The regrowth of right atrial noradrenergic nerves after 6-hydroxydopamine in genetically diabetic mice; effects of insulin treatment.

1 This study examined the rate of repletion of right atrial noradrenaline levels after a single dose (100 mg/kg i.p.) of 6-hydroxydopamine (6-OH Da) in diabetic and non-diabetic mice of the C57 BL/KS db/db strain. 2 In mice which received no 6-OH Da there was no significant difference, in endogenous noradrenaline levels, between diabetic and non-diabetic animals. The depletion of noradrenaline 24 h after 6-OHDa was slightly more profound in the diabetic mice than in non-diabetic controls. Thereafter the rate of repletion of noradrenaline was more rapid in the diabetic group. 3 The normal noradrenaline content was reinstated in diabetic mice between 7 and 10 days after 6-OHDa. In the non-diabetic group levels similar to those found in untreated mie were not reinstated until 14 days after 6-OHDa. 4 Ten days after 6-OHDa right atria from diabetic mice were markedly more responsive to stimulation of the intramural noradrenergic nerves than were preparations from non-diabetic mice. 5 A group of diabetic mice was treated with insulin (10 m Units/g daily) for 6 weeks. The right atria from these animals, examined 10 days after 6-OHDa, were similar in their responses to noradrenergic nerve stimulation to the preparations from the non-diabetic mice. 6 All these groups of atria gave similar responses to exogenous noradrenaline. These findings indicate that regrowth of noradrenergic terminals after 6-OHDa was more rapid in diabetic mice than in either insulin-treated diabetic mice or non-diabetic mice.