Altered pressure-volume relation of right atrium and venoatrial junction in diabetic rats

Previous studies have indicated a blunted volume reflex in diabetic rats. This alteration of the volume reflex may be due to differences in distensibility of the right atrium and venoatrial junction, which contain a large number of volume receptors. This study was designed to determine whether the distensibility of the right atrium and venoatrial junction is altered in the diabetic rat. The distensibility was assessed by measuring the stiffness constants [slope of pressure-volume (P-V) curve] of the right atrium and venoatrial junction in 2-wk streptozotocin-induced diabetic rats. The P-V data of the right atrium and venoatrial junction were measured in control and diabetic rats over a range of 0-10 mmHg by infusion of isotonic saline in KCl-arrested, in situ hearts. Similar P-V data also were determined in an additional group of diabetic rats under daily insulin treatment, which normalized plasma glucose. The mean slope of the P-V curve of the right atrium and venoatrial junction in the diabetic rats was significantly greater than the mean slope of the control and insulin-treated diabetic rats. The results indicate that diabetic rats have stiffer right atria and venoatrial junctions, which may reduce stimulation of the volume receptors to acute volume loading. In addition, the increased stiffness in the diabetic rats was prevented by chronic insulin treatment. An altered afferent limb of the volume reflex in diabetic rats contributing to blunted diuretic and natriuretic responses to volume loading may be due to these documented changes in the distensibility of the right atrium and venoatrial junction.