Histological characteristics following a long-term nitrate-rich diet in miniature pigs with parotid atrophy

Abstract

The aim of this study was to investigate the histological characteristics following a 2-year nitrate-rich diet in miniature pigs with parotid atrophy. Using averages collected data from three time points at 6, 12, and 24 months following the induction of parotid gland atrophy, salivary nitrate levels of the nitrate-diet parotid-atrophied group (17.3 ± 3.9 ng/µl) were close to those of the control group (19.6 ± 5.1 ng/µl). Compared to the control group, the nitrate-diet group had significantly higher nitrate levels in blood (P < 0.05) and urine (P < 0.001). Histological and electron microscopy analyses showed no abnormalities in the organs of experimental or control animals. No significant differences on apoptosis rate were found in liver and kidney tissues between the standard- and nitrate-diet groups. Therefore, dietary nitrate supplementation could restore salivary nitrate levels. High-dose nitrate loading for 2 years had no observed systemic toxicity in miniature pigs with parotid atrophy.

Keywords: Nitrate supplementation; histology; oral cavity; parotid atrophy; safety.

Figures

Figure 1

Light micrographs of four oral tissues stained with hematoxylin and eosin. A-D represent gingival, glossal tissue, parotid gland, and buccal mucosa, respectively, from control miniature pigs; E-H represent the four tissues from parotid-atrophied miniature pigs; I-L represent the four tissues from parotid-atrophied miniature pigs supplemented with nitrate.

Figure 2

Light micrographs of four organs. A-D represent gastric mucosa, liver, small intestine mucosa, and kidney, respectively, from control miniature pigs; E-H represent the four tissues from parotid-atrophied miniature pigs; I-L represent the four tissues from parotid-atrophied miniature pigs supplemented with nitrate. No histological differences were obtained among control, parotid-atrophied miniature pigs with or without nitrate supplementation.

Figure 3

TEM micrographs of oral tissues at 15,000× magnification. A-D represent gingiva, dorsal of tongue, buccal mucosa, and parotid gland, respectively, from control miniature pigs; E-H represent the four tissues from parotid-atrophied miniature pigs; I-L represent the four tissues from parotid-atrophied miniature pigs supplemented with nitrate.

Figure 4

TEM micrographs of four other organs at 15,000× magnification. A-D represent the gastric mucosa, liver, kidney, and small intestinal mucosa, respectively, from control miniature pigs; E-H represent the four tissues from parotid-atrophied miniature pigs; I-L represent the four tissues from parotid-atrophied miniature pigs supplemented with nitrate.

Figure 5

Effects of nitrate supplementation on renal apoptosis. Representative photomicrographs of the TUNEL in situ assay corresponding to control (A), parotid-atrophied group (B), and parotid-atrophied group with nitrate supplementation (C). Arrows indicate the TUNEL-positive cells. Bars represent percentages of TUNEL-positive nuclei (D).

Figure 6

Effects of nitrate supplementation on hepatic apoptosis. Representative photomicrographs of the TUNEL in situ assay corresponding to control (A), parotid-atrophied group (B), and parotid-atrophied group with nitrate supplementation (C). Arrows indicate the TUNEL-positive cells. Bars represent percentages of TUNEL-positive nuclei (D).