The effects of diabetes and autonomic neuropathy on parotid salivary flow in man

Stimulated parotid salivary flow studies were performed on 20 non-diabetic subjects and on 30 patients with insulin-dependent diabetes mellitus who had been screened for autonomic neuropathy using tests of cardiovascular reflexes. Electrical gustometry was performed to detect the taste threshold. The stimulated parotid salivary flow rates of diabetics with no autonomic neuropathy or early parasympathetic autonomic dysfunction alone were similar to those of non-diabetic subjects. Diabetic patients with established parasympathetic autonomic neuropathy had significantly higher salivary flow rates as did those with combined sympathetic and parasympathetic neuropathies. Taste thresholds did not correlate either with the duration of the diabetes or with the presence of autonomic neuropathy. The cause of the increased salivary flow associated with diabetic autonomic neuropathy is unclear. It may represent the removal of a neural inhibitory mechanism which modulates salivary flow, or the effects of long-standing diabetes on salivary secretion.