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      Decreased Stimulation of Adenylate Cyclase by Growth Hormone-Releasing Factor in the Anterior Pituitary of Old Rats

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          Adenylate cyclase activity was studied in anterior pituitary homogenates from young adult (6 months) and old (20 and 24 months) male rats. Basal, NaF-, GTP-, 5’-guanylimidodiphosphate (Gpp(NH)p)- and forskolin-stimulated activities were similar in the three groups, implying that the stimulatory guanyl nucleotide regulatory binding site (NS) and the catalytical unit were unaffected by aging. Vasoactive intestinal peptide (VΙP)-stimulated adenylate cyclase activity was also identical in the three groups. The efficacy (i.e., the maximum effect) of growth hormone-releasing factor [GRF(1-29)-NH<sub>2</sub>] on adenylate activity was reduced by 45–49% in old and senescent rats with no change in peptide potency (i.e., the concentration required for half-maximal enzyme stimulation). These results suggest that aging induced a selective loss of functional GRF receptors but influenced neither the coupling between receptors, NS and the catalytic unit nor the efficacy of the catalytic unit per se.

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          Author and article information

          S. Karger AG
          01 April 2008
          : 44
          : 4
          : 429-432
          aDepartment of Biochemistry and Nutrition, Medical School, Université Libre de Bruxelles, Brussels; bUCB Research Laboratories, Braine l’Alleud, Belgium
          124682 Neuroendocrinology 1986;44:429–432
          © 1986 S. Karger AG, Basel

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          Pages: 4
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