The effects of age and streptozotocin diabetes on the sympathetic innervation in the rat penis

Abstract

The objective was to describe the changes in catecholamine levels, noradrenaline (NA) release and the ultrastructural and immunohistochemical changes in the sympathetic nerves in the penis of STZ-diabetic rats. Amines were measured using HPLC. Nerves were studied using immunocytochemistry for tyrosine hydroxylase, and electron microscopy. Diabetic animals were compared with age-matched controls. The concentration of penile NA increases at least 2.5-fold after about 10 weeks of hyperglycaemia, is maintained for over 40 weeks. The rate of release of NA in the diabetics also increases approximately by fourfold. Immunohistochemical staining for tyrosine hydroxylase showed either no change or an increase in the levels of the enzyme around the central arteries and the outer coverings of the corpus cavernosum. Cavernosal nerves show increased intensity of staining for tyrosine hydroxylase, and the presence of dilated nerve fibres and engorged endings. The axons of the dorsal nerve of the diabetic penis have a smaller cross-sectional area that is most marked in unmyelinated axons. In the diabetic penis, the nerve endings appear to contain significantly more NA than the controls, and the turnover of noradrenaline is increased substantially. There is immunocytochemical evidence of an increase in staining for tyrosine hydroxylase, suggesting an increase in synthetic activity. These results are discussed in relation to the existing literature on the role of amines in normal and disordered erectile function. In particular, the increased concentration and turnover of NA in the diabetic rat contrasts with the fall in NA in cavernosal blood described during normal erection in humans.