Modulation of rat pituitary growth hormone by 670 nm light

In rat pituitary somatotrophs, cytochrome oxidase is co-packaged with growth hormone (GH) in some storage granules. Because this enzyme is thought to be the molecular photoacceptor of red-near infrared light, and because exposure of diverse tissue systems to 670 nm visible light affects their biological responses (e.g., wound healing), we tested the idea that exposure of rat pituitary cells, rat hemi-pituitary glands and rat pituitary homogenates to 670 nm light in vitro might alter GH storage and/or release. In this report we offer evidence to show that light treatment (670 nm, 80 s, intensity 50 mW/cm2, energy density 4 J/cm2) up-regulates GH release, in part by breakdown of intracellular, oligomeric GH as determined by gel filtration chromatography.