Dexamethasone Concentrations in Ovine Plasma During its Intravenous Infusion, its Relation to the Production of Some Endogenous Hormones, and Some of the Effects on Wool Growth

Abstract

Plasma concentrations of dexamethasone have been measured in sheep during an 8-day infusion of dexamethasone-21-phosphate. The dexamethasone concentration profiles generally revealed a reproducible pattern with three phases-a peak during the first 48 h infusion which was followed by falling concentrations during the next 5 days, and a small increase in dexamethasone concentration during the final 24 h infusion was not uncommon. The pattern of dexamethasone concentrations was retained when dosage was arranged in such a way as to infuse increasing quantities of hormonal analogue as infusion progressed. Aspects of the metabolism of the analogue are discussed.Endogenous thyroxine and cortisol were significantly depressed during infusion. In these experiments wool was completely shed in three out of four animals dosed at a rate of 8·5 mg dexamethasone/kg o · 75 • The recovery of wool growth to its pretreatment values occurred by about one month after infusion. The consumption of food and body weight increases were satisfactory during the post-infusion period.

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

“…The concentration profiles for dexamethasone here were similar to those of Panaretto and Wallace (1978b). Leish and Panaretto (1978) reported similar concentration patterns using [3H]dexamethasone.…”

“…The peaks in steroid concentration have not been investigated here. The possibilities that exist to explain the initial peaks have been discussed by Panaretto and Wallace (1978b). The secondary peaks observed during the final 48 h infusion might represent rises in unconjugated steroid particularly in the older sheep used.…”

Studies on Intravenously Infused Dexamethasone in Sheep

“…This approximated the dose, 8·5 mg kg-o. ?S, which was reported to cause the shedding of the whole fleece in the majority of sheep so treated (Panaretto and Wallace 1978a).…”

“…In animals infused intravenously with dexamethasone over a period of 8 days, Panaretto and Wallace (1978a) reported reproducible plasma concentration profiles with a peak during the first 48 h of infusion followed by falling levels with a small increase during the final days of infusion. Subsequently it has been found that the slow intravenous infusion of glucocorticoid analogues over an 8-day period caused wool shedding in a greater proportion of the total fibres than when the same dose was infused over a shorter period (Panaretto and Wallace 1978b).…”

“…1965) but only recently was its efficacy as a defleecipg agent evaluated and its plasma concentrations measured during its administration (Panaretto et al 1975;Panaretto and Wallace 1978a).…”