Effects of season and of manipulation of circulating prolactin concentrations on deiodinase activity in cashmere goat skin

The effects of season and of manipulations of circulating prolactin concentrations on the expression of monodeiodinase type II (MDII) and monodeiodinase type III (MDIII) expression in the skin of cashmere goats were investigated. Deiodinase enzymes control the rates of synthesis and degradation of triiodothyronine (T3), a hormone implicated in the control of hair follicle activity, and so changes in expression with season or prolactin profiles may affect cashmere fibre growth and moult. There was a very high degree of variation between animals in expression of each enzyme. There was also evidence of seasonal variation in expression within individuals, with a trend towards lower levels of activity of MDII during periods of long daylength (July and April) and highest levels in December, whereas levels of MDIII were highest in July and lowest in December. Collectively, these differences with season resulted in significant changes with date in the MDIII/MDII ratio. It is concluded that the seasonal changes in deiodinase activity, and in particular in the MDIII/MDII ratio, may have an important role in the regulation of follicle activity. Levels of MD activity were poorly correlated with circulating hormone profiles. Nevertheless, since manipulation of the circulating concentrations of prolactin induced additional changes in MDIII/MDII ratios, which were associated with treatment differences in follicle activity or moult, it is concluded that seasonal changes in prolactin may determine patterns of enzyme activity, with high concentrations of prolactin being associated with reduced net levels of T3 synthesis.