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Urotensin-II, a potent mammalian vasoconstrictor, may play a role in the etiology of essential hypertension. However, a species suitable for assessing such a role, one where a "classical" systemic hypertensive response (increase in mean blood pressure and systemic vascular resistance) is observed following bolus i.v. urotensin-II administration, has yet to be identified. The present study demonstrates that the cat may represent such a species since urotensin-II potently (pEC(50)s 9.68+/-0.24-8.73+/-0.08) and efficaciously (E(max) 73+/-15%-205+/-21% KCl) constricts all feline isolated arteries studied (aortae, renal, femoral, carotid, and mesenteric conduit/resistance). Accordingly, exogenous urotensin-II (1 nmol/kg, i.v.) effectively doubles both mean blood pressure (from 99+/-14 to 183+/-15 mmHg) and systemic vascular resistance (from 0.36+/-0.12 to 0.86+/-0.20 mmHg/ml/min) in the anaesthetized cat (without altering heart rate or stroke volume). Thus, in view of these profound contractile effects, the cat could be suitable for determining the effects of urotensin-II receptor antagonism on cardiovascular homeostasis in both normal and diseased states.

Human monocytic THP-1 cells were differentiated to macrophages by incubation with 1.0 microM phorbol myristate acetate (PMA) for 1 to 18 h; cells were then assayed for the ability to migrate to MCP-1. In comparison to undifferentiated monocytes, the chemotactic response of PMA-differentiated cells to MCP-1 decreased with treatment time. This loss of the chemotactic response to MCP-1 correlated with increased in cellular enzymes characteristic of differentiated macrophages. Receptors binding assays demonstrated a parallel decrease in specific binding of MCP-1 with increased incubation with PMA. Undifferentiated monocytes had 1175 +/- 387 receptors per cell with a Kd of 1.53 +/- 0.35 nM. Cells differentiated to macrophages with PMA rapidly lost the ability to bind MCP-1, with a significant decrease apparent following 3 h incubation with PMA. The reduction in specific binding of MCP-1 by M phi-THP-1 cells was due to a decrease in both receptor number and affinity; receptor number was reduced to 481 +/- 106 receptors/cells with a Kd of 3.16 +/- 0.7 nM on cells treated for 3 h with PMA. The demonstrated changes in receptor affinity and expression with differentiation may be a mechanism of controlling macrophage responsiveness to chemokines in inflammatory foci.

Fluorescent probes have been utilized to label leukocytes for both in vivo and in vitro studies of cell migration; however, the effects of such probes on migration have not been determined. The aim of this study was to examine the effects of two commonly used fluorescent probes on leukocyte chemotaxis. J774 macrophages were labeled with either calcein-acetoxymethyl ester (calcein-AM) or 2',7'-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein, acetomethyl ester (BCECF-AM), then assayed for their ability to migrate to zymosan-activated serum (ZAS). Cell migration was quantified by two methods: visual counting of cells and measuring cell fluorescence. Using the cell counts, comparison of unlabeled and fluorescently labeled macrophages demonstrated that BCECF-AM decreased the number of cells responding to ZAS, while calcein-AM had essentially no effect. Neither probe significantly affected the number of cells migrating to medium alone. The inhibitory effects of BCECF-AM on cell migration increased with probe concentration (0.1-1.0 microM) and cell fluorescence. Cell viability was unaffected by either probe. In contrast to the results obtained by visual counting, measuring fluorescence of migrated cells did not reveal a significant difference between the chemotactic response of macrophages labeled with BCECF-AM and those labeled with calcein-AM. These experiments indicated that fluorescent probes can affect the chemotactic response and that inhibitory activity of these probes may not be detected when chemotaxis is quantified solely by automated methods.

The cardiotonic activity of milrinone (Win 47203), a potent analogue of amrinone, was demonstrated in isolated guinea pig, cat, rabbit, rat, and hamster atria and papillary muscles. Milrinone, in concentrations of 0.1-300 micrograms/ml, caused concentration-dependent increases in guinea pig papillary muscle and atrial developed tension with minimal increases in atrial rate. Compared with the in vitro inotropic activity of amrinone, milrinone was approximately 30 times more potent. The inotropic and chronotropic effects of milrinone do not appear to be mediated by the release of endogenous norepinephrine, by the direct stimulation of beta-adrenergic or histaminergic receptors, or through the stimulation of prostaglandin synthesis. The inotropic response of the guinea pig papillary muscles to isoproterenol was potentiated when isoproterenol was given at the peak effect of a minimally effective concentration of milrinone or after prolonged incubation with milrinone. No potentiation was observed when isoproterenol was administered at the peak effect of a high concentration of milrinone, which suggests that the positive inotropic action of milrinone may not be solely attributable to cyclic AMP phosphodiesterase inhibition.