Effects of the Pineal Gland Upon the Hair Cycles in Mice

Abstract

Hair growth in rats and mice is cyclic, each hair follicle having alternate periods of growth and rest. Also, the hair follicles develop in waves of hair growth which cover gradually the skin with a new coat of hair (1, 2, 3, 4, 5). Diverse endocrine factors may be stimulants or inhibitors, modifying the initiation, advance and characteristics of the hair wave (6, 7, 8, 9, 10). The inhibitory honnonal factors appear to be of pituitary origin, and its effect on the adrenals and gonads (6, 9, 10, 11). The stimulating hormonal factors are in part hypophyseal and in part extrahypophyseal (10, 11). Part of the stimulating action of the pituitary is produced by means of the thyroid (7, 8, 12, 13). The nervous system also intervenes in the regulation of the hair cycle. Slow hair waves were found in hemiarquidecortieated rats. This inhibitory effect is that of gonad stimulation, as shown by its suppression through castration (14). Lesions of the olfactory cortex, especially the anterior and internal part of the tuberculum olfactoriurn, resulted in slower pace of advance of hair waves both in normal and in castrated mice (15). These data suggested the hypothesis of the neurohormonal control of the hair growth waves in rats and mice. Thus, mechanisms probably located in the nervous system, would regularly alter the balance between the stimulating and inhibitory factors (15). The pineal gland is considered to be a neuroendocrine transducer and to regulate ovarian function in mammals (16). Melatonin, active principle of the pineal gland, lightens the amphibian skin through its effect upon melanocytes