Plasma and salivary concentrations of glucose and cortisol during insulin-induced hypoglycaemic stress in healthy Nigerians

Abstract

We measured cortisol levels in plasma and saliva samples obtained simultaneously from 10 fasting adult Nigerians at 0900 h and at 60 and 90 min of hypoglycaemia induced by intravenous insulin. Salivary glucose levels (fasting and after i.v. insulin) were unaffected by hypoglycaemia and did not correlate with plasma glucose at any time point. Cortisol levels in plasma and saliva increased by 50% and 120%, respectively, from fasting to 90 min values (both P less than 0.05) after i.v. insulin. This increase was evident by 60 min (plasma 33% and saliva 40%, both P less than 0.05 compared to fasting values). There was a significant positive correlation between the percentage increases in plasma and salivary cortisol (r = 0.65, P less than 0.05). Salivary cortisol was always (0900 h and during hypoglycaemic stress) 15-20% of total plasma cortisol, a percentage similar to the reported values on the contribution of free plasma cortisol to total plasma cortisol. We conclude that increases in plasma cortisol are reflected in saliva, and salivary cortisol could be estimated as an alternative to free plasma cortisol in the dynamic assessment of adrenocortical function in humans.