Effect of acute levodopa on brain catecholamines after selective MAO and COMT inhibition in male rats

Interactions between a selective catechol-O-methyltransferase (COMT) inhibitor OR-462 and a monoamine oxidase (MAO)-A inhibitor clorgyline were studied measuring concentrations of L-dopa, dopamine and their metabolites in the rat hypothalamus and striatum after administration of levodopa/carbidopa (15/30 mg/kg i.p.). Part of the experiments were performed in rats pretreated with 6-OH-dopamine (6-OHDA) intracerebroventricularly (i.c.v.) to determine whether changes in dopamine metabolism occurred inside or outside catecholaminergic neurons. OR-462 was an effective COMT inhibitor at the doses 3 and 30 mg/kg i.p. Inhibition of 3-O-methyldopa (3-OMD) formation from L-dopa was reflected in the hypothalamus (45-81% decrease) and striatum (87-88% decrease), since 3-OMD penetrates the blood-brain barrier. Homovanillic acid (HVA) was decreased only in the striatum at 30 mg/kg of OR-462. Clorgyline (8 and 32 mg/kg i.p.) decreased 3,4-dihydroxyphenylacetic acid (DOPAC) formation in the hypothalamus and striatum by 61-91%. When given together, OR-462 and clorgyline elevated hypothalamic dopamine levels 3.2-4.6-fold, but striatal dopamine only 1.3-1.9-fold. The formation of 3-OMD and DOPAC remained suppressed and even brain HVA levels were decreased by 51-97%. 6-OHDA treatment decreased striatal and hypothalamic dopamine by 50% and noradrenaline by 75%. In these animals levodopa/carbidopa increased brain L-dopa 2.4-4-fold, those of 3-OMD 1.2-1.7-fold compared to intact animals, but the synthesis and metabolism of dopamine and the effects of COMT and MAO inhibitors were not significantly changed. Levodopa/carbidopa treatment decreased significantly prolactin and thyrotropin levels in serum but none of the additional treatments changed this action.

Site-dependent action of intracerebroventricular 5-hydroxytryptamine on the cold-stimulated thyrotropin secretion in male rats

The effects of central 5-hydroxytryptamine (5-HT) infusions on the cold-stimulated thyrotropin (TSH) levels were studied in male rats. Stainless-steel cannulas were implanted stereotaxically into the anterior or the posterior third ventricle or just lateral to the hypothalamic paraventricular nuclei bilaterally 7 days before experiments. Infusion of 5-HT (4.5 and 9 micrograms/rat) into the posterior third ventricle attenuated significantly the cold-stimulated TSH levels. Inversely, infusion of 5-HT (9 micrograms/rat) into the anterior third ventricle augmented significantly the TSH cold response. Bilateral 5-HT infusions into the vicinity of the hypothalamic paraventricular nuclei did not affect the TSH cold response. Serum prolactin levels increased significantly after 5-HT administration into the anterior and the posterior third ventricle, but no consistent effect on growth hormone (GH) levels could be detected. Infusion of 5-HT into the anterior and the posterior third ventricle decreased body temperature irrespective of the observed hormonal response to 5-HT. The results are in favor of a dual and possibly site-dependent role for 5-HT in the regulation of the cold-stimulated TSH secretion in the rat. The opposite effects of 5-HT on the TSH cold response may result from the predominant inhibition of either the thyrotropin-releasing hormone or the somatostatin-secreting cell groups.

Somatostatin, neuropeptide Y, GABA and cholinergic enzymes in brain of pentylenetetrazol-kindled rats

We studied the effect of pentylenetetrazol (PTZ)-induced kindling (35 mg/kg, i.p., daily) on somatostatin-like immunoreactivity (SOM) with special attention to the duration of changes (rats were sacrificed either 10 days or 4 months after the development of kindling) and to transmitters or modulators related to somatostatin (neuropeptide Y (NPY), GABA, choline acetyltransferase (ChAT), acetylcholinesterase (AchE]. In rats sacrificed 10 days after the last kindled seizure, SOM was elevated in frontal cortex and striatum (p less than 0.01); NPY was elevated in frontal cortex, striatum and hippocampus (p less than 0.05) of kindled or prekindled rats (i.e., rats which were treated daily with PTZ but did not express three consecutive generalized seizures). ChAT activity was slightly decreased (p less than 0.05) in cortex. GABA levels and AchE activity were unchanged in kindled cortex. In rats sacrificed 4 months after the development of kindling none of the parameters analyzed differed from controls. The present study suggests that the cortical and striatal neurons containing SOM/NPY are affected by PTZ-kindling. The cortical cholinergic system is affected to a much smaller extent. The neuropeptide changes are not persistent, as is the lowered seizure threshold, so they are probably not involved in the maintainance of the latter.

Efficacy of erythromycin acistrate (2'-acetyl erythromycin stearate) and erythromycin stearate in experimental infections in mice

The efficacy of erythromycin stearate (ES) and its 2'-acetyl ester (erythromycin acistrate, EA) was compared in eight experimental infections in mice of both sexes. In two studies the mice were made leukopenic by whole-body irradiation. Four absorption studies were also performed in parallel. In Streptococcus pneumoniae peritonitis, the protective dose 50% (PD50) value of EA and ES, given s.c., did not differ from each other. The bioavailability of EA was slightly inferior to that of ES. In three other peritonitis studies (2 Staphylococci and 1 Streptococcus), where the treatments were given s.c., EA seemed to lag behind ES in efficacy. The parallel absorption experiment showed, however, that, as compared to ES, only about one-half of EA was released from the s.c. injection site to the blood. The adjusted PD50 values of both erythromycins were about the same, with one exception. When the treatments were given i.p. both erythromycins were equally effective, and the difference in bioavailability was minor. On the contrary, the efficacy of 2'-ethylsuccinyl erythromycin was only about one-tenth that of the other erythromycins as was also the bioavailability. Oral treatment gave similar therapeutic results with EA and ES, with similar bioavailabilities, too. In the muscle abscess model, single s.c. injections of EA and ES were equally effective in reducing the growth of Staphylococcus aureus. These results suggest that there is no great difference in the in vivo antibacterial performance of ES and its 2'-acetyl ester, although the absorption problems complicate the interpretation. Hence EA performs better than expected if only the hydrolyzed drug were useful.

Comparison of the effects of intraventricular taurine, GABA and homotaurine on serum prolactin levels in male rats

The effects of taurine (2-aminoethanesulphonic acid), gamma-aminobutyric acid (GABA) and homotaurine (3-aminopropanesulphonic acid), a structural analogue of both taurine and GABA, on serum prolactin (PRL) levels were compared in conscious, unrestrained male rats. Taurine, injected into the lateral brain ventricles at doses of 6 and 10 mumol per rat, elevated serum PRL level by 52% (P less than 0.01) and 90% (P less than 0.001), respectively. GABA elevated serum PRL level (41%, P less than 0.05) only at the lowest dose (1 mumol) tested. Homotaurine was the most effective compound, eliciting increases of 353% and 449% (P less than 0.001) at 6 and 10 mumol per rat, respectively. The rank order of the three amino acids in elevating serum PRL level bears some similarity to their known rank order of potency in altering cerebral dopamine metabolism.

Synthesis of some novel potent and selective catechol O-methyltransferase inhibitors

A series of disubstituted catechol derivatives was synthesized and tested as potential COMT inhibitors. The most active compounds were more than 1000 times more potent (IC50 = 3-6 nM) in vitro than the known COMT inhibitor, 3',4'-dihydroxy-2-methylpropiophenone (U 0521, IC50 = 6000 nM). The new compounds were also highly selective COMT inhibitors with no activity against other essential enzymes involved in the synthesis and metabolism of catecholamines.

