The relationship between the size and shape of the wool follicle papilla and wool growth : with special reference to the effect of thyroxine

The wool follicle papilla which invaginates the follicle bulb at its proximal end has been suggested by Rudall (1955) as being the “chief determiner of the characteristics of the fibre produced”. It is variable size and shape have been shown by Rudall (1935, 1955) to have a direct influence of fibre output. The cross-sectional shape of the papilla has been related to the symmetry of the fibre in sheep, humans and rabbits by Durvard and Rudall (1955) and in birds by Lillie (1942). The position of mitotic figures in the wool follicle bulb around the periphery of the papilla (Auber (1950)), indicate a general cellular movement of the primordial of the fibre away and upwards from the papilla perimeter and the presence of blood vessels within the structure (Ryder (1955)) suggest a causal influence on wool growth. The variable occurrence of medulla and changes in wool fibre diameter have already been associated with changes in the size and shape of the papilla (Rudall (1935a), Auber (1950)) anad there are a number of reports that the diameter of wool fibres change with seasonal condtions (Norris and Claassens (1931), Burns (1931) and Nichols (1933)). Histochemically there is considerable evidence to suggest the probable importance of the papillae of human hair follicles contain many substances which are incorporated in the fibre body. (Montagna (1956), Braun-Falce (1956)) and Sylven (1950) believes that some compounds which play a role in supplying sulphur for keratinisation are derived from the papilla. Wool production is known to vary with season (Coop (1953)). Nutrition (Marston (1948)) and hormonal status (Magsoon (1950) , Marston and Pierce (1932) and Lindner and Fergusin (1956)), while Rudall (1955) has shown that the size and shape of the wool follicle papilla varies throughout the year, characterised by a marked depression in its length in winter when wool production is at a minimum (Coop (1953)). This parallel movement is suggestive of a site of action of these factors which stimulate or depress fibre output. It has been well shown by hart (1954, 1955, 1957), Labban (1957), Coop and Clark (1958), that the administration of exogenous thyroxin to sheep can substantially increase wool production. Thyroxin is known to play a fundamental role in control of general body metabolism and it is conceivable that the stimulating effect of exogenous thyroxin on fibre output is a mitogenic one in that the principal function of the thyroid hormone is that of a catalyst for the oxidative reactions of the body cells (Harper (1959)). Adequate oxygen and intercellular energy from oxidative processes are essential for normal mitotic activity (Bullough and Johnson (1951)). An index of the degree of mitotic activity in the follicle bulb would appear, from the results of Rudall (1955), to be the variation in size and shape of the papilla in that the primordia of fibre cells apparently “bud” from, or in the vicinity of, the papilla periphery. The experimental work described here was planned with the view of further elaborating the possible determinative role of the papilla in fibre growth. Dimensional changes of the papilla and of the fibre produced were studies in sheep whose wool production varied normally with season, (coop (1953) and in sheep artificially stimulated, by the administration of l-thyroxin, to produce wool at a level above the normal. (Hart (1954, 1955, 1957)).