Alpha-melanocyte stimulating hormone release in response to thyrotropin releasing hormone in healthy horses, horses with pituitary pars intermedia dysfunction and equine pars intermedia explants

Comparison of Cortisol andACTHResponses after Administration of Thyrotropin Releasing Hormone in Normal Horses and Those with Pituitary Pars Intermedia Dysfunction

“…Both ACTH and α‐MSH concentrations increase after TRH administration in normal horses and those with PPID, but the concentrations were higher in horses with PPID, similar to this study. To our knowledge, only 1 other study has examined both cortisol and ACTH concentration changes after TRH administration, but only baseline and 30‐minute samples were obtained . Unlike in this study where cortisol concentrations significantly increased only in the PPID horses, in that study, all horses had an increase in cortisol concentrations, but similar to the current study's findings, actual concentrations were not significantly different between normal horses and those with PPID.…”

“…A descriptive study on 11 horses without clinical signs and 2 with signs of PPID reported PPID horses had greater percentage increases in cortisol concentrations at 15 minutes (127–245%), but unaffected horses’ concentrations also increased, varying from 17% to 105% above very variable basal concentrations . In our study, PPID horses had a greater percentage increase in cortisol concentration at 14 minutes, but the mean cortisol concentrations and percentage increase in cortisol concentrations did not differ between the groups at 30 minutes after TRH administration, similar to another study that reported no significant difference in percentage increase or absolute cortisol concentration in horses with PPID compared with normal horses . The initial study showing a significant increase in cortisol in PPID horses did not compare the mean concentrations of the 2 groups at different times nor did it report a certain percentage increase as being diagnostic for PPID.…”

“…The premise of the TRH test is that TRH stimulates ACTH release from the pituitary gland, but cortisol originally was measured because of lack of a commercially available test for ACTH in horses at that time . Measuring ACTH concentrations has been shown to have high sensitivity and specificity for diagnosing PPID, and TRH has been shown to have a direct stimulatory effect on the pars distalis and the pars intermedia . Both ACTH and α‐MSH concentrations increase after TRH administration in normal horses and those with PPID, but the concentrations were higher in horses with PPID, similar to this study.…”

“…The combined dexamethasone suppression/TRH stimulation test was developed because of the potential influence of basal cortisol concentration on horses’ responses to TRH, and the hypothesis that TRH administration would override the induced cortisol suppression only in horses with PPID . A high sensitivity and specificity for adrenocorticotropin (ACTH) concentrations ≥35 pg/mL at 0 and at 30 minutes post‐TRH administration have been reported for differentiating between normal horses and those with PPID, and another study showed a greater increase in ACTH concentration, but a similar increase in cortisol concentration in PPID horses compared with normal horses 30 minutes after TRH administration . The major objectives of this study were to compare ACTH and cortisol responses to TRH administration in both normal horses and in those with PPID, determine whether the hormone concentration changes correlated, and determine whether measurement of 1 hormone more reliably differentiated between normal horses and those with PPID.…”

Prediction of incipient pasture‐associated laminitis from hyperinsulinaemia, hyperleptinaemia and generalised and localised obesity in a cohort of ponies

“…Plasma glucose, triglyceride and uric acid concentrations were assayed enzymatically by commercial kits and an automated analyser (CX5 Chemistry Analyzer) 3 . Plasma insulin (Coat-A-Count Insulin) 4 , leptin (Multi-species Leptin RIA) 5 , cortisol (Coat-A-Count Cortisol) 4 and ACTH (DiaSorin ACTH) 6 concentrations were measured by commercial radioimmunoassay previously validated for use in equine plasma (Freestone et al 1991;McManus and Fitzgerald 2000;McFarlane et al 2006). Plasma TNFα was measured by a commercially available equine-specific ELISA (Equine TNFα Screening Set) 7 previously validated in equine samples (Vick et al 2007).…”