Effect of erythromycin acistrate and erythromycin stearate on human colonic microflora

The effects of erythromycin acistrate (2'-acetyl erythromycin stearate), a new erythromycin derivative, and erythromycin stearate on the faecal microflora were compared in a randomized cross-over study. 12 healthy volunteers were given either drug 500 mg t.i.d. for 1 week. Their faeces were studied before, immediately after, and 1 week after the drug administration period. After a wash-out period of 4 weeks, the drugs were interchanged. Both erythromycin acistrate and erythromycin stearate induced changes in the normal colonic microflora to about the same extent. The most marked effect was the suppression of gram-negative anaerobic and aerobic rods. Clostridium difficile appeared in 1 subject on both drugs. Also the counts of aerobic gram-positive cocci were altered; enterococci increased in number. An increased resistance to erythromycin was noted among staphylococci and enterococci after both drugs.

Cholinergic regulation of thyrotropin secretion in male rats

The cold-stimulated thyrotropin (TSH) secretion in male rats was suppressed by muscarinic agonists, i.e. Oxa-22, McN-A-343 (an M1 agonist), oxotremorine (an M2 agonist) and methacholine (a quaternary compound). The inhibitory effect of Oxa-22 was antagonized by atropine, butylscopolamine and glycopyrrolate as well as by pirenzepine, an M1 antagonist and AF-DX 116, a new M2 antagonist. Various muscarinic antagonists were not active when given alone. Cytisine, a peripheral nicotinic agonist, was not active but nicotine significantly suppressed the cold-stimulated TSH secretion. Its effect was counteracted by mecamylamine but not by hexamethonium. The thyrotropin releasing hormone (TRH)-induced TSH secretion was not inhibited by Oxa-22, nicotine or methacholine. These results show that irrespective of the receptor subtype (muscarinic1 or muscarinic2, nicotinic), cholinergic activation inhibits the cold-stimulated TSH secretion. The results also suggest that this inhibitory effect is at the hypothalamic rather than the anterior pituitary level. The muscarinic action seems to occur outside the blood-brain barrier but the nicotinic action occurs inside this barrier.

Inhibition of catechol-O-methyltransferase activity by two novel disubstituted catechols in the rat

Catechol-O-methyltransferase (COMT) has an important role in the extraneuronal inactivation of catecholamine neurotransmitters and drugs with a catechol structure. Two novel COMT inhibitors, OR-462 and OR-486, were highly effective (IC50 = 18 and 12 nM, respectively) and selective in inhibiting COMT activity in vitro. Tyrosine hydroxylase was not inhibited until micromolar concentrations of these compounds were used: the IC50 values for OR-462 and OR-486 were 10 and 14 microM, respectively. The IC50 values for dopamine-beta-hydroxylase, dopa-decarboxylase and monoamine oxidase forms A and B were greater than 50 microM. In studies ex vivo oral OR-462 inhibited mainly the COMT activity in the duodenum while OR-486 inhibited COMT activity in the liver and red blood cells as well. Oral OR-462 did not penetrate into the brain in doses up to 30 mg/kg while the same dose of OR-486 had some effect on striatal COMT activity. When tested in combination with levodopa-carbidopa, orally administered OR-462 and OR-486 were more effective in reducing the formation of 3-O-methyldopa from levodopa than was the levodopa-carbidopa treatment alone. These results indicate that OR-462 and OR-486 are effective and long-lasting inhibitors of COMT activity.

Time course of the antibacterial activity of erythromycin stearate and erythromycin acistrate against two Staphylococcus aureus strains in vitro

The antibacterial efficacy of erythromycin stearate (ES) and a new erythromycin prodrug, erythromycin acistrate (EA, 2'-acetyl erythromycin stearate), was compared in two Staphylococcus aureus strains, one sensitive and the other resistant to erythromycin. The growth was continuously monitored turbidometrically for 24 h. With the sensitive S. aureus, the inhibitory effects of both ES and EA were visible within 1-2 h when the antibiotics were added at 0 or 1.5 h after the beginning of the incubation. When they were added at 3 h, their action was immediate at 0.5 and 1 mg/l, and 5 mg/l caused a complete inhibition of the growth. At 0.5 and 1 mg/l, however, ES was much more effective than EA. When EA and ES (1, 5 or 10 mg/l) were added at 0 or 1.5 h to the resistant staphylococcal culture, the lag phases (no detectable growth) were prolonged as a function of drug concentration but eventually the growth was restored. The action of EA was weaker and the lag phases were 2-5 h shorter than those after ES. When the compounds were added at 3 h, the antibacterial effect was visible immediately. The increase of absorbance was slowed down even by 1 mg/l of ES and almost prevented by 5 mg/l. At these concentrations EA was less effective than ES, but the two erythromycins were equally active at 10 mg/l. These results show that addition of EA acts on both staphylococci as rapidly as addition of ES but to a lesser extent. Evidently EA is antibacterially weaker than ES, or rapidly hydrolyzed to erythromycin after it has been added to the test system.

Further studies of serotonergic activity in the regulation of the cold stimulated thyrotropin secretion in male rats

Serotonergic agonists and antagonists were used to study the role of 5-HT in the regulation of thyrotropin (TSH) secretion in male rats. When given peripherally, the agonists like 5-HT, quipazine and m-chlorophenylpiperazine (mCPP) decreased dose-dependently the cold-stimulated TSH-secretion. The action of 5-HT was antagonized by metergoline but not by ketanserin. The effect of quipazine was counteracted by both antagonists. Small intraperitoneal doses of ketanserin seemed to be stimulatory on the TSH secretion while high doses of both ketanserin and metergoline clearly decreased the cold-stimulated TSH levels. Infusion of quipazine into the 3rd ventricle inhibited significantly the TSH cold-response whereas 5-HT and mCPP did not. The action of quipazine was only partially antagonized by ketanserin pretreatment. 5,7-dihydroxytryptamine (5,7-DHT) was used to make serotonergic lesions into different regions of the brain. The TSH lowering effects of intraperitoneal quipazine and mCPP were potentiated in the rats lesioned in the 3rd ventricle or bilaterally into the posterior hypothalamus but not in the rats lesioned bilaterally into the anterior hypothalamus. Hence serotonergic activity in the vicinity of the posterior part of the 3rd ventricle seems to decrease the cold-stimulated TSH secretion. Both 5-HT1 and 5-HT2 receptors appear to participate in this regulation.

