On the role of α-methyldopamine in the antihypertensive effect of α-methyldopa

Summary In renal hypertensive rats the cerebral concentration of -methyldopa, -methyldopamine, -methylnoradrenaline, dopamine and noradrenaline as well as the blood-pressure were determined simultaneously. The antihypertensive effect followed a time course identical to that of the increase in the cerebral concentration of -methyldopamine and of the decrease in the concentration of dopamine, whereas lowering of blood pressure on the one hand, and changes in the levels of -methylnoradrenaline and noradrenaline, on the other, were not related to each other. Dose-response relationships showed the same correlations and lack of correlations, respectively.These results suggest that non--hydroxylated catecholamines play a major role in mediating the antihypertensive effect of -methyldopa or, alternatively, that only the newly biosynthesized -methyl-noradrenaline is effective in lowering blood pressure.A preliminary communication has been presented at the Spring Meeting 1973 of the German Pharmacological Society at Mainz (Waldmeier et al., 1973).     

Consumers' perceptions of community pharmacy in Portugal: a qualitative exploratory study.

Objective: Pharmacists are health professionals who are ideally positioned to perform a primary health care role. However, the definition of professional value needs to be considered not just as professional education and skills, but also in terms of how consumers perceive it. The main aim of this work was to explore the publics perceptions and attitudes towards community pharmacy in Portugal. Methods: A pure qualitative approach was undertaken. The data were collected through a semi-structured interview, conducted with a snowball like sample. First, individuals (n = 15) were interviewed, allowing for adjustment and validation of the interview schedule, followed latter by group interviews with adults in rural and urban areas. Group participants (n = 25) were asked about their behaviour and beliefs, resulting from their perceptions of community pharmacies, pharmacists and medicines. Future expectations regarding the community pharmacy service were also explored. The interviews were tape recorded and transcribed verbatim. An iterative, reflexive coding process was applied, assisted by the qualitative software package QSR NUD*IST v4. The inductive analysis of the extracted codes assembled those codes into themes. Results and discussion: This article will mainly focuses on community pharmacy service representations and cognitions (theme A) and community pharmacy evaluative perceptions and behaviours (theme B). Participants displayed general and contradictory ideas about the actual functions of the pharmacist, including weak conceptualizations and a positive demand for services in relation to product supply. This superficial understanding is in line with previous results from satisfaction studies, confirming a low expectation level. The publics poor knowledge and low expectations can justify a reduced desire for an extended role of the pharmacist in the community. This uncertain service conceptualization does not define the professional responsibility from a consumers perspective. Conclusions: Although these results allow for the development of a framework to describe the perceptions of community pharmacy users, further research is needed to determine the prevalence of these and other possible results.     

Effects of clonidine on habituation and sensitization of acoustic startle in normal,decerebrate and locus coeruleus lesioned rats

Rats were presented with startle-eliciting tones after injection of clonidine (0.01, 0.02, 0.04, 0.08, 0.5, 1.0 or 2.0 mg/kg) or saline. Clonidine potently depressed startle amplitude and the effect was monotonically related to dose. Pretreatment with piperoxane (10 mg/kg) antagonized this effect but pretreatment with phentolamine (10 mg/kg) did not. Clonidine still depressed startle in acutely decerebrate rats and in rats with bilateral ablation of the locus coeruleus. Clonidine did not interfere with sensitization to background noise and did not interfere with the ability to startle but instead improved within-session habituation. The results represent one of the few instances in the literature where a drug appears to improve habituation without directly interfering with the ability to respond. The possibility that clonidine might affect startle by stimulating central epinephrine rather than norepinephrine receptors is discussed.     

