Serum elimination profiles of methyllycaconitine and deltaline in cattle following oral administration of larkspur (Delphinium barbeyi).

Abstract

To describe the simple elimination kinetics of methyllycaconitine (MLA) and deltaline and evaluate the heart rate response in cattle following oral administration of larkspur.
5 healthy Angus steers that were habituated to metabolism crates.
Tall larkspur (Delphinium barbeyi) in the early flowering stage was collected, dried, and ground. Each steer received a single dose of larkspur that was equivalent to 10.4 mg of MLA/kg and 11.0 mg of deltaline/kg via oral administration. Steers were housed in metabolism crates during a 96-hour period following larkspur administration; heart rate was monitored continuously, and blood samples were collected periodically for analysis of serum MLA and deltaline concentrations as well as assessment of pharmacokinetic parameters.
No overt clinical signs of poisoning developed in any steer during the experiment. Mean +/- SE heart rate reached a maximum of 79.0 +/- 5.0 beats/min at 17 hours after larkspur administration. Serum MLA concentration was correlated directly with heart rate. Mean times to maximal serum concentration of MLA and deltaline were 8.8 +/- 1.2 hours and 5.0 +/- 0.6 hours, respectively. Mean elimination half-life values for MLA and deltaline were 20.5 +/- 4.1 hours and 8.2 +/- 0.6 hours, respectively.
Following larkspur administration in 5 healthy steers, maximum serum concentrations of MLA and deltaline were detected within 10 hours, and changes in serum MLA concentration and heart rate were correlated. Results indicated that cattle that have consumed larkspur will eliminate 99% of MLA and deltaline from serum within 144 hours.

Full text

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Serum elimination profiles of methyllycaconitine
and deltaline in cattle following oral
administration of larkspur (Delphinium barbeyl)
Benedict T. Green, PhD; Kevin D. Welch, PhD; Dale R. Gardner, PhD; Bryan L. Stegelmeier, DVM, PhD;
T. Zane Davis, PhD; Daniel Cook, PhD; Stephen I. Lee, PhD; James A. Pfister, PhD; Kip E. Panter, PhD
Objective—To describe the simple elimination kinetics of methyllycaconitine (MLA) and
deltaline and evaluate the heart rate response in cattle following oral administration of
larkspur.
Animals-5 healthy Angus steers that were habituated to metabolism crates.
Procedures—Tall larkspur (Delphinium barbeit,) in the early flowering stage was collected,
dried, and ground. Each steer received a single dose of larkspur that was equivalent to
10.4 mg of MLA/kg and 11.0 mg of deltaline/kg via oral administration. Steers were housed
in metabolism crates during a 96-hour period following larkspur administration; heart rate
was monitored continuously, and blood samples were collected periodically for analysis
of serum MLA and deltaline concentrations as well as assessment of pharmacokinetic
parameters.
Results—No overt clinical signs of poisoning developed in any steer during the experiment.
Mean ± SE heart rate reached a maximum of 79.0 ± 5.0 beats/min at 17 hours after larkspur
administration. Serum MLA concentration was correlated directly with heart rate. Mean
times to maximal serum concentration of MLA and deltaline were 8.8 ± 1.2 hours and 5.0 ±
0.6 hours, respectively. Mean elimination half-life values for MLA and deltaline were 20.5 ±
4.1 hours and 8.2 ± 0.6 hours, respectively.
Conclusions and Clinical Relevance—Following larkspur administration in 5 healthy
steers, maximum serum concentrations of MLA and deltaline were detected within 10
hours, and changes in serum MLA concentration and heart rate were correlated. Results
indicated that cattle that have consumed larkspur will eliminate 99% of MLA and deltaline
from serum within 144 hours. (Am J Vet Res 2009;70:926-931)
T
that are produced by the plant and that are present in high
concentrations in plant tissues. Clinical signs associated
with the consumption of larkspur plants that have high
concentrations of toxic alkaloids include muscle weak-
ness and trembling, tachycardia, failure of voluntary
muscular coordination, sternal recumbency followed by
lateral recumbency, bloating, respiratory depression, and
death.' ,' The progression of these signs is often rapid, and
the clinical signs may not be observed—poisoned animals
are commonly found dead. In addition to these well-docu-
mented clinical signs of larkspur poisoning, less obvious
dose-dependent changes in heart rate and in the electrical-
ly evoked electromyographic response of the external anal
sphincter have been recently identified.' These changes
he toxic effects of larkspur (Delphinium spp) in cattle
have been attributed to the norditerpenoid alkaloids
Received August 13, 2008.
