Mammalian hair follicles are complex multicellular structures in the skin, which produce hair fibre under the influence of locally produced and systemic signalling systems. Investigation to determine mechanisms of regulation, follicular responses and the importance of nutritional supply have utilised a number of in vivo and in vitro approaches. Included in these are studies on isolated intact anagen secondary follicles singly or in groups with incubation in culture medium. These utilise techniques developed for investigation of follicles from human skin. Results from selected studies reviewed here demonstrate differences in capacity for hair growth and protein synthesis between secondary follicles from Angora and cashmere-bearing goats. Mohair follicles were shown to exhibit faster hair shaft elongation both in vivo and in vitro, to have greater DNA content per follicle and to deposit significantly more protein per follicle and per unit of DNA. Incubation of anagen mohair and cashmere follicles in the presence of melatonin or prolactin showed positive responses in hair shaft growth and protein synthesis to both signalling molecules. This result indicated directly acting effects on the follicle in addition to any indirect effects arising at a whole animal level in response to, for example, variation in photoperiod. Similarly, epidermal growth factor was shown to alter elongation and protein synthesis in mohair follicles and to produce, at higher concentration, club hair structures similar to effects observed in other species. The vitamin biotin was shown to be important in maintaining viability of isolated sheep secondary hair follicles where supplementation increased the proportion continuing to grow. Effects on growth and apparent protein synthesis suggested comparatively lesser effects on follicles, which remained viable. Histology on follicles indicated effects of biotin deficiency in reducing proliferation of basal keratinocytes. The final study, included in this review, demonstrated that supply of the essential sulphur-containing amino acid l-methionine was necessary to maintain the viability and growth of mohair follicles. l-cysteine was not required in the presence of l-methionine, although there was evidence of an optimisation when both amino acids were present in adequate concentrations. Consideration is given to the importance of transport mechanisms and capacity to utilise absorbed nutrients when considering optimising nutritional supply to individual follicles. These may then provide targets for attainment in applied nutrition of animals in vivo.
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