Barry A. Berkowitz

β-Adrenergic receptor decrease in diabetic rat hearts

Abstract Bradycardia has been found to accompany experimentally induced diabetes in rats. This negative chronotropic effect can be explained in terms of a decrease in the number of β-adrenergic receptors in diabetic rat ventricular tissue. A 28% decrease in ventricular β-adrenoceptors was found to accompany a 24% decrease in heart rate for diabetic rats relative to controls. No change in the affinity of the receptor was observed in the diabetic animals. The decrease in ventricular β-adrenoceptors with diabetes might account for the postulated “ventricular stiffness” previously used to explain myocardial dysfunction in diabetic dogs and humans.

Differential selectivity of endothelium-derived relaxing factor and nitric oxide in smooth muscle.

The selectivity of endothelium‐derived relaxing factor (EDRF) and nitric oxide (NO) on smooth muscle relaxation was examined and compared. EDRF released from bovine pulmonary arterial endothelium (BPAE) in culture and NO were superfused over vascular, tracheal, gastrointestinal and uterine smooth muscle. EDRF relaxed vascular smooth muscle but not tracheal, gastrointestinal or uterine smooth muscle. NO relaxed vascular and gastrointestinal smooth muscle but not tracheal or uterine smooth muscle. There was a differential selectivity between the relaxant effect of EDRF and NO on smooth muscle

SCH 23390 and SK&F 83566 are antagonists at vascular dopamine and serotonin receptors.

SCH 23390 and SK&F 83566 have been utilized as selective antagonists at postjunctional dopamine receptors. However, in the isolated rabbit thoracic aorta evidence for competitive antagonism of serotonin was obtained. The KB values were 11 and 34 nM for SK&F R-83566 and SCH 23390, respectively. The S-enantiomer of SK&F 83566 was a weaker antagonist at the vascular serotonin receptor (KB = 1.5 microM). Thus, these results indicate that SCH 23390 and SK&F 83566 are not totally specific for the dopamine DA-1 receptor because they can also be potent antagonists at the vascular serotonin receptor.

The DA1 receptor agonist fenoldopam (SK & F 82526) is also an α2-adrenoceptor antagonist

The alpha-adrenoceptor activity of fenoldopam was evaluated in three different in vitro tissue preparations. In rabbit isolated aortic rings fenoldopam displayed weak alpha 1-adrenoceptor antagonist activity (-log KB = 5.41) and displayed no alpha 1-adrenoceptor agonist activity. In contrast, fenoldopam demonstrated moderately potent antagonist properties at the alpha 2-adrenoceptor in two other tissue preparations. In in vitro model systems used for the characterization of alpha 2-adrenoceptors, fenoldopam competitively antagonized the effects of the alpha 2-adrenoceptor agonist B-HT 920. In the dog isolated saphenous vein and in the isolated field-stimulated guinea-pig ileum, fenoldopam antagonized the effects of B-HT 920 with -log KB values of 7.78 and 7.60, respectively. These data indicate that in addition to being an agonist at DA1 receptors, fenoldopam is also a relatively selective antagonist at alpha 2-adrenoceptors.

What is the relationship between the endothelium derived relaxant factor and nitric oxide

Nitric oxide gas in solution (NO) relaxes blood vessels with similar actions and pharmacodynamics as the endothelium derived relaxant factor (EDRF) and has been proposed to be a component of the materials released from stimulated endothelial cells. Certain data however suggest that EDRF and NO may not be identical. In some non-vascular smooth muscles, NO and EDRF exhibit markedly different pharmacologic profiles. Furthermore the interaction of EDRF and NO with anion exchange resins differ. The hypothesis that EDRF is identical to nitric oxide gas in solution or a nitrogen oxide containing compound is discussed.

Endothelial thromboxane receptors: biochemical characterization and functional implications

We have identified thromboxane specific receptors in membrane preparations of bovine pulmonary artery endothelial cells using a potent thromboxane specific antagonist, [125I]-PTA-OH in a binding assay. The binding was specific and saturable. Neither thromboxane B2, prostaglandin D2 nor prostaglandin F2 alpha displaced the ligand (0.1 nM) at concentrations up to 10 microM. However, binding was displaced by IPTA-OH greater than SQ29548 greater than U46619. In addition, we observed that thromboxane mimetic U46619 significantly lowered the basal production of prostacyclin and also markedly suppressed bradykinin-stimulated prostacyclin released by endothelial cells. We propose that an important biological effect of thromboxane on vascular endothelial cells may be the suppression of prostacyclin production.

2-Nor-leukotriene analogs: Antagonists of the airway and vascular smooth muscle effects of leukotriene C4, D4 and E4

A structural analog of LTD4, 4R-hydroxy-5S-cysteinylglycyl-6Z-nonadecenoic acid (4R, 5S, 6Z-2-nor-LTD1) has been synthesized and pharmacologically characterized. It significantly antagonized the contractile action of LTD4, LTC4 and LTE4 in guinea pig airways. In addition, this compound antagonized the in vitro vasoconstrictive effects of LTD4 in the guinea pig pulmonary artery. The study of a series of structural analogs of 4R, 5S, 6Z-2-nor-LTD1 suggests that the spatial separation of the C-1 (eicosanoid) carboxyl relative to the hydroxyl is a critical determinant in LTD4 agonist/antagonist activity.

Vascular Dopamine and Dopamine Receptor Agonists

Regulation and modulation of the sympathetic nervous system have been and remain cornerstone strategies for the treatment of cardiovascular disease. Whereas stimulating, mimicking or antagonizing norepinephrine and epinphrine have been the most frequently utilized approach to cardiovascular renal therapeutics, the possibility that dopamine and dopamine receptors serve as useful target sites for drug action has received less attention.

The inhibition of release of endothelium-derived relaxant factor by manoalide, a potent inhibitor of phospholipase A2.

1 The inhibitory action of manoalide on vascular relaxation was characterized. Manoalide was a potent inhibitor of endothelium‐dependent relaxations in the isolated aorta of the rabbit. Responses to acetylcholine (ACh), A23187 and substance P were reduced by manoalide in a dose‐dependent manner whilst those to nitroglycerin were unaffected. 2 Repeated washing of manoalide‐treated tissues did not restore the relaxant response to ACh, indicating an irreversible action of manoalide. Scanning electron microscopic studies revealed that the endothelium remained intact on manoalide‐treated tissues. 3 Rabbit aortae from which the endothelium had been removed relaxed in response to perfusion with ACh when delivered via an upstream endothelium‐bearing tissue, indicating release of an endothelium‐derived relaxant factor (EDRF). Incubation of the tissue without endothelium with manoalide (100 nm; 30 min) or inclusion of manoalide in the superfusate at a point just distal to the endothelium bearing tissue did not reduce the relaxant potency of EDRF. 4 Contractile responses of the guinea‐pig isolated ileum to ACh were not affected by manoalide and, furthermore, binding of [3H]‐quinuclidinyl benzilate to striatal membranes was not reduced by manoalide except at very high concentrations. 5 Manoalide therefore appears to inhibit vascular relaxation with a selectivity directed towards that mediated by EDRF. A direct antagonism of neither cholinoceptors nor EDRF receptors occurs and it is suggested that manoalide acts at a site within the endothelium to inhibit the synthesis and/or release of EDRF. Based upon these and previous data the possibility that EDRF is lipid‐like or controlled by an arachidonic acid metabolite must continue to be considered.