Accepted September 2, 2008.
From the USDA Agricultural Research Service, Poisonous Plant Re-
search Laboratory, 1150 E 1400 N, Logan, UT 84341.
Supported by the USDA Agricultural Research Service.
The authors thank Clint Stonecipher, Edward L. Knoppel, Danny
Hansen, Scott Larsen, Al Maciulis, Isabelle McCollum, and Rex
Probst for technical assistance.
Address correspondence to Dr. Green.
are detectable within 24 hours after administration of low
doses of larkspur when other signs are minimal or have
not yet developed.
Larkspur contains MSAL-lype and MDL-type nord-
iterpenoid alkaloids, of which the MSAL-type alkaloids
are the more toxic. Members of the MSAL-type alka-
loids include MLA, nudicauline, and 14-deacetylnudi-
cauline. 7 Plants that have high concentrations of MSAL-
type alkaloids are thought to have the most toxic effects
in cattle, and the concentrations of these alkaloids have
been used for the prediction of plant toxicity' Members
of the less toxic MDL-type alkaloids include deltaline
and 14-0-acetyldictyocarpine.5
ABBREVIATIONS
A,,?
AUC?
C?
max
MDL?
MLA?
MSAL?
nAChR?
t½?
T?
flax
Absorption half-life
Area under the curve
Maximal serum concentration
7,8-methylenedioxylycoctonine
M ethyl lycaconitine
N-(methylsuccinimido)
anthranoyllycoctonine
Nicotinic acetylcholine receptor
Elimination half-life
Time to maximal serum concentration
926AJVR, Vol 70, No. 7 Jury 2009

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Of the norcliterpenoid alkaloids, the elimination
kinetics and toxic effects of MLA have been most ex-
tensively studied. Turek et al"' reported that the serum
t 11 , of MLA in rats following oral administration of the
alkaloid was 408 minutes, whereas the 11/2 of MLA fol-
lowing IV administration of the alkaloid was only 18
minutes. Purified MLA has an LD,, of 4.5 mg/kg in
mice." By use of a mouse bioassay the simple elimina-
tion kinetics of MLA (administered IV) in serum and
kidney, liver, brain, and muscle tissues were evaluated,
and the t 11 s for those samples were 17.5, 21.1, 22.0,
15.6, and 10.2 minutes, respectively' 2 In sheep, MLA
is rapidly eliminated with a t 11, of 20 minutes after IV
injection)' More recently, Welch et al' s determined the
kinetics of purified MLA in brain and muscle tissues af-
ter IV administration of the alkaloid alone and in com-
bination with other larkspur alkaloids in mice. in mice,
IV administration of MLA in combination with delta-
line, 14-0-acetydictyocarpine, or lycoctonine did not
alter the bioavailahility or clearance of the alkaloids.13
In comparison, toxicokinetics and possible synergisms
of the MDL-type norditerpenoid alkaloids have been
investigated to a much lesser extent. Following IV ad-
ministration in mice, the LD ,, of deltaline (an MDL-
type alkaloid that lacks the N-lmethylsuccinyl]anthra
nilic acid ester at the C-18 position) was 115 mg/kg.'3
The serum t /7 of deltaline is approximately 20 minutes
after IV injection in sheep."' There is little informa-
tion available on the simple serum elimination kinetics
of MLA and deltaline or on the physiologic effects of
these alkaloids following oral administration to cattle,
even though grazing cattle are the single species known
to he fatally intoxicated by larkspurs. The purpose of
the study reported here was to describe the simple
elimination kinetics of MLA and dleltaline and evaluate
the heart rate response in cattle during a 96-hour pe-
riod following oral administration of dried ground tall
larkspur.