Comparative behavioral characterization of the neuroactive steroids 3α-OH,5α-pregnan-20-one and 3α-OH,5β-pregnan-20-one in rodents

Pregnan steroids have been shown to possess anesthetic, hypnotic, anticonvulsant and anxiolytic properties. In this study, two endogenous neuroactive steroid isomers, 3-hydroxy-5-pregnan-20-one (3,5-P) and 3-hydroxy-5-pregnan-20-one 3,5-P), were studied for differences in their pharmacological properties using behavioral assays. 3,5-P and 3,5-P were similar in their potencies and efficacies in blocking pentylenetetrazol-induced seizures in mice (ED₅₀: 3,5-P=2.8 mg/kg and 3,5-P=3.0 mg/kg). Similarly, both neuroactive steroids produced roto-rod deficits within the same range of potency (TD₅₀:3,5-P=18.8 mg/kg and 3,5-P=21.2 mg/kg). However, in animal models of anxiety, subtle differences were observed between the two isomers. In both the light/dark transition test and elevated plus-maze, 3,5-P was more efficacious than 3,5-P, though both compounds had similar potencies. In the Geller-Seifter test, 3,5-P was more potent and efficacious than 3,5-P. Neither compound had significant effects on unpunished responding within the dose range tested. Both compounds produced similar biphasic curves in the locomotor test. All together, the data indicate that 3,5-P and 3,5-P have similar anticonvulsant activity, but the 5-isomer possesses more potent and efficacious anxiolytic properties than the 5-isomer.     

Reserpine and alpha-methyldopa in the treatment of tardive dyskinesia

Thirty inpatients with evidence of tardive dyskinesia secondary to antipsychotic medications participated in this double-blind, controlled, randomized study comparing reserpine, -methyldopa and placebo. Reserpine at doses of 0.75–1.5 mg daily, or -methyldopa at doses of 750–1,500 mg daily, produced a statistically significant improvement in tardive dyskinesia symptomatology compared to the results obtained with placebo.Paper presented at the New Clinical Drug Evaluation Unit Program, Key Biscayne, Florida, May 22–24, 1979     

Dexmedetomidine synergism with midazolam in the elevated plus-maze test in rats

The anxiolytic profile of dexmedetomidine, a novel, highly-selective ₂-adrenergic agonist, was examined in rats in the elevated plus-maze test when administered either alone or in combination with the benzodiazepine agonist midazolam. Dexmedetomidine, 0.1–10 µg/kg, was inactive in modifying the rats' behavioral response in this test. Midazolam, 0.1–10 mg/kg, dose-dependently produced an anxiolytic-like profile characterized by an increased time spent in the open arms of the elevated plus-maze. A combination of dexmedetomidine 0.5 µg/kg and midazolam 0.5 mg/kg produced a synergistic interaction. This heterergic interaction of dexmedetomidine on midazolam's anxiolytic-like profile was dose-dependently blocked by pretreatment with an ₂-adrenergic antagonist, atipamezole, 10–50 µg/kg, and a benzodiazepine antagonist flumazenil, 1.0 and 10 mg/kg, but not by the ₁-adrenergic antagonist, prazosin, 0.1–10 mg/kg. While the transmembrane signal transduction pathways for benzodiazepine- and ₂-agonist responses do not share any molecular component, there does appear to be crosstalk between these two systems. These may involve GABA or noradrenergic downstream effects of either dexmedetomidine or midazolam, respectively.     

Depression of exploratory activity by clonidine in rats as a model for the detection of relative pre- and postsynaptic central noradrenergic receptor selectivity of α-adrenolytic drugs

Summary The effects of various -adrenoceptorblocking drugs on the depression of exploratory activity (ambulation and rearing) induced by 0.1 mg/kg i.p. clonidine were investigated in the rat. In parallel experiments, the effects of the same drugs on pre- and postsynaptic -receptors were determined in vitro (field-stimulated cortex slices and isolated vas deferens of the rat, respectively). Tolazoline, esproquine, yohimbine and piperoxan distinctly antagonized the inhibition of exploration produced by clonidine. All these drugs were found to possess relatively higher selectivity for the presynaptic -receptors, as judged by the ratios of the concentrations inducing a 50% increase in field-stimulated ³H-noradrenaline-overflow and the concentrations required to shift the EC₅₀ for the antagonism of noradrenaline-induced contractions of the vas deferens to the right by a factor of 2 (pA₂, ratio <1): In contrast, phentolamine and phenoxybenzamine which showed preferential postsynaptic -receptor blocking activity (ratio>1), potentiated rather than antagonized the effects of clonidine. Mianserin, although preferentially blocking the postsynaptic receptors, had no effect on clonidine-induced hypoactivity up to the high dose of 100 mg/kg i.p., probably because of its additional NA-uptake-inhibiting properties. The antagonism of clonidine by the selective presynaptic -receptor blockers was observed within a limited dose-range. Increasing the doses above an optimal level, which varied from one compound to another, resulted in a decrease in the effect. It is suggested that this phenomenon reflects the counter-balancing postsynaptic -adrenoceptor blockade occuring at higher concentrations of these drugs. In general, the results show a fairly good correlation between antagonism of clonidine in vivo and preferential blockade of presynaptic -receptors in vitro. Clonidine-induced suppression of exploration therefore seems to be a valuable model for the investigation of drug interactions with -adrenergic receptors in the central nervous system.These results were presented in part at the Spring Meeting of German Pharmacological Society, Mainz, 16–18 March, 1977     

