Method for detecting hemodynamic alterations following a single gavage in rats

Abstract

It is known that administering a gavage to rodents evokes a cardiac reflex, due to gastrointestinal stimulation. Consequently, it is difficult to evaluate changes in hemodynamics after a single oral dose of a pungent or astringent, which alters the circulation by increasing sympathetic activity. In the present study, we developed a method for administering a gavage without significantly affecting hemodynamics measurements. We marked a gastric tube at 10 cm from the tip, to mark the distance from the oral cavity to the stomach body of Wistar male rats. Rats were intubated under urethane anesthesia.After 10-15 min of stabilization, we measured the mean blood pressure (MBP), heart rate (HR), and blood flow (BF) in the cremaster arteriole under two different conditions; condition 1: a pointed gastric tube, room temperature distilled water, and injected at normal speed (approximately 3 ml/min); condition 2: a rounded gastric tube, 37°C distilled water, and injection at 1.0 ml/min. Under condition 1, we observed striking hemodynamic alterations, due to the somatic afferent reflex. In contrast, under condition 2, these hemodynamic changes were nearly eliminated. In addition, we could clearly detect hemodynamic changes in rats after a single gavage treatment of pungent (capsaicin) or astringent (cinnamtannin A2). We observed transient increases in the HR and MBP soon after treatment with capsaicin. Moreover, cremasteric BF was elevated with cinnamtannin A2. These results confirmed the utility of the gavage method developed in this study.

Keywords: blood pressure; cremasteric blood flow; gavage administration; heart rate; rat.

Fig. 1.

Measurements of heart rate (HR) and mean blood pressure (MBP) under two different gavage conditions. Condition 1: a pointed gastric tube, room-temperature distilled water, injected at normal speed (approximately 3 ml/min); condition 2: a rounded gastric tube, 37°C distilled water, and slow injection (1.0 ml/min). (a) Photograph of the equipment used in the experiment (BP98A system); (b) diagram of the experimental procedure; s.c.: subcutaneous; (c) representative measurements of HR and MBP in an anesthetized rat under condition 1; (d) representative measurements of HR and MBP in an anesthetized rat under condition 2.

Fig. 2.

Measurements of blood flow (BF) in the cremaster muscle arteriole under two different gavage conditions Condition 1: a pointed gastric tube, room-temperature distilled water, and injected at normal speed (approximately 3 ml/min); condition 2: a rounded gastric tube, 37°C distilled water, and slow injection (1.0 ml/min). (a) Photograph of the equipment used in the experiment (Periscan PIM-2); (b) diagram of the experimental procedure; s.c.: subcutaneous; (c) representative measurements of cremasteric arteriole BF in an anesthetized rat in condition 1; (d) representative measurement of cremasteric arteriole BF in an anesthetized rat in condition 2. au: arbitrary units.

Fig. 3.

Alterations in heart rate (HR) and mean blood pressure (MBP) in rats following a single gavage of 600 µg/kg capsaicin with the method developed in this study. Changes in (a) HR and (b) MBP are shown for rats injected with capsaicin (cap; open symbols; n=4) or vehicle (filled symbols; n=8). Values are the means ± SD. *P<0.05, **P<0.01 indicate significant differences from vehicle.

Fig. 4.

Alterations in cremasteric arteriole blood flow (BF) in rats following a single gavage of 10 µg/kg cinnamtannin A2 with the method developed in this study. Changes in BF are shown for rats injected with cinnamtannin A2 (A2, open symbols) or vehicle (filled symbols); n=8 per group. Values are the means ± SD. *P<0.05, **P<0.01 indicate significant differences from vehicle. au: arbitrary units.