Acromegaly and insulin resistance: a case study

Elevated levels of growth hormone (GH) alter both the glucose tolerance and the sensitivity of peripheral tissue to insulin. We have studied the relationship between impaired glucose metabolism and its variations with different plasma levels of endogenous GH in one patient with acromegaly. To do so, we studied the decline in blood glucose concentration, as induced by iv insulin infusion, from a given hyperglycaemic level. With high levels of GH (GH = 120 micrograms/l), the slope of the straight line representing the decrease in blood glucose after insulin infusion was -0.71, the time required to achieve normoglycaemic levels, 270 min, and the corrected area under the curve representing blood glucose 26 070 units2. After 10 months' bromocriptine treatment, GH plasma concentration fell to 8 micrograms/l, at which point the slope of the straight line was -1.40, the time required to achieve normoglycaemic levels 115 min, and the area under the curve 8956 units2. There was a greater total clearance of glucose when GH levels were lower (1.90 vs 1.00 ml/min/kg), as well as greater elimination of glucose from the extracellular glucose pool (4.02 vs 1.67 mg/min/kg). In conclusion, in this patient the elevated plasma levels of endogenous GH induced insulin resistance. Once GH levels were reduced by the administration of bromocriptine, glucose metabolism improved.