Reduction of synthetic and mitotic activity in the wool follicle by catecholamines

Abstract

Literature evidence on the effects of catecholamines on wool growth is scant and the short-term effects have not been investigated. Since catecholamines are relatively short-lived, three approaches were adopted to investigate their effects on cellular events in the wool follicle over periods as short as 4 h. In vitro culture of skin revealed a reduction of DNA synthesis in response to either adrenaline or noradrenaline added to the media (P < 0.001) in a dose-dependent manner (P < 0.001). Intradermal injections of adrenaline and noradrenaline significantly lowered the rate of cell division in wool follicles in comparison with control sites in vivo (P < 0.05). These results indicate that the catecholamines can rapidly lower the rate of proliferative events in the wool follicle. The left superior cervical ganglion was removed from 18 sheep. The animals were exposed to a cold environment and ear temperature was monitored to indicate the likely release of noradrenaline in the skin of the cheeks or adrenaline from the adrenals. With respect to the sympathectomized side, a reduction in ear temperature on the unoperated side was associated with lowered mitotic rate at the unoperated cheek site (P < 0.026). However, when the temperature of the unoperated side was not lowered, mitotic rate was not consistently lower on one side with respect to the other. Physiological levels of noradrenaline therefore mimicked the effects observed during the pharmacological studies, and the catecholamines may therefore play an important role in the regulation of wool growth.