Materials and Methods
Plant material—Tall larkspur (Delphinium barhey i)
in the early flowering stage was collected during July
2003 near Manti, Utah (latitude, 390 03.154' N; longi-
tude, 1110 30.752 W; Poisonous Plant Research Labo-
ratory collection No. 03-12), at an elevation of approxi-
mately 3,000 m above sea level. A voucher specimen
was deposited at the Utah State University Herbarium
(No. 237494). The plant material was air-dried, ground
until sufficiently fine to pass through a 2.38-mm mesh,
and mixed by use of a grinder-mixer. After processing,
the plant material was stored in plastic bags away from
direct light at room temperature (approx 9°C) until
use.
Alkaloid analysis—Dried ground larkspur samples
(5 replicates) were extracted," and analyzed for alkaloid
content by use of methods that have been previously
descnbed.' 4 Reserpine" at a concentration of 500 Vg
was used as an internal standard. Individual alkaloid
concentrations were quantified from peak areas in ion
chromatograms generated from their respective pro-
tonated ions in reference to calibration curves. These
alkaloid concentrations Were used for the calculation
of the doses of alkaloids in the form of dried ground
larkspur.
Serum samples were stored and extracted as pre-
viously described.'' Mass spectrometry analyses of the
serum samples and standards were also performed as
previously described." The extract of this larkspur col-
lection from the year 2003 contained 16 ing of norcli-
terpenoid alkaloids/g, of which 7 mg/g represented the
MDL-type alkaloids and 9 mg/g represented the MSAL-
type alkaloids.'
Cattle—Five black Angus steers (mean ± SE
weight, 596 ± 10 kg) were used in the study All animal
work was done under veterinary supervision with the
approval of the Utah State University Institutional Ani-
mnal Care and Use Committee. The steers were main-
tained on alfalfa grass hay with a mineral supplement
for at least 3 weeks before and during the experiments.
The steers were trained to the use of a halter, gentled,
and handled frequently so that they were highly trac-
table; these animals were habituated to the metabolism
crates.
Study design—In the first experiment, each steer
received a single dose of dried ground larkspur orally;
the dose provided 10.4 mg of MLA/kg and 11.0 mg of
deltalinc/kg. During a 96-hour period following lark-
spur administration, heart rate was monitored continu-
ously and blood samples were collected periodically for
analysis of serum MLA and deltaline concentrations.
Three weeks after administration of dried ground lark-
spur, the experiment was repeated with the exception
that the larkspur was replaced with similar amounts of
dried ground grass hay In this second experiment, the
steers were similarly monitored during a 72-hour pe-
riod, thereby allowing each to act as its own negative
control animal.
Procedures for the first experiment—Eighteen
hours prior to the start of each experiment, a 16-gauge
indwelling catheter was placed in a jugular vein of each
steer. To place the catheter, each steer was sedated with
acepromazine maleate" (0.05 mg/kg. IV). In the area
over the jugular vein that was selected for catheter in-
sertion, the hair was clipped and the site was washed
with a surgical scrub solution' and rinsed with 70%
ethanol. After site preparation, each steer was admin-
istered 5 mL of lidocaine hydrochloride" SC to provide
local anesthesia around the site of catheter placement.
The catheter was then inserted in the jugular vein. An
extension tube was glued to the catheter and skin at the
junction site with cyanoacrylate adhesive and sutured
in place to the skin at the junction site. The extension
tubing was positioned along the neck of the animal,
and the port was placed between its ears; the extension
tube was protected along its length with several layers
of elastic-adhesive tape.' The steer was then led into a
metabolism crate, and food was withheld during the
night prior to the start of the experiment.
During the day of the experiment, each steer was
handled in a gentle manner; baseline weight and physi-
ologic measurements (designated as 0-hour data) were
recorded. A single dose of finely ground dried larkspur
mixed in approximately I L of tap water was admin-
istered via oral gavage. At 0.25, 0.5, 0.75, 1.0, 1.5, 2.0,
AJVR, Vol 70, No. 7, July 2009?
927

Page 3

Figure 1—Mean ± SE serum MLA and deltaline concentrations and heart rate betore
(0 hours) and at intervals until 96 hours after administration (via oral gavage) of dried
ground larkspur in 11 L of tap water (a dose equivalent to 10.4 mg of MLA/kg and 11.0
mg of deltaline/kg) in 5 steers. Heart rate was assessed for 5 minutes immediately
prior to collection of each venous blood sample (19 time points).
