Hormone and forskolin-stimulated cyclic AMP accumulation in human lymphocytes: reliability of longitudinal time measurements

Subsensitivity of adenylyl cyclase-coupled receptors on mononuclear leukocytes from drug-free inpatients with a major depressive episode

Previous studies have demonstrated blunted beta-adrenergic responsivity in leukocytes from depressed patients. We sought to determine if this blunted cyclic adenosine monophosphate (AMP) response is specific for beta-adrenergic receptors (homologous), or whether other adenylyl cyclase-coupled receptors are also involved (heterologous), in order to localize this effect at the level of the receptor versus the coupling protein or the transducer, adenylyl cyclase. We studied adenylyl cyclase-mediated responses in peripheral blood mononuclear cells from 95 drug-free patients with a major depressive episode and 69 healthy controls. We found a similar degree of decrease in the peak cyclic AMP response to activation of the beta-adrenergic receptor (28%) and the prostaglandin receptor (34%) in the depressed patients, which indicated heterologous desensitization. Forskolin cyclic AMP responses were not blunted. Blunting of cyclic AMP responses to isoproterenol did not appear to correlate with levels of plasma norepinephrine and epinephrine or hypothalamic-pituitary-adrenocortical function. The absence of a decrease in the peak forskolin-generated cyclic AMP response, which involves direct activation of adenylyl cyclase, suggests an abnormality at the level of the coupling protein in these adenylyl-coupled receptors in depressed patients. Future studies need to determine whether this leukocyte signal transduction defect in depression also involves brain adenylyl cyclase-coupled receptors.

The effect of in vitro procedures on cyclic AMP accumulation in human leucocytes

The aim of this study was to investigate the effect of various methodological procedures or protocols on cyclic AMP formation in human leucocytes. The data showed that: (1) ATP content and lactate production was unaffected by hypotonic lysis during leucocyte isolation; (2) there was a linear relation between cell number/sample and the production of cyclic adenosine 3':5'-monophosphate (cAMP); (3) the interindividual variation markedly affected cAMP production during long observation periods (years), whereas day-to-day variation within a week was less important; (4) whole blood could be stored for up to 4 h (at 4 degrees C or 23 degrees C) without affecting cAMP accumulation; (5) isolated MNL could be stored for up to 2 h (at 4 degrees C) without affecting cAMP accumulation; and finally that (6) choice and concentration of phosphodiesterase inhibitors markedly influenced the basal and isoprenaline-induced cAMP accumulation. Evidence is provided that the rate of cAMP accumulation in response to isoprenaline of cells incubated in the presence of 2.5 mM 3-isobutyl-1-methyl-xanthine (IBMX) is reflecting the rate of cellular cAMP production.

Short-term delay in blood processing does not alter basal or isoproterenol-stimulated cyclic AMP accumulation in human lymphocytes

Isoproterenol-stimulated cyclic AMP (cAMP) accumulation in lymphocytes is an index of beta-adrenergic receptor functioning. It is not known if a delay between blood collection and subsequent cell preparation influences cAMP accumulation. We compared cAMP levels in lymphocytes processed from whole blood immediately after collection and following a 3.5 hour delay. There were no significant changes in either basal or stimulated levels of cAMP. This information may alleviate time constraints in certain experimental designs where immediate isolation of lymphocytes from whole blood may not be practical.