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 4oC 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°C with plasma that was stored at 25°C for 24 hours, 4oC 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. (Am J Vet Res 2004;65:1463–1468)
