Circannual variation in plasma adrenocorticotropic hormone concentrations in the UK in normal horses and ponies, and those with pituitarypars intermediadysfunction

Abstract

SummaryReasons for performing study: Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy, frequently diagnosed via plasma adrenocorticotropic hormone (ACTH) concentrations. Seasonal variation in plasma ACTH concentrations has been described in normal horses prompting caution in diagnosing PPID at certain times of the year. The aims of this study were to determine appropriate reference intervals for equine plasma ACTH throughout the year; and to examine the circannual variation of plasma ACTH concentrations in PPID cases. Hypothesis: Plasma ACTH can be used as a test for PPID throughout the year with the use of appropriate reference intervals. Methods: Data for reference interval calculations were obtained from samples collected from inpatients of Liphook Equine Hospital (non-PPID group, n = 156). Data from PPID cases (n = 941) were obtained from samples submitted to the Liphook Equine Hospital Laboratory from horses with a clinical suspicion of PPID found to have plasma ACTH concentrations greater than our upper reference interval for that time of year. Results: Upper limits for reference interval of plasma ACTH were 29 pg/ml between November and July and 47 pg/ml between August and October. Circannual variation in plasma ACTH occurred in both non-PPID and PPID horses with the highest ACTH concentrations found between August and October in both groups (P<0.0001). The greatest difference between the 2 populations also occurred between August and October. Conclusions: Plasma ACTH can be used for the diagnosis and monitoring of PPID throughout the year with the use of appropriate reference intervals. These findings demonstrate an increase in pituitary gland secretory activity during the late summer and autumn in both normal and PPID cases.

Monthly changes of standard serum liver parameters of clinically healthy horses over a period of 24 months

“…Gabe et al is described in the months from August to October (Copas and Durham 2012, Beech 2011, Donaldson et al 2005. These daylight changes correspond well with the fluctuations in serum GLDH, GGT, AST and bile acids in the present study.…”

Phenotypic, hormonal, and clinical characteristics of equine endocrinopathic laminitis

“…A small number of insulin samples (4%) was analyzed using a radioimmunoassay (Siemens Healthcare) at Cornell. These human‐specific assays have been adapted for use in the equine species and validation data have been published previously . However, because of differences between the 2 insulin assays, the insulin data from samples analyzed at Cornell have been removed from the statistical analyses (but were used for case definition).…”

“…A set of inclusion criteria was developed and if the case exhibited 2 or more of the inclusion criteria, or 1 of the criteria in the absence of an obvious nonendocrine initiating cause for laminitis, they were deemed acceptable for inclusion in the final data set. The inclusion criteria included an increased basal (resting) serum insulin concentration (>20 μIU/mL), an increased plasma ACTH concentration (>35 pg/mL or seasonally adjusted, location‐specific reference ranges if the sample was obtained during the autumn period, which were 47 pg/mL for the Northern hemisphere, and 77.4 pg/mL for the Southern hemisphere), a body condition score (BCS) ≥ 6/9, a cresty neck score (CNS) ≥ 2/5, regional adiposity, a history of recent access to lush pasture, a change in diet that included an increase in nonstructural carbohydrate (NSC) content without accompanying clinical signs of gastrointestinal disturbance (ie, not a sudden overload of grain with diarrhea, colic, acidosis, fever, lethargy, etc. ), being a breed at‐risk of developing EMS, a history of being an easy‐keeper, founder (divergent growth) rings in 1 or more hoof wall, a familial history of laminitis, a dysregulated postprandial serum insulin response to an oral glucose test (OGT) or an oral sugar test (OST), with the choice of dynamic test dependent on the clinician's preference.…”

Effect of Age, Season, Body Condition, and Endocrine Status on Serum Free Cortisol Fraction and Insulin Concentration in Horses

“…Free cortisol fraction has been measured in adult horses and foals,18, 19, 21, 22 but to our knowledge has not been assessed in horses with endocrine disease. In addition, the effect of season on HPA‐axis activity and total cortisol concentrations in horses and ponies is well‐described,15, 23, 24, 25, 26, 27, 28 but it is not known if season also impacts equine plasma cortisol‐binding dynamics and alters free cortisol availability.…”