title: The effect of H₁ and H₂ receptor antagonists on melanogenesis.
abstract: BACKGROUND
  Histamine was found to stimulate melanogenesis in cultured human melanocytes specifically mediated by histamine H 2 receptors via protein kinase A activation. Based on this finding, the effect of topically applied H 2 antagonist on UVB-irradiated Guinea pigs' skin was examined and found to be suppressive on the post-irradiation melanogenesis.
  
  
  OBJECTIVE
  In this study, we tried to explore the role of topically applied H 1 and H 2 receptor antagonists, in inhibition of UVB-induced melanization.
  
  
  METHODS
  The effect of topically applied H 1 and H 2 receptor antagonists in inhibition of melanization was done clinically and histochemically using Fontana Masson and DOPA reactions compared with placebo.
  
  
  RESULTS
  The post-irradiation pigmentation was found to be brownish/black instead of the original light brown color. This color change occurred below the shaved orange-red fur suggesting a switch of melanogenesis from pheomelanin to eumelanin. The induced pigmentation was suppressed by topically applied H 2 antagonist while both H 1 antagonist and vehicle had no effect. The microscopic examination showed that the keratinocytes in the H 2 antagonist-treated areas contained few melanosomes while the nearby dendrites are full of them.
  
  
  CONCLUSIONS
  H 2 antagonists' inhibition of UVB-induced pigmentation is not only due to suppression of melanization but also due to a specific action on melanosomes' transfer.
authors.affiliation: Department of Dermatology, Al-Minya University, Al-Minya, Egypt.
authors.forename: Tag S
authors.initials: TS
authors.lastname: Anbar
authors.forename: Wiete
authors.initials: W
authors.lastname: Westerhof
authors.forename: Nafisa A
authors.initials: NA
authors.lastname: Badawy
authors.forename: Amal T
authors.initials: AT
authors.lastname: Abdel-Rahman
authors.forename: Talal A
authors.initials: TA
authors.lastname: Abd El-Raheem
authors.forename: Saadea R
authors.initials: SR
authors.lastname: Sayed
authors.forename: Azza H
authors.initials: AH
authors.lastname: Ali
authors.forename: Hossam
authors.initials: H
authors.lastname: Salem
mesh_terms: D000818:Animals; D006801:Humans; D015603:Keratinocytes / Q000528:radiation effects; D008544:Melanocytes / Q000378:metabolism; D020460:Melanosomes; D011970:Receptors, Histamine H2; D012880:Skin Pigmentation; D014466:Ultraviolet Rays
chemical_list: D011970:Receptors, Histamine H2