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Short Term Changes in Plasma Corticoids in Dairy Cattle¹

Purdue University, Lafayette, Indiana 47907

Abstract

Plasma cortisol, corticosterone and total corticoids less progestins were determined in samples of blood that were collected via indwelling jugular vein cannulae, for 3 to 12 hr. at intervals of 10, 15 or 60 minutes. During blood collection each animal was subjected to one or more of the following treatments: intravenous injection of approximately 30 µg of corticosterone, ¹⁴C-corticosterone or ¹⁴C-cortisol and/or psychological stimulation by manipulation of the head and neck, anticipation of feeding and removal of companion animals.

The injection of 30 µg ¹⁴C-corticosterone did not cause an increase in endogenous corticosteroids; however, corticoid increases were associated with injection of similar quantities of ¹⁴C-cortisol and unlabeled corticosterone. The reason for the difference in response is unknown and seems paradoxical since the administration of glucocorticoids is known to suppress ACTH release. Increases in plasma corticoids were associated with the psychological stimuli used. However, the response varied greatly between animals. Increases were as much as four times for total corticoids and five times for cortisol in plasma from blood collected at consecutive 10-min. intervals. Short interval rates of decrease were considerably less as compared to short interval rates of increase. The sum of cortisol and corticosterone was not equal to total corticoids (total-protein-bindable steroids less proges-tins). These data indicate the presence of another steroid(s) which is released during psychological stress. Plasma levels of compounds corresponding to standard cortisone and deoxycorticosterone did not account for the differences observed.

¹ Paper No. 4437, Purdue University Agricultural Experiment Station. A contribution from the Department of Animal Sciences.

² Fellow, National Aeronautical and Space Agency, Grant No. 2779–82; present address: Ohio Agricultural Research and Development Center, Wooster 44691.