FIBER GROWTH INITIATION IN HAIR-FOLLICLES OF GOATS TREATED WITH MELATONIN

The sequence of structural changes in goat hair follicles was investig ated using melatonin implants to advance and synchronize spring hair g rowth. Ten pasture fed cashmere wethers each received a controlled rel ease formulation of 70 mg of melatonin on September 1 1989, and showed plasma melatonin elevated above physiological levels over 14 days pos t-treatment (914 +/- 154 pg/ml [mean +/- SEM] on day 14). In ten untre ated animals, daytime plasma melatonin was 19.9 +/- 4.7 pg/ml. Histolo gical examination of skin biopsies taken over the 14 days from the sta rt of the experiment showed that primary hair follicles of goats with manipulated hormone levels had initiated fiber growth (entered proanag en), whereas-primary follicles of untreated goats largely remained in the quiescent phase (telogen). A standardized terminology was used to describe the sequence of events during induced proanagen. Structural r eorganization of follicles began in treated animals between days 6 and 12 post-treatment, and emergent fibers grew by day 24. Advancement of spring fiber growth was associated with a suppression of the normal r ise in plasma prolactin concentration. Prolactin levels in untreated g oats increased from 7.4 +/- 1.8 ng/ml on day 1 to 12.8 +/- 1.6 ng/ml o n day 14, but declined in treated goats from 6.3 +/- 2.3 ng/ml to 2.2 +/- 0.8 ng/ml over the same period. (C) 1993 Wiley-Liss, Inc.