The effect of chronic propranolol treatment on overnight plasma levels of anterior pituitary and related hormones.

1 Treatment of eight healthy males with propranolol (80 mg twice daily) for 6 weeks resulted in a significant reduction in overnight plasma levels of prolactin and LH. 2 Plasma testosterone levels were elevated whilst GH and cortisol were unchanged by such treatment. 3 Measurement of overnight hormone levels 48 h after discontinuing treatment showed no evidence of a 'rebound' phenomenon. 4 Cortisol, GH, prolactin, and testosterone plasma levels all showed time dependent changes: propranolol treatment significantly altered the time course of cortisol but not of the other hormones. 5 The effects of chronic propranolol treatment are discussed in terms of a probable direct central action of the drug. In addition the lowered plasma prolactin levels may directly contribute to the hypotensive action of propranolol.