioprotective metabolites, the concentration of protector (milligram per gram tissue) in various organs at 30 min postinjection ranked as follows: kidney greater than submandibular gland much greater than liver = lung greater than gut greater than heart much greater than blood greater than skin greater than tumor greater than brain. High levels of 35S were achieved and retention times were long in certain normal tissues which respond at early or late times postradiation and may be dose limiting in radiotherapy: kidney, liver, salivary gland, and lung. These combined observations suggest that there is potential for protecting dose-limiting, late-responding normal tissue in the radiotherapy of human cancer with both neutrons and conventional radiotherapy.     

Sensitivity of mice to systemic hyperthermia: effect of the transplantation of ascites tumor cells modified by preheating, and by an injection of CDDP or interferon

Effects of preheating and injection of cis-DDP (CDDP) or interferon on tumor-induced sensitization to systemic hyperthermia (SH) was investigated in mice. LD50 of SH at 42.0 +/- 0.2 degrees C (core body temperature) was 43 min in normal mice and 8 min in mice which were i.p. transplanted with FMA3 cells at a dose of 10(5) one day before. In mice which had received the SH for 10 min one hour before, one hour after or one day before the transplantation, LD50 of the SH one day after the transplantation was 41, 35 and 22 min, respectively. An injection of CDDP given i.p. at a dose of 4 mg/kg one day after the transplantation, which was effective to kill about 99% of the tumor cells, did not change the course of thermosensitization after the transplantation. An i.p. injection of mouse interferon did not change the thermosensitivity of normal mice, but greatly suppressed the thermosensitizing effect of tumor cells when it was given one day before the transplantation.     

Voltage-dependent K+ channels regulate the duration of reactive hyperemia in the canine coronary circulation

We previously demonstrated a role for voltage-dependent K(+) (K(V)) channels in coronary vasodilation elicited by myocardial metabolism and exogenous H(2)O(2), as responses were attenuated by the K(V) channel blocker 4-aminopyridine (4-AP). Here we tested the hypothesis that K(V) channels participate in coronary reactive hyperemia and examined the role of K(V) channels in responses to nitric oxide (NO) and adenosine, two putative mediators. Reactive hyperemia (30-s occlusion) was measured in open-chest dogs before and during 4-AP treatment [intracoronary (ic), plasma concentration 0.3 mM]. 4-AP reduced baseline flow 34 +/- 5% and inhibited hyperemic volume 32 +/- 5%. Administration of 8-phenyltheophylline (8-PT; 0.3 mM ic or 5 mg/kg iv) or N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mg/min ic) inhibited early and late portions of hyperemic flow, supporting roles for adenosine and NO. 4-AP further inhibited hyperemia in the presence of 8-PT or L-NAME. Adenosine-induced blood flow responses were attenuated by 4-AP (52 +/- 6% block at 9 microg/min). Dilation of arterioles to adenosine was attenuated by 0.3 mM 4-AP and 1 microM correolide, a selective K(V)1 antagonist (76 +/- 7% and 47 +/- 2% block, respectively, at 1 microM). Dilation in response to sodium nitroprusside, an NO donor, was attenuated by 4-AP in vivo (41 +/- 6% block at 10 microg/min) and by correolide in vitro (29 +/- 4% block at 1 microM). K(V) current in smooth muscle cells was inhibited by 4-AP (IC(50) 1.1 +/- 0.1 mM) and virtually eliminated by correolide. Expression of mRNA for K(V)1 family members was detected in coronary arteries. Our data indicate that K(V) channels play an important role in regulating resting coronary blood flow, determining duration of reactive hyperemia, and mediating adenosine- and NO-induced vasodilation.     

Induction of micronuclei by vinyl acetate in mouse bone marrow cells and cultured human lymphocytes

A dose-dependent increase in micronucleated polychromatic erythrocytes was observed in the bone marrow of male C57B1/6 mice 30 h after a single intraperitoneal injection of vinyl acetate (250, 500, 1000 or 2000 mg/kg b.wt.; (9-14 animals per group). The effect was statistically significant at 1000 mg/kg (1.33 +/- 0.29% vs. 0.6 +/- 0.10% in olive oil-treated controls) and at 2000 mg/kg (1.57 +/- 0.19%) of vinyl acetate. These doses were fatal to 6 (1000 mg/kg) and 8 (2000 mg/kg) out of 14 animals in both groups. The ratio of polychromatic to normochromatic cells decreased as a function of vinyl acetate dose. Cyclophosphamide (20 mg/kg), used as a positive control chemical, induced a clear increase in micronucleated polychromatic erythrocytes (2.07 +/- 0.20%). None of the treatments affected the number of micronuclei in normochromatic erythrocytes. In human whole-blood lymphocyte cultures, micronucleus induction by a 48-h treatment with vinyl acetate (0.125, 0.25, 0.5, 1 and 2 mM; 24 h after culture initiation) was studied in lymphocytes with preserved cytoplasm from smear slides prepared by a method involving the removal of erythrocytes at harvest by sodium cyanide treatment to improve preparation quality. The frequency of micronucleated lymphocytes reached a peak at 0.5 mM (3.2 +/- 1.0% vs. 0.9 +/- 0.1% in control cultures) and 1 mM (3.1 +/- 0.7%), with a decline at 2 mM probably because of a toxic effect resulting in mitotic inhibition.     

Glucoregulatory effects of bombesin in lean and genetically obese hyperglycaemic (ob/ob) mice

1. Plasma glucose and insulin responses to bombesin were examined in 12-15-week-old 12 hr fasted lean and genetically obese hyperglycaemic (ob/ob) mice. 2. Bombesin (1 mg/kg ip) produced a prompt but transient increase of plasma insulin in lean mice (maximum increase of 50% at 5 min), and a more slowly generated but protracted insulin response in ob/ob mice (maximum increase of 80% at 30 min). Plasma glucose concentrations of both groups of mice were increased by bombesin (maximum increases of 40 and 48% respectively in lean and ob/ob mice at 15 min). 3. When administered with glucose (2 g/kg ip), bombesin (1 mg/kg ip) rapidly increased insulin concentrations of lean and ob/ob mice (maximum increases of 39 and 63% respectively at 5 min). Bombesin did not significantly alter the rise of plasma glucose after exogenous glucose administration to these mice. 4. The results indicate that bombesin exerts an insulin-releasing effect in lean and ob/ob mice. The greater insulin-releasing effect in ob/ob mice renders bombesin a possible component of the overactive entero-insular axis in the ob/ob mutant, especially if it acts within the islets as a neurotransmitter or paracrine agent.