Objective—To investigate effects of sample handling,
storage, and collection time and season on plasma α-melanocyte-stimulating hormone (α-MSH) concentration
in healthy equids.
Animals—11 healthy Standardbreds and 13 healthy
Procedure—Plasma α-MSH concentration was measured
by use of radioimmunoassay. Effects of delayed
processing were accessed by comparing α-MSH concentrations
in plasma immediately separated with that of
plasma obtained from blood samples that were stored at
4oC for 8 or 48 hours before plasma was separated.
Effects of suboptimal handling were accessed by comparing
α-MSH concentrations in plasma immediately
stored at -80°C with plasma that was stored at 25°C for 24
hours, 4oC for 48 hours or 7 days, and –20°C for 30 days
prior to freezing at –80°C. Plasma α-MSH concentrations
were compared among blood samples collected at 8:00
AM, 12 noon, and 4:00 PM. Plasma α-MSH concentrations
were compared among blood samples collected in
January, March, April, June, September, and November
from horses and in September and May from ponies.
Results—Storage of blood samples at 4°C for 48
hours before plasma was separated and storage of
plasma samples at 4°C for 7 days prior to freezing at
–80°C resulted in significant decreases in plasma α-MSH concentrations. A significantly greater plasma α-MSH concentration was found in September in
ponies (11-fold) and horses (2-fold), compared with
plasma α-MSH concentrations in spring.
Conclusions and Clinical Relevance—Handling and
storage conditions minimally affected plasma α-MSH
concentrations. Seasonal variation in plasma α-MSH
concentrations must be considered when evaluating
pituitary pars intermedia dysfunction in equids. (Am J Vet Res 2004;65:1463–1468)
Objective—To evaluate the correlation between plasma
α-melanocyte-stimulating hormone (α-MSH) concentration
and body mass index (BMI) in healthy horses.
Animals—82 healthy horses.
Procedure—Plasma α-MSH concentration was determined
by radioimmunoassay. At the time blood samples
were collected, body condition scores (BCS)
were determined and measurements of girth circumference,
body length, and height were obtained.
Weight was estimated by use of the following
formula: estimated weight (kg) = [girth (cm)2 × length
(cm)]/11,877. Body mass index was calculated as estimated
weight (kg)/height (m)2.
Results—A correlation was found between BMI and
BCS (rs = 0.60 [95% confidence interval (CI), 0.44 to
0.73]). A weak correlation was found between plasma
α-MSH concentration and BMI (rs = 0.25 [95% CI,
0.03 to 0.45]) and BCS (rs = 0.26 [95% CI, 0.04 to
0.46]). A correlation was found between plasma
α-MSH concentration and BMI in horses ≥ 10 years
old (rs = 0.49 [95% CI, 0.20 to 0.69]) but not in horses
< 10 years old (rs = –0.04). Horses in the upper
quartile of BMI had significantly greater plasma α-MSH concentration (median, 9.1 pmol/L; range, 2.0 to
95.3 pmol/L) than horses in the lowest quartile of BMI
(median, 7.0 pmol/L; range, 3.6 to 15.7 pmol/L).
Conclusions and Clinical Relevance—A correlation
exists between plasma α-MSH concentration and
BMI in horses. Further study is required to determine
whether melanocortin receptor defects underlie this
correlation or, alternately, whether plasma α-MSH
concentration is simply a correlate of adiposity. (Am J Vet Res 2004;65:1469–1473)
Objective—To determine prevalence and clinical features
of pituitary pars intermedia dysfunction (PPID)
in horses with laminitis.
Animals—40 horses with laminitis.
Procedures—Horses with laminitis that survived an
initial episode of pain and were not receiving medications
known to alter the hypothalamic-pituitary-adrenal
axis were tested for PPID by evaluation of endogenous
plasma ACTH concentration. Signalment, suspected
cause, month of onset and duration of laminitis,
Obel grade of lameness, pedal bone rotation,
physical examination findings, results of endocrine
function tests, treatment, outcome, and postmortem
examination findings were recorded.
Results—Prevalence of PPID as defined by a single
high plasma ACTH concentration was 70%. Median
age of horses suspected of having PPID (n = 28) was
15.5 years, and median age of horses without PPID
(12) was 14.5 years. Laminitis occurred most frequently
in horses with and without suspected PPID
during September and May, respectively. Chronic
laminitis was significantly more common in horses
suspected of having PPID. In horses suspected of having
PPID, the most common physical examination findings
included abnormal body fat distribution, bulging
supraorbital fossae, and hirsutism. Five horses suspected
of having PPID had no clinical abnormalities
other than laminitis. Seventeen horses suspected of
having PPID that were treated with pergolide survived,
and 3 horses that were not treated survived.
Conclusions and Clinical Relevance—Evidence of
PPID is common among horses with laminitis in a primary-care ambulatory setting. Horses with laminitis
may have PPID without other clinical signs commonly
associated with the disease. (J Am Vet Med Assoc