α1-Adrenoceptor subtype mediating contraction of the smooth muscle in the lower urinary tract and prostate of rabbits

Summary The -adrenoceptor subtype mediating contraction of the smooth muscle in the urinary bladder base (trigone), proximal urethra and prostate isolated from male rabbits was investigated by comparing the responsiveness to -adrenoceptor agonists and antagonists under condition where -adrenoceptors and neuronal and extraneuronal uptakes were inhibited. Noradrenaline (non-selective), phenylephrine (₁-selective) and clonidine (₂-selective) caused a dose-dependent contraction in the trigone, urethra and prostate. Phenylephrine acted as a full agonist whereas clonidine was a partial agonist. YM-12617 and prazosin (₁-selective), phentolamine (non-selective) and yohimbine (₂-selective) produced dose-dependent shifts to the right of the dose-response curves for noradrenaline, phenylephrine and clonidine in the all three tissues. YM-12617 (pA₂=9.77, 9.67 and 9.73 for trigone, urethra and prostate, respectively), prazosin (pA₂=8.26, 8.20 and 8.08), phentolamine (pA₂=7.67, 7.62 and 7.45) and yohimbine (pA₂=6.30, 6.30 and 5.94) showed constant pA₂ values irrespective of the agonists and tissues used, suggesting that only a single subclass of -adrenoceptors is present. The actual pA₂ values for these antagonists are comparable to those reported previously in tissues said to contain mainly ₁-adrenoceptors. Thus, we concluded that the postsynaptic -adrenoceptors of the rabbit trigone, urethra and prostate mediating contraction belong to the ₁-subtype.     

Effect of benzo(α)pyrene treatment on the benzo(α)pyrene hydroxylase activity in maternal liver,placenta, and fetus of the rat during day 13 to day 18 of gestation

Summary Pregnant rats were treated with an oral dose of 40.0 mg benzo() pyrene (BP) per kg body weight and were sacrificed 24 h later. Maternal liver, placenta, and fetus were assayed for BP-hydroxylase activity. The enzyme activity was measured from day 13 to day 18 of gestation. Pretreatment of rats with BP results in an approximately 15-fold increase of BP-hydroxylase activity in the maternal liver compared to the enzyme activity in the liver of control animals. These enzyme levels were maintained throughout the duration of gestation.No BP-hydroxylase activity could be measured in the fetus and the placenta of control animals. After treatment with BP maximal induction of BP-hydroxylase activity in the placenta was not achieved before day 15 of gestation. BP treatment resulted in a detectable enzyme activity in the fetus. However, the degree of induction increased with the age of the fetus. Electron microscopic pictures demonstrate a swelling and enlargement of the endoplasmic reticulum (ER) in the trophoblast cell of the placenta after BP treatment. In the fetal liver the ER is characterized by a moderate enlargement while there is no effect in the maternal liver after treatment of the animals with BP.This work was supported by a grant from the Deutsche Forschungsgemeinschaft given to the Sonderforschungsbereich 29, Embryonale Entwicklung und Differenzierung (Embryonal-Pharmakologie).Parts of this work were presented at the Spring Meeting of the German Pharmacological Society held in Mainz, March 1971.     

