Growth hormone internalization in mitochondria decreases respiratory chain activity.

Growth hormone (GH) is a signaling molecule regulating cell proliferation, differentiation and metabolism via activation of specific cell surface receptors and subsequent triggering of signal transduction pathways. This is associated with GH/GH receptor internalization and accumulation of GH in several subcellular compartments, including mitochondria. To assess the functional relevance of such mitochondrial accumulation, we first confirmed the occurrence of mitochondrial GH uptake ex vivo as early as 10 min after (125)I-GH injection to the rats.