Investigation into the association between endometriosis and pituitary pars intermedia dysfunction (PPID)

Abstract

Pituitary pars intermedia dysfunction (PPID) is an endocrine disorder associated with elevated adrenocorticotropin hormone (ACTH). Animals suffering from this disease have been found to have elevated systemic inflammation. It is unknown if this inflammation is noted within the reproductive tract, or if this inflammation is associated with fibrosis. Fibrosis of the endometrium, deemed endometriosis, is often noted in aged mares and is associated with subfertility. Therefore, the objective of this study is to evaluate endometriosis of the PPID mare. We hypothesize that elevated ACTH and its associated chronic inflammation will coincide with an increase in endometrial fibrosis. To evaluate this, 11 mares were screened for PPID in late summer using a thyrotropin-releasing hormone (TRH) stimulation test. In brief, ACTH concentrations were measured before and 1 h after stimulation with 1.0 mg TRH. Of these, 7 mares were found to be PPID positive (n = 7; ACTH >110 pg/mL), and 4 were found to be PPID negative (n = 4; ACTH <30 pg/mL). When mares were in diestrus (presence of a corpus luteum; uterine tone; P4 >4 ng/mL), 2 endometrial biopsies were then collected. One biopsy was processed for qPCR analysis of select inflammatory cytokines and the other was paraffin embedded for histology. Statistics were performed on SAS 9.4, and data were assessed for normality and equal variances utilizing a Bartlett's and Shapiro–Wilk test. Next, the impact of PPID on expression of transcripts associated with fibrosis (MMP1, MMP2, MMP9, TIMP-2, and TNF) were evaluated using an unequal variances t-test. Correlation between ACTH and expression of fibrosis markers was assessed using a Pearson correlation. Significance was set at P < 0.05. PPID was not found to affect the expression of any transcript evaluated, and this included MMP2 (P = 0.56), MMP9 (P = 0.91), TIMP-2 (P = 0.19), and TNF (P = 0.35). There was also no significant correlation between levels of ACTH and expression of fibrotic markers, including MMP2 (P = 0.61; R² = 0.04), MMP9 (P = 0.66; R² = 0.03), TIMP-2 (P = 0.97; R² < 0.01), or TNF (P = 0.53; R² = 0.05). Additionally, there was no significant difference when assessing fibrosis based on histology, as fibrosis was noted in 4 of 7 PPID animals and 2 of 4 control animals (P = 0.82). In conclusion, PPID does not appear to have a correlation with endometriosis.