Retinal growth hormone in perinatal and adult rats

Growth hormone (GH) mRNA and protein have recently been localized in the neural retina of embryonic chicks, in which exogenous GH promotes cell survival. GH is also expressed in the rat CNS, in which it has neuroprotective roles, although its presence in the rat neural retina is unknown and is the focus of the present study. GH immunoreactivity, to a 22-kDa protein, was present in extracts of fetal (embryonic day [ED]17) eyes and in extracts from the neural retinas of newborn pups, comparable to GH immunoreactivity in pituitary extracts. The GH immunoreactivity in the neural retina was widespread but was most intense in large rounded cells in the retinal ganglion cell (RGC) layer and in the optic fiber layer derived from the axons of the RGCs. A 693-bp cDNA was also generated by the RT-PCR of RNA extracted from the eyes of ED17 rats and from the neural retinas and eyes of newborn rats, when amplified in the presence of oligonucleotide primers for the rat GH cDNA. Expression of the GH gene in the neural retina was also shown by specific in situ hybridization of an antisense GH riboprobe to cells in the neural retina, particularly those in the RGC layers of fetal and adult rat eyes. These results demonstrate GH expression in the neural retinas of fetal, newborn, and adult rats, in which retinal GH might have neuroprotective roles.