Effect of chronic morphine treatment on thyrotropin and prolactin levels and acute hormone responses in the rat

The effects of three chronic morphine regimens on basal and cold-stimulated thyrotropin (TSH) and on prolactin levels were studied in male rats with and without acute morphine challenge. All the chronic regimens decreased basal and cold-stimulated TSH levels, but only one regimen (10 mg/kg b.i.d.) significantly enhanced the prolactin levels. The altered cold-stimulated TSH and prolactin levels were recovered within about 96 and 48 hr, respectively, after the last morphine injection on the 7-day pretreatment period. After the chronic administration (14 days), acute morphine challenges were performed either when cold-stimulated TSH secretion was suppressed (12- and 24-hr lag time) or when the response to cold was normalized (96-hr lag time). When the TSH levels were still low, the small challenge doses of morphine (10 and 15 mg/kg) no longer suppressed the TSH secretion. This was due neither to the real tolerance nor to the persistent effect of chronic morphine but to the withdrawal stress, which was also reflected as elevated corticosterone levels. However, after a 96-hr lag time, the challenge doses of morphine decreased TSH secretion after each morphine regimen as effectively as in the naive rats. Thus, the regimens did not induce the development of tolerance to the effect of morphine on cold-stimulated TSH secretion. Most regimens seemed to cause some tolerance to the stimulatory effect of morphine on prolactin secretion irrespective of the duration of the lag time. Even after the mildest regimen (10 mg/kg once a day), a tolerance developed to the antinociceptive effect of morphine, and it lasted well up to 96 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations of erythromycin, 2'-acetyl erythromycin, and their anhydro forms in plasma and tonsillar tissue after repeated dosage of erythromycin stearate and erythromycin acistrate

The concentrations of erythromycin, 2'-acetylerythromycin (2'-AE) and their anhydro forms in plasma and tonsillar tissue were analyzed after a 3-day repeated-dosage regimen of erythromycin stearate (ES; 500 mg twice a day [b.i.d]) and erythromycin acistrate (EA), a new erythromycin prodrug, at two doses (400 and 500 mg b.i.d.). The tonsils of 40 patients were removed at 112 to 329 min after intake of the last dose. Blood samples were collected at the time of tonsillectomy and at 0, 2, and 6 h after the last dose. At all time points, EA produced severalfold more total antibiotic (erythromycin + 2'-AE) concentrations in plasma compared with ES. There were two nonabsorbers in the ES group, but none in the two EA groups. The mean total antibiotic levels in tonsillar tissue after EA treatment exceeded the levels after treatment with ES by a factor of 3 (for EA at 400 mg b.i.d.) and 4.5 (for EA at 500 mg b.i.d.). The ratios of erythromycin concentration in tonsil to that in plasma at the time of tissue removal were quite similar for all groups (means, 0.51 to 0.54). In the EA groups, 2 of 26 (8%) patients had no measurable erythromycin in the tonsillar tissue samples, whereas in the ES group, 3 of 14 (21%) patients had no measurable erythromycin in the same tissue. The degree of hydrolysis of 2'-AE to erythromycin was about 25% in plasma at the time of tonsillectomy for both EA groups and about 40% in tonsillar tissue. There were negligible amounts of anhydro forms in plasma after EA administration, whereas in the ES group, anhydroerythromycin levels were, from time to time, even higher than erythromycin levels. Very high levels of anhydro forms were detected in tonsillar tissue after ES treatment, whereas only low levels were found after EA administration.

Comparative liver toxicity of various erythromycin derivatives in animals

The hepatotoxicity of a new erythromycin derivative, erythromycin acistrate (EA, 2'-acetyl erythromycin stearate), was compared with that of erythromycin stearate (ES), erythromycin estolate (EE) and erythromycin-11,12 cyclic carbonate (EC) in 4-5-day, 28-day and 6-month oral toxicity studies in rats and dogs. In the 4-day rat study, EC caused fatty metamorphosis in the liver. ES caused similar, but milder changes at a dose nearly five times higher. The 5-day dog study revealed markedly increased serum alanine aminotransferase (S-ALAT), serum aspartate aminotransferase (S-ASAT), serum alkaline phosphatase (S-APHOS) and serum gamma-glutamyl transpeptidase (S-gamma-GT) values in the EC- and EE-groups, and slightly elevated S-ALAT values also in the EA- and ES-groups. Microscopy revealed cholangitis, pericholangitis and phlebitis in the portal areas in the EC-group at all doses. Epithelial hyperplasia was observed also in the bile ducts. EE caused similar but milder changes. The changes in the EA-group were small, but mildly atypical bile duct epithelium was seen in female dogs receiving 2 x 200 mg/kg of EA. The ES-group was practically without changes and very much like the EA-group. Thus the dog proved to be a more sensitive model for assessing the hepatotoxicity of erythromycin derivatives. In the 28-day studies, only EA and ES were investigated. In the rat study, slightly elevated serum enzyme levels within the normal range were measured in the high-dose regimens of both drugs. In the dog study, 300 mg/kg of EA caused slightly elevated S-ALAT in males, but the values returned to normal after a 2-week off-dose period. Only EA was studied in the 6-month study. In male rats, 400 mg/kg of EA caused slightly elevated enzyme levels and neutral fat droplets in centrilobular hepatocytes. In male dogs given 150 mg/kg of EA, S-ALAT, S-APHOS, and S-gamma-GT values were elevated after four weeks of treatment but returned to normal thereafter. No severe changes were seen in the liver histopathology. In conclusion, EC and EE were clearly hepatotoxic in dogs, and EC also in rats. EA, and to a somewhat lesser extent ES, showed signs of mild hepatotoxicity only at high doses. This evidently reversible effect was considered a common characteristic of erythromycins.

Fate of single oral doses of erythromycin acistrate, erythromycin stearate and pelleted erythromycin base analysed by mass-spectrometry in plasma of healthy human volunteers

The kinetics of erythromycin acistrate (EA). a new ester prodrug of erythromycin, were studied in three comparative, randomized, cross-over studies in 29 healthy volunteers. A new mass-spectrometric method was used to assay separately erythromycin, 2'-acetyl erythromycin and their anhydro (spiroketal) forms. In Part I, the total antibiotic concentration was higher after EA than after erythromycin stearate (ES; 1.8-fold) and enterocoated pellets of erythromycin base (EB, enterocapsules; 1.4-fold). In plasma, however, only about one third of 2'-acetyl erythromycin was hydrolysed to active erythromycin. Moreover, after unprotected EA tablets, a considerable proportion of erythromycin and 2'-acetyl erythromycin was inactivated by gastric acid as reflected by high concentrations of respective anhydro (spiroketal) forms. In Part II, the unprotected (regular tablets) and acid-protected tablets (dissolution starts at pH 4.5) were compared. The protected tablet, albeit not an enterotablet, was not destroyed by gastric acid. Its absorption was slightly delayed but the bioavailability was good. In this study, the absorption of total antibiotic was 2.8-fold (unprotected tablet) and 3.9-fold (protected tablet) that after enterocapsules. In Part III, the bioavailabilities of 200 and 400 mg tablets (both acid-protected) were equal.

Absorption of erythromycin acistrate and erythromycin base in the fasting and non-fasting state

Absorption of erythromycin acistrate (EA) and two erythromycin base (EB) preparations (enterotablet A and B) taken after an overnight fast or immediately before a standard breakfast was studied in 29 healthy volunteers in three separate studies, in a cross-over, randomized design. In Study I, the absorption of a single dose (400 mg) of EA was similar in the fasting and non-fasting state. There was, however, more interindividual variation and in two subjects absorption was markedly impaired in the presence of food. Cimetidine given at two doses (400 + 800 mg) had no effect on the pharmacokinetics of erythromycin acistrate. In Study II, the effect of food on the bioavailability of the two EB preparations was studied after a single dose of 500 mg (2 x 250 mg enterocoated tablets) and after multiple dosing (2 x 250 mg tid). When given with a standard breakfast, erythromycin base was significantly better absorbed from enterotablet A than from enterotablet B, whether given as a single dose or in repeated doses. Study III followed the same design as Study II except that the tablet size of both enterotablets A and B was now 500 mg. Even in this study the absorption of enterotablet A was significantly better than that of enterotablet B. EA is adequately absorbed when taken before a meal. Cimetidine does not interfere with its elimination. Concomitant food intake produced considerably dissimilar absorption of two commercially available enterocoated EB preparations. Although at steady-state this was less prominent than after a single dose, it may have some clinical significance.

