Electrophysiological analysis of the nature of adrenoceptors in the XXXX basilar artery during development.

@entity1169 @entity5521 @entity3044 @entity35 @entity1063
The nature of adrenoceptors in basilar arteries of neonatal @entity35 was investigated by means of electrophysiological techniques. In immature (2-6 day postnatal) @entity35 , micro-injection of @entity1063 elicited a depolarization which consisted of two components. The initial 'fast' component (time to peak of 0.3-4s) was slightly reduced by @entity5521 and was not antagonized by @entity1169 . The second 'slow' component (time to peak of about 50s) was not blocked by @entity5521 but was antagonized by low concentrations (10(-7) M) of @entity1169 . In immature @entity35 , micro-injection of @entity3044 was more potent than @entity1063 in evoking the 'slow' depolarization but less effective in eliciting the 'fast' response. The pharmacology with respect to adrenoceptor antagonists of both components of the @entity3044 - and @entity1063 -induced depolarizations was similar. There was some evidence of inhibitory beta-adrenoceptors in immature @entity35 basilar vessels. In adult @entity35 (6 week old) @entity1063 produced a large 'fast' depolarization which was followed by a 'slow' tail response. Both components were not antagonized by @entity5521 or @entity1169 . It appears that in the basilar artery of neonatal @entity35 there are excitatory alpha- and inhibitory beta-adrenoceptors but the major responses to @entity1063 and @entity3044 are mediated by gamma- and excitatory beta-receptors. In adult animals the gamma-adrenoceptor predominates. Experiments were carried out in which agonists were applied by ionophoresis. These results confirm the presence of excitatory beta-receptors in neonatal basilar vessels and show the response has slow kinetics and it is likely that the beta-receptors are distributed uniformly over the smooth muscle surface. In adult animals it was not possible to elicit an excitatory beta-receptor-mediated response. The ionophoretic application of @entity1063 never evoked a perceptible depolarization which could be attributed to gamma-adrenoceptor stimulation. This result is discussed in terms of receptor distribution with respect to synaptic function in a syncytium.
