The absence of an age-related change in the pituitary response to growth hormone-releasing factor in rats

The capability of the anterior pituitary gland to secrete growth hormone (GH) in response to an intravenous injection of growth hormone-releasing factor, hpGRF-44, was evaluated in male rats ranging from 22 days to 24 months of age. The increase in GH concentrations following a submaximal dose of hpGRF-44 (0.5 microgram/kg) was similar among the different aged rats suggesting there is no age-related change in pituitary sensitivity to hpGRF-44. Likewise, the response to a maximal dose of this peptide (25 micrograms/kg) was not different in young and old animals indicating there is no decrease in the readily releasable pool of GH. Thus, the age-related changes in GH secretion observed in rats do not appear to be due to a change in the pituitary response to the hypothalamic growth hormone-releasing factor.