4.0, 6.0, 8.0, 10.0, 12.0, 18.0, 24.0, 36.0, 48.0, 60.0,
72.0, and 96.0 hours after administration of larkspur,
blood was collected. Catheters were used to collect
samples (approx 10 mL each) of venous blood. Use
of the catheter minimized stress during blood sample
collection, which avoided stress-induced alterations in
heart rate. The catheter and tubing were flushed with
heparinized saline (0.9% NaCl) solution between blood
sample collections; a 10-rnL volume was discarded at
each time point to clear the catheter and tubing prior
to sample collection. Each steer was fed grass hay ap-
proximately 3 hours after treatment with larkspur, and
grass hay was provided during the remainder of time in
the metabolism crates. The catheter was removed at the
end of the first experiment.
Procedures for the second experiment—Three
weeks after completion of the first experiment, each
steer underwent procedures identical to those used
in the first experiment, except that dried ground pas-
ture grass hay mixed in 11 L of tap water was admin-
istered via oral gavage as a control treatment. The
amount of dried ground pasture grass hay adminis-
tered was equivalent to the amount of dried ground
larkspur administered in the first experiment. Blood
sample collections were performed before (baseline
[0 hours]) and at the same time points after admin-
istration of the control treatment. As in the first ex-
periment, each steer was fed grass hay approximately
3 hours after receiving the control treatment, and grass
hay was provided during the remainder of the time in
the metabolism crates. The catheter was removed at the
end of the second experiment.
Heart rate monitoring—Heart rate signals were re-
corded by use of an analog-to-digital converter, and sig-
nals were amplified with an aniplifier. e, Heart rate was
detected with repositionable monitoring electrodes5
that were cemented in place with a cyanoacrylate ad-
hesive.i The leads were placed as described by Chen
ci al, 15 except that the ground electrode
was attached to the lumbar region of the
back. The heart rate signal was amplified
with a gain range of ± 500 fiV and was
filtered with a mains filter, 60-liz notch
filter, 120-Hz low-pass-0.1-Hz high-pass
filter, and a digital band-pass filter with
a high cutoff frequency of 45 Hz and a
low cutoff frequency of 0.1 Hz. The cy-
clic measurements feature of a software
package' was used to calculate heart rate
(beats/mm).
Data analysis—Heart rate data are
expressed as the mean ± SE values. Data
recordings of the heart rate in each steer
were allowed to form a stable baseline and
were then analyzed by use of 2 methods.
First, one hundred ninety-two 5-minute
time blocks throughout each 96-hour
experiment (one 5-minute block every
30 minutes) were selected for heart rate
analysis, and the mean heart rate derived
from the 5-minute block was calculated.
Second, the mean heart rate was calcu-
lated for an approximately 5-minute period just prior
to each of the 19 venous blood sample collections. The
mean heart rate values obtained prior to the venous
blood sample collections were used to assess the corre-
lation between serum alkaloid concentrations and heart
rate via Spearman correlation analysis.
The kinetic profiles of MLA and deltaline were ana-
lyzed by use of standard pharmacokinetic software.' A
curve-stripping procedure' was used to determine the
basic pharinacokinetic parameters for the rates of elimi-
nation phases of the MLA and deltaline concentration
curves. The following parameters were determined for
each alkaloid: t 11, (ie, 0.693/k,..), C, T, and
AUC. A trapezoidal method was used to determine
the AUC of a concentration versus time graph. Com-
parisons of mean values derived following control and
larkspur treatments were made by use of an ANOVA
followed by a Dunneti test,' as indicated. Comparisons
between 2 means were made by use of a 2-tailed t test.'
For all comparisons, the limit for significance was set at
a value of P < 0.05.
Results
Five steers received dried ground larkspur at a dose
that was equivalent to 10.4 mg of MLA/kg and 11.0 mg
of deltaline/kg via oral gavage during the first experi-
ment and a similar amount of dried ground pasture
grass hay during the second experiment. For the dura-
tion of both experiments, heart rate was recorded con-
tinuously (data not shown) and venous blood samples
were collected at intervals. During the entire 96-hour
period following administration of larkspur, the 5 steers
developed no overt clinical signs of poisoning.
