THE LOCALIZATION AND CHARACTERIZATION OF INSULIN-LIKE GROWTH-FACTOR-IRECEPTORS AND THE INVESTIGATION OF MELATONIN RECEPTORS ON THE HAIR-FOLLICLES OF SEASONAL AND NONSEASONAL FIBER-PRODUCING GOATS

To define the hormonal influences that are directly involved in the ha ir follicle cycles of animals with differing patterns of fibre growth and moulting, we have investigated the possible presence of IGF-I and melatonin receptors on the dermis and hair follicles of cashmere and A ngora goats, sampled in February, March and June, using quantitative i n vitro autoradiography. The presence of IGF-I receptors in the dermis of both breeds of goat was determined using cryostat sections incubat ed with 50 PM I-125-labelled IGF-I in the presence or absence of 50 nM IGF-I. Sections of the growing tip of deer antlers containing the car tilaginous zone, a tissue known to contain high concentrations of spec ific IGF-I receptors, were used as a positive control. As the producti on of antler velvet uniquely involves the generation of hair follicles Ae novo, the presence of IGF-I receptors in the velvet-producing regi on was also investigated. In both breeds of goat, specific I-125-IGF-I binding was localised over the inner and outer root sheath, the matri x, the germinal matrix, the dermal papilla and the sebaceous glands an d satisfied the basic kinetic criteria considered to be representative of a specific IGF-I receptor. Analysis of saturation isotherms using a one-site binding model revealed dissociation constants (K-d) in the range 0.1-0.9 nM and theoretical maximal numbers of binding sites (B-m ax) between 21.4 and 45.6 fmol/mg tissue. K-d and B-max values derived from cashmere and Angora goats sampled at different times of the year did not differ significantly between breeds or sampling times. Specif ic I-125-IGF-I binding was also localised to the developing follicles on the deer antler dermis. The presence of melatonin receptors within the goat dermis was also investigated. Sections were incubated with 10 0 pM 2-[I-125]iodomelatonin with or without 0.1 mu M melatonin, along with sections of sheep pan tuberalis which are known to contain high l evels of high-affinity melatonin receptors. No displaceable 2-[I-125]i odomelatonin binding was found on any sections of the cashmere or Ango ra skin analysed. It is therefore concluded that melatonin receptors a re not present on the hair follicles or associated structures. IGF-I r eceptors are present on the hair follicle and sebaceous gland and may be involved in the growth of both seasonally and non-seasonally produc ed fibre and in the development of antler velvet.