A comparison of the effects of repeated administration of cyclophosphamide, cytosine arabinoside or their combination on smooth and skeletal muscle

The pharmacological effects of repeated administration of 2 mg Kg-1 cytosine arabinoside, 40 mg Kg-1 cyclophosphamide or their combination, all given once weekly for 5 weeks, have been investigated in chicks. Cyclophosphamide did not affect responses to noradrenergic nerve stimulation or phenylephrine, depressed responses of the expansor secundariorum muscle to acetylcholine but sensitised the muscle to direct stimulation. Cytosine arabinoside depressed noradrenergic transmission and enhanced responses of the expansor muscle to phenylephrine and acetylcholine. The combination of both drugs enhanced responses to noradrenergic nerve stimulation due to increased alpha-adrenergic receptor mediated contraction and direct muscle sensitisation. Cyclophosphamide, cytosine arabinoside or their combination produced a non-specific depression of the upper oesophagus and ileum. The exception was the marked increase in response of the ileum from the combination group to agonist drugs, indicating synergism. The non-specific skeletal muscle depressant actions of cyclophosphamide and the combination groups were more pronounced than that of the cytosine arabinoside group.     

Neurofilament isoform alterations in the rat cerebellum following cytosine arabinoside administration

A number of neurotoxic agents could potentially exert their action by degrading or modifying cytoskeleton components like neurofilaments (NF). Cytosine arabinoside (AraC) is an anticancer drug commonly used in leukemia treatment. Its side effects include neuronal cell death in the cerebellum and severe motor coordination deficits. We have previously shown that AraC administration (400 mg/kg bw) in adult rats reduced NF immunostaining in cerebellar neurons. To further delineate the susceptibility of individual NF isoforms (NF-H, NF-M, NF-L) to AraC, in the present study we used Western blot analysis to quantify their level. A significant and selective reduction of NF-H isoform was observed in the cerebellum of AraC-treated animals, compared to the controls. Administration of the antioxidant N-acetylcysteine (NAC) for a period of 14 days (prior to and during AraC treatment), which was previously shown to ameliorate the AraC-induced motor deficits in these animals, largely prevented the reduction in NF-H isoform. Given the significant role of NF proteins and particularly NF-H in maintaining structural integrity and synaptic transport, the observed loss of this isoform may be a key-target of AraC action in cerebellar neurons. Moreover, this study provides further data on the neuroprophylactic role of NAC in vivo against chemotherapy-induced toxicity.     

Hormonal effects on the development of rat brain gangliosides--I. Cortisol.

Ganglioside N-acetylneuraminic acid (NANA) content and distribution and that of incorporated radionuclide from 1-[¹⁴C]glucosamine were investigated under conditions of normal development and after administration of 500 μg of cortisol at 1 day of age. Cortisol delayed significantly the rise in tissue concentration of NANA usually occurring between 2 and 20 days of age. Cerebellum was most severely affected and brainstem least. The incorporation of radionuclide was depressed during the developmental lag then increased beyond controls from 6 to 10 days, and was again below that of controls in cerebrum and brainstem at 20 days. Individual study of seven chromatographically distinct resorcinol-positive compounds indicated that cortisol treatment favored accumulation and labeling of the more polar gangliosides initially, but resulted at 20 days of age in an abnormal ganglioside pattern with less polar compounds present disproportionately.     

Hormonal effects on the development of rat brain gangliosides--II. thyroxine.

Rats were given thyroxine ( ～ 1 μg/g of body weight) on days 2–4 of life. After this, endogenous ganglioside levels and incorporation of radionuclide from 1-[¹⁴C]glucosamine were determined at various ages up to 3 weeks. Thyroxine caused an initial stimulation of ganglioside development, maximal at 1 week of age, followed by a diminution in production, resulting in decreased ganglioside levels at 20 days. The brainstem was affected least and the cerebellum most severely. Of seven resorcinol-positive materials studied individually, the initial stimulation was particularly noticeable in G_M1, G_D1a and G_T1 with G_D1b in some cases decreased. The ganglioside pattern at 20 days showed an abnormal preponderance of the less polar compounds.     

A comparison of adenine and some derivatives on pig isolated tracheal muscle

We studied the muscle relaxation induced by adenine and several adenine derivatives in strips of tracheal smooth muscle from pigs; in addition their metabolism by the tissue was examined. Adenine relaxed tissue which was contracted by carbachol, histamine, or KCl. Adenine's potency was similar to that of adenosine and ATP (threshold about 4 X 10(-5)M). In tissues with carbachol-induced tone, the adenine effect differed from adenosine and ATP by being slower in onset and in 'washout' time. Furthermore, neither dipyridamole nor theophylline modified the response to adenine. The relationship was examined between pharmacological effects and the metabolism of [3H]-adenosine and [3H]-adenine. Both substrates were taken up by the tissue and converted to nucleotides, but relaxation correlated with nucleotide accumulation only in the case of [3H]-adenine. We conclude that the site and mechanism of adenine-induced relaxation is different from that of adenosine and ATP in porcine tracheal muscle.     

