Korean J Urol.  2009 Feb;50(2):179-185.

Effects of Metformin on Penile Expression of Nitric Oxide Synthase in OLETF Rats

• Song PH
• Bae IS
• Kim YW
• Moon KH

Abstract

PURPOSE
It is well known that metformin, an oral biguanide insulinsensitizing agent, targets AMP-activated protein kinase (AMPK), which activates endothelial nitric oxide synthase (eNOS), which may be associated with erectile dysfunction. The aim of this study was to evaluate whether metformin activates eNOS in the penile tissue of a genetically obese rat model.
MATERIALS AND METHODS
We measured phospho-eNOS levels and eNOS expression in the penile tissue of Otsuka Long Evans Tokushima Fatty (OLETF) rats after 3 days of treatment with metformin (150 or 300 mg) to evaluate whether metformin activates eNOS in the penile tissue of this genetically obese rat model. Seven-month-old OLETF rats were used, and eNOS expression was analyzed by real-time polymerase chain reaction (PCR). The experimental groups were compared with use of the Kruskal-Wallis or Mann-Whitney test.
RESULTS
Seven-month-old OLETF rats had severe visceral fat deposition and elevated serum leptin concentrations. eNOS expression analyzed by real-time PCR was lower in the penile tissue of OLETF rats than in Long Evans Tokushima Otsuka (LETO) rats. Short-term treatment with metformin did not change visceral fat mass or serum leptin levels. However, metformin treatment increased eNOS mRNA expression in the penile tissue as determined by real-time PCR. The levels of phospho-eNOS and phospho-AMPK (pAMPK) in penile tissue revealed a dose-dependent tendency to increase with metformin treatment; however, there was no statistical difference by Kruskal-Wallis test among the experimental groups. The pAMPK level was dose-dependently elevated in the soleus by metformin treatment. There was no significant change in pSTAT3 by metformin treatment in the soleus.
CONCLUSIONS
Metformin activates eNOS mRNA expression in the penile tissue of OLETF rats. Further study on the relation between erectile function and eNOS levels is needed for clinical application.

Keyword

Nitric oxide synthase; AMP-activated protein kinase; Penis

MeSH Terms

AMP-Activated Protein Kinases
Animals
Erectile Dysfunction
Intra-Abdominal Fat
Leptin
Male
Metformin
Nitric Oxide
Nitric Oxide Synthase
Nitric Oxide Synthase Type III
Penis
Rats
Rats, Inbred OLETF
Real-Time Polymerase Chain Reaction
RNA, Messenger
AMP-Activated Protein Kinases
Leptin
Metformin
Nitric Oxide
Nitric Oxide Synthase
Nitric Oxide Synthase Type III
RNA, Messenger

Figure

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  Fig. 1 The expression of endothelial nitric oxide synthase (eNOS) of penile tissues in Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats. LETO; n=4, OLETF; n=4, Bars are mean±SEM of four experimental cases. a: p<0.05.

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  Fig. 2 Changes in AMP-activated protein kinase (AMPK) and phospho-AMPK (pAMPK) in soleus muscle measured by Western blot in Otsuka Long Evans Tokushima Fatty (OLETF) rats. pSTAT3: phospho-signal transducer and activator of transcription 3, GAPDH: glyceraldehyde-3-phosphate dehydrogenase.

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  Fig. 3 Quantitative comparisons of phospho-AMP-activated protein kinase (pAMPK) expression by Western blot of soleus muscle in Otsuka Long Evans Tokushima Fatty (OLETF) rats. Bars are mean±SEM. Values that do not share a common superscript are significantly different at p<0.05. GAPDH: glyceraldehyde-3-phosphate dehydrogenase.

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  Fig. 4 Changes in endothelial nitric oxide synthase (eNOS) and AMP-activated protein kinase (AMPK) expression in penile tissue by Western blot in Otsuka Long Evans Tokushima Fatty (OLETF) rats. GAPDH: glyceraldehyde-3-phosphate dehydrogenase.

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  Fig. 5 Quantitative comparisons of phospho-AMP-activated protein kinase (pAMPK) (A) and phospho-endothelial nitric oxide synthase (eNOS) (B) expressions by Western blot of penile tissue in Otsuka Long Evans Tokushima Fatty (OLETF) rats. Bars are mean±SEM. GAPDH: glyceraldehyde-3-phosphate dehydrogenase.

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  Fig. 6 Changes in endothelial nitric oxide synthase (eNOS) expression by real-time polymerase chain reaction (PCR) in penile tissue. Bars are mean±SEM. Values that do not share a common superscript are significantly different at p<0.05.

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