A method for determination of subpicomole concentrations of tetrahydropapaveroline in rat brain by high-performance liquid chromatography with electrochemical detection.

A sensitive and selective method for detection of tetrahydropapaveroline (THP) in rat brain has been developed. The procedure employs a multiple-stage separation scheme that selectively isolates THP from rat brain tissue and utilizes the sensitivity and resolution of reversed-phase high-performance liquid chromatography with electrochemical detection to provide an analysis with high specificity for THP. The mean (+/- SD) recovery of THP from rat brain homogenates, fortified at levels ranging from 0.25 to 3.0 pmol per whole brain, was 43.4 +/- 3.5%. The concentration of THP in brains of rats pretreated with L-dopa was 0.44 +/- 0.14 (SD) pmol per gram. The limit of detection of THP was approximately 0.1 pmol (0.03 ng) per gram brain.

Effect of acute ethanol administration on brain levels of tetrahydropapaveroline in L-dopa-treated rats.

The effect of ethanol on the concentration of the aberrant dopamine metabolite, tetrahydropapaveroline (THP), in brains of L-dopa-treated rats has been evaluated. THP was isolated from rat brain extract by a newly developed multiple stage separation technique that is highly specific for the alkaloid. THP, dopa, and dopamine were assayed by high-performance liquid chromatography with electrochemical detection. THP was not found in brains of untreated animals. However, levels of 0.42 pmol THP per g brain were observed in animals that received L-dopa (200 mg/kg) by intraperitoneal injection (IP) 90 min before decapitation. Administration of ethanol (3g/kg) IP to L-dopa-treated animals at time intervals ranging from 60 to 240 min before decapitation resulted in significant increases in brain levels of THP as compared to L-dopa-treated animals. Maximum levels of THP (4.02 to 4.82 pmol/g brain) were observed when ethanol was given at time intervals ranging from 80 to 180 min before the animals were killed. Administration of ethanol and L-dopa, as compared to the administration of L-dopa only, markedly increased brain levels of dopa and dopamine. Maximum brain levels of THP, dopa, and dopamine in animals administered ethanol plus L-dopa as compared with L-dopa-treated animals represented a 1048%, 325%, and 84% increase, respectively. These results strongly support the concept that the concentration of THP in the brain of intact animals can be enhanced by ethanol administration.

Regioselective O-methylation of tetrahydropapaveroline and tetrahydroxyberbine in vivo in rat brain.

Enzymatic O-methylation is a primary pathway for the metabolism of catecholamines in mammals and of isoquinoline alkaloids in plants. This report describes the differential O-methylation patterns of the racemates and enantiomers of two catecholamine-derived alkaloids, tetrahydropapaveroline (THP) and 2,3,10,11-tetrahydroxyberbine (THB), in the brain of the rat. One hour after intracerebroventricular administration of a specific isomeric form of each alkaloid, the O-methylated metabolites were isolated from the rat brain and subsequently quantified using high performance liquid chromatography. The isomeric form of THP or THB which was administered markedly influenced the pattern of O-methylation. The racemate and R-(+)-enantiomer of THP were mono-O-methylated predominantly at the 7 and 3' positions, while the S-(-)-enantiomer of THP was mono-O-methylated to an essentially equal degree at the 6, 7 and 3' positions. Minimal mono-O-methylation at the 4' position was detectable only with the racemate and (-)-enantiomer of THP. The racemate and enantiomers of THB were mono-O-methylated predominantly at the 2 and 11 positions and to a lesser extent at the 3 and 10 positions. Although minimal with the R-(+)-enantiomer, the 3 and the 10-O-methylation pathways were enhanced significantly with the S-(-)-enantiomer of THB. These results demonstrate that both enantiomers of THP and THB are O-methylated in vivo in rat brain and that the chiral centers of these alkaloids influence the position of O-methylation, thereby dictating the relative amounts of specific products formed.

Interaction of catecholamine-derived alkaloids with central neurotransmitter receptors.

Catecholamine-derived alkaloids of the simple tetrahydroisoquinoline, 1-benzyl-tetrahydroisoquinoline and tetrahydroprotoberberine classes have been tested for their ability to inhibit the binding of seven different radioligands to neurotransmitter receptors of brain synaptic membranes. Alkaloids of all three classes were active in inhibiting 3H-clonidine binding to alpha 2-adrenergic receptors. Stereoselectivity of tetrahydropapaveroline in binding to alpha 2-adrenergic receptors was evidenced by the marked activity of the S-(--) isomer (IC50 = 0.65 microM) in comparison to the R-(+) enantiomer (IC50 = 50 microM). The simple tetrahydroisoquinolines (3,4-dihydroxytetrahydroisoquinoline and salsolinol), the four isomeric mono-O-methyl derivatives of 2,3,10,11-tetrahydroxyberbine and tetrahydropapaveroline were the most potent inhibitors of 3H-apomorphine binding to dopaminergic receptor agonist sites. The tetrahydroprotoberberines, as a class, were the most potent inhibitors of 3H-spiroperidol binding to dopaminergic receptor antagonist sites and of 3H-WB-4101 binding to alpha 1-adrenergic receptors. The 1-benzyl-tetrahydroisoquinolines exhibited varying degrees of interaction with beta 1-adrenergic receptors. Tetrahydropapaveroline (IC50 = 0.3 microM) was the most active of the 24 alkaloids tested in inhibiting binding of 3H-dihydroalprenolol to beta 1-adrenergic receptors. None of the alkaloids significantly affected 3H-QNB binding to muscarinic-cholinergic receptors, and selected alkaloids from each class interacted only moderately with serotonergic receptors.