A comparison of the metabolic effects of bovine growth hormone and growth factor from Spirometra mansonoides on rat liver in vivo.

The effects of bovine growth hormone(GH) and Spirometra growth factor (SGF) on the in vivo concentrationions of glycolytic and citricacid (TCA) cycle intermediates in rat liver were investigated. The effects of these agents on the mitochondrial and cytoplasmic redox states, liver phosphorylation states, and adenylate kinase activity were also evaluated. The effects of SGF were studied in both normal and hypophysectomized rats,wheras GH effects ere examined only in hypophysectomized rats. Growth homrone(0.25mg/rat) was injected dayily for 9 days...     

The effects of reserpine and 6-hydroxydopamine on the concentrations of some arylakylamines in rat brain.

1 The concentrations of p- and m-tyramine were measured in the caudate nucleus of the rat brain following subcutaneous injection of reserpine or intraventricular injection of 6-hydroxydopamine, beta-Phenylethylamine was analysed in the hypothalamus after reserpine. 2 Endogenous levels of p-tyramine and m-tyramine in the caudate nucleus, and beta-phenylethylamine in the hypothalamus were 8.02, 2.25 and 2.52 ng/g respectively. 3 Tyramine concentrations were reduced to less than 20% of control values one day after a reserpine injection of 1 or 10 mg/kg. A single dose of reserpine (0.4 mg/kg) significantly decreased the content of both tyramines in the caudate nucleus. The effects became apparent as early as 45 min after drug case of m-tyramine. 4 The hypothalamic content of beta-phenylethylamine was unaffected by reserpine. 5 Ten days after an intraventricular injection of 6-hydroxydopamine (250 mug), p- and m-tyramine concentrations in the caudate nucleus were significantly below control levels. 6 The results suggest that p- and m-tyramine may be stored by an intraneuronal reserpine-sensitive storage mechanism. Alternatively, the tyramines may replace some of the catecholamines from their storage granules and then be released as false transmitters by the nervous impulse. The observed changes in tyramine levels might also the fact that these amines may be metabolically related to another amine which is stored in reserpine-sensitive granules.     

Pharmacokinetics of cytosine arabinoside in patients with acute myeloid leukaemia.

1 The pharmacokinetics of cytosine arabinoside were studied after a single i.v. bolus of 2 mg/kg ara-C in patients with newly diagnosed untreated AML, using a bioassay and GC-MS method to measure the plasma concentrations. 2 Most patients showed a bi- or tri-phasic decline in plasma concentrations with time. Plasma clearance was 3.9 to 18.1 l/min as measured by the GC-MS method, and terminal half-lives varied from 7--107 min. 3 There was poor correlation of the GC-MS assay with the bioassay, probably because the latter was interfered with by the release of endogenous nucleosides from blasts after after ara-C. 4 Plasma concentrations were measured by GC-MS during continuous infusions in 14 patients. Plasma clearances were much lower than after a bolus, 0.39 to 5.25 l/min. 5 There was no correlation of response (remission or fall in peripheral blast count) with exposure to ara-C calculated from infusion dose, clearance and duration of infusion. 6 This study shows that ara-C pharmacokinetics varies markedly from patient to patient and that there is a wide range in the plasma concentrations associated with therapeutic response.     

Effects of acronycine, bleomycin and cytosine arabinoside on the cell cycle. Some aspects of their interaction with radiation determined by pulse cytophotometry.

The influence of three chemotherapeutic agents, acronycine, bleomycin and cytosine arabinoside, alone and combined with radiation, on cell cycle progression and viability of L-cells was examined. The percentages of cells in G1, S and (G2 + M)-phases as derived from pulse cytophotometric DNA distribution patterns were recorded as a function of exposure time. After 24-h treatment with 10 microgram/ml acronycine, 46.4% of cells were accumulated in (G2 + M)-phase compared to 12.1% in the controls. This accumulation was significantly enhanced by an irradiation with 150 rads of X-rays resulting in arresting 63.1% of cells in this phase. Similar findings were obtained after a 24-h treatment with 100 microgram/ml bleomycin. 54.4% of cells were arrested in (G2 + M)-phase by the chemical treatment alone, while the combined treatment, bleomycin and radiation, yielded an accumulation of 66.3% of cells in G2 + M. A 24-h exposure to 0.2 microgram/ml cytosine arabinoside (Ara-C) produced a reversible block of 72.8% of cells in S phase compared to 27.4% in the control cultures. This S block was less pronounced after the combined treatment (51.1%). Some implications of the results for combined therapy are discussed.     

