Changes Associated with the Peri-Ovulatory Period, Age and Pregnancy in ACTH, Cortisol, Glucose and Insulin Concentrations in Mares

Abstract

Although there are many hormonal changes associated with reproduction, the effects of ovulation and early pregnancy on adrenocorticotropic hormone (ACTH) and insulin concentrations are poorly described. We hypothesise that both ovulation and early pregnancy will alter ACTH and insulin concentrations in healthy mares. Eighteen mares showing no clinical signs suggestive of, or laboratory findings consistent with, pituitary pars intermedia dysfunction PPID and insulin dysregulation (ID) are enrolled. ACTH, cortisol, insulin and glucose concentrations are measured over their peri-ovulatory period, as determined via ultrasounds and progesterone concentrations. The mares are grouped by age and gestation status, and a two-way repeated-measures ANOVA is used to determine the effects of age and early pregnancy, along with the peri-ovulatory period, on analyte concentrations. No significant effect of age, ovulation or early pregnancy is detected on the mares’ cortisol, insulin or glucose concentrations; however, there is a significant effect of early pregnancy and ovulation on ACTH concentrations (p = 0.04 and p = 0.04 respectively). ACTH concentrations change around ovulation and with early pregnancy. Therefore, knowledge of a mare’s reproductive status might be beneficial when interpreting ACTH concentrations.

Short-Term Effects of Temperature and Thyrotropin-Releasing Hormone Stimulation on Adrenocorticotropin Stability in Horses

“…Horses were kept on the same pasture. In total, 8 horses were diagnosed with PPID in mid-summer (December and January) by either a baseline ACTH concentration over 35 pg/mL or ACTH concentration over 65 pg/mL 30 min post-TRH stimulation [8][9][10]19]. All horses assigned to the PPID-positive group either had clinical signs or developed them during the following 12 months.…”

Repeatability of a thyrotropin‐releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses

“…Baseline ACTH concentration is considered as an excellent test to diagnose PPID with an overall test accuracy above 90%, a median sensitivity above 75% and a median specificity above 75%; however, in autumn, test characteristics decline reducing its diagnostic value 6,7 . Considering that baseline ACTH concentrations fluctuate with seasonal changes, stress, exercise and disease status, the thyrotropin‐releasing hormone (TRH) stimulation test was developed to standardize ACTH concentrations and improve diagnosis 8‐14 . The results of TRH stimulation tests vary with environmental factors, the test still performs better than baseline ACTH with a greater accuracy, sensitivity, and specificity 6 …”

“… 6 , 7 Considering that baseline ACTH concentrations fluctuate with seasonal changes, stress, exercise and disease status, the thyrotropin‐releasing hormone (TRH) stimulation test was developed to standardize ACTH concentrations and improve diagnosis. 8 , 9 , 10 , 11 , 12 , 13 , 14 The results of TRH stimulation tests vary with environmental factors, the test still performs better than baseline ACTH with a greater accuracy, sensitivity, and specificity. 6 …”