Isoquinoline alkaloids. Inhibitory actions on cation-dependent ATP-phosphohydrolases.

Representatives of eleven different classes of isoquinoline alkaloids inhibit Na+, K+-ATPase and Mg2+-ATPase in rat brain microsomal preparations. In most cases the Na+, K+-ATPase is more sensitive than Mg2+-ATPase to inhibition by the alkaloids. The classes of alkaloids can be ranked according to potency of inhibition of Na+, K+-ATPase. Protoberberines are most effective, followed in decreasing order by benzophenanthridines, benzylisoquinolines, aporphines, tetrahydroprotoberberines, pavines, protopines, isoquinolines, tetrahydrobenzylisoquinolines, morphinanes, and tetrahydroisoquinolines. As specific representatives of each of the first four classes of alkaloids, berberine, sanguinarine, papaveroline and 1,2,10,11-tetrahydroxyaporphine, respectively, prove most valuable in kinetic studies because they exhibit the greatest inhibitory action on brain Na+, K+-ATPase. Kinetic analyses plotted in double reciprocal form reveal that berberine and 1,2,10,11-tetrahydroxyaporphine are simple linear competitive inhibitors with respect to ATP, whereas sanguinarine and papaveroline are simple linear noncompetitive inhibitors. These four representative alkaloids exhibit non-linear competitive inhibition with respect to Na+-activation. Additionally, these alkaloids significantly inhibit rat brain microsomal K+-activated pNPPase. The results demonstrate that certain members of several classes of isoquinoline alkaloids markedly affect various cation-dependent phosphohydrolases in vitro.

Influence of catecholamine-derived alkaloids and beta-adrenergic blocking agents on stereospecific binding of 3H-naloxone.

Alkaloids containing a catecholamine moiety, viz., tetrahydroisoquinolines and tetrahydroprotoberberines, and a group of beta-adrenergic blocking agents were examined for their effects on the binding of tritiated naloxone by rat brain homogenate. The stereospecific binding of the opiate antagonist was weakly inhibited by the catecholamine-derived alkaloids. The concentration of alkaloids producing 50% inhibition of binding ranged from 0.06 to 0.37 mM. The inhibitory effects of the beta-adrenergic blocking agents appear to parallel their reported relative local anesthetic actions.

Low birth weight: some considerations in a Zambian population.

A retrospective analysis of 2401 consecutive births revealed a lowbirth weight rate of 11.4 percent of all births and 14.2 percent all live borns. Sixty-five percent of late fetal and first week neonatal deaths were low birthweight babies. The cause of low birthweight labour was unknown in 48.2 percent of cases. The major known associations with low birthweight labour and delivery were twin birth, antepartum haemorrhage, premature rupture of the membranes and toxaemia of pregnancy. Nutritional factors were considered to be of significance in the incidence of low birthweight. The earlier attendance of mothers at ante-natal clinics and the availability of experienced medical and nursing personnel with adequate facilities are necessary for perinatal mortality to be significantly reduced in the low birthweight group.

Singleton breach presentation planned for vaginal delivery.

A retrospective study of 156 consecutive cases of singleton breach presentation planned for vaginal delivery is presented. The incidence of caesarean section was not increased when compared with that for all Hospital and Clinic confinements. The perinatal mortality and prematurity rates were high. The incidence of cord prolapse was increased especially with the footling breech. The need for an experienced Obstetrician and Anaesthetist to conduct all deliveries was demonstrated. Factors influencing the assessment of feto-pelvic proportion and the occurrence of trauma and asphyxia in the management of breech labour and delivery are discussed. The continued place of external cephalic version is justified by the perinatal mortality rate.

Disposition of catecholamine-derived alkaloids in mammalian systems.

Tetrahydropapaveroline, the tetrahydroisoquinoline alkaloid derived from dopamine, is converted in vivo by rats and by rat liver and brain preparations to tetrahydroprotoberberine alkaloids. The latter alkaloids have also been identified for the first time in the urine of parkinsonian patients receiving L-dopa therapy. These findings suggest that man, like plants, may have the ability to elaborate several classes of alkaloids with potentially important pharmacological consequences. Thus, this newly demonstrated ability of mammalian systems to evoke the biosynthesis of benzyl-tetrahydroisoquinoline-derived alkaloids - a capability previously considered unique to plants - elects the tetrahydroprotoberberine alkaloids as representative of the first class of a possible constellation of complex mammalian alkaloids elaborated from the neuroamines.