Age-related changes in growth hormone (GH)-releasing hormone and somatostatin neurons in the hypothalamus and in GH cells in the anterior pituitary of female mice.

We have observed growth hormone-releasing hormone (GHRH)-immunoreactive (ir) neurons in the arcuate nucleus (ARC), somatostatin (SS)-ir neurons in the periventricular nucleus (PeN), and pituitary growth hormone (GH)-ir cells in female C57BL/6J mice at 2 months old (2 M), 4, 12 and 23 M, using immunocytochemical and morphometric methods. The number of GHRH-ir neurons decreased with age. The number of SS-ir neurons increased from 2 to 4 M, but decreased after 4 M. The volume of the anterior pituitary and the number of adenohypophysial parenchymal cells fell from 12 to 23 M. The proportion of GH-ir cells decreased significantly from 2 to 4 M and decreased in number from 12 to 23 M as well as in size from 2 to 4 M and from 12 to 23 M. Our results show that both GHRH-ir neurons and SS-ir neurons are fewer in old female mice, but the ratio of the number of SS-ir neurons to GHRH-ir neurons increases in old females. We suggest that the fall in the number and size of GH-ir cells in the pituitary gland with age may be involved in the increase in the ratio of the number of SS-ir neurons to GHRH-ir neurons in the hypothalamus in female mice, as well as in males.