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

Abstract

Sheep were treated with dexamethasone (1) as the water-soluble 21-phosphate intravenously or (2) subcutaneously, and (3) as the water-insoluble parent compound subcutaneously.In (1) the infusion was continued for 8 days and plasma· concentrations of dexamethasone exceeded 40 ng/ml. The analogue 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 fibres that made up the fleece at the time when the sheep were infused had been shed, and it was possible to defleece three of the four treated animals by brushing the wool off manually.In (2) plasma concentrations of dexamethasone reached very high levels (maximum c. 8 jlg/mi) but only for a relatively short period ( < 48 h). Wool growth was depressed by about 30 % 17 days after treatment. No fibre shedding was evident, and the animals could not be defleeced. Recovery in wool growth was almost complete 1 month after treatment.In (3) plasma concentrations of dexamethasone were in the range of 3-10 ng/ml 15 days after dosage (three out of four animals); dexamethasone could not be detected in the plasma of the fourth animal 12 days after treatment. Wool growth was decreased by about 80% 77 days after steroid administration. Three out of four treated animals could be defleeced manually and in all of them wool growth was depressed 3 months after treatment.It was concluded from this work that high concentrations of dexamethasone had to be sustained for long periods (8 days) before the majority of sheep could be defleeced manually. A similar result was ultimately achieved following 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.

Protein supply influences the nutritional penalty associated with the development of immunity in lambs infected with Trichostrongylus colubriformis

“…Corticosteroid treatment of ISIF animals provided a crude method of immuno-suppression and has previously been shown to have a wide range of effects on metabolism including a net catabolic effect that may result in reduced wool production (Panaretto, 1979) and decreased fractional synthesis rates of protein in the muscle and intestine (Huang et al, 1998;Turini et al, 2003). Their effect on intake in sheep has been varied, with small single doses of 0.1 mg dexamethasone/kg (equivalent to 0.5 mg methylprednisolone) stimulating short-term increases (Adams and Sanders, 1992) while larger single doses of 6 mg dexamethasone/kg have resulted in a short-term depression of intake (Panaretto, 1979).…”

“…Their effect on intake in sheep has been varied, with small single doses of 0.1 mg dexamethasone/kg (equivalent to 0.5 mg methylprednisolone) stimulating short-term increases (Adams and Sanders, 1992) while larger single doses of 6 mg dexamethasone/kg have resulted in a short-term depression of intake (Panaretto, 1979). The chronic weekly administrations of 1.3 mg/kg LW to IS animals in the current study, perhaps surprisingly, did not cause a reduction in wool growth, but did stimulate fat deposition, reduced muscle deposition and had no significant effect on intake, observations that are consistent with those of Greer et al (2005b).…”

Some Effects of Dexamethasone on Nucleic Acid Metabolism in Skin of Merino Sheep

“…Plasma dexamethasone concentrations were determined by radioimmunoassay (Panaretto 1979). The limit of sensitivity of the assay was 3· 1 ng ml-'.…”

“…Adrenal glucocorticoid hormones or their analogues are known to stimulate or inhibit anagen wool follicles (Chapman and Bassett 1970;Panaretto 1979). In order to induce shedding of the majority of wool fibres, Panaretto and Wallace (1978a) and Panaretto (1979) found that it was necessary to maintain elevated glucocorticoid concentrations in the plasma of Merino sheep for 8 days.…”

“…In order to induce shedding of the majority of wool fibres, Panaretto and Wallace (1978a) and Panaretto (1979) found that it was necessary to maintain elevated glucocorticoid concentrations in the plasma of Merino sheep for 8 days. Although the molecular mechanism of action of this class of chemicals on wool growth remains unknown, several studies with various cells in tissue cultures suggested that the inhibitory effects of glucocorticoids were associated with reductions of the rate of synthesis of deoxyribonucleic acid (Fodge and Rubin 1975;Armelin and Armelin 1977).…”