Drastic effect of cell density on the cytotoxicity of daunorubicin and cytosine arabinoside

White blood cell count (WBC) is generally accepted as a prognostic risk factor in acute myeloid leukemia (AML) outcome and displays a marked interindividual variation. The dose regimen currently used ignores the size of the tumor burden and the standardization of the dose is generally based on body surface area. In this study we have investigated the effect of cell density on the cytotoxic activity of daunorubicin (DNR) and cytosine arabinoside (AraC) towards HL60 cells and leukemic cells isolated from patients with AML. We demonstrate that drug cytotoxicity decreased with cell density and that apoptosis induction by DNR in isolated leukemic cells was greatly reduced at higher cell density. A marked reduction of the uptake of DNR and AraC in HL60 parental and mitoxantrone resistant cells was observed with increasing cell density. Such a drug depleting effect by cells at high density has been previously described for vincristine, doxorubicin and paclitaxel. By extrapolating the in vitro results to the in vivo situation, one could hypothesize that a high WBC can lower the plasma concentration through high uptake in the tumor burden, leading to a shortage of drug in leukemic blasts. Patients with high WBC might therefore benefit from a dose increase of DNR and/or AraC.     

Free-operant and auto-titration brain self-stimulation procedures in the rat: a comparison of drug effects.

Rats were implanted with bipolar stimulating electrodes aimed at the medial forebrain bundle of the lateral hypothalamus, and trained to press a lever in one of two different procedures in order to receive electrical stimulation through the electrodes. In a free-operant procedure, each response produced a 200 msec train of electric pulses at a suprathreshold current, the intensity of which remained constant throughout the session. In an auto-titration procedure, each response produced an electrical stimulus which was initially set at a suprathreshold intensity. Every 15th response reduced the stimulation current by 3 muA. The animal could reset the current to its initial intensity at any time by pressing a second lever in the test chamber. The average current at which the animal pressed the reset lever was defined as the reinforcement threshold. Dose-response functions were determined for d- and l-amphetamine, alpha-methyltyrosine, and haloperidol. The reinforcement threshold was decreased by both d- and l-amphetamine, increased by haloperidol, and not changed by alpha-methyltyrosine. These effects on reinforcement threshold were not consistently related to the drug-induced changes in response rate in either procedure. The auto-titration procedure may be useful for distinguishing between drugs which cause nonspecific changes in the rate of ongoing behavior and those which specifically modify the reinforcement efficacy of brain stimulation.     

A comparison of some extra-renal effects of spironolactone and canrenone.

1 Measurement of changes in trans-mural rectal potential difference (t.m.r.p.d.) and plasma aldosterone levels have been used in a comparison of the extra-renal activities of spironolactone and its major metabolite canrenone. 2 A characteristic pressure artifact was observed during measurement of t.m.r.p.d. When pressure artifacts were eliminated, there was a log-linear relationship between increasing doses of intravenous aldosterone and maximum increase in t.m.r.p.d. 3 Pre-treatment for 5 days with spironolactone or canrenone produced a similar attenuation of the increase in t.m.r.p.d. produced by infused aldosterone, suggesting that canrenone is the active metabolite of spironolactone in the rectum. This is in contrast to the significantly greater renal activity of spironolactone that has been demonstrated after a similar treatment period. Neither antagonist treatment produced significant changes in pre-infusion plasma aldosterone concentrations. 4 The need for assay of the extra-renal activities of aldosterone antagonists in the assessment of their therapeutic potential is discussed.     

The toxicological effects of pure dietary adenine base in the rat.

Ethylenebisdithiocarbamate of manganese (maneb) and zinc (zineb) and their degradation and metabolic product, ethylenethiourea (ETU), have produced similar teratogenic anomalies in rats. The mode of teratogenicity of maneb, deduced from the protective effects of zinc acetate following their simultaneous administration, has been attributed to its ability to chelate zinc. Whether ETU has a similar mode of action was investigated. Mated females from five control groups were fed a standard diet for the entire period of pregnancy. Dams in five other groups were fed the standard diet to which 0.0444% zinc (as zinc acetate) was added during the period from the 11th to the 14th day of pregnancy. On the 13th day of pregnancy, control dams and those given supplemental zinc were not treated, treated with distilled water, or with 80, 120, or 160 mg/kg ETU sc. A necropsy was performed on some dams 3 hr postinjection and concentrations of zinc were measured in the conceptus and maternal serum. The remaining dams were sacrificed and a necropsy performed on the 22nd day of gestation and their fetuses were examined for external, visceral, or skeletal anomalies. Zinc acetate was ineffective in reducing ETU-induced malformations, and concentrations of zinc in the conceptus and maternal serum were not affected by feeding zinc acetate or injecting ETU.