Changes in Muskox Blood Progesterone Concentration between Collection and Centrifugation

Abstract

Jugular blood was collected from 4 muskoxen (Ovibos moschatus) during late pregnancy, in either heparinized or untreated tubes. The tubes were either refrigerated (4 C) or kept at room temperature (21 C) for periods of 6, 12, or 24 hours. The samples were then centrifuged and the serum or plasma was frozen (-18 C) prior to radioimmunoassay for progesterone. Samples designated Time 0 were handled identically but were centrifuged within 1 hour of collection. A significant decline in progesterone concentration had occurred in all samples between collection and centrifugation, and this was more rapid at 21 than at 4 C. Heparinization had no effect on the rate of decline. These results indicate that care should be taken to minimize the effects of handling on progesterone levels, particularly when blood is collected in the field. J. WILDL. MANAGE. 51(4):901-903 Radioimmunoassay (RIA) of circulating steroid hormones is being applied with increasing frequency to the study of wild species, such as Rocky Mountain bighorn sheep (Ovis canadensis) (Ramsay and Sadlier 1979, Whitehead and McEwan 1980), white-tailed deer (Odocoileus virginianus) (Plotka et al. 1977a,b, 1980) and roe deer (Capreolus capreolus) (Sempere 1977, Hoffman et al. 1978). RIA techniques are subject to strict controls, but few standards exist for handling blood samples between collection and centrifugation. This is of particular importance in relation to field collections for progesterone assay, since it is known that in some species, notably cattle, progesterone is rapidly degraded in whole blood. This degradation is slower in sheep (Wiseman et al. 1982) and goats (Fahmi et al. 1985) than in cattle and it is negligible in horses and pigs (Wiseman et al. 1982). As might be expected, the amount of progesterone lost increases with the time and temperature of storage and may be influenced by the anticoagulant used. In ewes Wiseman et al. (1982) found that blood stored in heparinized tubes at 22 C for 24 hours showed a significant decrease in plasma progesterone but blood without anticoagulant did not. In goats a significant progesterone decline occurred in samples stored at room temperature (22 C), regardless of anticoagulant, but this decline was not significant if the tubes were kept at 5 C (Fahmi et al. 1985). In cattle progesterone concentrations decline dramatically with time, regardless of the technique used. The decline is greatest in heparinized samples held at 22 C, in which progesterone concentrations are reduced to 5% of their original value after 12 hours (Wiseman et al. 1982, Vahdat et al. 1984). The decline in progesterone concentration in whole blood is greatly reduced if the red blood cells are removed shortly after collection (Vahdat et al. 1984). Although Lesniewski et al. (1984) found a 17% decrease in assayable progesterone in stored plasma, this only occurred after prolonged incubation (48 hours) at a relatively high temperature (35 C). This suggests that, in addition to rapid plasma separation, plasma should be immediately frozen to prevent further progesterone decline. Muskoxen, cattle, and sheep all belong to the Bovidae and have many common characteristics. We, therefore, felt that it was necessary to investigate the behavior of progesterone in whole muskox blood stored under various conditions, in order to optimize our techniques of sample collection in field and laboratory situations. This study was supported by Natl. Sci. and Eng. Res. Counc. Can., operating grant A2759 and infrastructure grant A2793. Samples were assayed by Reprod. Endocrine Assay Systems, Reprod. Endocrine Lab. West. Coll. Vet. Med., Saskatoon. We especially thank S. Cooke for advice regarding the assay and C. Stevens for skilled and dedicated care of the animals.