Effects of two erythromycins, doxycycline and phenoxymethylpenicillin on human leucocyte chemotaxis in vitro

The effect of erythromycin, doxycycline and phenoxymethylpenicillin on human polymorphonuclear leucocyte (PMNL) chemotaxis was studied in vitro with Boyden's filter technique. Both erythromycin base and 2'-acetyl erythromycin stearate increased the PMNL chemotaxis significantly at concentrations greater than or equal to 50 microM, 2'-acetyl erythromycin stearate also at concentrations of 2.5-5 microM. Phenoxymethyl-penicillin reduced migration at 500 microM but lower concentrations had no significant effect. Doxycycline prevented migration significantly at concentrations greater than or equal to 50 microM.

Antibiotic concentration in suction skin blister fluid and saliva after repeated dosage of erythromycin acistrate and erythromycin base

The drug concentration in plasma, suction skin blister fluid (SBF), urine and saliva after repeated dosage of either erythromycin acistrate (EA) or enterocoated pellets of erythromycin base (EB) was studied in young healthy volunteers with a cross-over design in two separate studies. In Study I, the total drug concentration (erythromycin + 2'-acetyl erythromycin) after EA (400 mg tid) was slightly higher than the erythromycin concentration after EB (500 mg tid). The concentration of erythromycin after EA was about half of that after EB. In SBF the total antibiotic concentration after EA and erythromycin concentration after EB were 49 and 46% of the corresponding plasma concentrations, respectively. The degree of hydrolysis of 2'-acetyl erythromycin was higher in SBF (44%) than in plasma (39%). An equal proportion (7.3-7.5%) of the dose was excreted in urine after administration of both drugs. The degree of hydrolysis of 2'-acetyl erythromycin in urine was 58%. In Study II, the plasma/saliva concentration ratio ranged from 0.11 to 0.17 after EA 400 mg tid, 0.12 to 0.20 after EA 500 mg tid and 0.17 to 0.22 after EB 500 mg tid. The degree of hydrolysis of 2'-acetyl erythromycin was considerably higher in saliva (61-78%) than in plasma (27-41%). In plasma, the percentage of hydrolysis of 2'-acetyl erythromycin was inversely correlated with the concentration of acid-alpha 1-glycoprotein. The penetration of 2'-acetyl erythromycin and erythromycin into the extravascular space as evaluated from SBF and saliva levels was equal, and adequate concentrations of erythromycin were obtained for the treatment of bacterial infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Tonsillar penetration of erythromycin and its 2'-acetyl ester in patients with chronic tonsillitis

Concentrations of erythromycin and 2'-acetyl erythromycin were analysed in serum or plasma and tonsil tissue after repeated dosage of erythromycin acistrate (EA), a new erythromycin prodrug, in two separate studies in 61 young patients. The reference preparations were: (1) enterocoated tablets of erythromycin base (EB enterotablets, (2) erythromycin base as enterocoated pellets (EB enterocapsules) and (3) erythromycin stearate (ES). All drugs were given 500 mg tid for three days before scheduled tonsillectomy. Tonsils were removed about 3 h after intake of the last dose. Blood samples were collected at 0, 2 and 6 h and at the time of tonsillectomy. At all time points EA produced several-fold higher total drug (erythromycin + 2'-acetyl erythromycin) concentrations in serum or plasma than any of the reference preparations. Similarly, after EA the mean total antibiotic levels in tonsil tissue exceeded the erythromycin levels after the reference preparations by at least a factor of 3. Tonsil/serum or plasma ratios of the total antibiotic were quite similar with all preparations (means 38-50%). Peak erythromycin levels in circulation did not differ significantly from each other in spite of two nonabsorbers after EB enterotablets. The same was true of tonsil tissue. There were, however, 15 tonsils with undetectable erythromycin: 4/25 (16%) with EA, 5/12 (42%) with EB enterotablets, 2/12 (17%) with EB enterocapsules and 4/12 (33%) with ES. The degree of hydrolysis of 2'-acetyl erythromycin to erythromycin was 23-43% higher in tonsil tissue than in circulation.

Comparative studies on the dependence liability of morphine hydrochloride, codeine phosphate and two novel antitussive compounds vadocaine hydrochloride and N-(2',4'-dimethyl-6'-methoxyphenyl)-4-(diethylamine) butanamide hydrochloride in mice

The effects of two novel antitussive compounds, vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl)propionanilide+ ++ hydrochloride, OR K-242-HCl; INN: vadocaine) and N-(2,4-dimethyl-6-methoxyphenyl)-4-(diethylamine)butanamide hydrochloride (OR K-269-HCl) on the suppression of withdrawal signs (hypothermia and weight loss) induced by repeated morphine administration were compared to those of acute morphine and codeine administrations. Moreover, spontaneous and precipitated withdrawal-induced hypothermia, weight loss and behavioural changes from repeated codeine, vadocaine and OR K-269-HCl administrations were studied. Acute administration of morphine clearly reversed the hypothermia and weight loss induced by spontaneous withdrawal from morphine. Codeine was not able to suppress the hypothermia and weight loss induced by morphine withdrawal. Acute injections of vadocaine and OR K-269-HCl did not alter these withdrawal signs either. Moreover, acute administration of codeine tended to prevent the weight loss induced by codeine withdrawal and caused behavioural changes. Spontaneous or precipitated withdrawal from repeated vadocaine or OR K-269-HCl administration caused neither hypothermia, weight loss nor behavioural changes. These results support the view that compounds vadocaine and OR K-269-HCl are free from morphine-like addictive properties.

First human studies on the safety and antitussive activity of vadocaine hydrochloride

Vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl)propionanilide+ ++ hydrochloride, OR K-242-HCl; INN: vadocaine) is a new anilide derivative which resembles lidocaine in chemical structure. The safety and antitussive effects of this new compound were studied in 6 healthy male volunteers in the first Phase I clinical trial. Vadocaine was administered in single doses of 5, 10, 15, 20, 30 and 50 mg. At these dose levels vadocaine had no effects on the cardiovascular system, the haematological variables, blood biochemistry or urinary sediment examined as safety evaluation. The antitussive properties of the compound were studied using inhaled citric acid for induction of the cough response. The antitussive properties of vadocaine were most effective at a dose of 15 mg, although no statistical significance was found. Neither was any dose-response relationship noted. However, at this dose level vadocaine is apparently safe and its antitussive properties seem promising enough for further evaluation.

Studies on the nonspecific central nervous system effects of the novel antitussive compound vadocaine hydrochloride

Vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl) propionanilide hydrochloride, OR K-242-HCl; INN: vadocaine) is a novel antitussive compound which is effective in several animal models at doses of 2.5-6 mg/kg. It has both central and peripheral local anaesthetizing properties. The present studies were aimed at exploring the specificity of the central antitussive activity of vadocaine. Vadocaine administered in doses of 25 and 50 mg/kg was not found to be effective in any of a series of experiments, although some antinociceptive activity was shown in the hotplate test and in the writhing test at a dose of 75 mg/kg. Some deteriorative activity was noted at a dose of 75 mg/kg in tests measuring motor coordination (rotarod) and spontaneous motility. This high dose of vadocaine did not affect pentobarbital sodium-induced sleeping time nor protect the animal from pentetrazole-induced convulsions. As expected, codeine phosphate was found to be a more potent antinociceptive drug than vadocaine, also enhancing spontaneous motility. Both the control anaesthetics benzonatate and lidocaine proved rather ineffective. Benzonatate (50 mg/kg) did not alter any of the results, whereas lidocaine (50 mg/kg) caused a decrease in the number of writhings. In conclusion, vadocaine can be said to initiate minor deterioration of the central nervous system only at doses about 10 times higher than those which show antitussive activity. Acute lethal doses are still 2 to 5 times higher. The central antitussive action of vadocaine can therefore be considered fairly specific.

