IS THERE A ROLE OF THE ENDOGENOUS NEUROPEPTIDE OXYTOCIN IN THE PATHOPHYSIOLOGY OF ERECTILE DYSFUNCTION (ED)?

The pro-erectile effects of the activation of dopaminergic receptors in the brain, for example, by the receptor agonist apomorphine, involves oxytocinergic pathways descending from the hypothalamus to spinal centers. In male rats, the injection of oxytocin into the paraventricular nucleus or the hippocampus induced penile erection. However, the significance of the peptide in the control of sexual arousal and the process of penile erection still is only poorly understood. The present study investigated through different conditions of sexual arousal (as exemplified by the penile conditions flaccidity, tumescence/rigidity and detumescence) the courses of oxytocin (OT) in the systemic and cavernous blood of healthy males and a cohort of patients with ED.

25 healthy adult males (HAM, mean age: 25 ys) und 30 subjects with ED (mean age: 52 ys) were exposed to visual and tactile erotic stimuli in order to elicit a penile response. Blood was taken from the corpus cavernosum (CC) and a cubital vein (CV) at the penile conditions flaccidity, tumescence, rigidity (attained only by the healthy subjects) and detumescence. Following extraction from the plasma, oxytocin was measured by means of a radioimmunometric assay.

In both groups, an increase was observed in OT plasma levels (given in pg/ml) in the systemic and cavernous blood when the flaccid penis became tumescent (HAM vs. ED; CV: 71 to 79; CC: 67 to 75 vs. CV: 102 to 111; CC: 103 to 113). In the HAM, from tumescence to rigidity, OT further rose in the cavernous blood (to 81), whereas it remained unaltered in the systemic circulation. During detumescence, oxytocin plasma levels dropped in the cavernous blood of the HAM (to 71) but increased further in the patients with ED (to 119). At the penile conditions flaccidity, tumescence, and detumescence, plasma levels of OT were significantly higher in the group of patients.

Through the arousal process, in healthy males and subjects with ED, there are marked differences with regard to the overall concentrations of OT in the systemic and cavernous blood and also the courses of the neuropeptide.

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