Vasoactive intestinal polypeptide levels and distribution in the penis of old rats

Erectile dysfunction in the elderly: epidemiology, etiology and approaches to treatment

PURPOSE

Erectile dysfunction is experienced at least some of the time by most men who have reached 45 years of age, and it is projected to affect 322 million men worldwide by 2025. The prevalence of erectile dysfunction is high in men of all ages and increases greatly in the elderly.

MATERIALS AND METHODS

This paper reviews the epidemiology of erectile dysfunction with an emphasis on the experience of older men, normal age related changes in the structure and function of the penis that may contribute to increased risk with age, how the accumulation of risk factors with age may contribute to the high prevalence of the disease in older men, and established and emerging therapies. The normal aging process and age related risk factor accumulation contribute to the increased prevalence of erectile dysfunction in the elderly.

RESULTS

Remarkable progress has been made in the treatment of erectile dysfunction. At present inhibition of phosphodiesterase 5 with oral agents such as sildenafil would appear to be the initial treatment of choice. These drugs have been shown to be safe and effective, and sildenafil has demonstrated efficacy in patients with many of the comorbidities observed in older men with erectile dysfunction. New treatments, in particular transfection with genes for key mediators of erectile function that are known to be down-regulated in elderly men, also hold promise.

CONCLUSIONS

Further research into the neural, vascular and molecular mechanisms involved in penile erection will lead to the development of even safer, more effective and more convenient therapies for men with erectile dysfunction.

Characterization of VIP and PACAP receptors in cultured rat penis corpus cavernosum smooth muscle cells and their interaction with guanylate cyclase-B receptors

Penile corpus cavernosum smooth muscle relaxation can be induced by both cyclic AMP and cyclic GMP-elevating agents, but possible interactions between these two signalling pathways are still poorly understood. Using in vitro cultured rat penile corpus cavernosum smooth muscle (CCSM) cells, we have characterized the local expression and functional activities of receptors for the cAMP-elevating peptides, PACAP and VIP, and for the cGMP-elevating peptides, CNP and ANP. Stimulation of the cells with various concentrations of PACAP(-27/-38) or VIP resulted in rapid and dose-dependent increases in cyclic AMP levels. RT-PCR analyses revealed gene expression of PAC(1) and VPAC(2) but not of VPAC(1) receptors in the cells. The natriuretic peptide, CNP, and the nitric oxide donor, sodium nitroprusside, were capable of enhancing cyclic GMP formation, indicating the presence of membrane-associated in addition to soluble guanylate cyclase (sGC) activities in these cells. Findings that cyclic GMP formation was preferentially activated by CNP but not by the related peptide, ANP, were consistent with RT-PCR analyses, demonstrating gene expression of the CNP receptor, GC-B, but not of the ANP receptor, GC-A, in these cells. Prior exposure of the cells to 10(-8) M PACAP resulted in a marked down-regulation of GC-B activity, whereas sGC was not affected. These findings provide functional and molecular evidence for the presence of three receptors, PAC(1), VPAC(2) and GC-B, involved in cyclic nucleotide signalling in penile CCSM cells. The observed cross-talk of the PACAP/VIP receptors with GC-B but not with sGC may have implications for the therapy of erectile dysfunction.

Age-related changes in substance P and vasoactive intestinal polypeptide immunoreactivity in the rat stomach and small intestine

Immunoreactivity for substance P (SP-LI) and vasoactive intestinal polypeptide (VIP-LI) in the stomach, duodenum, jejunum and ileum of young (3-month-old), adult (12-month-old) and old (28-month-old) male Wistar rats were determined by radioimmunoassay. SP-LI and VIP-LI did not show changes in the stomach or in the small intestine portions investigated in adult in comparison with young rats. In old rats SP-LI levels were unchanged in the stomach and in the duodenum, reduced in the jejunum and increased in the ileum. VIP-LI concentrations were unchanged in the stomach, and remarkably reduced in the duodenum, jejunum and ileum of old rats. Since the two neuropeptides investigated are localized primarily within different intrinsic gastrointestinal neurons, the present findings suggest that the various populations of gastrointestinal neurons are affected in a different manner during aging.

Age-related changes in vasoactive intestinal polypeptide levels and distribution in the rat lung

Vasoactive intestinal polypeptide (VIP) levels and distribution were studied in the lung of young-adult (3-month-old) and aged (28-month-old) male Wistar rats by radioimmunoassay and immunofluorescence. VIP concentrations were reduced approximately by 60% as the animal ages. The density of VIP-immunoreactive nerve fibres was remarkably reduced within bronchial smooth muscle and bronchial glands. Moreover, the number of VIP-immunoreactive nerve cell bodies located in intraparenchymal ganglia was decreased in old rats. The density of VIP-containing perivascular plexuses was slightly reduced in senescence. The present data are indicative that VIP neuronal system is impaired in the lung of old rats. In view of the significant age-dependent loss of VIP-immunoreactive nerve fibres that supply the bronchial tree and bronchial glands it cannot be excluded that the relaxant action exerted by peptide on airway smooth muscle and the control of bronchial secretion exerted by VIP are impaired in old age.