Subacute skeletal myopathy induced by 2,4-dichlorophenoxyacetate in rats and guinea pigs

The action of 2,4-Dichlorophenoxyacetic acid on the isolated heart of insect and amphibia

The action of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on the isolated heart of the frog (Rana ridibunda) and two insects, the honeybee (Apis mellifera macedonica) and the beetle (Tenebrio molitor), was investigated using basic electrophysiological methods. The results of this study showed that a concentration of 1 μM 2,4-D was required to reduce the force and the frequency of the isolated heart of the honeybee to about 70% of the initial contraction in less than 20 min. To cause the same effects on the atria of the frog, 45 μM 2,4-D was required and on the isolated heart of the beetle, over 1000 μM of 2,4-D. The presence of an extensive system of gap junctions found in the honeybee is most probably the cause of the unusual sensitivity of its heart to 2,4-D, compared with the heart of the beetle, where no gap junctions were identified.

A distinctive type of infantile inflammatory myopathy with abnormal myonuclei

Four infants developed progressive muscle weakness after a normal initial postnatal development. All patients had a moderate elevation of serum creatine kinase (CK) activity. Muscle biopsies revealed, in addition to myopathic features, endomysial and perivascular inflammation. Electron microscopy disclosed prominent myonuclear abnormalities. Corticosteroids in 3 patients were moderately beneficial. This appears to be a clinicopathologically distinct form of inflammatory myopathy of infants.

Oculopharyngeal muscular dystrophy: clinical and morphological follow-up study reveals mitochondrial alterations and unique nuclear inclusions in a severe autosomal recessive type

Oculopharyngeal muscular dystrophy (OPMD) is usually a late onset, autosomal dominant dystrophy that affects extraocular eye muscles, pharyngeal muscles, and the trunk and limb musculature. In the present presumably recessively inherited case, with a clinical history of oculopharyngeal myopathy and distal weakness, paracrystalline mitochondrial inclusions and unique nuclear inclusions were found. In a biopsy obtained from the erector spinae muscle, marked muscle fibre atrophy and hypertrophy, occasional muscle fibre necrosis, and considerable fibrosis of the endomysium were noted. Similar signs of a chronic myopathy could already be detected in a biopsy from the anterior tibial muscle that had been obtained 10 years before. In both muscles, nuclear inclusions were seen in numerous severely affected, atrophic muscle fibres. These inclusions consisted of straight or helically wound 2-4 nm filaments. The outer diameter of the double helix was 12-15 nm and the periodicity of its repeats was about 15 nm. The filaments were often accumulated in clusters with a paracrystalline arrangement. No nuclear inclusions consisting of 8.5 nm tubular filaments, typically found in cases of OPMD, were detected. In addition, paracrystalline inclusions were present in a large number of mitochondria in several muscle fibres of the erector spinae muscle indicating that mitochondria could be primarily involved in the disease.

Biochemical alterations in skeletal muscle induced by 2,4-dichlorophenoxyacetic butyl ester during chick embryonic development

2,4-Dichlorophenoxyacetic butyl ester (2,4-D b.e.) (3.1 mg/egg) was applied on fertile hen eggs before starting the incubation. Chicks hatched from treated eggs showed motor dysfunctions, postural troubles and edematous muscles. The electromyography revealed muscular weakness, prolonged motor distal latency, and myotonia. The biochemical composition of leg and complexus muscles from 1-day-old chicks was determined. A significant diminution (24%) in the glycogen level of leg muscles was produced by the treatment. There was a small increase (15%) in sarcoplasmic proteins from leg muscles and an increase of a 20 kD protein in the myofibrillar proteins from complexus muscles. Even though total lipid content was not changed, 2,4-D b.e. treatment produced a diminution of sterol esters (20%) and phosphatidylcholine (11%) and an increase of phosphatidylserine (61%), triglycerides (37%) and free fatty acids (FFA) (448%) in leg muscles. Increases of phosphatidylethanolamine (16%), sterols (58%) and FFA (267%) were detected in complexus muscles. A remarkable increase (700-1500%) of unsaturated FFA, e.g. oleic, linoleic and arachidonic acids, was observed. Considering the avian embryo lipid metabolism, it is proposed that FFA and triglycerides were accumulated because they could not be metabolized in the mitochondria. Since FFA are potent cytotoxic compounds, their increase may be a key factor in the 2,4-D b.e. toxic action in muscle and other tissues during embryonic development.

