Synthesis and structure-activity relationships of a new series of antiarrhythmic agents: 4,4-disubstituted hexahydro-3H-pyrido[1,2-c]pyrimidin-3-ones and related compounds.

A series of 4,4-disubstituted tetrahydro- and 4,4-disubstituted hexahydro-3H-pyrido[1,2-c]pyrimidin-3-ones (4 and 5, respectively) were prepared from 2-aryl-2-(2-piperidinyl)-4-[N,N-bis (1-methylethyl)amino] butanamides (2). Individual racemates of the piperidinyl amides 2 were converted to pure racemic diaza bicyclic compounds that were evaluated for antiarrhythmic activity in the Harris dog model and anticholinergic activity in a muscarinic receptor binding assay. Selected compounds were subsequently evaluated for hemodynamic effects in anesthetized dogs where blood pressure depression and negative inotropic activity were assessed. Of this group, 4a (R = CH3) and 5a (R = CH3) showed the most favorable pharmacological profiles; the former compound was chosen for toxicity testing over the latter due to its lack of noncompetitive inhibition of acetylcholine-induced contractions of guinea pig ileum segments. Clinical evaluation is now under way.

Inotropic effects of 1-alpha-acetylmethadol (LAAM).

Inotropic effects of 1-alpha-acetylmethadol, 1-alpha-acetylnormethadol and 1-alpha-acetyldinormethadol were studied uilizing isolated left atria of guinea pigs. All three agents produced a biphasic response. Lower concentrations produced a slight, but significant increase in contractile force (p less than 0.05) and higher concentrations decreased contractile force (p less than 0.05). Significant drug interactions also were observe. The parent compound, 1-alpha-acetylmethadol, decrease the maximum positive inotropic response obtained with ouabain as well as that obtained with norepinephrine.

Inhibition of 3H-1-norepinephrine uptake by ouabain is species dependent.

Tissue slice to medium ratios of 3H-1-norepinephrine (3H-1-NE) were used to study the effect of ouabain on uptake of norepinephrine. The effects of ouabain were studied in slices of heart and spleen from three different species: rat, guinea pig, and dog. The drug produced a species as well as a concentration dependent inhibition of norepinephrine uptake in both types of tissue. In order of decreasing sensitivity, the following relationship between species was observed: dogs greater than guinea pigs greater than rats. Since 3H-1-norepinephrine uptake under the present experimental conditions represents uptake into sympathetic nerve terminals, it was concluded that Na+-K+-ATPases of sympathetic nerve terminals have species dependent differences in ouabain sensitivity similar to those of myocardium.

Differential species sensitivity to the inhibitory effect of cardiac glycosides on 3H-1-noradrenaline accumulation by tissue slices.

Effects of three cardiac glycosides on the accumulation of 3H-1-noradrenaline (3H-1-NA) by slices of heart and spleen were studied. Ouabain, digitoxin and digoxin, all produced a concentration dependent inhibition of 3H-1-NA uptake in both types of tissue slices. The maximum amount of 3H-1-NA accumulated as well as the rate of uptake was decreased. Digitoxin and ouabain were equipotent; however, digoxin was significantly less potent. Tissues from different mamalian specis did not exhibit the same degree of sensitivity to the inhibitory effect of cardiac glycosides on 3H-1-NA accumulation. Dogs were most sensitive and guinea-pigs an order of magnitude less sensitive. Rats were least sensitive by roughly two orders of magnitude when compared with guinea-pigs. The relationship of the effect of digitalis on 3H-1-NA accumulation to digitalis-induced cardiac arrhythmias is discussed. Finally, the pattern of species sensitivity found here is compared with that observed in relation to inhibition of Na+-K+-ATPase by cardiac glycosides.

Relationship between effects of ouabain on accumulation and efflux of noradrenaline in tissue slices.

The primary goal of this investigation was to identify the mechanism by which ouabain decreases accumulation of noradrenaline by tissue slices. Secondary goals were: 1) to construct the concentration-effect curve for the action of ouabain to increase efflux of noradrenaline from tissue slices, and 2) to determine whether species sensitivity exists for the action of ouabain on efflux. In tissues from dogs and guinea-pigs, the concentration-effect curves were steep, a characteristics of many actions of digitalis. Dogs were approximately an order of magnitude more sensitive than guinea-pigs. The effect of ouabain to increase efflux appears to be the primary mechanism by which the drug decreases accumulation of noradrenaline by tissue slices. Ouabain may increase efflux from two different intraneuronal compartments. The intraneuronal site appears to be dependent upon the concentration of ouabain.