At 17 hours after administration of larkspur, mean
± SE heart rate attained a peak value of 79 ± 5 beats/
mm; this value was based on data from 4 steers because
1 steer had removed its monitoring leads at 17 hours,
although they were subsequently reattached. The heart
928?
AJVR, Vol 70, No. 7, July 2009

Page 4

Table 1-Toxicokinetic data for MLA and deltaline in 5 steers fol-
lowing administration (via oral gavage) of ground dried larkspur in
11 L of tap water (a dose equivalent to 10.4 mg of MLNkg and
11.0 mg of deltaline/kg).
Alkaloid
Parameter?
MLA?
Deltaline
Ta,,, (h)?
C,,, (ng/mL(?
AUC (ng.h/mL(?
t½ (h)?
A 1 (hI?
8.8?
368 ± 86.6?
10,423 z 2,707?6,981 ± 1,280
20.5 ± 4.1?
3.0 ± 0.5?
1.2?
5.0 it 0.6
485 ± 61.4
8.2 z 0.6
1.4?
0.6
*For this parameter, the VILA value is significantly (P < 0.05)
different from the deltaline value.
rate at 17 hours in larkspur-treated cattle was signifi-
cantly different from both the mean baseline heart rate
in that first experiment (59 ± 2.0 beats/mm; P = 0.004
In = 5]) and the mean heart rate at 17 hours among
cattle receiving the control treatment (52 it 4 heats/mm;
P = 0.005 [41). After reaching the maximum heart rate
at 17 hours, the rate declined to a value of 54 ± 6 beats/
min at 96 hours (n = 5). A similar peak heart rate value
was not detected in cattle following administration of
the dried ground pasture grass hay; from 10 to 20 hours
after administration of the control treatment (the peri-
od corresponding to the period of maximum heart rate
in larkspur-treated cattle), mean heart rate was 56 ± 3
beats/mm, and during the second experiment overall,
the mean heart rate was 61 ± 2 heats/mm.
Peak serum concentrations of MLA and deltaline
were detected at the 10- and 6-hour time points, respec-
tively. The peak serum MLA concentration was 305.9 ±
94.2 ng!mL, and the peak serum deltaline concentration
was 476.5 ± 62.8 ng/mL (Figure 1). At 96 hours, the se-
rum MLA concentration was 17.1 ± 8.4 ng!mL and the
serum deltaline concentration was less than the limit of
detection. The T values for MLA and deltaline were
calculated from data obtained from all 5 steers and were
8.8 and 5.0 hours, respectively (Table 1). The T val-
ues for the 2 diterpenoid alkaloids were significantly (P
= 0.022) different. The t,,,s for MLA and deltaline were
also significantly (P = 0.018) different. On the basis of
data from all 5 steers, there was a significant direct cor-
relation (Spearman r = 0.75; P < 0.001) between serum
MLA concentration and heart rate. No such correlation
was detected between serum deltaline concentration
and heart rate (Spearman r = 0.33; p = 0.2 In = 51).
Discussion
In a previous study' performed by our group, dose-
dependent increases in heart rate and decreases in the
evoked electromyographic response of the external anal
sphincter were detected in cattle that received larkspur
orally. On the basis of those findings, the dose of lark-
slur used in the present study was selected to provide
an equivalent dose of alkaloids that could be safely ad-
ministered to cattle without the loss of voluntary mus-
cle coordination. The larkspur collection used in the
present study contained norcliterpenoid alkaloids, of
which deltalmne and MLA were in greatest abundance;
the dose of larkspur administered to the cattle provided
the equivalent doses of 10.4 mg of MLA/kg and 11.0 mg
of deltaline/kg. 3 This alkaloid dose was tolerated well
by the 5 Angus steers, with no development of nota-
ble muscle weakness or overt clinical signs of larkspur
toxicosis. In a previous pea-based study' involving the
same larkspur collection, mixed-breed cattle that re-
ceived this dose did develop overt voluntary muscle
weakness. The lack of muscle fatigue in the present
study may have been attributable to breed differenc-
es or, more likely, to the fact that confinement of the
steers in metabolism crates (which limits movement)
minimized exertion, thereby reducing muscle fatigue.
