Nitric Oxide and Superoxide in Genetic Hypertension: Effects of Age and Gender

McIntyre, Martin (1998) Nitric Oxide and Superoxide in Genetic Hypertension: Effects of Age and Gender. PhD thesis, University of Glasgow.

Full text available as:
[thumbnail of 13818691.pdf] PDF
Download (10MB)


Nitric oxide (NO) is now recognised as an important regulatory molecule in the cardiovascular system. NO is synthesised from the amino acid L-arginine by a family of three isoenzymes, the nitric oxide synthases (NOS). NOS III is the isoform constitutively expressed in the endothelium, but its expression can be regulated by shear stress and oestrogens among other factors. Endothelium derived NO seems to play a role in preventing atherosclerosis, but its role in hypertension is less clear. Some animal and human studies favour an important role, whereas others do not. Gender differences in cardiovascular disease, endothelial function and NO are well recognised, but the underlying mechanism remains unclear. There are theoretical reasons, and indeed experimental evidence, to implicate oestrogens, although again there is some debate about possible mechanism(s). The process of ageing is thought to be related to oxidative stress and hypertension has been described as an accelerated form of ageing, but the role of superoxide anion (O2 ) and superoxide dismutase (SOD) in hypertension and ageing is only now becoming clearer. To determine blood pressure and gender differences in NO availability, rings of thoracic aorta from 16 week old males and females, normotensive Wistar-Kyoto rats (WKY) and stroke prone spontaneously hypertensive rats (SHRSP) were studied in classic organ bath experiments. Stimulated NO availability was assessed by carbachol relaxation (10e8 - 10e5 mol/L) and basal NO availability was assessed by contraction to the NOS inhibitor NG-nitro- L-arginine methyl ester (L-NAME, 100mumol/L). The contribution of the 02/S0D system was assessed in the organ bath by examining the effects of inhibiting endogenous SOD with diethyldithiocarbamate (DETCA, 10 mmol/L) and adding exogenous SOD (45U/mL). In vitro NOS III activity was assessed in the 4 groups using the L-arginine/L-citrulline assay. Endothelial NOS gene (Nos3) expression was measured by reverse transcription-polymerase chain reaction. Expression of intracellular copper zinc SOD (Sodl) and mitochondrial manganese SOD (Sod2) mRNA was measured by northern blotting and expressed as a ratio to glyceraldehyde phosphate dehydrogenase (GAPDH) mRNA. The effect of age on endothelial function was assessed by measuring the response to L-NAME (100mumol/L) in aortic rings from the same 4 groups of rats at 4, 6 and 12 months of age. The effect of oestrogen was assessed by administering 17beta-oestradiol (20mug per day, intraperitoneally, for 2 weeks) to a group of 1 year old WKY females and comparing basal and stimulated NO availability and Nos3 gene expression, as above, with a group of controls. In the organ bath, maximum relaxation to carbachol (Emax) was significantly greater in aortic rings from WKY compared to rings from SHRSP (p=0.015). Within the SHRSP strain the carbachol concentration causing 50% relaxation (EC50) was significantly less in females compared to males (p=0.003). There were no other significant gender differences in carbachol Emax or EC50. These data suggest that stimulated NO availability may be greater in WKY compared to SHRSP and perhaps SHRSP females compared to SHRSP males. The contraction of aortic rings to L-NAME was significantly greater in WKY compared to SHRSP (p=0.015). Further, this contraction in rings from WKY females was significantly greater than WKY males (p=0.00004). Similarly, the contraction in rings from SHRSP females was significantly greater than SHRSP males (p=0.0006). These data suggest that basal NO availability is greater in WKY compared to SHRSP and in females compared to males in both strains. The SOD inhibitor DETCA attenuated the relaxation to carbachol of SHRSP significantly more than WKY (p=0.0008). There were no strain or gender differences in the effect of adding exogenous SOD to the water bath. These data suggest that in aortas of SHRSP, SOD is more active, or O2 accumulates faster, or a combination of both. NOS III activity was significantly greater in the aortas from SHRSP compared to WKY (p=0.016). In both strains NOS III activity tended to be higher in males compared to females, but the differences did not reach statistical significance. Nos3 mRNA expression was greater in SHRSP compared to WKY, although the difference just failed to reach statistical significance when corrected for triple comparisons (p=0.02). Again there was a tendency for Nos3 expression to be greater in males compared to females in both strains. These data combined suggest that the reduced NO availability in SHRSP is not due to reduced NO production.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: John Connell
Keywords: Medicine, Genetics, Physiology
Date of Award: 1998
Depositing User: Enlighten Team
Unique ID: glathesis:1998-75937
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 17:14
Last Modified: 19 Nov 2019 17:14

Actions (login required)

View Item View Item


Downloads per month over past year