Effects of season and sample handling on measurement of plasma α-melanocyte-stimulating hormone concentrations in horses and ponies

Abstract

Objective - To investigate effects of sample handling, storage, and collection time and season on plasma α-melanocyte-stimulating hormone (α-MSH) concentration in healthy equids. Animals - 11 healthy Standardbreds and 13 healthy semiferal ponies. Procedure - Plasma α-MSH concentration was measured by use of radioimmunoassay. Effects of delayed processing were accessed by comparing α-MSH concentrations in plasma immediately separated with that of plasma obtained from blood samples that were stored at 4°C for 8 or 48 hours before plasma was separated. Effects of suboptimal handling were accessed by comparing α-MSH concentrations in plasma immediately stored at -80° with plasma that was stored at 25°C for 24 hours, 4°C for 48 hours or 7 days, and -20°C for 30 days prior to freezing at -80°C. Plasma α-MSH concentrations were compared among blood samples collected at 8:00 AM, 12 noon, and 4:00 PM. Plasma α-MSH concentrations were compared among blood samples collected in January, March, April, June, September, and November from horses and in September and May from ponies. Results - Storage of blood samples at 4°C for 48 hours before plasma was separated and storage of plasma samples at 4°C for 7 days prior to freezing at -80°C resulted in significant decreases in plasma α -MSH concentrations. A significantly greater plasma α-MSH concentration was found in September in ponies (11-fold) and horses (2-fold), compared with plasma α-MSH concentrations in spring. Conclusions and Clinical Relevance - Handling and storage conditions minimally affected plasma α-MSH concentrations. Seasonal variation in plasma α-MSH concentrations must be considered when evaluating pituitary pars intermedia dysfunction in equids.