A 30-year-old woman, who has two healthy children, notes that she has had no menstrual periods for the past 6 months, but she is not pregnant and has been taking no medications. Within the past week, she has noted some milk production from her breasts. She has been bothered by headaches for the past 3 months. After nearly hitting a bus while changing lanes in her vehicle, she is concerned with her vision and visits an optometrist, who finds her lateral vision to be reduced. On physical examiantion she is afebrile and normotensive. Which of the following laboratory test findings is most likely to be present in this woman? a. Lack of growth hormone suppression b. Hyperprolactinemia c. Increased serum cortisol d. Decreased serum TSH e. Abnormal glucose tolerance test