Dopamine agonists were used in the past to prevent breast engorgement when breast-feeding was not desired. Their use for this purpose has been discouraged because of toxicity (see Toxicity & Contraindications).
C. Acromegaly
A dopamine agonist alone or in combination with pituitary surgery, radiation therapy, or octreotide administration can be used
A Dopamine agonist therapy during the early weeks of pregnancy 0 2 4 6 8 1012141618202224 Weeks of cabergoline therapy has not been associated with an increased risk of spontaneous abortion or congenital malformations. Although there has been a longer experience with the safety of bromocriptine during early pregnancy, there is growing evidence that cabergoline is also safe in women with macroadenomas who must continue a dopamine agonist during pregnancy. In patients with small pituitary adenomas, dopamine agonist therapy is discontinued upon conception because growth of microadenomas during pregnancy is rare. Patients with very large adenomas require vigilance for tumor progression and often require a dopamine agonist throughout pregnancy. There have been rare reports of stroke or coronary thrombosis in postpartum women taking bromocriptine to suppress postpartum lactation.
The two posterior pituitary hormones—vasopressin and oxytocin— are synthesized in neuronal cell bodies in the hypothalamus and transported via their axons to the posterior pituitary, where they are stored and then released into the circulation. Each has limited but % of patients
FIGURE 37–4 Results from a clinical trial of cabergoline in women with hyperprolactinemia and anovulation. A: The dashed line indicates the upper limit of normal serum prolactin concentrations.
B: Complete success was defined as pregnancy or at least two consecutive menses with evidence of ovulation at least once. Partial success was two menstrual cycles without evidence of ovulation or just one ovulatory cycle. The most common reasons for withdrawal from the trial were nausea, headache, dizziness, abdominal pain, and fatigue. (Adapted from Webster J et al: A comparison of cabergoline and bromocriptine in the treatment of hyperprolactinemic amenorrhea. N Engl J Med 1994;331:904.) to treat acromegaly. The doses required are higher than those used to treat hyperprolactinemia. For example, patients with acromegaly require 20–30 mg/d of bromocriptine and seldom respond adequately to bromocriptine alone unless the pituitary tumor secretes prolactin as well as GH.
Dopamine agonists can cause nausea, headache, light-headedness, orthostatic hypotension, and fatigue. Psychiatric manifestations occasionally occur, even at lower doses, and may take months to resolve. Erythromelalgia occurs rarely. High dosages of ergot-derived preparations can cause cold-induced peripheral digital vasospasm. Pulmonary infiltrates have occurred with chronic high-dosage therapy. Cabergoline treatment at high doses for Parkinson’s disease is associated with higher risk of valvular heart disease, but probably not at the lower dose used for hyperprolactinemia. Cabergoline appears to cause nausea less often than bromocriptine. Vaginal administration can reduce nausea, but may cause local irritation.
important clinical uses.
Oxytocin is a peptide hormone secreted by the posterior pituitary. Oxytocin stimulates muscular contractions in the uterus and myoepithelial contractions in the breast. Thus, it is involved in parturition and the letdown of milk. During the second half of pregnancy, uterine smooth muscle shows an increase in the expression of oxytocin receptors and becomes increasingly sensitive to the stimulant action of endogenous oxytocin.
A. Structure