Pharmacokinetics of graded single doses of the novel antitussive compound vadocaine hydrochloride in healthy male volunteers

Vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl)propionanilide+ ++ hydrochloride, OR K-242-HCl; INN: vadocaine) is an anilide derivative with antitussive and local anaesthetic properties. The pharmacokinetics of this new compound were studied in two Phase I clinical trials during safety evaluation. 6 (Part I) and 8 (Part II) healthy male volunteers participated in these studies. The pharmacokinetics were studied after single oral doses of 5, 10, 15, 20, 30 and 50 mg (Part I) and 100, 200, 300, 400 and 500 mg (Part II) of vadocaine in aqueous solution. Vadocaine was rapidly absorbed at each dose level. The AUCo----infinity value and 24-h urinary recovery of intact compound increased linearly as functions of the dose. The elimination half-life varied from 2.2 +/- 0.2 h to 3.7 +/- 1.6 h in a dose range from 5 to 50 mg, and from 2.7 +/- 0.3 h to 4.0 +/- 1.0 h in a dose range from 100 to 500 mg. The peak concentration of vadocaine after the highest dose was 2317.3 +/- 31.5 ng/ml at 1 h. When higher doses were used renal clearance did not change, although total body clearance seemed to diminish. Over 90% of vadocaine is metabolized, and the metabolic pathways may become saturated at a dose of 400 mg.

Tissue distribution of the novel antitussive compound vadocaine hydrochloride in white female mice studied by whole-body autoradiography

The tissue distribution of tritium-labelled vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl)propionanilide+ ++ hydrochloride, OR K-242-HCl; INN: vadocaine) was studied in female mice by whole-body autoradiography at different times (15 min - 24 h) after intravenous injection. Radioactivity disappeared rapidly from blood and was fairly selectively localized in the liver, the gall bladder and the intestinal contents. Vadocaine is evidently metabolized in the liver and a remarkable part of the drug and its metabolites are excreted into the bile. Accumulation of radioactivity in the kidneys shows that also renal elimination is important. A considerable accumulation into the lungs supports the peripheral anaesthetizing mechanism in the antitussive action of vadocaine. No detectable penetration into the brain was seen. At 24 h, only traces of the radioactivity could be detected in the liver and lungs.

Antitussive action of the new anilide derivative vadocaine hydrochloride compared with codeine phosphate in four animal models

Vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl) propionanilide hydrochloride, OR K-242-HCl; INN: vadocaine) is a novel antitussive compound structurally resembling local anaesthetics. Its antitussive profile was studied in several animal models. In guinea-pigs, vadocaine reduced by about 70% the cough episodes induced by sulphur dioxide or ammonia. The effective dose was 2.5 mg/kg p.o., and codeine phosphate was less effective. In cats, vadocaine (3 mg/kg i.v.) inhibited by about 80% for 10 min the cough reflex initiated by mechanical irritation of the trachea. When vadocaine was given via the vertebral artery, it was about 10 times more active than by the intravenous route. Codeine was 3 times as active as vadocaine by both routes. This result indicates an important central component in the antitussive action of vadocaine. In another cat model, 5 mg/kg of vadocaine was somewhat weaker than 1 mg/kg of codeine in inhibiting the cough caused by electrical stimulation of the laryngeal nerve (Domenjoz' method). In dogs, both oral and intravenous doses of 6 mg/kg of vadocaine and 2 mg/kg of codeine were approximately equiactive, inhibiting by 60-80% the cough induced by electrical stimulation of the trachea. Concentrations of vadocaine in serum were around 1 microgram/ml during oral administration. By both routes, the antitussive activity (inhibition of cough by 50% or more) lasted at least 2 h. Vadocaine caused local anaesthesia in the guinea-pig wheal preparation at concentrations of 0.25% and 0.5%, and on the guinea-pig cornea at 0.5%. Duration of anaesthesia was longer than that of lidocaine. Vadocaine did not affect the guinea-pig tracheal strip preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary pharmacokinetics of the new antitussive compound vadocaine hydrochloride in animals

The absorption and fate of vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl)propionanilide+ ++ hydrochloride, OR K-242-HCl; INN: vadocaine) was studied using both unlabelled compound (rabbits, rats and dogs) and tritium-labelled compound (rats). Although vadocaine was orally absorbed in dogs, no oral absorption was found in the rabbits. The elimination of the intravenously given compound was very fast (t1/2 only about 0.6 h in the rabbits). Most of the drug was metabolized both in rats and dogs. In rats, less than 0.2% of the compound was found intact in 24-h urine. In dogs, the 24-h recovery was 1-5% of the dose. After intravenous injection to rats, 43% of the radioactivity given as tritium-labelled vadocaine was recovered in urine and 19% in faeces. After oral dosing, 37% was recovered in urine and 31% in faeces. Hence, the total 7-day recovery of the radioactivity given as tritium-labelled vadocaine was 62-68% of the dose.

Opiate receptor subtypes in the regulation of thyrotropin and prolactin secretion in the rat

In the present study both MR 2034 (kappa-agonist) and DAMME (mu-agonist) decreased thyrotropin (TSH) secretion stimulated by cold in the rat when infused into the 3rd ventricle. After infusion into the posterior hypothalamus (PH), a small dose of MR 2034 increased the TSH response to cold whereas other doses did not. The stimulatory (at PH) but not the inhibitory (at 3rd ventricle) effect of MR 2034 was antagonized by naloxone. DAMME had no statistically significant effect at this location. Both the mu- and kappa-agonist stimulated prolactin secretion when infused into the 3rd ventricle, but DAMME was more effective than MR 2034. Furthermore, the stimulatory effect of DAMME, but not that of MR 2034, on prolactin secretion was antagonized by naloxone.

Properties of novel effective and highly selective inhibitors of catechol-O-methyltransferase

Novel bisubstituted catechols were found to be potent and highly selective COMT inhibitors in vitro. One of them, OR-462 (3-(3,4-dihydroxy-5-benzylidene)-2,4-pentanedione), was studied also in vivo. When administered to rats orally together with levodopa and carbidopa, OR-462 greatly improved the bioavailability of levodopa and effectively reduced the formation of 3OMD. The levels of levodopa and dopamine were increased also in the striatum, and the 3OMD levels were decreased. The metabolic profile of dopamine demonstrated that COMT inhibition occurred in the peripheral tissues but not in the striatum. OR-462 thus resembled the peripheral inhibitors of dopadecarboxylase. These potent, selective and orally active COMT inhibitors offer a new tool for interfering in the metabolism of various COMT substrates.

Potentiation of central effects of L-dopa by an inhibitor of catechol-O-methyltransferase

The effects of a COMT-inhibitor, U-0521, and a MAO-B-inhibitor, 1-deprenyl, on L-dopa-induced circling behaviour were compared in 6-OHDA-lesioned rats. The actions of U-0521 and 1-deprenyl on the anti-cataleptic effect of L-dopa were also studied. Both U-0521 and 1-deprenyl were found to potentiate L-dopa-induced circling behaviour and anti-cataleptic effect of L-dopa. In both test systems the L-dopa potentiation of 1-deprenyl was longer-lasting than that caused by U-0521. Thus inhibition of COMT, like inhibition of MAO, is able to enhance the central effects of L-dopa. This principle might be beneficial in the treatment of Parkinson's disease especially if COMT-inhibitors with greater performance can be developed.

