Long-term changes in sympathetic innervation in the corpus cavernosum of the STZ-diabetic rat

Abstract

The noradrenaline (NA) concentration in the rat corpus cavernosum (CC) increased to approximately 350% of control values after about 8 weeks of hyperglycaemia induced by the intraperitoneal injection of streptozotocin (STZ) at 10 weeks of age. These changes were maintained for at least a further 32 weeks of hyperglycaemia and occurred without any significant change in the weight in the tissue. Smaller but significant increases in NA concentration occurred in the glans penis (GP) reaching 150-175% of the control levels during the period of prolonged hyperglycaemia. In contrast, there was no significant change in the NA concentration in the penile urethra. Measurements have also been made that relate to changes in the synthesis and reuptake of NA in the CC during the period during which high NA concentration is maintained. Immunohistochemical studies for the synthetic enzyme tyrosine hydroxylase in the CC indicate that the intensity of staining in the tissue had increased after 10, 20 and 32 weeks of hyperglycaemia, relative to the tissues from control animals. Dilated nerve fibres and engorged endings were present in the CC of the diabetic animals at these times. Reuptake of tritiated NA by the terminal axonal membranes in the CC was raised to 181% of control values after 12 weeks of hyperglycaemia (P<0.05), but later declined to values that are not significantly different from the control levels (after 26 and 64 weeks of hyperglycaemia). There are few studies of the effects of prolonged diabetes on functional aspects of sympathetic postganglionic neurones in the CC, and this paper suggests that the changes described represent remodelling of noradrenergic axonal terminals starting about after 8-10 weeks of hyperglycaemia; this delay in onset of the neuropathic changes is also a feature of type I diabetes in humans.