Jerome H. Fleisch

Beta-Receptor Activity in Aorta: Variations with Age and Species

Helically cut thoracic aortic strips (from rats, rabbits, and guinea pigs) in a state of low to moderate tone and under the influence of alpha-receptor blockade relaxed in response to isoproterenol. Propranolol blocked these relaxations. Helically cut thoracic aortic strips from cats and abdominal aortic strips from rats, rabbits, and cats were not relaxed by isoproterenol. In addition, aortic beta-receptor activity of rats and rabbits decreased with increasing age. The ability of thoracic aortas to be relaxed by isoproterenol was lost when rats were 90 days old and when rabbits were 2 years old. Significant loss of beta-receptor activity was not evident in rat trachea and stomach. Sodium nitrite completely relaxed thoracic and abdominal aortas from all species including thoracic aortas from old rats and rabbits. We conclude: (1) there are species differences in the response of thoracic aortic strips to beta-receptor stimulation; (2) a gradient in beta-receptor activity exists in the aorta with greater activity in the thoracic aorta and a relatively small amount of activity in the abdominal aorta; and (3) aortic beta-receptor activity decreases with increasing age.

Vascular Smooth Muscle Reactivity in Normotensive and Hypertensive Rats

Aortic strips from spontaneously hypertensive rats were less responsive than normal animals to the contractile effects of norepinephrine, serotonin, and potassium chloride but more reactive to the relaxant effects of the stimulant of beta receptors, isoproterenol. Thus, hypertension is not the result of an absence of beta receptor or a hypersensitivity of the vascular smooth muscle.

Pharmacologic Receptor Activity of Rabbit Aorta: Effect of Dithiothreitol and N-Ethylmaleimide

N-ethylmaleimide (NEM), an alkylating agent that covalently binds sulfhydryl groups, and dithiothreitol (DTT, Clelands reagent), which reduces disulfide bridges to sulfhydryl groups, affected drug-induced contractions of rabbit aorta. NEM depressed aortic responses to potassium chloride (KCl), norepinephrine, serotonin, histamine, and angiotensin II. This action was attributed to an interaction of NEM with sulfhydryl groups vital to either the membrane function or the contractile apparatus. DTT had minimal effects on responses to KCl, norepinephrine, and serotonin; it potentiated aortic contractions produced by histamine and abolished responses to angiotensin II. Enhancement of the histamine response by DTT was not accompanied by an effect on the histamine-metabolizing enzymes or by an alteration in the KB and pA2 values for pyrilamine. The results suggest that a disulfide bridge plays a prominent role in both histamine and angiotensin receptor activity of rabbit aorta. With regard to the histamine receptor system, two possibilities exist: (1) reduction of a disulfide bridge at some vital point increases receptor activity or (2) the histamine receptor system, normally in a reduced state, is oxidized in the artificial environment of the tissue bath and needs to be reduced to regain full activity.

Adenyl cyclase activity of rabbit aorta.

Adenyl cyclase activity in homogenates of thoracic and abdominal aorta from young and old rabbits was neither stimulated nor inhibited by isoprenaline, noradrenaline, 5‐hydroxytryptamine, or histamine but was markedly increased by sodium fluoride. Sodium fluoride‐stimulated adenyl cyclase activity was significantly higher in the abdominal than in the thoracic aorta. Neither the basal nor sodium fluoride‐stimulated adenyl cyclase activity of thoracic aorta changed with increasing age of the aorta. On the other hand, the abdominal aorta showed an increase in sodium fluoride‐stimulated activity but no change in basal activity with increasing age. After the ATP pool of intact thoracic aorta was prelabelled with [14C]‐adenine, isoprenaline did not enhance the formation of labelled cyclic AMP in intact aortic strips. Based on these data no correlation could be made between adenyl cyclase activity and the β‐receptor activity of this tissue.

