Pineal regulation of growth hormone synthesis and release in blinded and blinded-anosmic male rats1

Removal of eyes from young male rats led to slight retardation in body weight gain, tibial length, and tail length compared with respective parameters measured in normal rats. Young rats lacking eyes and pineal glands presented body weights, tibial lengths, and tail lengths that approached normal. Pituitary levels of radio-immunoassayable growth hormone (GH) were significantly lower in blinded rats with intact pineal glands compared with levels in normal or blinded-pinealectomized rats. Plasma levels of GH tended to be lower in blinded and blinded-pinealectomized rats relative to normal levels; however, due to the wide range of GH levels in all groups, no statistically significant differences were observed. Blindness and anosmia in young male rats severely retarded body weight gain, tibial length, and tail length relative to respective parameters of normal, blinded, blinded-pinealectomized, and blinded-anosmic-pinealectomized rats. Blinded-anosmic-pineal-ectomized rats grew subnormally, with body weights equal to those of blinded rats. Plasma GH concentrations were low in blinded-anosmic rats, but due to the overlapping values, statistical significance was not attained. In general, the size of reproductive organs correlated well with inhibition of body growth, being moderately smaller in blinded rats and markedly so in blinded-anosmic rats. These differences in the size of the reproductive organs were not observed if pineal-ectomy was performed simultaneously with blinding and olfactory bulb removal. It is concluded that, in young male rats that are deprived of light by blinding, there is a dramatic inhibition of GH production and release by the pituitary gland. This response, like the response of the reproductive organs, is enhanced when rats are deprived of both smell and light. These phenomena only occur in the presence of the pineal gland. Therefore, the pineal gland plays an important role in these processes. It is further concluded that anosmia or perhaps non-specific surgical stress may alter GH synthesis and/or release from the pituitary gland.