Spontaneous Cardiac Hypertrophy in a Crl:CD(SD) Rat

Abstract

Cardiac hypertrophy was observed in a 9-week-old Crl:CD(SD) rat that died unexpectedly. The animal was allocated to the control group of a toxicity study, and no abnormalities in its general conditions, body weight or food intake were observed. Necropsy revealed an increase in heart weight. Gross examination indicated cardiac enlargement with thickening of the right and left ventricular walls. Histopathological examination revealed hypertrophy of the cardiomyocytes in the right and left ventricular walls and the interventricular septum. Electron microscopic examination indicated bizarre nuclei and accumulation of an increased number of various sizes of mitochondria in the perinuclear region of the hypertrophied myocytes. Hypertrophied myocytes connected by intensely folded intercalated disks were also observed. Based on these findings, the animal was diagnosed with cardiac hypertrophy. This is the first case report of cardiac hypertrophy in this strain.

Keywords: SD rat; heart; hypertrophy.

Fig. 1.

Gross appearance of cardiac hypertrophy in the 9-week-old SD rat (present case, H). Cardiac enlargement and thickening of the right and left ventricular walls compared with a 10-week old normal SD rat (N) are observed in the (a) whole heart and (b) transverse sections of the heart.

Fig. 2.

Cross sections of the heart (present case, a–d) of the 9-week-old SD rat that developed spontaneous cardiac hypertrophy and (e–h) of a 10-week-old normal SD rat. Hypertrophy of the myocytes can be seen in the (b) right ventricular (RV) wall, (c) interventricular septum (IVS) and (d) left ventricular (LV) wall. Normal myocytes can be seen in the (f) RV wall, (g) IVS and (h) LV wall. HE staining. b, c, d, f, g, and h: ×400.

Fig. 3.

Comparison of the short diameters of hypertrophic cardiomyocytes with those in a 10-week-old normal SD rat. The cardiomyocytes of the rat with cardiac hypertrophy are significantly larger in all layers, except for the middle interventricular septum (IVS) layer. *: p < 0.05, **: p < 0.01, ***: p < 0.001. RV, right ventricular wall; LV, left ventricular wall.

Fig. 4.

(a) Myocardial degeneration, (b) infiltration of mononuclear cells and (c) interstitial/perivascular fibrosis at the interventricular septum (IVS) of the hypertrophic heart. a: HE staining, ×100; b: HE staining, ×400; c: Masson’s trichrome, ×400.

Fig. 5.

Electron microscopic findings of cardiomyocytes obtained from the SD rat that developed spontaneous cardiac hypertrophy. (a) Various sizes of mitochondria and an increase in the number of mitochondria in the cytoplasm, (b) bizarre nuclei and (c) an intensely folded intercalated disk connecting two adjacent myocytes can be seen. (d–f) Cardiomyocytes from a 10-week-old normal SD rat.