Age-related changes in growth hormone (GH) cells in the pituitary gland of male mice are mediated by GH-releasing hormone but not by somatostatin in the hypothalamus

Using immunocytochemical and morphometric methods, we examine changes with age of growth hormone-releasing hormone (GHRH) in the arcuate nucleus (ARC), changes of somatostatin (SS) in the periventricular nucleus (PeN) of the hypothalamus, and changes of growth hormone (GH) cells in the anterior pituitary in male C57BL/6J mice at 2 months old (2 M), 4 M, 12 M and 24 M. The number of GHRH-ir neurons decreased significantly with age. The number of SS-ir neurons did not differ significantly between these all age groups. The volume of the anterior pituitary and the number of adenohypophysial parenchymal cells fell dramatically from 4 to 12 M. The proportion of GH-ir cells decreased significantly with age, and in absolute number from 4 to 12 M and in size from 2 to 4 M and from 4 to 12 M. These results suggest that the reduction in GH-ir cells in male mice is modulated by the reduction in GHRH-ir neurons, but not by SS-ir neurons.