Striatal membrane-bound and soluble catechol-O-methyl-transferase after selective neuronal lesions in the rat

Activities of the two forms of catechol-O-methyltransferase (COMT), viz. the soluble (S-COMT) and the membrane-bound (MB-COMT), have been studied in the rat striatum to characterize their localization in relation to the nigrostriatal dopaminergic neurons. Selective unilateral nigrostriatal dopaminergic lesions were produced by an intranigral injection of 6-hydroxydopamine (6-OHDA; 8 micrograms/site). 6-OHDA caused an extensive lesion of the dopaminergic neurons as revealed by non-detectable concentrations of dopamine in the striata of the lesioned sites. In spite of that neither S-COMT nor MB-COMT activities were altered in comparison with the intact control striata. The intrastriatal injection of kainic acid significantly increased S-COMT activity but to some extent decreased MB-COMT activity. Kainic acid did not alter the striatal concentration of dopamine. These results suggest that both S-COMT and MB-COMT reside postsynaptically the nigrostriatal dopaminergic neurons. S-COMT seems to be found mainly in striatal glial cells, whereas striatal MB-COMT might be located both in postsynaptic neuronal and extraneuronal cells.

Opioid peptides in the regulation of TSH and prolactin secretion in the rat

The effect of beta-endorphin, met-enkephalin and leu-enkephalin on cold-stimulated TSH and prolactin secretion after infusion of the drugs into the 3rd ventricle or into the posterior hypothalamus (PH) was investigated in male rats. beta-endorphin (0.25 microgram/rat, but not 0.05, 0.5 and 1 microgram/rat) increased and met-enkephalin (20 and 100 micrograms/rat) decreased TSH secretion when infused into the 3rd ventricle. After bilateral infusion into the PH, beta-endorphin (0.25 microgram/side, but not 0.05 and 1 microgram/side) increased TSH secretion, but met-enkephalin (1 and 10 micrograms/side) induced no changes. beta-endorphin (0.05-1 microgram/rat) and met-enkephalin (100 micrograms/rat) both increased prolactin secretion when infused into the 3rd ventricle, but only a high dose of beta-endorphin (1 microgram/side) was effective after infusion into the PH. Leu-enkephalin had no effect on TSH or prolactin secretion at the hypothalamic level. These results favour the hypothesis that mu-receptors mediate the inhibitory effect and other types (possible epsilon-receptors) of opiate receptors mediate the stimulatory effect of opioid peptides on TSH secretion at periventricular sites. However, only stimulatory mu-receptors affect prolactin secretion at these sites. After infusion into the PH, the effect of a high dose of beta-endorphin on prolactin secretion may also be mediated through periventricular sites, but its effect on TSH secretion is evidently mediated through opiate receptors in the PH.

Effect of enzyme induction and inhibition on the fate of metronidazole and tinidazole in the rat

The excretion routes of intact metronidazole and tinidazole were studied in rats kept in metabolism cages and cannulated for continuous bile collection. The nitroimidazoles were given intraarterially either alone or after a 5-day pretreatment with phenobarbitone (70 mg/kg/day intravenously) or after a single dose of cimetidine (50 mg/kg intraarterially). After 30 mg/kg, 27.0% of the metronidazole dose was excreted intact in 24-hr urine and 2.2% in bile. After tinidazole, the recoveries of the intact drug in urine and bile were 48.1% and 1.7%, respectively. After 90 mg/kg, the total recoveries of both drugs were 25-28% smaller than after 30 mg/kg. Phenobarbitone pretreatment did not affect metronidazole levels in plasma but decreased tinidazole levels at 4 hrs. The 24-hr recoveries of the intact nitroimidazoles in urine were significantly reduced by phenobarbitone while the 24-hr bile recoveries were not. Cimetidine treatment enhanced both metronidazole (at 1, 2 and 3 hrs) and tinidazole (only at 1 hr) concentrations in plasma, but this shift was not reflected in the 24-hr urine recoveries of the intact nitroimidazoles. Cimetidine doubled, however, the 24-hr bile recovery of the intact tinidazole. The calculations of the apparent degree of metabolism, assuming no methodological losses, showed that phenobarbitone increased the metabolism of tinidazole by about 62% and that of metronidazole only by about 16%. The effect of a single dose of cimetidine was negligible.

Tumor-producing and skin-irritating activity of dithranol (anthralin) and its 10-acyl analogues in SENCAR mice

The tumor-producing and skin-irritating activity of the antipsoriatic drug dithranol and its 10-acyl analogues butantrone (10-butyryl dithranol), 10-isobutyryl dithranol and 10-valeryl dithranol were studied in 650 SENCAR mice using a two-stage skin carcinogenesis assay. An initiation with 20 micrograms of 7,12-dimethylbenz(alpha)anthracene (DMBA) was followed 2 weeks later by three applications per week of the test compounds in 50 microliter of acetone for 21 weeks. In addition the compounds were studied without DMBA pre-treatment using application periods of 21 and 36 weeks. The concentration of dithranol was the maximum tolerated, 3.5 mM. For the less irritating 10-acyl analogues 30 mM solutions were used. The first signs of skin irritation were observed after an application period of 1-2 weeks and the irritation continued to the end of the experiment in all groups except the acetone controls. Dithranol caused the most severe irritation although the differences between the groups were not pronounced. On histopathology, the majority of animals had hyperplasia and other inflammatory changes of the skin. The first papillomas appeared 8-11 weeks after initiation and the incidences of papillomas at the end of the experiment were 85% (dithranol 3.5 mM), 16% (butantrone 30 mM), 36% (10-isobutyryl dithranol 30 mM) and 50% (10-valeryl dithranol 30 mM). Without initiation the incidences were 6 and 2% (dithranol), 2 and 2% (butantrone) and 2 and 0% (10-valeryl dithranol) in the 21- and 36-week studies, respectively. Histologically, the papillomas were mostly squamous papillomas and only a few keratoacanthomas were found. It is concluded that the tumor-producing and skin-irritating activity of dithranol is clearly greater than that of butantrone, 10-isobutyryl dithranol and 10-valeryl dithranol.

Toxicological studies with dithranol and its 10-acyl analogues

The oral LD50 values of an antipsoriatic drug, dithranol, were 1542 mg/kg in NMRI mice and 3216 mg/kg in Wistar rats. Three 10-acyl analogues of dithranol (10-acetyl, 10-propionyl and 10-butyryl dithranol or butantrone) were more toxic both in mice and rats. They were mutagenic only in TA1537 of the five Salmonella typhimurium strains tested. None of them were mutagenic in two Escherichia coli strains. Butantrone was least toxic to test bacteria and had the lowest mutagenic activity on TA1537. In metaphase analysis of in vitro treated human lymphocytes, dithranol, 10-acetyl dithranol and 10-propionyl dithranol produced significant increases in the number of chromosome and chromatid gaps but without a clear dose-response relationship, and without inducing significant breaks. Butantrone did not cause significant increases in gaps or breaks. In the mouse micronucleus test, dithranol and butantrone caused no increases in micronucleated polychromatic or normochromatic erythrocytes, indicating lack of clastogenic activity in vivo at maximum tolerated doses. Hence, dithranol and its 10-acyl analogues have a weak mutagenic activity in vitro. The mutagenic activity of butantrone is lower than that of the other analogues and dithranol.