LY393615, a novel neuronal Ca2+ and Na+ channel blocker with neuroprotective effects in models of in vitro and in vivo cerebral ischemia

In the present studies we have examined the effects of a new calcium channel blocker, LY393615 ((N-Butyl-[5,5-bis-(4-fluorophenyl)tetrahydrofuran-2-yl]methylamine hydrochloride, NCC1048) in a model of hypoxia-hypoglycaemia in vitro and in a gerbil model of global and in two rat models of focal cerebral ischaemia in vivo. Results indicated that LY393615 protected against hypoxia-hypoglycaemic insults in brain slices and also provided significant protection against ischaemia-induced hippocampal damage in gerbil global cerebral ischaemia when dosed at 10, 12.5 (P<0.05) or 15 mg/kg i.p. (P<0.01) 30 min before and 2 h 30 min after occlusion. The compound penetrated the brain well after a 15 mg/kg i.p. dose and had a half-life of 2.5 h. In further studies LY393615 was protective 1 h post-occlusion when administered at 15 mg/kg i.p. followed by 2 doses of 5 mg/kg i.p. 2 and 3 h later. LY393615 dosed at 15 mg/kg i.p. followed by 2 further doses of 5 mg/kg i.p. (2 and 3 h later) also produced a significant reduction in the infarct volume following Endothelin-1 (Et-1) middle cerebral artery occlusion in the rat when administration was initiated immediately (P<0.01) or 1 h (P<0.05) after occlusion. The compound was also evaluated in the intraluminal monofilament model of focal ischaemia. The animals had the middle cerebral artery occluded for 2 h, and 15 min after reperfusion LY393615 was administered at 15 mg/kg i.p. followed by 2 mg/kg/h i.v. infusion for 6 h. There was no reduction in infarct volume using this dosing protocol. In conclusion, in the present studies we have reported that a novel calcium channel blocker, LY393615, with good bioavailability protects against neuronal damage caused by hypoxia-hypoglycaemia in vitro and both global and focal cerebral ischaemia in vivo. The compound is neuroprotective when administered post-occlusion and may therefore be a useful anti-ischaemic agent.

Pharmacology of the Aorta

This brief review discusses some aspects of drug action on the spirally cut mammalian aorta. Drugs interact with one or more of five major areas: nerves innervating the tissue; drug receptors presumab

Release of slow reacting substance from various tissues by A23187

Release of slow reacting substances (SRS, leukotrienes) from lung in response to antigen (Brocklehurst 1960) or divalent cationic ionophores (Bach & Brashler 1974; Piper & Seale 1979) has been well documented. In addition to lung, SRS can be released from various sensitized guinea-pig tissues by antigen challenge (Brocklehurst 1960). However, limited information exists regarding comparative amounts of SRS capable of being released from tissues other than lung by ionophores. In the present investigation, we used A23187t (Wong et al 1973) to survey a variety of tissues from guinea-pig for their ability to synthesize and release SRS.

QUINOLINE-SUBSTITUTED DIHYDROINDOLES AS CYSLT1 (LTD4 RECEPTOR) ANTAGONISTS

Abstract A series of quinoline-substituted dihydroindoles has been synthesized and evaluated as antagonists of the cysLT 1 receptor. This series, exemplified by 2 (LY302905; pKi = 8.3 for inhibition of binding of 3 H-LTD 4 to guinea pig lung membranes), represents reduced analogues of the corresponding indoles that were previously shown to be potent, orally active cysLT 1 receptor antagonists. These dihydroindole compounds generally displayed increased in vitro and in vivo (oral) activity.

Synthesis and Leukotriene D4/E4 Receptor Antagonist Activity of LY223468 and LY281761, “Carba” Analogues of LY171883

Structures containing the 3-propyl-4-alkoxy-o-hydroxyacetophenone moiety have an affinity for leukotriene D,/E, receptors.’ Compounds containing this group are represented by LY 171 883 and LY 137123.2,3 In considering the structure-activity relationships for members of this series, we asked what contribution the oxygen atom para to the acetyl group made to the observed antagonist activity. Analogues of LY171883 and LY137123 were synthesized in which the tetrazole was linked to the hydroxyacetophenone moiety by an all-methylene carbon chain (FIGURE 1). A key step in the synthesis involved a Wittig olefin-forming reaction between 3-methoxy-2-propylbenzaldehyde and the ylide derived from (4-carboxybuty1)triphenylphosphonium bromide to form the desired carbon chain. A regioselective Fries rearrangement was employed to form the ortho-hydroxyacetophenone. Compounds in which the tetrazole was separated from the acetophenone by four (LY223468) and five (LY281761) methylene groups were compared to the corresponding derivatives in which an oxygen atom linked the tetrazole chain to the aromatic ring for their ability to antagonize LTD,or LTE,-induced contractions of the isolated guinea pig ileum (TABLE 1). LY171883 and its “carba” analogue, LY28 1761, showed nearly identical LTD, antagonist activity. The LTE, antagonist activity of these two compounds also was very similiar, with both showing somewhat