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. Under 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 once a day, the patients underwent non-invasive ambulatory blood pressure monitoring for 24 hours. The average 24-hour blood pressure before hydrocortisone replacement was 92.9 +/- 1.0 (systolic)/53.2 +/- 0.8mmHg (diastolic), while that after hydrocortisone replacement once or twice 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-hydroxycorticosteroids in hydrocortisone replacement once a day were 7.7mg/12hr (daytime) and 1.4mg/12hr (nighttime), respectively, while those in hydrocortisone replacement twice a day were 3.9mg/12hr (daytime) and 3.6mg/12hr (nighttime), respectively. Urinary 17-ketosteroids, epinephrine and norepinephrine did not show any differences between hydrocortisone replacement once and twice a day. These results suggest that hydrocortisone administration is one of the factors which modulate the circadian variation of blood pressure in patients with hypopituitarism, and may also suggest that the circadian change of cortisol secretion participates, at least in part, in the formation of an intrinsic circadian rhythm of blood pressure.