Effect of neurotensin on contractile activity and [3H]acetylcholine release in cat terminal ileum during different postnatal periods.

The effect of neurotensin (NT) on the contractile activity of circular and longitudinal strips from the terminal ileum of 15-, 30-, 60-day-old and adult cats as well as on the resting and electrically-evoked release of 3H]acetylcholine (ACh) was studied. Radioactivity was measured by liquid scintillation spectrometry and the effect of NT was evaluated by the S2/S1 ratio. In the circular muscle strips NT (1-100 nM) inhibited spontaneous contractions in all age groups. In the longitudinal strips the effect of NT was concentration- and age-dependent. NT at a concentration of 1 nM had no effect on the spontaneous activity in 15-day-old cats, but in the other age groups in 70-80% of the cats it inhibited spontaneous contractions. The response to 10 and 100 nM NT was either biphasic (relaxation followed by contraction) or inhibitory: in 15-day-old cats the response was biphasic only and with increasing age the percentage of strips responding with inhibition of the contractions increased. Neither substances affecting adrenergic and cholinergic transmission nor TTX changed the inhibitory response to NT. The contractile component of the biphasic response was TTX-resistant in all age groups and was significantly decreased by scopolamine in 60-day-old and adult cats. NT increased both resting and electrically-evoked release of 3H]ACh which was not changed by TTX. In the presence of the peptide the S2/S1 ratio increased as NT-induced 3H]ACh release in the strips of adult cats was higher than that in young cats.(ABSTRACT TRUNCATED AT 250 WORDS)