[Study of growth hormone in spontaneous dwarf rat]

In 1977, in the Research Laboratories, Morishita Pharmaceutical Co. Ltd., we were fortunate to discover that small mutant rats named Spontaneous Dwarf Rat (gene symbol dr), inherited an autosomal recessive. In previous papers, we reported that these rats might be characterized by a defect of growth hormone (GH). In this paper, we carried out the studies of the secretory cells and GH deficiency in the pituitary glands of +/dr and dr/dr rats using immunohistochemistry, electron microscopy and acrylamide gel electrophoresis. ACTH, PRL and GH secretory cells in the pituitary gland respectively identified with antiserum to porcine ACTH, rat PRL and ovine GH by indirect method of immunohistochemistry. In the pituitary of dr/dr rats, ACTH and PRL secretory cells were confirmed, but none of the cells were stained with ovine GH antiserum. Using electron microscopy, GH secretory cells could not be identified precisely although the other cells were identified in the pituitary gland of dr/dr rats. With the analysis of pituitary homogenate by acrylamide gel electrophoresis, PRL band appeared in dr/dr rats but GH did not. These results obviously indicated that the inhibition of body weight in dr/dr rats was caused by the absence of GH in the anterior pituitary. Therefore, the Spontaneous Dwarf Rat may be a useful animal model for human dwarfism caused by isolated GH deficiency.