Evaluation of plasma ACTH, alpha-melanocyte-stimulating hormone, and insulin concentrations during various photoperiods in clinically normal horses and ponies and those with pituitary pars intermedia dysfunction.
OBJECTIVE
To measure plasma ACTH, alpha-melanocyte-stimulating hormone (aloha-MSH), and insulin concentrations during various photoperiods between February and October in horses and ponies with and without pituitary pars intermedia dysfunction (PPID).


METHODS
Cohort study.


METHODS
13 clinically normal (control) ponies, 14 clinically normal (control) horses, 7 ponies with PPID, and 8 horses with PPID.


METHODS
Blood samples were collected from February through October during 8 photoperiods: 1, February 13 through March 2; 2, April 4 through 6; 3, June 19 through 22; 4, August 6 through 7; 5, August 14 through 17; 6, September 4 through 6; 7, September 26 through 28; and 8, October 16 through 18. Plasma ACTH, alpha-MSH, and insulin concentrations at each photoperiod were compared among groups.


RESULTS
Log ACTH concentration was increased during photoperiod 4 through 8, compared with photoperiod 1 through 3, in all groups. In photoperiod 3 through 7, log ACTH concentrations were higher in horses and ponies with PPID, compared with values for control horses and ponies. alpha-Melanocyte-stimulating hormone (log and raw value) concentration was higher in photoperiod 2 through 8, compared with photoperiod 1, in control horses and ponies. In horses and ponies with PPID, log alpha-MSH concentration was higher in photoperiod 3 through 8, and alpha-MSH concentration was higher in photoperiod 4 through 8, compared with photoperiod 1. In control horses and ponies, plasma insulin concentration was lower in photoperiod 3 than in photoperiod 1.


CONCLUSIONS
Plasma alpha-MSH and ACTH concentrations increased as daylight decreased from summer solstice (maximum daylight hours) to 12 hours of daylight.
Beech
Jill
J
Department of Clinical Studies, New Bolton Center, University of Pennsylvania, Kennett Square, PA 19348, USA.
Boston
Raymond C
RC
McFarlane
Dianne
D
Lindborg
Sue
S
D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D005260:Female; D006734:Horse Diseases / Q000097:blood*; D006736:Horses; D007328:Insulin / Q000097:blood*; D008297:Male; D017440:Photoperiod; D010900:Pituitary Diseases / Q000097:blood / Q000378:metabolism / Q000662:veterinary*; D052716:Pituitary Gland, Intermediate / Q000378:metabolism*; D000521:alpha-MSH / Q000097:blood*
D007328:Insulin; D000521:alpha-MSH; D000324:Adrenocorticotropic Hormone