Effects of alpha-adrenoceptor agonists and antagonists in a maze-exploration model of ‘fear’-motivated behaviour

Summary An elevated X-maze with alternating open and enclosed arms was investigated as a model for the study of fear-induced behaviour. As predicted, the anxiolytics diazepam and amylobarbitone increased, and the putative anxiogenics ACTH and picrotoxin decreased the proportion of open arm entries. The ₁-adrenoceptor agonists phenylephrine and ST587, and the ₂-adrenoceptor antagonists idazoxan, piperoxane, RS-21361 and yohimbine decreased relative open-arm entries, thus resembling the putative anxiogenics. On the other hand, azepexole, clonidine and guanabenz, agonists at ₂-adrenoceptors, and the ₁-adrenoceptor antagonists prazosin and thymoxamine, enhanced the proportion of open arm entries at low doses, suggesting anxiolytic-like properties. A paradoxical fall in open arm entries occurred with these agents at higher doses. These results provide further evidence for the involvement of noradrenergic systems in fear-motivated behaviour.     

Inhibition of Nuclear Transcription Factor-κB by Specific IκB Kinase Peptide Inhibitor

Pharmaceutical Research -     

Pre- and postsynaptic effects of yohimbine stereoisomers on noradrenergic transmission in the pulmonary artery of the rabbit

Summary Effects on noradrenergic neurotransmission of five stereoisomers of yohimbine and of the closely related compound yohimbol were studied in strips of the pulmonary artery of the rabbit. In some experiments the tissue was preincubated with ³H-noradrenaline. Three effects were observed. Firstly, antagonism to the contractile effect of noradrenaline and of sympathetic nerve stimulation; the antagonism reflected competitive blockade of postsynaptic -adrenoceptors. Secondly, an increase in the stimulation-evoked overflow of total tritium and ³H-noradrenaline; the increase appeared to be due to blockade of presynaptic -adrenoceptors. Thirdly, an increase in the basal outflow of ³H-3,4-dihydrophenylglycol, presumably by impairment of the vesicular storage of ³H-noradrenaline. According to their relative potencies in eliciting these effects, the drugs could be divided into three groups. Rauwolscine, -yohimbine and yohimbol preferentially blocked the presynaptic -adrenoceptor; rauwolscine and -yohimbine, like yohimbine, at low concentrations increased the contractile response to sympathetic nerve stimulation. Corynanthine preferentially blocked the postsynaptic -adrenoceptor. Pseudoyohimbine and 3-epi--yohimbine were very weak antagonists at either receptor; they mainly accelerated the basal outflow of ³H-3,4-dihydroxyphenylglycol.From these results and those of a previous study it is concluded that, in a series of twelve -adrenolytic drugs, rauwolscine shows the greatest preference for presynaptic and corynanthine the greatest preference for postsynaptic -adrenoceptors. In view of the chemical similarity of the two compounds these opposite properties are striking. Corynanthine and rauwolscine might be useful tools for the subclassification of -adrenoceptors.     

Effect of chronic lithium administration on adrenoceptor binding and adrenoceptor regulation in rat cerebral cortex

Summary Lithium (Li) at a concentration, which exerts prophylactic effects in affective disorders is known to alter noradrenaline turnover and the -adrenoceptor-dependent cAMP accumulation. In the present study the action of chronic Li administration (at least 5 weeks) on agonist and antagonist binding to adrenoceptors and on the regulation of adrenoceptors was investigated in rat cerebral cortex. Li treatment caused a small but significant decrease in the number of -adrenoceptor binding sites by 10% (³H-dihydroalprenolol binding) leaving the number of ₁- and ₂-adrenoceptor binding sites (³H-prazosin and ³H-rauwolscine, respectively) unchanged. The affinity of the radioligands as well as the affinity of agonists to these binding sites were not altered. The up-regulation of -adrenoceptor binding sites produced by repeated reserpine injections was inhibited by 32% in rats treated concomitantly with Li, although the noradrenaline depleting effect of reserpine was not impaired. In contrast, Li treatment had no effect on the up-regulation of -adrenoceptor binding induced by 6-OH-dopamine, nor did it alter the -adrenoceptor down-regulation following chronic administration of desipramine. The up-regulation of ₁-adrenoceptor binding sites caused by reserpine or 6-OH-dopamine also remained unaffected by Li. It is concluded that chronic Li has limited effects on cortical adrenoceptors and their regulation. The inhibition of -adrenoceptor up-regulation caused by reserpine may reflect an action of Li on non-adrenergic systems rather than a general stabilizing effect on adrenoceptors proposed previously.Send offprint requests to: G. Gross     