Ca2+ homeostasis alterations induced by 2,4-dichlorophenoxyacetic butyl ester and 2,4-dichlorophenoxyacetic acid on avian skeletal muscle

Fertilized hen eggs were treated externally with 2,4-dichlorophenoxyacetic butyl ester (2,4-D b.e.) (3.1 mg/egg) before the start of the incubation. Actomyosin and sarcoplasmic reticulum adenosine triphosphatase (ATPase) activities from leg and complexus muscles of chicks hatched from treated eggs were measured. No significant variations were detected in the ATPase activities of actomyosin, but the sarcoplasmic reticulum Mg2(+)-activated ATPase and Ca2+, Mg2(+)-activated ATPase were inhibited 50 and 38% respectively. 45Ca2+ uptake into soleus muscle was increased by the 2,4-D b.e. treatment. The compartmental analysis of 45Ca2+ uptake kinetics showed increases in Ca2+ fluxes in sarcolemma and mitochondria and in the mitochondrial calcium pool. Isolated soleus muscles were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) or 2,4-D b.e. [14C]2,4-D reached it highest level in these muscles after 1 hr of treatment. The in vitro treatment with 2,4-D or 2,4-D b.e. increased 45Ca2+ uptake into the muscles. 2,4-D b.e. produced greater alterations than 2,4-D. The compartmental analysis of the 45Ca2+ uptake kinetics also showed increases of the mitochondrial Ca2+ pool and Ca2+ fluxes through sarcolemma and mitochondria. These results led to a hypothesis based on Ca2+ permeability alterations for explaining the myopathic actions of these phenoxyherbicides.

Toxicity of mixtures of parathion, toxaphene and/or 2,4-D in mice

The toxicity of the mixtures of parathion (PA), toxaphene (TOX) and/or 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in ICR male mice (21-24 g) by oral intubation, in corn oil, daily for up to 14 days. On Day 15, the exposure was discontinued, and animals were monitored for an additional period of 7 days for the possible reversibility of the toxicity. The body weight gain decreased with the mixtures, as well as with the individual agricultural chemicals (ACs), during the 14-day period. The cholinesterase (ChE) activity in the serum and brain was inhibited in the animals of the groups of PA (1-10 mg kg-1) and PA (5 mg kg-1)-containing mixtures. TOX (50-200 mg kg-1) caused initial inhibitory effects of 20-65% on the serum ChE (Day 1) before producing increases of 53-64% in the enzyme activity by Day 15, with little effects on the brain ChE levels. 2,4-D (50-200 mg kg-1) resulted in significantly elevated levels of the serum ChE, with substantial decreased in the brain ChE activity. The serum glutamic pyruvic transaminase level was up (38-630%) in TOX (50 mg kg-1), 2,4-D (50 mg kg-1) or their mixture group. No pathological changes at the light microscopic level in the brain and liver were noticed. TOX and TOX-containing mixtures significantly increased the liver/body weight ratio and decreased the pentobarbital (60 mg kg-1, i.p., in saline)-induced sleep.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuromuscular effects of acute 2,4-dichlorophenoxyacetic acid (2,4-D) exposure in dogs

2,4-Dichlorophenoxyacetic acid (2,4-D) was administered once orally to adult female mongrel dogs at 0, 25, 50, 75, 100 or 125 mg/kg of body weight (n = 4 per group). Clinical neurological examinations, electromyography (EMG) and motor nerve conduction velocity measurements were carried out before exposure, and on days 1, 3, 7, 14, 21 and 28 post-exposure. On day 7, two dogs per group were killed. Samples of the medial and lateral plantar nerves were removed for teased fiber and semi-thin section analysis; samples of appendicular muscles were removed for histology and histochemistry. Necropsy included histopathological examination of the brain and spinal cord at multiple levels. Remaining dogs were killed on day 28 and their tissues were processed similarly. Transient generalized myotonic discharges were found in skeletal muscles of dogs receiving 50 mg/kg or more of 2,4-D. A few dogs in the higher dosage groups also had mild muscle stiffness, myotonic dimpling and/or lethargy, lasting up to 3 days post-exposure. Other parameters remained within normal limits.

The effect of topically applied n-butylester of 2,4-dichlorophenoxyacetic acid on the immune response in mice

Six-week-old female CD-1 mice were administered the n-butylester of 2,4-dichlorophenoxyacetic acid (2,4-D). The 2,4-D ester was applied dermally at dosages ranging from 0 to 500 mg/kg (2,4-D content) in the acute studies and 0 to 300 mg/kg in the 3 week subacute studies. Following acute exposure, antibody production against sheep red blood cells was suppressed at higher exposure levels. Evidence of clinical toxicity, myotonia and depression, and histopathological alterations in the central nervous system including perivascular edema and ganglial cell necrosis, was also seen in the mice. No alterations were observed in the T- and B-lymphocyte proliferative responses induced by concanavalin A, a T-lymphocyte mitogen, or Escherichia coli lipopolysaccharide, a B-lymphocyte mitogen. Subacute 2,4-D ester exposure which produced minimal clinical or pathological alterations, had no effect on antibody production, but did enhance the B- and T-lymphocyte proliferative responses. The immunosuppressive effects of acute 2,4-D ester exposure which were observed in this study, were unlikely a direct immunological alteration, but rather a secondary manifestation of the clinical syndrome. Since the subacute exposure levels may be more comparable to occupational or environmental exposure, it is unlikely that 2,4-D esters will have any major immunotoxicological significance in agricultural communities.

