Comparisons of the Plasma Steroid Concentration Profiles and Wool Growth Responses After Administration of Two Forms of Dexamethasone to Sheep

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Abstract
Sheep were treated with dexamethasone (1) as the water-soluble 21P i.v. or (2) s.c. and (3) as the water-soluble water-insoluble parent compound s.c. In (1) the infusion was continued for 8 days and plasma concentrations of dexamethasone exceeded 40 ng/ml. The analog quickly disappeared from the circulation after the infusion was stopped. Compared with pretreatment values wool growth decreased by about 80% 17 days after cessation of the infusion. By 31 days, wool growth was almost back to normal. At this stage most of the fibers that made up the fleece at the time when the sheep were infused were shed and it was possible to defleece 3 of the 4 treated animals by brushing the wool off manually. In (2) plasma concentrations of dexamethasone reached very high levels (maximum concentration 8 .mu.g/ml) but only for a relatively short period (< 48 h). Wool growth was depressed by about 30% 17 days after treatment. No fiber shedding was evident and the animals could not be defleeced. Recovery in wool growth was almost complete 1 mo. after treatment. In (3) plasma concentrations of dexamethasone were in the range of 3-10 ng/ml 15 days after dosage (3 out of 4 animals) dexamethasone could not be detected in the plasma of the 4th animal 12 days after treatment. Wool growth was decreased about 80% 77 days after steroid administration. Out of 4 treated animals 3 could be defleeced manually and in all of them wool growth was depressed 3 mo. after treatment. Apparently, high concentrations of dexamethasone had to be sustained for long periods (8 days) before the majority of sheep could be defleeced manually or after an undesirably prolonged period of wool growth depression when relatively low concentrations of dexamethasone were sustained for > 15 days. Very high steroid concentration for about 2 days did not have sufficient effect to permit defleecing.