MODULATION OF CIRCADIAN-RHYTHM OF BLOOD-PRESSURE BY CORTISOL IN PATIENTS WITH HYPOPITUITARISM

We conducted a study to determine the effect of exogenous cortisol on circadian blood pressure changes in patients with hypopituitarism. Und er replacement with hydrocortisone of 15 to 25mg either once (8:00) or twice a day (8:00 and 20:00), and with prednisolone of 3.75 to 5mg on ce a day, the patients underwent non-invasive ambulatory blood pressur e monitoring for 24 hours. The average 24-hour blood pressure before h ydrocortisone replacement was 92.9 +/- 1.0 (systolic)/53.2 +/- 0.8mmHg (diastolic), while that after hydrocortisone replacement once or twic e a day and prednisolone replacement significantly increased to 108.2 +/- 1.4/63.5 +/- 0.9mmHg, 109.1 +/- 1.6/62.3 +/- 1.0mmHg, and 105.4 +/ - 1.2/62.3 +/- 0.9mmHg, respectively. Hydrocortisone replacement once a day showed a significant increase in day-night differences of blood pressure, while hydrocortisone replacement twice a day did not. There were no differences in nocturnal decrease in pulse rate between these two replacements. The daytime and nighttime urinary excretions of 17-h ydroxycorticosteroids in hydrocortisone replacement once a day were 7. 7mg/12hr (daytime) and 1.4mg/12hr (nighttime), respectively, while tho se in hydrocortisone replacement twice a day were 3.9mg/12hr (daytime) and 3.6mg/12hr (nighttime), respectively. Urinary 17-ketosteroids, ep inephrine and norepinephrine did not show any differences between hydr ocortisone replacement once and twice a day. These results suggest tha t hydrocortisone administration is one of the factors which modulate t he circadian variation of blood pressure in patients with hypopituitar ism, and may also suggest that the circadian change of cortisol secret ion participates, at least in part, in the formation of an intrinsic c ircadian rhythm of blood pressure.