The Effect of Season on the Histologic and Histomorphometric Appearance of the Equine Pituitary Gland

Cordero, Melissa; McFarlane, Dianne; Breshears, Melanie A.; Miller, Lisa M.; Miller, Margaret A.; Duckett, Wendy M.

doi:10.1016/j.jevs.2011.01.003

« Previous Next »Journal of Equine Veterinary Science
Volume 32, Issue 2 , Pages 75-79, February 2012

The Effect of Season on the Histologic and Histomorphometric Appearance of the Equine Pituitary Gland

Melissa Cordero, DVM
- Department of Physiological Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK
Dianne McFarlane, DVM, PhD
- Department of Physiological Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK
- Corresponding author at: Dianne McFarlane, DVM, PhD, Department of Physiological Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74074.
Melanie A. Breshears, DVM, PhD
- Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK
Lisa M. Miller, DVM, PhD
- Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada
Margaret A. Miller, DVM, PhD
- Department of Comparative Pathobiology, School of Veterinary Medicine, Purdue University, West Lafayette, IN
Wendy M. Duckett, DVM, MS
- Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada

Received 26 July 2010; received in revised form 9 October 2010; accepted 11 January 2011. published online 07 March 2011.

Abstract

The objective of this study was to determine the effect of season on the histologic and histomorphometric appearance of the normal equine pituitary gland. Pituitary glands were collected at necropsy from 121 horses throughout the year. Plasma was also collected from 59 of these horses before euthanasia. Hematoxylin and eosin stained median sagittal sections of each pituitary were evaluated and histologically graded by three pathologists. Histomorphometric analysis was performed on the same slides. Plasma α-melanocyte stimulating hormone was measured by radioimmunoassay in a subset of horses (n = 59). A total of 118 pituitary glands were included in the study after exclusions were made on the basis of the presence of pars intermedia (PI) adenomas (>5 mm). There was a positive correlation between PI hormone concentration (α-melanocyte stimulating hormone) and PI area. Pituitary gland measurements and grades from samples collected in the fall were compared with those collected in the nonfall months using t-test. The PI area, total pituitary area, and PI/total pituitary ratio were significantly greater in the fall compared with nonfall months (P < .0001, P < .01, P < .0001, respectively). Pituitary grades were also higher in the fall compared with nonfall months (P < .001). There was no seasonal difference in pars distalis or pars nervosa area. The results of this study show that the normal equine pituitary shows seasonal changes in appearance and size. These changes must be considered when using postmortem histologic evaluations in the diagnosis of pituitary pars intermedia dysfunction or for validation of antemortem diagnostic tests.

Keywords: Equine, Pituitary, Season, Histomorphometry, Pars intermedia