Identification of 11-cis-retinal and demonstration of its light-induced isomerization in the chicken pineal gland.

Direct evidence is not available that (1) rhodopsin-like photopigment exists in the chicken pineal and that (2) the visual pigment is responsible for the light sensitivity of the gland. Therefore, the objective of this study was to test for the existence of visual pigment in the chicken pineal by means of the identification of 11-cis-retinal in this organ. 11-cis- and all-trans retinoids were extracted from light- and dark-adapted chicken pineals and analyzed by high performance liquid chromatography (HPLC) using the formaldehyde method. 11-cis-Retinal was initially identified by coelution with an authentic standard. Further characterization was carried out by collecting the retinal from the HPLC eluant, subjecting it to reduction by sodium borohydride and then identifying the derived 11-cis-retinol using HPLC. Proportions of 11-cis-retinal to total pineal retinals were also studied from decapitated heads after light and dark adaptation. Analyses of dark-adapted, pooled chicken pineals revealed equal proportions of 11-cis and all-trans retinals at 2 h after dark and at night. Two hours of light adaptation resulted in the reduction of the 11-cis proportion (from 50%) to 26% of total retinals. These observations prove that 11-cis-retinal exists in the chicken pineal and that it undergoes light-induced cis to trans isomerization in a manner similar to the visual pigment chromophores in the vertebrate retina.