The effect of oral exposure to the n-butylester of 2,4-dichlorophenoxyacetic acid on the immune response in mice

Six week old female BDF1 mice were administered the n-butylester of 2,4-dichlorophenoxyacetic acid (2,4-D) by gastric intubation at dosages ranging from 0 to 200 mg/kg (2,4-D content) in the acute studies and 0 to 100 mg/kg in the subacute studies. Following acute exposure, the antibody production against sheep red blood cells and the induction of DNA synthesis with Escherichia coli lipopolysaccharide, a B-lymphocyte mitogen, were enhanced. Comparable T-lymphocyte mitogen responses induced by concanavalin A, a T-lymphocyte mitogen, were not affected by 2,4-D, though 2,4-D did exhibit a weak, non-specific, dose-related mitogenic effect. Subacute exposure to the 2,4-D ester did not alter antibody production. B-lymphocyte mitogen responses were enhanced, though a linear dose-response relationship was not observed. Histopathological alterations in the brain and spinal cord and clinical symptoms of toxicity were observed in the 200 mg/kg treatment group (acute exposure). Similar effects were not seen in the subacute study. The immunostimulatory effects of 2,4-D were observed at relatively high exposures. It is unlikely that these immune alterations will have any major toxicological significance in agricultural communities utilizing 2,4-D herbicides, though further studies with commercial grade formulations which may contain other compounds in addition to the pure 2,4-D esters must be evaluated at similar levels of exposure.

Effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on the contractile properties of reinnervated rat skeletal muscle

2,4-Dichlorophenoxyacetic acid (2,4-D), a common herbicide, was administered to rats (100 mg/kg, i.p.) during 24 days to determine whether or not it is toxic to regenerating peripheral nerve and reinnervating muscle. The peroneal nerve was crushed 1 cm proximal to the extensor digitorum longus muscle and recordings made in vivo after 1 to 24 days. Functional reinnervation was observed by day 10 and recovery was similar in rats receiving 2,4-D or vehicle. Distal motor latencies and muscle action potentials returned toward normal during the 24 days in a similar manner in 2,4-D and controls. Isometric twitch tensions per muscle weight on indirect stimulation returned to intact values by 17 days, but in the 2,4-D animals they became larger (P less than 0.01) than controls by day 24. The twitch:tetanus ratios were increased at day 10 and returned toward normal values in the controls but remained increased (P less than 0.01) in the 2,4-D animals at 24 days. Similar results were obtained on direct muscle stimulation. The data suggest that 2,4-D is not toxic to nerve during regeneration or muscle reinnervation in the rat, but that it does affect both twitch and tetanus tensions suggesting proliferation as well as disruption of myofibrils.

2,4-Dichlorophenoxyacetic acid (2,4-D) does not cause polyneuropathy in the rat

2,4-Dichlorophenoxyacetic acid (2,4-D), a component of Agent Orange, was injected intraperitoneally into adult male Fisher rats for 3-12 weeks. During the period of study gait and toe-spreading reflexes remained normal and distal motor latencies, motor and mixed nerve conduction velocities and amplitudes remained similar (P greater than 0.05) in animals receiving 2,4-D or vehicle. This study suggests that 2,4-D is not toxic to peripheral nerves in the rat.

2,4-Dichlorophenoxyacetic acid (2,4-D) reduces acetylcholinesterase activity in rat muscle

A single dose (200 mg/kg body weight, i.p.) of 2,4-dichlorophenoxyacetic acid (2,4-D), commonly used as a herbicide, caused significant decreases in acetylcholinesterase (AChE) activity in diaphragm and other muscles of the rat. The 4S, 10S, and 16S forms of AChE were affected. The effect was maximal 15 to 24 h after injection. Choline acetyltransferase (CAT) activity was not affected. Neither AChE nor CAT activities changed in sciatic nerve from 2,4-D-treated animals. Spontaneous locomotor activity decreased dramatically 4 h after 2,4-D treatment. Myotonia that was present 1.5 h after 2,4-D injection became maximal at 2 to 6 h. Twenty-four hours after drug injection, when animals were recovering from myotonia, spontaneous locomotor activity was still depressed to 50% of control values. Prolonged distal motor latencies were observed 15 to 24 h after drug administration. AChE activity and spontaneous locomotor activity returned to control values at 48 h. Thus, 2,4-D causes a decrement of end-plate AChE, as well as behavioral and electrophysiologic changes. Decreased activity of AChE may be an early step in development of the myopathy that occurs after large dose 2,4-D.