These steers had extensive training and habituation to
the experimental protocol and metabolism crates that
certainly would reduce stress during each 96-hour ex-
periment. Additional research is needed to determine
the factors behind the observed differences in clinical
effects between the pen-based investigation and the
present study.
We have previously posed the hypothesis that
MSAL-type alkaloids acting at a7-nAChRs in the inter-
cardiac ganglia were responsible for the increases in
heart rate in cattle that are poisoned with larkspur. 1 In
the present study, heart rate was significantly increased,
compared with baseline values, at 17 hours after oral
administration of larkspur. Moreover, there was a sig-
nificant correlation between serum MLA concentration
and heart rate. The fact that there was a correlation be-
tween serum MLA concentration, but not serum del-
taline concentration, and heart rate in cattle provides
support for that previous hypothesis. Methyllycaconi-
tine is a potent and selective competitive antagonist
with nanomolar affinity at a7-nAChRs.'" Deltaline
is a significantly less potent nicotinic receptor blocker;
MLA is > 100 times as potent as deltaline at reducing
compound muscle action potentials in lizard extensor
digitorum longus muscle preparations."' On the basis
of results of the present study and a previous dose-re-
sponse study' in cattle, it is likely that the inhibition
of cholinergic neurotransmission by diterpenoid alka-
loids is responsible for the observed clinical effects in
cattle. Further research to elucidate the actions of pu-
rified MSAL-type and MDL-type alkaloids in cattle is
needed.
Measurements of kinetic parameters in the pres-
ent study also provided insight into the time of onset
of clinical effects following larkspur ingestion and the
clearance times of MLA and deltaline in cattle. Previous
research at our laboratory has revealed that cattle typi-
cally collapse to recumbency at 5 to 8 hours after oral
administration of dried ground larkspur .' 202 ' These
observations coincide with the T
for MLA and cleltaline. Although the kinetics of toxin
elimination from cattle that are treated with fresh lark-
spur plant preparations, as occur when grazing cattle
are poisoned, may he different, results of our study sug-
gested that clinical intoxication correlates closely with
the T,, values of MLA and deltaline and that clinical
signs are likely to develop or be most severe at 6 or 7
hours after exposure. More work is needed to ascertain
the clinical importance of these findings because many
cattle ingest larkspur over extended periods when graz-
ing, thereby developing so-called repetitive dosing or
equilibrium kinetics whereby many tissues have rela-
., values calculated
AJVR, Vol 70, No. 7, July 2009?
929

Page 5

tively constant cyclic toxin concentrations. These ani-
mals become intoxicated when too much additional
larkspur is eaten too quickly
Although MLA is more potent than deltaline, the
high serum concentrations of both alkaloids that were
detected early in larkspur-treated cattle in our study
may be biologically important. In experiments with
mice, IV coadministration of MLA and deltaline In-
creases the toxic effects, compared with the effects of
MLA alone; the LD, of the MLA-deltaline combination
is3.1,2.2.and l.5gIkgat ratios of1:1, 1:5, and l:25,
respectively, whereas the LD 0 of MLA alone is 4.4 mg/
kg)' These findings suggest that concentrations of both
alkaloids contribute to larkspur toxicity and determine
the risk of poisoning-associated clinical effects.
In the cattle of the present study, MLA was still de-
tectable in serum at 96 hours after treatment with lark-
spur. Given that 7 t 1 s are required for 99% elimination
of the alkaloid from serum, it would require a period
of 144 hours or 6 days to clear 99% of the MLA from
the serum in these cattle. The t 11, for MLA in our study
(approx 20 hours) is considerably longer than previ-
ously reported values (approx 20 nhinutes)J°
explanation for this discrepancy is species differences.
Methyllycaconitine may he eliminated more slowly in
cattle than it is in sheep, rats, or mice. However, cau-
tion should be taken when estimating the A 11, and t,,, of
a compound on the basis of data derived from experi-
ments involving oral administration because of flip-flop
kinetics. A flip-flop kinetic model occurs when the ab-
sorption of a compound is much slower than its elimi-
nation, and this type of kinetic model can be generated
whenever A,,, and t i,, are estimated from oral adminis-
tration data alone. 22 In rats, a large difference between
the t, 2s of MLA following oral and IV administration
has been detected," which is suggestive of flip-flop ki-
netics because the true elimination rate of a compound
will he the same for both methods of administration.
