Growth Hormone Axis

A 28-year-old woman presents with amenorrhea for 8 months and galactorrhea. She denies headaches or visual symptoms. On examination, there is no thyroid enlargement or other endocrine stigmata. Serum prolactin is 180 ng/mL (normal <25 ng/mL), TSH is normal, and free T4 is normal. MRI pituitary shows a 0.8 cm lesion in the anterior pituitary with no suprasellar extension. GH and cortisol levels are normal. A pregnancy test is negative. Which of the following findings would BEST differentiate this patient's condition from secondary hyperprolactinemia due to hypothyroidism or medications?

A 32-year-old man presents to the endocrinology clinic with complaints of progressive joint pain, carpal tunnel syndrome, and coarsening of facial features over the past 5 years. His wife notes that his shoe size has increased from 8 to 11 over this period. On examination, he has prognathism, macroglossia, and enlarged hands with spade-like appearance. Fasting blood glucose is 156 mg/dL. A random serum GH level is 8 ng/mL (normal <2 ng/mL). Oral glucose tolerance test (OGTT) shows failure of GH suppression below 1 ng/mL after 75 g glucose load. MRI pituitary shows a 2.2 cm sellar mass with suprasellar extension. Which of the following is the most appropriate next step in management?

Which hormone exerts the strongest inhibitory effect on growth hormone (GH) secretion from the anterior pituitary?

Growth hormone exerts its metabolic effects primarily through which mechanism?