Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA351

Poster Communications

High salt diet in Sprague Dawley rats alters relaxation response of abdominal aortic ring preparation and reduces eNOS mRNA expression.

A. Adejare1, A. Oloyo1, O. Sofola1

1. Physiology, College of Medicine, University of Lagos, Lagos, Nigeria.

In the pressurized mesenteric artery preparation of Sprague Dawley (SD) rats, high salt diet produced identical relaxation response to acetylcholine (Ach) as in control rats. However following blockade with L-NAME, the Ach induced relaxation was not affected in high salt rats but was attenuated in control rats and the lack of response was reversed by Apamin and Charybdotoxin, suggesting that EDHF rather than EDRF-NO might play a more significant role in the response in salt loaded rats (Sofola et al, 2002). In view of the lack of effectiveness of L-NAME in high salt fed rats, the present experiments were designed to evaluate the relaxation responses to Ach and also determine the expression of EDRF-NO in the two groups of rats. Weanling SD Rats were fed a high salt diet (SR) containing 8% NaCl for 6 weeks while control rats (NR) had normal rat chow containing 0.3% NaCl. At the end of the feeding period, the rats were euthanized by cervical dislocation, the abdomen was opened and 2mm rings from the abdominal aorta were isolated and mounted in perfusion chamber containing Physiological Salt Solution (PSS, Sofola, 2002), at 37°C and gassed with 95%O2-5% CO2 gas mixture. After pre-contraction of the rings with 10-7M phenylephrine, relaxation responses to Ach, from 10-9 to 10-4M were determined, in the absence or presence of L-NNA as well as response to sodium nitroprusside (SNP). Percent relaxation (Mean±SEM) was obtained, plotted as cumulative response curves and analysed by ANOVA and SNK postHoc test with significance at P<0.05. Total RNAs were isolated from homogenates of abdominal aorta from SR and NR usingAurumTM Total RNA Mini Kit and cDNA was synthesized from total RNA using Omniscript RT Kit. The eNOS mRNA amplicons obtained were separated by electrophoresis on 1.5% agarose gel and visualized by ethidium bromide staining under UV light. Results show that relaxation response curves to Ach in the absence of L-NNA were similar in both NR (n=5) and SR (n=5) (P>0.5). However in the presence of L-NNA, relaxation response to Ach was significantly attenuated in NR (P<0.05, ANOVA) but was virtually unchanged in SR (P>0.05). Specifically, at Ach dose of 10-4M, percent (%) relaxation was reduced in NR from 86.4±7.0 to 57.5±8.7 (P<0.001) but not in SR, 78.3±8.9 to 73.0±6.3; (P>0.05). In both groups the percent relaxation to 10-5 M SNP was the same at 100%. The expression of eNOS mRNA in the abdominal aorta of salt-loaded rat was much reduced when compared with that of the control group.These results indicate that, following the earlier suggestion of signaling switch for relaxation from EDRF-NO to EDHF in high salt fed rats (Sofola et al,2002), the present results show the reduction of eNOS expression in SR which will explain the switch in signaling mechanism.

Where applicable, experiments conform with Society ethical requirements