Effects of clonidine on the pituitary hormonal response to pelvic surgery

We have investigated the effects of the central alpha 2 adrenoreceptor agonist, clonidine, given i.v. before induction of anaesthesia, on the haemodynamic and endocrine responses to pelvic surgery. Twenty patients were allocated randomly to receive either clonidine 3 micrograms kg-1 or an equivalent volume of 0.9% sodium chloride solution. Arterial pressure, heart rate, and circulating concentrations of cortisol, growth hormone, glucose and lactate were measured during and in the 24 h after total abdominal hysterectomy. Arterial pressure and heart rate decreased significantly in the clonidine group during surgery and in the early postoperative period. There were no differences between groups in serum cortisol or growth hormone concentrations throughout the study. Despite an effective decrease in the cardiovascular response to surgery, clonidine 3 micrograms kg-1 i.v. had no significant effect on pituitary hormone secretion.