Previous research has established that growth hormone pulse amplitude declines with increasing age. The purpose of this study was to determine whether this decline is associated with (1) increased pituitary response to somatostatin, and/or (2) increased number or affinity of pituitary somatostatin receptors. In the first study, pituitary slices from young (3–4 months), middle-aged (12–14 months), and old (22–24 months) male Fischer 344 rats were superfused with minimal essential medium (1 ml/min) and fractions collected at 5-min intervals. Tissues were stimulated with 10–7M hpGRF (1–44) for 1 min and, 40 min later, with hpGRF in the presence of 5 × 10–9M somatostatin-14 or somatostatin-28. Two pituitaries from each age group were super-fused simultaneously and the experiment replicated 4 times. Growth hormone release was measured by radioimmunoassay. In a second study, somatostatin receptors in purified pituitary membranes from the three age groups were compared using iodo-[Tyr⁰]-D-Trp8 somatostatin-14. Animals from each age group were pooled, membranes extracted, and incubated with increasing doses of cold peptide. Binding characteristics were analyzed by Scatchard analysis and Ka and Bmax calculated. Results indicated that (1) basal growth hormone release diminished both with age and somatostatin administration, (2) GRF-induced release of growth hormone was similar in all age groups when data were expressed as percent increase from baseline, and (3) in the presence of somatostatin-14, GRF-induced release of growth hormone was attenuated in old as compared to young or middle-aged rats (p < 0.01). Although somatostatin receptor number and affinity appeared to diminish with age, these differences were not statistically significant. We conclude that postreceptor changes in pituitary response to somatostatin contribute to diminished growth hormone release with age.

Keywords:
Aging, Growth hormone, Somatostatin
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© 1989 S. Karger AG, Basel
1989
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