In vivo studies on alpha-adrenergic receptor subtypes in human veins

Summary We studied in vivo responsiveness of venous ₁ and ₂-adrenoceptors, measuring the diameter changes in superficial veins in response to -adrenergic agonists and antagonists in healthy human volunteers. The dorsal hand vein technique was used because it permits complete dose-response studies of venous constriction without confounding reflex alterations.Local infusions of all agonists studied induced dose-dependent contraction of the hand vein; the maximal effects (Emax) were: norepinephrine (88% ± 10%), methox amine (97% ± 5%), phenylephrine (95% ± 6%), clonidine (54% ± 12%), and azepexole (68% ± 26%). Clonidine reduced the norepinephrine-induced venoconstriction by 11% ± 10%. Oral doses of 1 mg prazosin antagonized the venoconstriction induced by norepinephrine, methoxamine, and clonidine, but not by azepexole. Yohimbineantagonism was observed against all agonists studied. Inhibition by yohimbine of clonidine-induced venoconstriction was irreversible over 60–180 min.Results show that the in vivo effects on veins of -adrenergic agonists are in good agreement with results from in vitro experiments. Agonists with ₁- and ₂-adrenoceptor subtype selectivity cause venoconstriction in vivo, but ₂-receptor mediated constriction is intrinsically weaker. Clonidine acts as a partial antagonist against norepinephrine, presumably on postsynaptic ₂-receptors. At high doses, ₂-adrenoceptor subtype selectivity of clonidine and yohimbine appear to be partially lost in vivo. Send offprint requests to H. G. Eichler at the above address     

Liberation of α-methyldopamine as a “false” sympathetic transmitter after pretreatment of cats with α-methyldopa and disulfiram

Summary Pretreatment of cats with -methyldopa (3×200 mg/kg i.p. given over a period of 28 hrs) and simultaneous inhibition of dopamine -hydroxylase by disulfiram (4×400 mg/kg p.o. given over a period of 44 hrs) diminished the norepinephrine content of the heart to 31% and of the spleen to 15% of control levels. The missing norepinephrine was only partially replaced by -methyldopamine and the total catecholamine content of spleen and heart amounted to 51 and 70% respectively of untreated controls. In spinal cats the response of the nictitating membrane to sympathetic nerve stimulation was markedly diminished, whereas the effect of intravenously injected norepinephrine on blood pressure and nictitating membrane was considerably potentiated. In the isolated perfused spleen the contractile response to sympathetic nerve stimulation was also diminished and the pressor activity (expressed in terms of norepinephrine) of the venous effluent was reduced to 40% at a stimulating rate of 6/sec and to 39% at 10/sec. Together with the diminished amounts of norepinephrine -methyldopamine appeared as a false sympathetic transmitter in the perfusion fluid. The two amines were liberated by sympathetic nerve stimulation in the same proportions in which they were stored in splenic tissue.From this and previous studies it becomes apparent that several aspects must be considered in correlating biochemical and functional findings: amounts of normal transmitter in tissues versus amounts liberated by sympathetic nerve stimulation, quantitative aspect of replacement of the physiological by the false transmitter in tissues and in the output from stimulated nerves, potency of the false transmitter at adrenergic receptors and its possible interference with transmitter inactivation.Preliminary results of this report have been communicated to the German Pharmacological Society in Mainz at the Spring meeting 1966.     

Water Vapor Adsorption and Desorption Isotherms of Biologically Active Proteins

Using a protein isolated from soy, a dynamic water adsorption method was developed and the data were compared with those obtained from a static gravimetric procedure. Both methods gave comparable results, showing that Type II isotherms with considerable hysteresis were obtained. However, the dynamic procedure was preferred since it provided data rapidly and used significantly less material. Using the dynamic method, water adsorption isotherms at 25°C were also determined for four biologically active proteins: -amylase, (-glucuronidase, lipase, and urease. BET (Brunauer, Emmet, and Teller) parameters were calculated and the specific surface areas for the native, biologically active proteins were found to be similar, 238.4 ± 20.2 m²/g. On the other hand, the specific surface area for the denatured soy protein isolate was 144.6 m²/g. Nevertheless, the heat of absorbance for all of the proteins examined was similar, suggesting that they have comparable degrees of hydrophilicity.     