If MLA follows a flip-flop kinetic model in cattle, then
the t 1,2 of MLA in the present study would be approxi-
mately 3 hours—a value that is much closer to the half-
life values reported previously, although not as rapid
as the 20-minute t,, 2) °
t i,,, data obtained from animals following oral and IV
administrations are needed. 22 To perform an IV kinet-
ics study in cattle, large quantities of purified MLA and
deltaline would be required, which is not presently fea-
sible. If the absorption of MLA is the rate-limiting step
in cattle, then the administration of activated charcoal
to decrease the absorption of MLA could be a possible
treatment for larkspur poisoning; however, additional
research is needed to determine whether that treatment
would be effective.
In the present study, most deltaline was cleared from
serum after a period equivalent to 7 t 1,2s, and although
it was still present at 60 hours, the serum concentration
was less than the limit of detection at 96 hours. The
initial toxicity data and these relatively rapid clearances
associated with deltaline (compared with clearances of
the MSAL-type alkaloids) suggested that deltaline con-
tributes little to the toxic effects of larkspur in cattle;
however, results of a recent study" in mice suggest that
the apparently less toxic MDL-type alkaloids enhance
2 One
2 To correctly estimate A 1,2 and
the toxicity of the more toxic MSAL-type alkaloids. Be-
cause of species differences, further research is needed
to investigate the effects of MDL-type and MSAL-type
larkspur alkaloids combined in different ratios and the
role of those alkaloids in the toxic effects and toxicoki-
netics of larkspur in cattle. It should be noted that there
are differences in the potency and binding affinities of
larkspur alkaloids depending on the type of tissue and
species. 21.24 For example, cattle are more susceptible
to the toxic effects of larkspur than are sheep. The ef-
fects of low doses of larkspur alkaloids in other species
such as humans are unknown, and the possibility of an
anaphylactic reaction or other response to these toxins
does exist. It is suggested that in animals that have been
exposed to larkspur, the time to allow complete clear-
ance of larkspur alkaloids is 6 to 7 days.
In the 5 steers in the present study, maximum se-
rum concentrations of MLA and deltaline were detected
within a period of 10 hours after oral administration of
larkspur; of the 2 alkaloids, MLA has a slower t i,, (20.5
hours), compared with that of deltaline (8.2 hours).
Because the clearance of MLA is relatively prolonged,
a withdrawal time of 7 days is suggested to allow poi-
soned animals to eliminate larkspur-associated toxins.
Given that serum MLA concentration was correlated
with heart rate, development of tachycardia may be
an early indicator of poisoning. Additional research is
needed to better determine the biological, effects and
mechanisms of MSAL and MDL interactions in intoxi-
cation and to determine why some animals or species
are more susceptible to poisoning.
a.
b.
c.
d.
C.? Bemadine surgical scrub, Purdue Products, Stamford, Conn.
f.
Elastikon tape, The Kendall Co, Mansfield, Mass.
g.
Powerlab and Octal Bioamp, ADlnstrumcnts Inc, Colorado
Springs. Cob.
h.
3M Red Dot model 2670 repositionabte monitoring electrodes,
3M Corp. Saint Paul. Minn.
i.
Henkel Consumer Adhesive Inc, Avon. Ohio.
J .?
Chit software package, version 5, AD]nstrument.s inc. Colo-
rado Springs, Cob.
k.?
PR solutions 2.0 for noncompartmental pharmacokinetic data
analysis. Summit Research Services, Montrose, Cob.
I.?
GraphPad Prism. vcrsion 4.03 for Windows, GraphPad Soft-
ware, San Diego, Calif.
Mix-All Grinder-Mixer, model 55, Gehl Co. West Bend, Wis.
Sigma Chemical Co. Saint Louis, Mo.
Ahbocath-T, Abbot Hospitals, North Chicago, Ill.
Vecico Inc, St Joseph. Mo.
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AJVR, Vol 70, No. 7 July 2009