Accumulation of norepinephrine by tissue slices from spontaneously hypertensive rats.

Accumulation of 3H-1-norepinephrine (3H-1-NE) by heart and spleen slices from different aged spontaneously hypertensive rats (SHR) was compared with accumulation by slices from comparably aged normotensive rats (Wistar-Kyoto, WKY). Between weeks 4 and 9 there was a significant increase in accumulation by heart slices of the WKY; there was no further increase at weeks 13 and 16. The developmental pattern in slices of WKY spleen was different. Accumulation was the same at weeks 4 and 9; subsequently, there were significant increases at weeks 13 and 16. Slices of heart from SHR showed the same pattern of development as those from WKY. However, accumulation by slices of SHR spleen was significantly different from that by slices of WKY spleen. At all ages studied, SHR slices accumulated less 3H-1-NE. Furthermore, there was no significant increase in accumulation with age. The data show: 1. the course of development of the adrenergic neuron transport system is different in heart and spleen, and 2. accumulation of 3H-1-NE by SHR spleen, but not heart slices, is different from accumulation by the respective control tissues.

Effect of autonomic blocking agents on chronotropic actions of 1-alpha-acetylmethadol.

The objective of this investigation was to determine whether or not autonomic receptors are involved in the chronotropic responses to 1-alpha-acetylmethadol (LAAM) and congeners (1-alpha-acetylnormethadol, norLAAM; 1-alpha-acetyldinormethadol, dinorLAAM). The effects of atropine were studied in vitro using isolated guinea-pig right atria and in vivo in anesthetized dogs. The effect of d,l-propranolol, a beta-adrenergic receptor blocking agent was studied in vitro only. Atropine attenuated, but did not block completely, the negative chronotropic responses to the narcotic agonists. Propranolol blocked completely the positive chronotropic response to norLAAM and appeared to increase the negative chronotropic response to dinorLAAM. It is concluded that: 1) muscarinic cholinergic receptors play a role in the negative chronotropic response; 2) the positive chronotropic response to norLAAM involves activation of beta-adrenergic receptors.

Peripheral sympatholytic effects of 1-alpha-acetylmethadol.

1-alpha-Acetylmethadol (LAAM), 1.4 mg/kg or greater, decreased the response of the cat nictitating membrane to pre- and postganglionic sympathetic nerve stimulation. LAAM had a greater effect on the low-frequency (0.5 Hz) than on the high-frequency (5-20 Hz) responses. No difference was observed between the effects of LAAM on the pre- as opposed to the postganglionic responses. The responses ot the nictitating membranes to intravenous epinephrine were not affected by LAAM. LAAM appears to act at the nerve terminal. The minimum dose of LAAM (1.4 mg/kg) which decreased the nictitating membrane responses also decreased blood pressure and heart rate. Naltrexone, 300 micrograms/kg, s.c., antagonized the effects of LAAM on the nictitating membrane responses and the cardiovascular actions of the drug. In anesthetized dogs, naltrexone completely blocked the blood pressure response to LAAM and partially blocked the effects of LAAM on heart rate and contractile force. The data suggest that LAAM may produce its cardiovascular effects, in part, by an action on the peripheral sympathetic nervous system which involves opiate binding sites. LAAM also appears to have direct actions on the heart to decrease heart rate and contractile force that do not involve opiate binding sites.

Inhibition of sympathetic neuronal transport and ouabain-induced cardiac arrhythmias.

The objective of the present investigation was to determine whether a correlation exists between the effect of ouabain to inhibit activity of the sympathetic neuronal transport system and the effect of the drug to produce cardiac arrhythmias. 3H-d,1-Metaraminol was used to monitor activity of the transport system in intact animals as well as in isolated perfused hearts. Accumulation by myocardial tissue (LV; RV), spleen (S), and gastrocnemius muscle (GM) of the guinea pig was not altered by the lowest dose of ouabain, 100 microgram/kg. A subarrhythmic dose, 150 microgram/kg, as well as the arrhythmic dose of ouabain, 212+/-24 microgram/kg, decreased accumulation by LV, RV, and S. Several different concentrations of ouabain were studied in the isolated perfused guinea pig heart preparation. Only the highest concentration, 5 X 10(-6)M was capable of decreasing accumulation of metaraminol. However, all but the lowest concentration of ouabain produced toxic arrhythmias. Thus, neither in intact animals nor in isolated perfused hearts could the dose of ouabain required to inhibit the sympathetic neuronal transport system be correlated with the dose of ouabain required to produce cardiac arrhythmias. It is concluded that ouabain inhibition of the sympathetic neuronal transport system does not play a role in the genesis of ouabain-induced cardiac arrhythmias.

