الفهرس 
Introduction and aim of the workOnly 14 pages are availabe for public view
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Abstract
The color of hair, skin, and eyes in animals mainly depends on the ~uantity, quality, and distribution of the pigment melanin. Melanocytes are responsible for the synthesis of melanin within membrane-bound organelles (melanosomes) and the transport of melanosomes to keratinocytes. Melanocytes in mammals and birds produce two chemically distinct types of melanin pigments, the black to brown eumelanin and the yellow to reddish pheomelanin. Typical eumelanin is a heteropolymer consisting of different dihydroxyindolic and phenolic Units. This pigment appears to be chemically resistant and it absorbs a wide range of ultraviolet radiation and visible light. Pheomelanin is a hetero-polymeric pigment consisting of phenolic and mlfur-containing benzothiazine units, which can be formed from either 2and 5-S-cysteinyldopa. This melanin is less stable and its UV -absorbing capacity is less pronounced. In addition, UV irradiation of this pigment has been shown to lead to generation of free radicals. The cutaneous melanin is always mixture of eumelanin and pheomelanin.
This study was carried out on 20 female guinea pigs with a patchy black and yellow hair. Their hair was shaven from dorsal skin of each animal by using an electric shaver to avoid injuring of the epidermis. The dorsal skin of each animal was classified into five areas.
Area 1: (control area) not exposed to NB-UVB or treatment with drugs. Area 2: Exposed to NB-UVB and treated with Vaseline twice daily.
Area 3: Treated with topical Hz antagonist (2% famotidine in Vaseline).