Comparison of the effects of chronic chloroquine treatment and denervation on noradrenergic mechanisms.

Nine or 52 day old chicks were treated with daily intraperitoneal of 75 mg/kg chloroquine diphosphate for 14 days. The response of the sympathetically innervated expansor secundariorum muscle to electrical stimulation or to noradrenaline were then measured in vitro. Noradrenergic nerves were examined by fluorescence histochemistry. The main effect observed 30-90 min after the last dose of chloroquine was supersensitivity to exogenous noradrenaline. This was no longer detectable from expansor muscles taken 18-24 h after the last dose of chloroquine. However, noradrenergic nerves in tissues from chronically treated chicks taken 18-24 h after the last dose of chloroquine were less fluorescent than those from control animals. Chronic chloroquine treatment reduced the body weight of chicks. There was also a reduction in the weight of the expansor muscle, due to a reduction in both muscle mass and water content. Surgical denervation increased the weight of the expansor muscle by increasing its muscle mass and abolished the fluorescence of its noradrenergic nerves 3 days after surgery. The denervated expansor muscle responded very weakly to electrical stimulation and its supersensitivity to noradrenaline was maximal 3-5 days after surgery. The denervated expansor muscle developed a lower maximum response to noradrenaline.