Effects observed during subchronic administration of l-alpha-acetylmethadol (LAAM) to guinea pigs.

l-Alpha acetylmethadol in water was administered by gavage to male and female guinea pigs over a period of 4 weeks: Mondays and Wednesdays, 2 mg/kg; Fridays, 3 mg/kg. Appropriate volumes of water were administered to control animals on the same schedule. Treated animals consumed significantly less feed (p less than .05) and weighed less (p less than .05) than control animals. After 4 weeks, heart rates in treated animals were less than heart rates in control animals (p less than .05). There was a higher mortality rate associated with the treated group. Dry and dull coats, runny or loose stools, scabs and sores, and alopecia were observed frequently in the treated group of animals.

Cardiac and hepatic effects of pre- and postnatal exposure to polybrominated biphenyls in rats.

Body weight gain and hepatic concentrations of vitamin A were reduced in Sprague-Dawley rats by pre- and postnatal exposure to 100 ppm polybrominated biphenyls (PBBs). The ratio of liver weight to body weight, activity of hepatic delta-aminolevulinic acid (ALA) synthetase, and urinary excretion of uro- and coproporphyrins were increased by PBBs. Treatment with PBBs also increased the left atrial inotropic response to calcium. However, PBBs had no effect on development of the adrenergic neuronal transport system in heart, left atrial baselike peak tension, or inotropic response to ouabain. Thus PBBs retarded body weight gain and produced a variety of alterations in liver, but had little effect on cardiac contractile function.

The pharmacokinetics of 8-methoxypsoralen following i.v. administration in humans.

1. 8-methoxypsoralen (8-MOP) is a naturally occurring photoreactive substance which, in the presence of u.v. light, forms covalent adducts with pyrimidine bases in nucleic acids. For many years, 8-MOP has been used in PUVA therapy for treatment of psoriasis. Recently, the drug has been found to inactivate effectively bacteria spiked into platelet concentrates. The purpose of this study was to determine the pharmacokinetics and safety of 8-MOP administered intravenously in the bactericidal dosage range. 2. Eighteen volunteers were divided into three treatment groups to receive, respectively, 5, 10, and 15 mg 8-MOP infused over 60 min. Frequent arterial samples were gathered, and the blood and plasma were assayed for 8-MOP concentration. The pharmacokinetic parameters were determined by moment and compartmental population analysis, the latter performed with the program NONMEM. Haemodynamics, ventilatory pattern, and subjective effects were recorded throughout the study. 3. The intravenously administered 8-MOP was well tolerated in all individuals, and no acute toxicity was observed. 4. The pharmacokinetics of 8-MOP were best described by a three-compartment mammillary model in which the volumes and clearances were proportional to weight. The mean pharmacokinetic parameters for the plasma concentrations were: V1 = 0.045 1 kg-1, V2 = 0.57 1 kg-1, V3 = 0.15 1 kg-1, CL1 (systemic) = 0.010 1 kg-1 min-1, CL2 = 0.0067 1 kg-1 min-1, CL3 = 0.012 1 kg-1 min-1. The mean pharmacokinetic parameters for the blood concentrations were: V1 = 0.061 1 kg-1, V2 = 1.15 1 kg-1, V3 = 0.21 1 kg-1, CL1 (systemic) = 0.015 1 kg-1 min-1, CL2 = 0.011 1 kg-1 min-1 and CL3 = 0.015 1 kg-1 min-1. 5. The plasma pharmacokinetic model described the observations with a median absolute error of 17%, and the blood pharmacokinetic model described the observations with a median absolute error of 18%. Analysis of the relative concentration of 8-MOP between plasma and red blood cells suggested concentration-dependent partitioning. 6. The addition of 7.5 mg 8-MOP to 300 ml platelet concentrate would produce bactericidal concentrations of 25 micrograms ml-1. Simulations based upon our data show that intravenous administration of 7.5 mg over 60 min would result in systemic concentrations of 8-MOP similar to those observed with conventional PUVA therapy. We conclude that the extensive safety history established in PUVA therapy will be applicable to this new application of 8-MOP.