DECREASED BLOOD-PRESSURE RESPONSE TO INFUSED NORADRENALINE IN NORMOTENSIVE AS COMPARED TO HYPERTENSIVE PATIENTS WITH PRIMARY HYPOTHYROIDISM

OBJECTIVE AND PATIENTS To further explore the difference in plasma nor adrenaline in normotensive and hypertensive hypothyroid patients we ha ve investigated the presser response to exogenous noradrenaline in 11 normotensive and five hypertensive patients with primary hypothyroidis m before and after thyroxine replacement. Seven healthy subjects serve d as controls. DESIGN The patients were studied under metabolic ward c onditions and received a Na+ and K+ defined diet for 4 days. The contr ols received the same diet on an ambulatory basis for 3 days and were admitted to the ward in the evening on the third day. In the morning o f day 4 a graded noradrenaline infusion was given. When the increase i n systolic blood pressure in two consecutive registrations was at leas t 20 mmHg as compared to basal values the noradrenaline infusion was s topped. The dose required to increase systolic blood pressure by 20 mm Hg (I-20) was determined. RESULTS During hypothyroidism the I-20 was 1 20 ng/kg BW/min in normotensive patients and 39 in hypertensive patien ts as compared to 62 in controls. The 120 was higher in normotensives as compared to hypertensives (P=0.041). The I-20 was not different in hypertensives as compared to controls. When the patients had become eu thyroid I-20 decreased to 51 ng/kg BW/min (P=0.04) in the normotensive s, but remained unchanged in the hypertensives. There was no differenc e in I-20 between normotensive and hypertensive patients in the euthyr oid state, or when compared to controls. CONCLUSION The presser respon se to noradrenaline was decreased in normotensive hypothyroid as compa red to hypertensive hypothyroid patients, indicating a decreased perip heral sensitivity to noradrenaline in normotensive hypothyroid patient s. Following thyroxine replacement the decreased response became norma l.