Turnover of adrenergic receptors under normal and desensitized conditions

Perioperative hypertension in phaeochromocytoma patients undergoing adrenalectomy

This study was designed to compare perioperative blood pressure (BP) management in hypertensive patients with phaeochromocytoma undergoing preoperative α-blockade and in patients with other suprarenal gland tumors. Perioperative hemodynamic data and immediate postoperative outcome in two groups undergoing adrenalectomy were compared. 483 medical charts from urologic patients with tumors were analyzed. In the hypertensive (n = 168) group, 20 patients with suprarenal gland tumors were identified (phaeochromocytoma n = 11, other tumors n = 9). Demographic data, intraoperative consumption of fentanyl and phentolamine, preoperative hospital stay and postoperative ICU stay were compared. Mean arterial pressure (MAP) was registered on the day before surgery, before anesthetic induction, during surgery, and upon admission in the intensive care unit (ICU). Although BP values did not differ significantly on the day before anesthesia, before induction and during operation, significantly more antihypertensive drugs were used for BP regulation in phaeochromocytoma patients versus the other tumor group. The phaeochromocytoma group required significantly more fentanyl during surgery (370±87 vs. 242±35 µg; p = 0.04). MAP upon ICU admission was significantly lower (85.1 vs. 97.4, p = 0.02) after adrenalectomy in phaeochromocytoma patients versus the other tumor group. The postoperative MAP decreased significantly in the phaeochromocytoma group (21.51 mmHg, p = 0.005), whereas significant differences according to preoperative values were not observed in the other tumor group (5.5 mmHg, p = 0.416). Prolonged preoperative hospital stay (24.6 vs. 10.0 days, p = 0.005) and ICU stay were registered in the phaeochromocytoma group. Pheochromocytoma patients had more pronounced perioperative BP oscillations, needed more antihypertensive drugs, analgesics and required prolonged hospital stay than patients with other adrenal tumors. Prolonged α-blockade may have contributed to these effects.

Modulation of the Na(+)-H(+) antiport activity by adrenaline on erythrocytes from normal and obese individuals

The effect of adrenaline on normal and obese human Na(+)-H(+) antiport (NHE 1) erythrocyte activity has been studied. Adrenaline increased both intracellular pH (pHi) and Na(+) influx in erythrocyte suspensions. This effect of adrenaline was inhibited by amiloride or EIPA, indicating that adrenaline stimulated NHE 1. Phorbol myristicate ester (PMA), a protein kinase C (PKC) stimulator, increased the activity of NHE 1 whereas calphostin C, a PKC inhibitor, partially inhibited NHE 1 activation induced by adrenaline. The effect of adrenaline to NHE 1 was counteracted by prazocin and by propranolol as well indicating the involvement of both alpha and beta 2 adrenergic receptors. The effect of adrenaline on erythrocyte NHE 1 activity was significantly more profound in obese compared to normal subjects. These data indicate that adrenaline induces an increase of pHi and Na(+) uptake of human erythrocytes through stimulation of NHE 1 activity. The significantly more profound stimulation of NHE 1 activity by adrenaline in obese as compared to normal subjects is discussed.

Recovery of beta-receptors and adenylate cyclase from desensitization induced by short term heat exposure in rat parotid glands

1. The recovery of rat parotid beta-adrenergic receptors (beta-AR) and adenylate cyclase (AC) from heat (33 degrees C)-induced desensitization was studied. 2. Down-regulated cell surface beta-AR and AC activity in response to isoprenaline (IPR) returned to the control level 120 hr after the termination of heat exposure. 3. However, beta-AR in parotid crude membranes increased over the control level for 48-120 hr. 4. Coupling between beta-AR and G protein(s) was attenuated at 120 hr. 5. These data suggest that beta-AR on the cell surface, but not those internalized, can transduce biological responses.

Failure of ritodrine to prevent preterm labor in the sheep

OBJECTIVES

The purpose of this study was to determine whether continuous infusion of ritodrine could prevent preterm delivery in sheep.

STUDY DESIGN

Sheep in preterm labor induced by RU 486 (mifepristone) received infusions of either ritodrine (n = 5) or saline solution (n = 5), and the progress of labor was monitored. beta 2-Adrenergic receptor density and function (agonist-induced cyclic adenosine monophosphate production) was measured in myometrial samples from both groups.

RESULTS

Ritodrine initially inhibited labor contractions. This inhibition was only maintained for 16 hours, after which both the amplitude and frequency of electromyographic bursts and contractions returned. The failure of the myometrium to respond to ritodrine (desensitization) was associated with significant reductions in agonist-induced cyclic adenosine monophosphate production and beta 2-adrenergic receptor concentration in myometrial tissue collected from these animals compared with the saline solution-treated controls.

CONCLUSIONS

Continuous infusion of ritodrine to sheep in preterm labor produces only a transient inhibition of contractions. This desensitization is caused by a down-regulation of myometrial beta 2-adrenergic receptors.