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G-proteins and adenylyl cyclase signalling in hypertension
1Department of Physiology, Faculty of Medicine, University of Montreal, Quebec, Canada.
Insights
Increased inhibitory G-proteins (Gi alpha-2 and Gi alpha-3) and altered adenylyl cyclase activity precede hypertension development in rats, suggesting a role in blood pressure regulation.
Area of Science:
- Cardiovascular Physiology
- Molecular Biology
- Hypertension Research
Background:
- Hypertension is a complex cardiovascular disease with multifactorial origins.
- G-proteins and adenylyl cyclase play crucial roles in regulating cellular responses to hormones.
Purpose of the Study:
- To investigate alterations in adenylyl cyclase activity and G-protein levels (Gs alpha and Gi alpha) in cardiovascular tissues of spontaneously hypertensive rats (SHR).
- To determine if these changes precede or are a consequence of elevated blood pressure.
Main Methods:
- Quantitative analysis of adenylyl cyclase activity, Gs alpha, and Gi alpha protein and mRNA levels in hearts and aortas of SHR and Wistar Kyoto (WKY) rats.
- Utilized immunoblotting and Northern blotting techniques.
- Examined rats at various developmental stages (3-5 days, 2, 4, and 8 weeks) to correlate molecular changes with blood pressure development.
Main Results:
- Decreased adenylyl cyclase responsiveness to stimulatory hormones and increased inhibition by inhibitory hormones were observed in SHR.
- Significantly higher levels of Gi alpha-2 and Gi alpha-3 proteins and mRNA were found in SHR hearts and aortas compared to WKY rats.
- Gs alpha levels remained unchanged in SHR. These Gi alterations were detectable as early as 2 weeks of age, before significant blood pressure increase.
Conclusions:
- The increased expression of Gi alpha-2 and Gi alpha-3, along with altered adenylyl cyclase activity, precedes the development of hypertension in SHR.
- These molecular changes may be a contributing factor in the pathogenesis of hypertension.
Abstract:
The present studies were undertaken to examine if adenylyl cyclase activity and the levels of G-proteins (Gs alpha and Gi alpha) are altered in cardiovascular tissues in hypertension. Adenylyl cyclase activity and its responsiveness to stimulatory and inhibitory hormones as well as the expression of G-proteins (Gs and Gi) were determined at protein and mRNA levels by using specific antibodies and cDNA probes in hearts and aorta from 12 week old spontaneously hypertensive rats (SHR) and their age-matched control Wistar Kyoto (WKY) rats. The stimulatory effects of guanine nucleotides, isoproterenol, glucagon etc. on adenylyl cyclase activity were decreased in SHR rats as compared to the WKY rats, whereas, the inhibitory hormones inhibited enzyme activity to a greater extent in SHR rats as compared to WKY rats. Furthermore, the levels of Gi alpha-2 and Gi alpha-3 proteins and Gi alpha-2 and Gi alpha-3 mRNA as determined by immunoblotting and Northern blotting techniques respectively were higher in SHR as compared to WKY rats. However, the levels of Gs alpha were unaltered in SHR. To further investigate if these alterations are the cause or effect of hypertension, the SHRs at various ages of development of blood pressure (3-5 days, 2, 4 and 8 weeks) and their age-matched WKY were used for G-protein expression and adenylyl cyclase activity. The increased expression of Gi alpha-2 and Gi alpha-3 protein and mRNA levels in hearts and aorta were observed as early as in 2-weeks old SHR as compared to WKY, when the blood pressure was still normal. However, the levels of Gs alpha in SHR were not different from WKY rats. In addition, the altered responsiveness of adenylyl cyclase to hormone stimulation and inhibition was also observed as early as in 2 week old SHR. These results suggest that the increased expression of Gi alpha-2 and Gi alpha-3 and decreased levels of cAMP precedes the development of blood pressure and may be one of the contributing factors in the pathogenesis of hypertension.