Neurofilament subunit--related proteins in neuronal intranuclear inclusions

Well-preserved nuclei were isolated from the brain of a patient with neuronal intranuclear inclusion disease ( NIID ). The inclusions in situ stained for proteins and, by immunohistochemical techniques, for the 200K and 68K components of the neurofilament protein triplet but were negative for the 145K neurofilament protein. At the electron microscopic level the inclusions were seen to consist of straight, randomly arranged tubular filaments 8.5 to 9.5 nm in diameter. They were resistant to extraction with hot buffer containing sodium dodecyl sulfate (SDS) and 2-mercaptoethanol, indicating that the proteins of NIID inclusions are probably cross-linked by covalent bonds other than disulfide. This feature is also exhibited by the paired helical filaments occurring in brain in Alzheimer's disease. No major differences were found in the polypeptide composition of nuclei in NIID and control nuclei resolved by SDS-polyacrylamide gel electrophoresis. The inclusions isolated from SDS-extracted nuclei were shown by immunohistochemical techniques to stain for all three neurofilament subunits, indicating that 145K -related antigenic sites were uncovered during the extraction procedure.

Prevention of skeletal muscle fiber necrosis in hamster dystrophy

Necrosis and widespread central nucleation of skeletal muscle cells, which are the main features of skeletal muscle pathology in genetically dystrophic hamsters (UMX-7.1 strain), were not present in muscles of 45- to 65-day-old animals which had been surgically denervated at 15 to 18 days of age. Necrosis and widespread central nucleation were also absent in hind leg muscles at 30 to 60 days of age after transection of the high thoracic spinal cord at 15 to 18 days. Normal excitation or contraction of the skeletal muscle fibers in early age appears necessary for the microscopic pathological expression of the dystrophic gene in skeletal muscles in the UMX-7.1 strain hamsters. These experiments constitute a rare and clear example of consistent prevention of skeletal muscle cell destruction in vivo in an inherited myopathy.

An experimental morphometric study of neutral lipid accumulation in skeletal muscles

The neutral lipid content of skeletal muscle fibers was determined by computing the lipid accumulation index (LAI) on transverse cryostat sections stained with Oil Red O. The LAI was defined as: (total area of neutral lipid droplets in a fiber) x 100/(total cross-sectional area of a fiber). The biceps, diaphragm, and soleus muscles were studied in 3 groups of guinea pigs: normal animals, animals fasted for 48 hours, and animals subjected to muscle denervation and then fasted for 48 hours. In normal animals, the highest mean LAI was found in the diaphragm (4.93) in comparison with lower values in the biceps (2.25) and soleus (2.09). After fasting, these values were markedly increased; there was also a concomitant increase in plasma free fatty acid (FFA) concentration. Prior denervation further increased the LAI in biceps and soleus but reduced it in the diaphragm. Type 2A fibers tended to show high lipid accumulation when the plasma FFA concentration was high. Type 2B fibers never accumulated much lipid under any circumstances. Type 1 fibers varied in their response in the different muscles.

Myotonia as a side effect of diuretic action

1. Commonly used loop diuretics produce side effects in man which are similar to chemically induced myotonia. These diuretics have structural affinity with known myotonic agents. 2. We have observed EMG myotonia in vivo in leg muscles of rats treated with intravenous frusemide. 3. In the presence of several different diuretics, rat isolated diaphragm, soleus and extensor digitorum longus muscles as well as frog sartorius muscles produce typically myotonic contractions with relaxation times up to several seconds. 4. Intracellular recording of action potentials from diuretic-treated muscles reveals long lasting after-discharges following a brief electrical stimulus, again typical of chemically induced myotonia. 5. Having demonstrated a myotonic action of several diuretics we suggest a need for caution in using these drugs in persons with hereditary myotonia and a need to be aware of possible provocation of myotonia in subclinical cases. Myopathies and neuropathies which are known to result from chronic exposure to myotonic agents also need to be considered. 6. In our study, the diuretic, acetazolamide, unmasked subthreshold myotonia. This seems to be at variance with reports of its usefulness in the treatment of myotonia. 7. Diuretics should probably not be employed in the treatment of herbicide intoxication where their myotonic activity would be expected to add to the known myotonic activity of the herbicide.

Probable hypothyroid myopathy: glycogen-deficient type 2b fibers

Described herein is a case of hypothyroid myopathy with selective atrophy and glycogen depletion of type 2b fibers shown by light and electron microscopy. Although the pathogenesis of such findings is obscure, it is possible that hypothyroidism in conjunction with a superimposed process might explain paradoxically glycogen-deficient fibers.