Avian Muscular Dystrophy: Muscle Ultrastructure and Histochemistry
Following Isaxonine Treatment
Authors: Shay Jerry W. , Stauver Marguerite Guimond 
Published: June 2020

Due to many similar properties, including high serum creatine
phosphokinase (CPK) levels and histological signs of muscle degeneration,
inherited muscular dystrophy of the chicken has been used for over 20 years
as a model for hereditary muscular dystrophy in humans. Line 413 dystrophic
chickens were selected for this drug study because they are homozygous for
muscular dystrophy (disease appears with 100% incidence), they have a
characteristic elevation in CPK activity, they have extensive signs of
muscle autolysis, and they demonstrate a reproducible and measurable onset
of functional disability in a flip-test procedure. Since the earliest
detectable clinical sign of the disease is the inability of the dystrophic
bird to right itself from the supine position, any therapeutic agent which
can delay the onset of this condition is usually considered beneficial
therapy. In this study we investigated the drug, Isaxonine (N-isopropyl
amino pyrimidine phosphate) which has been shown to have a nerve
growth-promoting action. Dystrophic chickens (413) were injected daily with
Isaxonine (50mg/kg weight) from day 3 exc ovo to day 40 and compared to
normal controls (412) and non-injected dystrophics. In addition to the flip
test, we measured the effect of this drug on serum CPK levels and muscle
histology and ultrastructure. The results of these experiments indicate that
14., 20 and 40 day Isaxonine injected dystrophic animals are greatly
improved compared to non-injected dystrophic animals. For example, Figure 1
is an electron micrograph of pectoralis skeletal muscle from a 20-day-old
normal chicken injected daily with Isaxonine (CPK 560mU/ml plasma, Flip 25)
showing normal ultrastructure. Figure 2 is an electron micrograph of
pectoralis skeletal muscle from a 20-day-old uninjected dystrophic chicken
(CPK 1370mU/ml plasma, Flip 2) illustrating extensive ultrastructural
deterioration. Figure 3 is a representative micrograph of pectoralis
skeletal muscle from a 20-day-old dystrophic chicken injected daily with
Isaxonine (CPK 840mU/ml plasma, Flip 13). Note that the ultra-structural
morphology appears more similar to the normal than to the dystrophic
animals. Figure 4 is an electron micrograph of pectoralis skeletal muscle
from a 20-day-old dystrophic chicken injected every other day with Isaxonine
(CPK 1218mU/ml plasma, Flip 3). The ultrastructure of this treatment group
more closely resembles the dystrophic rather than the normal control muscle.
As is apparent in these figures and confirmed with light microscopic
histologic sections of similar tissue, the daily injected animals appear to
have greatly improved muscle ultrastructure compared to the dystrophic or
every-other-day injected animals. Even though the mode of action of
Isaxonine is unknown at present, it does appear that it must be injected
daily to have therapeutic value and that cessation of drug administration
results in the dystrophic phenotype reappearing. Finally, in another
dystrophic strain of chickens (304), we have found Isaxonine to be
beneficial, as measured by a 50% reduction in serum CPK levels after 20 days
of drug administration.