The Effects of Noradrenergic Denervation on Muscarinic Receptors of Smooth Muscle

Abstract

Changes in the response to acetylcholine of expansor secundariorum muscles from chicks have been analysed by pharmacological techniques and by [3‐3H]‐quinuclidinyl benzilate ([3‐3H]‐QNB) binding to quantify the muscarinic receptor population. The expansor secundariorum muscle responded to acetylcholine up to the age of 30 days; the response declined thereafter. This developmental decrease in response to acetylcholine was prevented by surgical denervation. In chicks aged less than 25 days, denervation did not affect the sensitivity of the expansor muscle to acetylcholine. In older chicks (above 40 days) denervation gradually restored the sensitivity of the expansor muscle to acetylcholine. Responses of the expansor muscle were always abolished by atropine (1 μm) indicating they were mediated by muscarinic receptors. Binding studies with [3‐3H]‐QNB showed that changes in response of expansor muscles to acetylcholine were primarily due to changes in the muscarinic receptor population. It is suggested that the noradrenergic innervation of the expansor muscle influences the number of muscarinic receptors expressed in the tissue.

The consequences of loss followed by recovery of noradrenergic nerve function on muscarinic receptors in the chick expansor secundariorum muscle

“…All responses to ACh were mediated by stimulation of muscarinic receptors since they were always abolished by atropine, a known muscarinic receptor antagonist. These findings strengthen the suggestion that the noradrenergic innervation of the ESM influences the number of muscarinic receptors expressed in the tissue (Bennett et al, 1982).…”

“…Injections were given through the brachial vein. Subsequently, the animals were killed at different times by an overdose of ether, the ESM removed and set up in organ baths as described by Bennett et al (1982).…”

“…In chicks older than 40 days, surgical denervation or sympathectomy with guanethidine gradually increases the sensitivity of the ESM to acetylcholine (ACh) (Kuromi & Hagihara, 1976;Bennett et al, 1982). The supersensitivity following surgical denervation is associated with hypertrophy of the ESM (Campbell et al, 1977;Lot & Bennett, 1982a) making this procedure unsuitable in the present study.…”

“…However, the ESM also possesses muscarinic receptors in chicks younger than 10 days post-hatching; these receptors disappear by day 40 post-hatching (Kuromi & Hasegawa, 1975;Bennett et al, 1982).…”

“…The expansor secundariorum muscle (ESM), a smooth muscle in the wing of birds, is innervated by postganglionic noradrenergic nerves only (Buckley & Wheater, 1968;Lot & Bennett, 1982b). However, the ESM also possesses muscarinic receptors in chicks younger than 10 days post-hatching; these receptors disappear by day 40 post-hatching (Kuromi & Hasegawa, 1975;Bennett et al, 1982).…”