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Accumulation and overflow of 3H following incubation of the guinea-pig gall bladder with [3H]-noradrenaline |
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| Authors: | Sheila A. Doggrell and Lynn Vincent |
| Abstract: | 1 Strips of guinea-pig gall bladder readily accumulate 3H following incubation in the presence of 5 × 10-8 M (-)-[3H]-noradrenaline. This accumulation was reduced by lowering the incubation temperature (from 37° to 23°C), by cocaine (10-6 M), by nortriptyline (10-8, 10-6 and 10-4 M) and following incubation of the tissues with 6-hydroxydopamine (10-3 M for 3 h). At 10-6 M, (-)-noradrenaline and (-)-adrenaline, but not (-)-isoprenaline, inhibited the accumulation of 3H. 2 Following preloading of strips of guinea-pig gall bladder with 3.6 × 10-7 M (-)-[3H]-noradrenaline for 1 h, the spontaneous overflow of 3H was observed. Cocaine (10-4 M), nortriptyline (10-6 M), (-)-isoprenaline (10-5 M), acetylcholine (10-5 M) and adenosine 5′-triphosphate (ATP, 10-4 M) had no effect on the spontaneous overflow of 3H. KCl (10-1 M), (-)-noradrenaline (10-5 M), (-)-adrenaline (10-5 M), and tyramine (10-5 M) increased the overflow of 3H. These results illustrate similar characteristics of the guinea-pig gall bladder to other noradrenergically-innervated tissues in accumulating and releasing 3H following incubation in the presence of [3H]-noradrenaline. 3 Following incubation in the presence of 3.6 × 10-7 M (-)-[3H]-noradrenaline, field stimulation, at 5 Hz, of strips of gall bladder, in the absence or presence of 10-6 M atropine, increased the overflow of 3H and, simultaneously, induced contractions. The contractile responses to 5 Hz were smaller in the presence than in the absence of 10-4 M lignocaine. Lignocaine (10-4 M) reduced the overflow of 3H evoked by field stimulation at 5 Hz. It is suggested that the contractile responses to 5 Hz are due to nerve stimulation and that the increased overflow of 3H is due to the stimulation of noradrenergic nerves. 4 The overflow of 3H evoked by field stimulation at 5 Hz was unaltered and increased by propranolol (10-6 M) and phentolamine (10-6 M), respectively. Clonidine (5 × 10-5 M) had no effect in the absence but reduced the amount of 3H which overflowed in response to field stimulation at 5 Hz in the presence of 10-6 M atropine. The contractile responses to field stimulation at 5 Hz were reduced by phentolamine (10-6 M) or clonidine (5 × 10-6, 10-5 and 5 × 10-5 M) whether or not atropine (10-6 M) was present. These results illustrate the presence of postsynaptic α-adrenoceptors and suggest the presence of presynaptic α-adrenoceptors in the gall bladder of the guinea-pig. |
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