Abstract
The contractile effect of methacholine, prostaglandin F 2α (PGF 2α) and electrical stimulation of cholinergic neurones, and the relaxant effect of nitric oxide (NO), vasoactive intestinal polypeptide (VIP) and electrical stimulation of inhibitory non-adrenergic non-cholinergic (NANC) neurones were studied in longitudinal smooth muscle strips of the gastric fundus of young (3 months), adult (12 months) and old (24 months) male Wistar rats. The contractile responses to methacholine and to electrical stimulation of cholinergic neurones were not significantly different between the three age groups. The responses to PGF 2α were significantly more pronounced in young than in adult and old rats. The relaxant response to electrical stimulation of NANC neurones with a cumulative increase in frequency showed a decreased response in old rats at the higher stimulation frequencies. This was mimicked by a decreased response to VIP, suggesting that there is a decrease in muscular sensitivity to VIP rather than an impaired capacity to VIP release with increasing age. The relaxant response to electrical stimulation of NANC neurones with short trains was similar in the three age groups, while the sensitivity to exogenous NO increased with age. The latter might be a compensatory mechanism for a decrease in stimulation-induced NO release with age.
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