Cardiovascular Characteristics of Zucker Fatty Diabetes Mellitus Rats, an Animal Model for Obesity and Type 2 Diabetes

Abstract

Zucker fatty diabetes mellitus (ZFDM) rats harboring the missense mutation (fa) in a leptin receptor gene have been recently established as a novel animal model of obesity and type 2 diabetes (T2D). Here, we explored changes in cardiovascular dynamics including blood pressure and heart rate (HR) associated with the progression of obesity and T2D, as well as pathological changes in adipose tissue and kidney. There was no significant difference in systolic blood pressure (SBP) in ZFDM-Lepr^fa/fa (Homo) compared with ZFDM-Lepr^fa/+ (Hetero) rats, while HR and plasma adrenaline in Homo were significantly lower than Hetero. The mRNA expression of monocyte chemotactic protein-1 in perirenal white adipose tissue (WAT) from Homo was significantly higher than Hetero. Interscapular brown adipose tissue (BAT) in Homo was degenerated and whitened. The plasma blood urea nitrogen in Homo was significantly higher than Hetero. In summary, we demonstrated for the first time that HR and plasma adrenaline concentration but not SBP in Homo decrease with obesity and T2D. In addition, inflammation occurs in WAT from Homo, while whitening occurs in BAT. Further, renal function is impaired in Homo. In the future, ZFDM rats will be useful for investigating metabolic changes associated with the progression of obesity and T2D.

Keywords: adipose tissue; cardiovascular dynamics; diabetes; kidney; obesity; sympathetic nerve activity.

Figure 1

The metabolic characteristics of male Zucker fatty diabetes mellitus (ZFDM)-Lepr^fa/+ (Hetero) and ZFDM-Lepr^fa/fa (Homo) rats. (A) Changes in body weight (BW) of ZFDM rats at 12 (n = 10), 13–16 (Hetero: n = 9, Homo: n = 10), 17–35 (Hetero: n = 8, Homo: n = 10), and 36–38 (Hetero: n = 8, Homo: n = 9) weeks old. (B,C) Changes in body length (B) and body mass index (BMI) (C) of ZFDM rats at 17–35 (Hetero: n = 8, Homo: n = 10) and 36–38 (Hetero: n = 8, Homo: n = 9) weeks old. BMI was calculated via dividing BW by body length squared. (D) Blood glucose level in ZFDM rats at 12, 16 (Hetero: n = 9, Homo: n = 10), and 36–38 (Hetero: n = 8, Homo: n = 9) weeks old was determined by an enzymatic electrode method. (E) The insulin concentration in heparin (1 U/mL)-anticoagulated plasma of ZFDM rats at 12, 21, and 36–38 weeks old (n = 5) was measured by a commercially available enzyme-linked immunosorbent assay (ELISA) kit. (F,G) The plasma triglyceride and total cholesterol levels of ZFDM rats at 19 and 36–38 weeks old (Hetero: n = 8, Homo: n = 10) were determined by a colorimetric method. Results were expressed as means ± standard error of the mean (SEM). * p < 0.05, ** p < 0.01 vs. Hetero.

Figure 2

The cardiovascular dynamics of ZFDM rats. (A,B) The systolic blood pressure (SBP) (A) and heart rate (HR) (B) of ZFDM rats at 12 (n = 10), 13–16 (Hetero: n = 9, Homo: n = 10), 17–35 (Hetero: n = 8, Homo: n = 10), and 36–38 (Hetero: n = 8, Homo: n = 9) weeks old were measured by a tail-cuff method under conscious condition. (C) The adrenaline concentration in heparin (1 U/mL)-anticoagulated plasma of ZFDM rats at 15 and 25 weeks old (n = 5) was measured by a commercially available ELISA kit. Results were expressed as means ± SEM. * p < 0.05, ** p < 0.01 vs. Hetero.

Figure 3

Histological analysis of ventricles and mesenteric arteries from ZFDM rats. Thin sections (4 μm) were made from paraffin-embedded isolated ventricles and mesenteric arteries from ZFDM rats at 36–38 weeks old (Hetero: n = 8, Homo: n = 9). (A,B) Representative hematoxylin and eosin (HE)-stained sections for ventricles. (C,D) Representative picrosirius red stained sections (4 µm) for ventricles. Collagen was stained in red, and cytoplasm was stained in yellow. (E–H) Representative HE-stained sections for mesenteric arteries. (I) Medial wall thickness of the mesenteric arteries was calculated and shown as means ± SEM. Scale bar: 2 μm (A,C), 100 μm (E), and 50 μm (G). Arrow: medial wall of the artery.

Figure 4

Morphology and mRNA expression in white adipose tissue (WAT) and brown adipose tissue (BAT). Thin sections (10 μm) were made from paraffin-embedded isolated perirenal adipocytes (WAT) and interscapular adipocytes (BAT) from ZFDM rats at 36–38 weeks old (Hetero: n = 8, Homo: n = 9). (A,B) Representative HE-stained sections for WAT. (C) The mRNA expression levels of monocyte chemotactic protein (MCP)-1 and adiponectin in WAT were measured by a reverse transcription quantitative polymerase chain reaction (RT-qPCR). The data normalized to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA was shown as fold increase relative to Hetero and expressed as means ± SEM. (D,E) Representative HE-stained sections for BAT. (F) The mRNA expression levels of uncoupling protein (UCP)-1, peroxisome-proliferator-activated receptor γ coactivator-1α (PGC-1α), and adiponectin in BAT were measured by RT-qPCR. The data normalized to GAPDH mRNA was shown as fold increase relative to Hetero and expressed as means ± SEM. Scale bar: 200 μm (A,D). * p < 0.05, ** p < 0.01 vs. Hetero.