| || |
Buy Flavoxate Hcl
Buy Flavoxate Hcl
Special Internet Prices.
Fast & Guaranteed Worldwide Delivery!
Secure & FAST Online Ordering.
Our Drugstore Is The Most Trusted Online Drug Supplier.
Related post: It is diminished by depression of the muscle, produced by cold or excessive heat;
by fatigue (Fig. 22); or by muscular depressants, such as potassium or ether.
(If the veratrin action is weak, cold increases the Contracture, probably by adding its
own contracture to that of the veratrin. Sollmann.)
FIG. 22. Effect of fatigue on veratrin curve: a., normal veratrin tracing; b, after partial fatigue;
\^ natural size.
Double Peak Curve. A careful inspection of veratrin-curves generally reveals two
contractions (Fig. 21) : a primary contraction (a), which occurs with the normal rapidity,
.but is somewhat higher than normal, and which tends to relax quickly; and a secondary
contraction (b), which occurs more slowly and lasts longer. The two contractions are
more or less fused (v. Bezold), but the form varies with conditions (Mostinski, 1904).
Overend, 1889, attributed this phenomenon to the different contraction velocity of the
white and red muscle fibers. Cervello and Weiss, 1899, showed, however, that uniform
muscles exhibit the same phenomenon.
Boltazzi, 1901, suggested that the veratrin curve is due to the fusion of two contrac-
tions; the first peak representing the normal contraction of the fibrils, and the further
portion of the curve the contraction of the sarcoplasmic substance, which he assumes
has the properties of smooth muscle. According to this the veratrin action would con-
sist essentially in raising the excitability of the sarcoplasmic substance above the
threshold. There is, however, no direct evidence that the sarcoplasm has contractile
functions (Mueller, 1908); and the modern theories of muscle contraction render this
very improbable. Woebbecke, 1913, has modified the theory somewhat. He believes
that muscle has two distinct functions, but that these are not specifically connected
with the histologic constituents. Verzar and Felter, 1914, attribute the action to
increased sensitiveness to normal stimuli.
Veratrin acts directly on the muscle substance, for the effects occur after curare
(Prevost, 1867), and in the nerve-free end of the sartorius muscle. When a muscle is
immersed in a dilute solution, a single stimulus produces at first a normal contraction,
then fibrillary twitching (Lamm, 1912). The excitability of curarized muscle to direct
electric stimulation is not increased; it is diminished by large doses Buy Flavoxate Hcl (Boehm, 1913).
Large doses of veratrin, however, paralyze the motor endings without previous stimulation.
Spontaneous Contraction of Muscle. The immersion of a muscle in veratrin causes
a slowly developing contracture, even in the absence of spontaneous stimulation. High
concentrations paralyze all forms of muscle completely (Koellicker, 1856).
MANUAL OF PHARMACOLOGY
Other Substances Producing Veratrin Effects. The prolonged contracture which
is so characteristic of veratrin, is by no means confined to this alkaloid, but is also pro-
duced by Digitalin, Helleborein, Muscarin, Strychnin; by aldehyds (Verzar and Felter,
1915), etc., by cold, and by very strong electric stimulation. This wide occurrence
signifies that the phenomenon is of fundamental physiologic importance. These
measures also prolong the contraction of cardiac and smooth muscles.
The Action of Glycerin on Muscle. The muscles of frogs poisoned with glycerin
respond to single stimuli by prolonged contraction, the curve having a superficial
resemblance to that of veratrin, but being rather more irregular. The glycerin contrac-
tion is, however, a true tetanus, due to greater irritability of the muscle substance; the
action-current of each contraction sufficing to start another contraction. The phe-
nomenon occurs also after curarization (Santesson, 1903).
Nerve Trunks. Direct application of veratrin lessens their excitability
Circulation. The effects are complex. Those on excised hearts
resemble aconite and digitalis (slowing with increased systole). In intact
animals, stimulation of the vagus center (Fig. 23) predominates at first
(marked slowing); later, the fall of pressure from vasomotor paralysis
FlG. 23. Cevadin (Veratrin) on Blood pressure; showing the stimulation of the vagus center.
Intravenous injection of 0.02 mg. per Kg. into anesthetized dog; artificial respiration.
Mammalian Circulation. Small doses sometimes cause primary quickening of the
heart. With larger doses (0.025-0.05 mg. per Kg.) there is sudden and marked slowing
with corresponding fall of blood pressure (Bezold and Hirt, 1874; Lissauer, 1887;
Pilcher and Sollmann, 1915). The slowing is greatest soon after the injection, often
with marked arythmia or Flavoxate Hcl 100 Mg temporary arrest. This acute effect is due to stimulation of
the vagus center (see, however, under Veratrum), for section of the vagi largely abolishes
it, and stimulation of the vagus trunk does not produce further slowing (Busquet,
1907). With divided vagi, large doses may cause primary quickening and gene-ally
moderate rise of blood pressure (Bezold; Pilcher and Sollmann). The fall of blood pres-
sure is mainly due to the slowing, although some fall may occur independently (Lissauer).
The vasomotor center is moderately stimulated by the respiratory embarrassment,
even when the vagi are cut. The stimulation does not occur if artificial respiration is
maintained (Pilcher and Sollmann, 1915). Reflex stimulation causes vasoconstriction.
VERATRIN (CEVADIN) 431
Late Effects. The acute effect soon passes off. The heart then beats with a steady,
moderately slowed rate. This slowing is not removed by atropin and is therefore
The blood pressure falls progressively, occasionally interrupted by spasmodic rise
from central vasomotor stimulation. The strength of the heart is not impaired, for it
reacts well to compression of the aorta, and beats efficiently just before death. The fall
must therefore be vasomotor; and accordingly, sciatic stimulation or asphyxia fails to
raise the pressure (Lissauer, 1887). The vagus remains excitable. The cerebral vessels
are constricted (Dixon and Halliburton, 1910).
The isolated mammalian heart (Hedbom-Langendorff) shows a primary slowing from
stimulation of the peripheral vagus mechanism; then irregularity, and finally paralysis
of the cardiac muscle. The tone is increased.
Frog's Heart. The effects resemble aconite and digitalis. They involve mainly the
ventricle and consist in slowing (no further slowing on vagus stimulation; Busquet,
1907); prolonged systole and increased tonus; sudden change in the rate to one-half;
"peristaltic" contractions; and final median standstill. High concentrations cause
prompt systolic standstill, with continued shortening. The auricles continue much
longer. The same effects occur on the excised and perfused heart (Lissauer, 1887;
Related links: retirement alliance nh, Glyburide Micronase, how to get avodart prescription, valtrex for cold sores during pregnancy, tizanidine 2 mg tablets, Buy Depo Medrol, will generic maxalt available, 12.5 mg paxil, mouthwash containing tetracycline, revista motor precios usados coches motos bicis
| || |