INTRODUCTION: Hyperprolactinemia is a common side-effect of antipsychotic treatment. Antipsychotics and hyperprolactinemia are both considered risk factors of metabolic disturbances and diabetes. Investigations on prolactin response to meal ingestion in antipsychotic-treated patients are missing.

MATERIAL AND METHODS: In a case-control design, 49 antipsychotic-treated, clinically stable, non-diabetic, schizophrenia spectrum male patients were compared with 93 healthy male controls by age (33.1, SD 7.4 vs. 32.9, SD 6.6 years), body mass index (26.2, SD 4.6 vs. 26.1, SD 3.9 kg/m(2)) and waist circumference (96.4, SD 13.0 vs. 96.7, SD 11.9 cm). Serum-prolactin was measured in the morning and 90 min after ingestion of a standardized liquid meal (2268 kJ).

RESULTS: Fasting prolactin levels varied considerably, and mean fasting prolactin levels did not significantly differ between patients and controls (12.33, SD 11.58 vs. 10.06, SD 8.67 ng/ml, p = 0.623). In the controls, postprandial serum prolactin was significantly reduced (Δ -2.53, SD 9.75 ng/ml, p = 0.016). In antipsychotic-treated patients postprandial serum prolactin tended to increase (Δ 2.62, SD 10.96 ng/ml, p = 0.081). Analyses of subgroups based on the prolactinogenic liability of their antipsychotic treatment indicated 22 to 65% higher postprandial prolactin levels with high and intermediate prolactinogenic antipsychotics.

DISCUSSION: A physiological postprandial suppression of serum prolactin appears absent in antipsychotic-treated males. Marked variability in fasting prolactin levels may reflect individual variations in the diurnal cycle. Uniform acquisition procedures accounting for diurnal variation and food intake may enhance reliability of prolactin levels in antipsychotic-treated male patients.