Adrenalectomy modifies the effect of intracerebral histamine on the cold-stimulated TSH secretion in male rats

Cold-stimulated TSH secretion remained normal after adrenalectomy in conscious male Sprague-Dawley rats, but the inhibitory effect of a small dose of histamine (1.0 micrograms/rat into the 3rd ventricle, i.c.v.) on the TSH secretion was abolished. Adrenaline (0.01-1.0 mg/kg s.c.) inhibited dose-dependently the cold-stimulated TSH secretion. However, although adrenalectomy causes a prominent decrease in releasable adrenaline, a larger dose of histamine (2.5 micrograms/rat i.c.v.) decreased the TSH secretion. The effect of histamine was not modified after pretreatment with either corticosterone or dexamethasone, irrespective of whether intact or adrenalectomized rats were studied. Corticosterone decreased and dexamethasone increased the cold-stimulated TSH secretion when given intraperitoneally. Chlorisondamine (10 mg/kg i.p.), a peripheral ganglionic blocking drug, suppressed the TSH cold-response in intact rats. Histamine (1.0 microgram/rat i.c.v.) had no additional inhibitory effect after chlorisondamine. The results suggest that the effect of intracerebral histamine on cold-stimulated TSH secretion is caused neither by stimulation of the hypothalamus-pituitary-adrenocortical axis nor by increased adrenomedullary catecholamine release. Further, the effect of intracerebral histamine is obviously not due to enhanced neurosympathetic activity. The effect of histamine is modified by adrenalectomy, but the adrenal glands are not essential for it.

A 6-month dermal toxicity test with dithranol and butantrone in miniature swine

Continuous topical administration of dithranol and butantrone for 6 months caused different irritation profiles in miniature swine. In paraffin wax sticks in white petrolatum, butantrone gave rise to much less initial irritation than dithranol, but after 2-3 weeks the situation had equalized. In gel formulations, butantrone was initially more irritant than dithranol. The vehicles themselves induced significant irritation. Signs of skin hyperplasia (parakeratosis and acanthosis) and inflammation were frequent histopathological findings at the end of the study, but no malignant changes were found. Dithranol and butantrone did not produce any chemical, hematological or serious histological abnormalities during the treatment, suggesting a lack of systemic toxicity. No evidence of systemic absorption was found. This long-term study did not predict delayed irritation of butantrone observed in about 1/3 of the psoriatic patients after treatment for 1-2 months.

Concentrations of metronidazole and tinidazole in male genital tissues

The steady-state concentrations of metronidazole and tinidazole in male genital tissues were analyzed in patients subjected to elective gonadal surgery. The nitroimidazoles were administered orally at 500 mg every 8 h, beginning 5 days before the operation. Eight hours after the last dose, the concentrations of tinidazole were 24.1 +/- 2.5 micrograms (mean +/- standard error of the mean)/g of prostatic tissue, 29.1 +/- 2.9 micrograms/g of vas deferens, 22.1 +/- 2.1 micrograms/g of epididymis, and 18.6 +/- 2.3 micrograms/g of testis. The corresponding values of metronidazole were 14.3 +/- 1.8 micrograms/g, 15.9 +/- 1.2 micrograms/g, 14.0 +/- 1.2 micrograms/g, and 12.5 +/- 1.7 micrograms/g, respectively.

The effect of an increased ratio of carbidopa to levodopa on the pharmacokinetics of levodopa

A randomized, cross-over study was designed to compare the effects of an increased ratio (from 1:10 to 1:4) of carbidopa to levodopa on the fate of levodopa and carbidopa in 11 healthy subjects. Four combinations of carbidopa/levodopa (10 mg/100 mg, 25 mg/100 mg, 25 mg/250 mg, 62.5/250 mg) were used. Plasma levodopa, carbidopa, dopamine and dopac concentrations as well as urinary excretions of levodopa and dopac were determined by a sensitive high-performance liquid chromatography with electrochemical detection after a single carbidopa/levodopa tablet. As the ratio of carbidopa to levodopa increased, there was a significant increase in apparent t1/2 and AUC values of levodopa. At the same time the urinary excretion of levodopa increased and that of dopac decreased. The plasma ratios of levodopa/dopamine and levodopa/dopac and the urinary ratio of levodopa/dopac also increased. There were less subjective side-effects in the 1:4 groups than in the 1:10 groups. It is concluded that increasing the amount of carbidopa in relation to levodopa may be beneficial and further clinical studies are clearly indicated.

Studies on the site and mechanism of the inhibitory action of intracerebral histamine on the cold-stimulated thyrotropin secretion in male rats

The locus of the inhibitory action of histamine on cold-stimulated TSH secretion was studied in male rats. Various histaminergic drugs were given either into the median eminence (ME), the third ventricle, the rostral and caudal part of anterior hypothalamus (rAH and cAH) or the posterior hypothalamus (PH) of conscious rats. When infused into ME, histamine (5 and 10 micrograms/rat) decreased and mepyramine (2.5 micrograms) increased the cold-stimulated TSH secretion while a larger dose of mepyramine (10 micrograms/rat), impromidine (0.05 and 0.1 microgram/rat), 2-pyridylethylamine (2-PEA; 5 and 10 micrograms/rat) and cimetidine (2.5 and 7.5 micrograms/rat) had no effect. The inhibitory action of histamine (5 micrograms/rat) was most marked 30 min after the infusion into ME and it remained significant for at least 50 min. Neither cimetidine (50 and 100 mg/kg i.p.) nor mepyramine (10 and 20 mg/kg i.p.) antagonized the inhibitory action of histamine (5 micrograms/rat) in ME. Histamine (10 micrograms/side) inhibited the cold-stimulated TSH secretion likewise when infused bilaterally either into rAH, cAH or PH. TSH secretion induced by exogenous TRH (100 ng i.p.) was also inhibited by histamine (1 microgram/rat) given into the third ventricle. In conclusion, histamine seems to have an inhibitory action on the cold-stimulated TSH secretion. This action is apparently mediated through areas close to the third ventricle. The mechanism of this action seems to be fairly non-specific, i.e. it is mediated through neither H1- nor H2-receptors.

Impairment of captopril bioavailability by concomitant food and antacid intake

Single oral doses of captopril (50 mg) were given in a randomized cross-over study to 10 healthy volunteers after fasting, after a standardized breakfast (440 kcal; 1804 kJ) or with 50 ml of an antacid suspension. Blood and urine samples were analyzed by gas chromatography. The peak captopril concentrations attained were 701 +/- 81 ng/ml (mean +/- s.e.m.) after fasting, 351 +/- 56 ng/ml with an antacid (p less than 0.05) and 140 +/- 14 ng/ml after a meal (p less than 0.01). The peak concentrations were reached in 0.5, 0.9 and 1.5 h (p less than 0.01), and the areas under the blood concentration-time curves were 782 +/- 86, 456 +/- 60 (p less than 0.05) and 344 +/- 47 ng X h/ml (p less than 0.01), respectively. The relative bioavailability of captopril was 0.66 and 0.48 with antacid and after food, respectively. The deleterious effect of food - but not that of antacid - was reflected as a delayed hypotensive activity of captopril.

