Counter-regulatory hormone responses to insulin-induced acute hypoglycemia in hypopituitary patients

Risk for severe hypoglycaemia with unawareness in GH-deficient patients during the insulin tolerance test

OBJECTIVE

The insulin tolerance test (ITT) has been suggested as the gold standard for diagnosing GH deficiency (GHD). The ITT is, however, potentially hazardous. Glucose monitoring during the ITT varies between centres and there is surprisingly little information on the actual level of blood glucose nadir and the duration of hypoglycaemia in patients undergoing the ITT. The aim of the present study was to closely monitor the blood glucose level and to register the presence of symptoms and signs of hypoglycaemia during the ITT.

DESIGN AND PATIENTS

Sixteen patients (seven women), aged 22-59 years were consecutively recruited for an ITT, and showed GHD (peak GH < 3 microg/l).

RESULTS

In five (31%) of the patients unawareness of hypoglycaemia was recorded, the median nadir blood glucose level was 1.4 mmol/l (range 1.1-1.9) and the duration of blood glucose < 2.2 mmol/l was 25 min (range 20-33). The remaining 11 patients were symptomatic, and tiredness (n=6) and dizziness (n=3) were the most frequent symptoms. In these symptomatic patients the median nadir blood glucose level was 1.3 mmol/l (range 1.0-1.6) and the duration of blood glucose < 2.2 mmol/l was 25 min (range 15-30).

CONCLUSIONS

In patients with GHD subjected to the ITT, symptoms of hypoglycaemia were scarce and a third showed unawareness. Close blood glucose monitoring is recommended at the ITT as low nadir blood glucose levels and long duration of hypoglycaemia may be present irrespective of symptoms of hypoglycaemia. Recommendations for intervention with intravenous glucose, at unacceptable low blood glucose levels or at prolonged hypoglycaemia, are warranted.

Low dose of insulin for assessment of growth hormone and cortisol release in short children

OBJECTIVE

In 55 prepubertal children with growth failure, aged 8.62 +/- 2.89 years, we evaluated the efficacy of a test using only half the usual dose of insulin by comparing the results with those obtained during a classical arginine tolerance test, performed separately.

PATIENTS AND METHODS

The patients were randomly divided into two groups: group A consisting of 37 children received 0.05 U/kg insulin, while group B consisting of 18 patients received 0.1 U/kg insulin. Each child received the same dose of arginine per kg during the second test.

RESULTS

Serum growth hormone (GH) peak levels were significantly (p < 0.01) lower in children of group A (6.59 +/- 4.10 ng/ml) than in those of group B (10.12 +/- 5.80 ng/ml). No differences of GH peak levels were found in patients of the two groups after arginine infusion. The injection of 0.05 U/kg insulin induced a significantly (p < 0.0001) lower percent decrease of serum glucose than 0.1 U/kg. No difference of the percent increase of serum cortisol induced by insulin at 0.05 U/kg and 0.1 U/kg was observed.

CONCLUSION

The diagnosis of GH deficiency in children can be supported by a blunted GH response after two or more pharmacological stimuli including hypoglycaemia induced by only half the usual dose of insulin.

Defect in epinephrine production in children with craniopharyngioma: functional or organic origin?

Despite pituitary hormone replacement, patients with craniopharyngioma often complain of fatigue. They may have deficient control of catecholamine secretion caused by hypothalamic lesion. Another hypothesis is a functional defect in catecholamine production through either glucocorticoid deficiency because high intraadrenal glucocorticoid concentration is necessary for epinephrine synthesis or unrecognized hypoglycemia, which can intrinsically alter epinephrine secretion. We measured catecholamine response to insulin-induced hypoglycemia and orthostasis, and 24-h urinary catecholamine excretion, in 16 children with craniopharyngioma (patients) and 27 sex- and age-matched short children. We also studied the influence of a 4-fold increase in the usual daily dose of hydrocortisone on catecholamine excretion (50 vs. 12 mg/m(2) of body surface area) in the glucocorticoid-deficient patients. Last, we compared 24-h continuous sc glucose in patients and 10 sex- and age-matched healthy children. The results are expressed as medians (25th, 75th). For a similar blood glucose nadir after insulin administration, peak plasma epinephrine in response to hypoglycemia was lower in patients vs. controls [420 (120, 715) vs. 730 (460, 1200) ng/liter, P < 0.01], whereas peak plasma norepinephrine was higher [390 (280, 550) vs. 270 (180, 280) ng/liter, P < 0.05]. Catecholamine response to orthostasis did not differ between groups. Urinary epinephrine was significantly lower in patients (P < 0.001), whereas urinary norepinephrine was similar. The extent of epinephrine deficiency correlated with neither tumor size nor hypothalamic involvement. A 4-fold higher hydrocortisone dose did not correct the defective epinephrine excretion in the glucocorticoid-deficient patients. Last, the 24-h sc glucose values were similar between patients and controls. In conclusion, children with craniopharyngioma have a defect in epinephrine but not norepinephrine production. There is no proof of a univocal origin, either organic or functional. Whether abnormal catecholamine secretion alters glucose level during fasting or acute illness, or hampers adaptation to exercise, requires further studies.

Increased insulin sensitivity in young, growth hormone deficient children

OBJECTIVE

Although growth hormone (GH) has well documented insulin antagonistic effects, GH deficient adults often demonstrate insulin resistance. In young GH deficient children, increased susceptibility to hypoglycaemia might indicate increased insulin sensitivity; however, this has not been documented. We therefore determined insulin sensitivity in GH deficient and GH sufficient children.

DESIGN AND PATIENTS

Prospective study of children undergoing insulin tolerance tests for clinical investigation of GH or cortisol secretion at a regional Paediatric Endocrine/Growth Clinic between October 1986 and December 1997. Ninety-one tests were performed in children with GH deficiency and 142 tests in children with normal GH response to insulin (peak GH > or = 20 IU/l).

MEASUREMENTS

The standard insulin tolerance test was modified to permit frequent measurements of glucose (0, 5, 10, 15, 20, 30, 45, 60 and 90 minutes). Rate of log glucose disappearance in the first 15 minutes was calculated as a direct measure of insulin sensitivity.

RESULTS

GH deficient children were more insulin sensitive than GH sufficient children (P = 0.004) and had lower glucose nadirs post-insulin (P = 0.005). Subgroup analysis revealed that these differences were greater in younger (< 12 years old) or pre/early pubertal children. In 14 prepubertal children, exogenous sex steroid priming resulted in lower insulin sensitivity (P < 0.05) compared to nonprimed tests.

CONCLUSIONS

Young GH deficient children were more insulin sensitive than children with normal GH secretion. This difference attenuated with age and puberty, possibly secondary to pubertal sex steroids; however, insulin resistance as reported in GH deficient adults, was not observed in adolescents.