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Effect of age on the beta-adrenergic receptor population in the longitudinal muscle layer of the rat ileum
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24 months 5454 __.690 ( P < 0.002). The underlying cause of this finding remains to be explored. No significant differences were recorded for myelinated axons which account for 1-2% of the total axon population of the trunk. The morphological data for the SCG presented above are consistent with the finding that the activity of tyrosine hydroxylase [4] and the level of its mRNA [3] are undiminished in the aged rat SCG. These data suggest that the cervical ganglionic compo-
nent of the sympathetic system of the rat is essentially unchanged in old age. References 1 Baker, D.M. and Santer R.M., Mech. Aging Dev., 139 (1988) 139-145. 2 Gundersen, H.J., J. Microsc. 143 (1985) 3-45. 3 Kedzierski, W. and Porter, J,C., Mol. Brain Res.; 7 (1990) 45-51. 4 Reis, D.J. et al., Brain Res., 136 (1977) 465-474.
Effect of age on the beta-adrenergic receptor p o p t / t i o a in the muscle layer of the rat ileum D.M. Baker 1, S.P. Watson 2 and R.M. Santer 3 J Department of Surgery, City Hospital, Nottingham, e Department of Pharmacology, Unioersity of Oxford, Oxford, and ~ Department of Anatomy, University of Wales College of Cardiff, U.K.
Morphological and histochemical evidence suggests that the influence of the sympathetic innervation on intestinal function declines with age [1,2]. The present study investigates functional consequences of this age-related reduction in the sympathetic innervation of the small intestine by assessing pharmacological responses of the betaadrenoceptor population in the longitudinal muscle layer of the muscularis externa of the rat ileum. Longitudinal muscle strips of the ileum were prepared from Wistar rats aged 6 or 24 months (5 animals in each group) and mounted under tension in organ baths. An initial concentration response curve to carbachol was determined. Once a reproducible response to carbachol (including a maintained plateau phase) had been obtained, a concentration response curve for isoprenaline-induced relaxation following the pre-contraction with carbachol was determined in the presence of the alpha-adrenoceptor antagonist phentolamine. The EC50 values, Hill slopes and maximal tension for carbachol-induced contrac-
tion of the ileal muscle strips were not significantly different between the two age groups. Neither were the EC50 and Hill slope values for concentration response curves for isoprenaline-induced relaxation different between the two age groups. However. the maximal degree of relaxation developed by isoprenaline in strips precontracted with carbachol was about 25~ ( P < 0.02) smaller in the 24 month animals. This suggests that with age there is either a decrease in the beta-adrenoceptor number in relation to the muscarimc receptor density or a decrease in the coupling of the beta.adrenoceptor with adenylate cyclase, thus providing pharmacological evidence for the decline with age in the influence of the sympathetic system on intestinal function. References 1 Baker, D.M. and Santer. R.M.. Mech. Age. Dev., 42 ~1988) 139-145 and 147-158. 2 Baker, D.M. and Santer, R.M., J. Histochem. Cytochem,, 38 (1990) 525-531.
24 months 5454 __.690 ( P < 0.002). The underlying cause of this finding remains to be explored. No significant differences were recorded for myelinated axons which account for 1-2% of the total axon population of the trunk. The morphological data for the SCG presented above are consistent with the finding that the activity of tyrosine hydroxylase [4] and the level of its mRNA [3] are undiminished in the aged rat SCG. These data suggest that the cervical ganglionic compo-
nent of the sympathetic system of the rat is essentially unchanged in old age. References 1 Baker, D.M. and Santer R.M., Mech. Aging Dev., 139 (1988) 139-145. 2 Gundersen, H.J., J. Microsc. 143 (1985) 3-45. 3 Kedzierski, W. and Porter, J,C., Mol. Brain Res.; 7 (1990) 45-51. 4 Reis, D.J. et al., Brain Res., 136 (1977) 465-474.
Effect of age on the beta-adrenergic receptor p o p t / t i o a in the muscle layer of the rat ileum D.M. Baker 1, S.P. Watson 2 and R.M. Santer 3 J Department of Surgery, City Hospital, Nottingham, e Department of Pharmacology, Unioersity of Oxford, Oxford, and ~ Department of Anatomy, University of Wales College of Cardiff, U.K.
Morphological and histochemical evidence suggests that the influence of the sympathetic innervation on intestinal function declines with age [1,2]. The present study investigates functional consequences of this age-related reduction in the sympathetic innervation of the small intestine by assessing pharmacological responses of the betaadrenoceptor population in the longitudinal muscle layer of the muscularis externa of the rat ileum. Longitudinal muscle strips of the ileum were prepared from Wistar rats aged 6 or 24 months (5 animals in each group) and mounted under tension in organ baths. An initial concentration response curve to carbachol was determined. Once a reproducible response to carbachol (including a maintained plateau phase) had been obtained, a concentration response curve for isoprenaline-induced relaxation following the pre-contraction with carbachol was determined in the presence of the alpha-adrenoceptor antagonist phentolamine. The EC50 values, Hill slopes and maximal tension for carbachol-induced contrac-
tion of the ileal muscle strips were not significantly different between the two age groups. Neither were the EC50 and Hill slope values for concentration response curves for isoprenaline-induced relaxation different between the two age groups. However. the maximal degree of relaxation developed by isoprenaline in strips precontracted with carbachol was about 25~ ( P < 0.02) smaller in the 24 month animals. This suggests that with age there is either a decrease in the beta-adrenoceptor number in relation to the muscarimc receptor density or a decrease in the coupling of the beta.adrenoceptor with adenylate cyclase, thus providing pharmacological evidence for the decline with age in the influence of the sympathetic system on intestinal function. References 1 Baker, D.M. and Santer. R.M.. Mech. Age. Dev., 42 ~1988) 139-145 and 147-158. 2 Baker, D.M. and Santer, R.M., J. Histochem. Cytochem,, 38 (1990) 525-531.