Rats with regenerating adrenals are more hypertensive in the morning than afternoon

Abstract

In rats following unilateral nephroadrenalectomy and contralateral adrenal enucleation, adrenocortical tissue regenerates and secretes some steroids in abnormal amounts but with a diurnal rhythmicity. This study investigated whether the level of blood pressure (BP) in these rats also varies with the time of day. Systolic BP was measured by the tail-cuff method twice daily [between 0700 and 1000 h (A.M.) and again between 1400 and 1700 h (P.M.)] in conscious Wistar rats before and after unilateral nephroadrenalectomy and either contralateral adrenal-enucleation (AE) or sham-operation (SO); all rats were given 1% NaCl to drink postoperatively. During the 4th wk after surgery, systolic BP in AE rats was higher than in SO rats at both times of day, but the difference was greater A.M. (SO = 142 +/- 2 mmHg, AE = 176 +/- 4 mmHg) than P.M. (SO = 138 +/- 2 mmHg, AE = 150 +/- 2 mmHg). The hypertension and the A.M.-P.M. changes in BP in AE rats were also seen with intra-arterial recording. These phenomena were not directly associated with changes in plasma volume, plasma Na+ concentration, or in the plasma levels of corticosterone or 18-hydroxydeoxycorticosterone.