INSULIN TEST: PRECISIONS OF AND CORRELATIONS BETWEEN GLUCOSE AND HORMONE RESPONSES

Abstract

ABSTRACT Insulin test was given twice to each of 41 reference subjects and 31 hypopituitary patients to establish the most precise parameters of glucose and hormone responses, and the intra-individual dependence of these responses on each other. The precision was highest for the glucose response, intermediate for the cortisol and epinephrine responses and lowest for the GH response. The most precise parameters were: for blood glucose, recovery index, maximum per cent decrement, maximum absolute decrement and minimum level; for plasma cortisol, maximum level, post-insulin area and increment area; for plasma GH, maximum level and post-insulin area; and for epinephrine excretion, absolute post-insulin rate and absolute post-insulin increment. Unacceptably poor precision was established for some parameters in common use: the maximum and 60 min increments in cortisol and GH, and the per cent increment in epinephrine. The intra-individual correlations suggest differences in the mode of stimulation of the different hormone secretions in response to acute hypoglycaemia. While the cortisol response correlated best with the absolute glucose decrement, the epinephrine response correlated best with the absolute minimum glucose level. Per cent glucose decrement showed no correlation with the hormone responses. GH response showed no correlation with any parameter of acute hypoglycaemia. Prolonged hypoglyaemia leads to responses in cortisol, GH and epinephrine secretion. No intra-individual correlations were present between the responses of these hormones, but the basal cortisol level was correlated both with the basal rate and with the response in epinephrine excretion. For maximum clinical information strict standardization of the test procedure is necessary, with use of the most precise parameters of the responses. For plasma cortisol and GH responses the preferable parameters are the maximum levels. The cortisol maximum should be corrected for its dependence on the basal level, so increasing its precision. For the epinephrine response the absolute post-insulin rate of excretion is convenient and precise.