Effects of excess 1,25-dihydroxycholecalciferol in young rats

The oral administration for 5 days of excess 1,25-dihydroxychole-calciferol [1,25(OH)₂D₃] at doses of 1, 5, and 25 g/kg to rats, beginning at the age of 2 or 10 days, produced dose-dependent reductions in weight development and additional calcification near the skeleton. Alizarin red S stained skeleton revealed calcific deposits near the bones of the head, near the neural arches, between the ribs, along the bones both of the fore limbs and, to a lesser extent, of the hind limbs.Historically, the deposits appeared to be localized primarily in the subepithelial connective tissues. Starting treatment with 1,25(OH)₂D₃ (25 g/kg for 5 days) at the age of 20 days produced additional calcification in 1 of 8 rats at only 1 location (lower jaw). Additional calcification as described above could no longer be induced by 1,25(OH)₂D₃ in 30-day-old rats using doses up to 25 g/kg and 10 daily treatments. We conclude that the sensitivity of young rats to 1,25(OH)₂D₃-induced additional calcification, which differs in localization from that observed in adult rats, decreases with the maturation of the animals.     

Characterisation of postjunctional α-adrenoceptors in isolated human femoral veins and arteries

Summary In order to characterise the pharmacological properties of postjunctional -adrenoceptors, both the contractile effects of -adrenoceptor agonists and the blocking potencies of selective -adrenoceptor antagonists were studied in isolated human femoral veins and arteries.The veins were more sensitive to noradrenaline than the arteries. Guanfacine had a higher intrinsic activity in veins than in arteries, whereas the reverse was true for phenylephrine.The antagonists rauwolscine and yohimbine were more potent against noradrenaline in the veins than in arteries, while corynanthine was equally potent in either tissue. They antagonised the noradrenaline response in a competitive manner. Prazosin proved to be the most potent competitive antagonist in arteries, while in veins it exerted weak and noncompetitive antagonism.The results suggest that the -adrenoceptor population at the postjunctional site differs between human femoral veins and arteries. The veins seem to contain more ₂- than ¹-adrenoceptors postjunctionally, whereas in the arteries the ₂-subtype prevails. The results indicate the possibility of influencing selectively adrenergic reactions in the capacitance and resistance vessels.     

Chronic clorgyline treatment enhances release of norepinephrine following sympathetic stimulation in the rat

Summary Plasma catecholamine levels were determined in pithed rats during electrical stimulation of the entire sympathetic nervous system. In animals treated chronically with clorgyline (1 mg/kg daily for 21 days) the increment in plasma norepinephrine concentration during stimulation was greather than in control animals, whereas a single dose of clorgyline (2 mg/kg 2 h before pithing), which produced the same degree of inhibition of arterial MAO type A and a similar increase in arterial norepinephrine content, had no effect on the plasma norepinephrine response to stimulation. Injection of yohimbine (1 mg/kg) produced the same degree of enhancement of plasma norepinephrine response to stimulation in chronically treated and control animals, showing that the overall gain of the ₂-adrenoceptor inhibitory loop in vascular sympathetic nerves was not affected. Plasma epinephrine concentration during electrical stimulation was also increased by chronic but not by acute clorgyline treatment. Chronic clorgyline treatment did not significantly affect the total systemic metabolic clearance rate of infused norepinephrine, thus the increased plasma norepinephrine response to stimulation reflects an increased release rate from sympathetic neurons.In rats treated chronically with clorgyline, the pressor response to norepinephrine in the presence of yohimbine (0.3 mg/kg) was significantly reduced, whereas the pressor response to guanabenz was unchanged. There was also no change in the guanabenz-induced inhibition of the tachycardic response to electrical stimulation. These results show that the enhanced norepinephrine release produced by chronic clorgyline treatment leads to down-regulation of post-synaptic ₁-adrenoreceptors with no change in post-synaptic ₂-adrenoceptors or in cardiac presynaptic ₂-adrenoreceptors, and are in agreement with an intrasynaptic location of ₁-adrenoceptors and an extra-synaptic location of ₂-adrenoceptors in the rat vasculature.