Prolactin and β-endorphin responses to hypoglycemia are reduced in well-controlled insulin-dependent diabetes mellitus

Abstract

Several pituitary hormones, including corticotropin (ACTH), growth hormone (GH), prolactin, and β-endorphin (but not thyrotropin, follicle-stimulating hormone, or luteinizing hormone), are released in response to hypoglycemia in normal subjects. In patients with insulin-dependent diabetes mellitus (IDDM), the degree of glycemic control is known to alter ACTH and GH responses to hypoglycemia. The current study was performed to examine the effect of glycemic control on prolactin and β-endorphin responses to hypoglycemia in subjects with IDDM. We performed 3-hour stepped hypoglycemic-hyperinsulinemic clamp studies (12 pmol/kg/min) during which plasma glucose was decreased from 5.0 mmol/L to 2.2 mmol/L in steps of 0.6 mmol/L every 30 minutes in 20 subjects with uncomplicated IDDM (12 males and eight females; age, 26 ± 2 years; IDDM duration, 10 ± 1 years; body mass index, 23.6 ± 0.6 kg/m 2) and 10 healthy subjects (five males and five females aged 30 ± 1 years). The 10 diabetic subjects in good glycemic control (mean hemoglobin A 1 [HbA 1], 7.5% ± 0.3%; normal range, 5.4% to 7.4%) were compared with the 10 poorly controlled patients (mean HbA 1, 12.6% ± 0.5%; P < 0.001 v well-controlled diabetic group). During hypoglycemia, prolactin levels in the well-controlled diabetic group did not change (7 ± 1 μg/L at plasma glucose 5.0 mmol/L to 9 ± 2 μg/L at plasma glucose 2.2 mmol/L), whereas prolactin levels increased markedly in the poorly controlled diabetic group (7 ± 2 μg/L to 44 ± 17 μg/L) and healthy volunteers (12 ± 2 μg/L to 60 ± 19 μg/L, P < .05 between IDDM groups). The plasma glucose threshold required for stimulation of prolactin secretion was 2.2 ± 0.1 mmol/L in well-controlled IDDM, 3.0 ± 0.4 mmol/L in poorly controlled IDDM, and 2.4 ± 0.1 mmol/L in healthy subjects ( P < .05 between IDDM groups). Responses in males and females were similar. The increase in β-endorphin levels was also attenuated in well-controlled IDDM patients (4 ± 1 pmol/L at plasma glucose 5.0 mmol/L to 11 ± 4 pmol/L at plasma glucose 2.2 mmol/L) versus poorly controlled IDDM patients (5 ± 1 pmol/L to 26 ± 7 pmol/L) and healthy subjects (8 ± 1 pmol/L to 56 ± 13 pmol/L). The plasma glucose threshold required for stimulation of β-endorphin release was again lower in well-controlled IDDM versus poorly controlled IDDM patients (2.2 ± 0.1 v 3.0 ± 0.3 mmol/L) and healthy subjects (2.5 ± 0.4 mmol/L, P < .05 between IDDM groups). In conclusion, prolactin and β-endorphin responses to a standardized hypoglycemic stimulus (plasma glucose, 2.2 mmol/L) are reduced and plasma glucose levels required to stimulate release of prolactin and β-endorphin are lower in well-controlled IDDM compared with poorly controlled IDDM and healthy subjects. Thus, stress hormones not previously considered to have a primary role in plasma glucose recovery from hypoglycemia are affected by glycemic control, suggesting a more generalized alteration of hypothalamic-pituitary responses to hypoglycemia in IDDM patients with strict glycemic control.