Essential hypertension (EH) is a risk factor for many cardiovascular disorders. Treatment of established EH, especially for prolonged control of this pathogenic process, represents a great challenge. Moreover, hypertension is considered an important risk factor for the development of many other diseases, e.g. erectile dysfunction. <p> Hemin and other heme derivatives, e.g. heme-L-lysinate (HLL) and heme-L-arginate, have been used extensively to upregulate expression of heme oxygenase (HO) and production of endogenous carbon monoxide (CO). Short-term hemin administration for 4-5 days has been shown to markedly decrease high blood pressure (BP) in spontaneously hypertensive rats (SHR), but not in normotensive Wistar-Kyoto (WKY) or Sprague Dawley (SD) rats. This short-term therapy was effective in treating young, but not adult SHR. In the present study, hemin (15 mg/kg/day) was administered to 12-week old adult SHR through subcutaneously implanted osmotic minipumps for 3 consecutive weeks (the hemin protocol). Into the second week of the hemin protocol, BP of SHR was normalized from 203.2 ± 2.5 to 123.4 ±1.9 mmHg (n=20, p<0.001). There was no further decrease of BP in the remaining days of the hemin protocol. Normalization of BP in these treated SHR was maintained for 9 months after the removal of hemin pumps. <p>To further investigate the metabolic characteristics of hemin during hemin protocol administration, we attempted to monitor circulatory heme levels. A valid standard calibration curve was established using hemin or HLL in <i>in vitro</i> experiments. It was established that the basal serum level of heme was negligible in all rat strains prior to hemin protocol initiation. During the hemin protocol, serum heme level of all rats was significantly elevated; however, it quickly dropped to basal levels thereafter. <p>At the end of the 3-week hemin protocol, HO-1 expression, HO activity, soluble guanylyl cyclase (sGC) expression, and cyclic guanosine monophosphate (cGMP) content were all increased, but phosphodiesterase-5 (PDE-5) expression was down-regulated in the mesenteric arteries. The hemin protocol also reversed SHRs decreased arterial lumen size, and increased expression levels of vascular endothelial growth factor. These changes lasted 9 months after the hemin protocol. The hemin protocol did not cause hepatic or renal toxicity. Our study thus unmasks a novel hemin protocol that will not only normalize BP in SHR with established hypertension but, more importantly, also provide long-lasting anti-hypertension protection. Sustained upregulation of the HO-regulated signaling pathways and reversal of vascular remodeling in small peripheral vessels in treated SHR are among potential underlying mechanisms for the anti-hypertensive effect of the hemin protocol.<p>We further studied if the beneficial effects of hemin protocol on BP of SHR could be extended to improvement of their penile erection. Intracavernosal pressure changes after electrical stimulation of the cavernous nerve (CN) were monitored in adult SHR and age-matched normotensive SD rats after administration of either hemin or hydralazine. Expression levels of HO-1, HO-2, sGC, and PDE-5 in penile tissues were also examined. Frequency-dependent intracavernosal pressure (ICP) changes were reduced in adult SHR. Three weeks after hemin treatment, ICP responses to CN stimulations were significantly increased to the level of normotensive rats, which was linked to normalization of BP of hemin-treated SHR. Hydralazine-treated SHR experienced normalization of BP but not ICP after 3 weeks of treatment. Expression of HO-1 and sGC was upregulated and that of PDE-5 downregulated in hemin-treated SHR. Decreased ICP response in adult SHR can be improved through chronic hemin treatment of SHR. Prolonged upregulation of HO-1 and sGC as well as lowered expression of PDE-5 may account for normalization of erectile dysfunction in SHR subsequent to hemin treatment. <p>This thesis reports for the first time that 21-day hemin administration led to a 9-month normalization of high BP of adult SHR. These effects were mediated through sustained stimulation of the HO/CO system and its downstream effectors targets. Increased activity of HO-1 led to normalization of the abnormally high expression level of VEGF in peripheral mesenteric arteries of adult SHR. Subsequently, this resulted in reversal of the eutrophic remodeling of these arteries, which seems to be the priniciple determinant of the long-term normalization of BP observed for 9 months after stoppage of hemin treatment. The invention of hemin protocol offers a new therapeutic approach for the clinical management of established hypertension for a long duration.<p>Our study, for the first time, correlated changes in serum heme levels with BP levels after injection of hemin or HLL in normotensive and hypertensive rats. Application of this heme monitoring technology will also pave the way for clinical application of hemin therapy in treatment of EH.<p> Another intriguing finding in this thesis is that upregulation of HO-1, through the hemin protocol, led to improvement of abnormally low ICP encountered in adult SHR. Upregulation of HO-1 may represent a novel therapeutic approach to treat hypertension-related erectile dysfunction.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-11292006-143445 |
| Date | 30 November 2006 |
| Creators | Shamloul, Rany Mohamed |
| Contributors | West, Nigel, Wang, Rui, Sulakhe, Prakash, Gopalakrishnan, Venkat, Fisher, Thomas E., Desautels, Michel |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-11292006-143445/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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