Dual action of morphine on cold-stimulated thyrotropin secretion in male rats

The effect of morphine infused into 4 hypothalamic locations and the periaqueductal gray (PAG) on cold-stimulated thyrotropin (TSH) secretion was studied in male rats. Morphine decreased TSH cold-response when infused into the 3rd ventricle (1-20 micrograms/rat) or the median eminence (5 and 10 micrograms/rat). Infusions bilaterally into the anterior hypothalamus (1-10 micrograms/side) or PAG (1 and 10 micrograms/rat) were ineffective, while those given into the posterior hypothalamus (1 and 5 micrograms/side, but not 10 micrograms/side) significantly enhanced TSH cold-response. Naloxone pretreatment (2 or 5 mg/kg, s.c.) reversed the decreasing effect of morphine in the 3rd ventricle (1 microgram/rat) and the increasing effect of morphine in the posterior hypothalamus (1 microgram/side). We conclude that morphine has a dual hypothalamic action on cold-stimulated TSH secretion: an inhibition periventricularly, and a stimulation in the posterior hypothalamus.

Single- and multiple-dose pharmacokinetics of pipemidic acid in normal human volunteers

The pharmacokinetic profile of pipemidic acid was studied in two groups of young healthy volunteers by using a new, sensitive, high-pressure liquid chromatography procedure for quantitation of pipemidic acid in biological fluids. After oral or intravenous administration, the disposition of pipemidic acid may be described as a one- or a two-compartment open model, respectively. Oral bioavailability was 93.1 +/- 11% (mean +/- standard error). After administration of a 100-mg tablet, 13.4 +/- 2.7% was bound to serum proteins at the time of peak drug concentration in serum. Excretion of pipemidic acid in saliva was negligible, the saliva/serum ratio being about 0.32. At steady state after the twice-daily administration of a 500-mg tablet, which is a recommended dosage regimen, a peak drug concentration in serum of 4.3 +/- 0.5 micrograms/ml was attained in 1.2 +/- 0.1 h. The apparent volume of distribution was 1.9 +/- 0.2 liters/kg, and the elimination half-life was 3.4 +/- 0.2 h. The renal clearance was 4.3 +/- 0.7 ml/min per kg, and the total clearance was 6.3 +/- 0.5 ml/min per kg. Despite a considerable water load, the minimum concentration in urine at the end of a dosing interval averaged 100 micrograms/ml, which widely exceeds the known MIC of pipemidic acid against bacteria commonly causing urinary tract infections.

Tumor-producing activity of dithranol (anthralin) and two of its 10-acyl analogs in the dorsal skin of female NMRI mice

The tumor-producing activity of local applications of dithranol, 10-propionyl dithranol and butantrone was studied in 420 female white NMRI mice. An initiation with 20 micrograms of 7,12-dimethyl-benz(alpha)anthracene (DMBA) was followed 2 weeks later by three applications per week of the test compounds in 50 microliters of acetone for 50 weeks. Several control groups receiving only acetone or DMBA and test compounds without DMBA were included. Dithranol and 10-propionyl dithranol caused transient, although serious, skin irritation during the first 2 weeks of the treatment. Hyperplasia was a common finding in the same groups at the end of the treatment. Dithranol (3.5 mM) induced 11 papillomas in 8 mice (26.7%) without DMBA and 29 papillomas in 17 mice (56.7%) with DMBA. 10-Propionyl dithranol was tumorigenic as well: 3.5 mM caused 15 papillomas in 11 mice (36.6%) without DMBA and 28 papillomas in 17 mice (56.7%) with DMBA and 1.5 mM with DMBA caused 7 papillomas in 6 mice (20%). In the butantrone groups, there was only one single papilloma with the 1.5 mM concentration plus DMBA. It is concluded that, in contrast to dithranol and 10-propionyl dithranol, butantrone (3.5 mM) is not tumorigenic in the dorsal murine skin.

Different isotonic density gradients in separation of renin granules from rat kidney cortex

Crude renin granule preparations isolated from the rat renal cortex were further purified in isotonic conditions (300 mOsm/kg) using various density gradient materials. It was not possible to separate renin granules from other subcellular organelles using dextran, 40,000-sucrose or metrizamide-sucrose gradients at about 300 mOsm/kg. When osmolality of dextran-sucrose gradients was increased, some separation was found but both renin granules and mitochondria gained density. During a short centrifugation (4640 X g, 30 min) renin granules remained intact and appeared in two populations in Percoll-sucrose gradients. The apparently heavier (larger) particles (at 1.12-1.13 kg/l) were greatly purified from mitochondria (80 X purification vs. the whole homogenate), protein (120 X) and lysosomes (24 X). Electron micrographs demonstrated many dense core granules. The fraction containing apparently lighter (small) granules (at 1.08-1.09 kg/l) was heavily contaminated with mitochondria and lysosomes. During longer centrifugation (4640 X g, 60 min), only one major peak showing renin activity was observed at 1.12-1.13 kg/l, and other cell organelles were lighter. Hence the two renin populations evidently do not differ in density but rather in size. In the animals kept on a low-sodium diet, both types of renin granules were increased.

Comparative pharmacokinetics of metronidazole and tinidazole as influenced by administration route

Serum kinetics of metronidazole and tinidazole were compared in four separate randomized crossover studies. Single doses of each drug were given to healthy volunteers through intravenous infusion (500 mg over 20 min, six persons), by mouth (500 mg, nine persons), by rectum (1,000 mg, six persons), or intravaginally (500 mg, six persons). Concentrations of the unchanged drugs in serum, measured by high-pressure liquid chromatography, were similar after oral and intravenous administration, with mean peaks of 9.0 and 9.4 micrograms/ml for metronidazole and 7.5 and 10.1 micrograms/ml for tinidazole. Concentrations of tinidazole were significantly higher than those of metronidazole from 4 h onwards after intravenous infusion, and from 3 h onwards after administration by mouth. After rectal administrations, a significant difference was seen only at 48 h. After vaginal dosing, however, concentrations of metronidazole were significantly higher than those of tinidazole between 1.5 and 12 h. Bioavailability of either drug, calculated according to the formula (area under the curve for oral administration)/(area under the curve for infusion), was practically complete after oral administration and was poorer after rectal and especially vaginal administration. Whenever the parameters were calculable, the elimination half-life of tinidazole (range of means, 14.0 to 14.7 h) was significantly longer and total clearance (40.3 to 47.6 ml/min) was lower than the corresponding values of metronidazole (7.9 to 8.8 h and 71.8 to 80.1 ml/min, respectively).

Inhibition of the TSH secretion by histamine in male rats

The effect of histamine (HA) on the cold-stimulated and the TRH-induced TSH secretion was studied in male rats utilizing HA and specific HA antagonists and histaminergic drugs as tools. L-histidine (1000 and 1500 mg/kg ip) inhibited the cold-stimulated but not the TRH-induced TSH secretion. Mepyramine (5-50 mg/kg ip) and cimetidine (50-250 mg/kg ip) had no effect on the TSH-cold-response, but the TRH-induced TSH secretion was enhanced by them. HA (1 mg/kg sc), 2-pyridylethylamine (2PEA; 10 mg/kg ip) and impromidine (1 mg/kg sc) decreased the TRH-induced TSH secretion but did not affect the TSH cold-response. When infused into the third ventricle HA (1-50 micrograms/rat), impromidine (0.1 and 1.0 microgram/rat) and 2PEA (50 micrograms/rat) decreased the cold-stimulated TSH-secretion. The locus of the inhibitory action of HA seems to be both at the anterior pituitary, where it is mediated through H1- and H2-receptors and in the hypothalamus, where the effect appears to be mediated through H2-receptors. At least a part of this particular action might be explained by other mechanisms since neither H1- nor H2-receptor antagonists were able to counteract the effect of HA.

Studies on the mechanism of the enhanced cold-induced TSH secretion in spontaneously hypertensive rats

Various noradrenergic and tryptaminergic antagonists as well as pinealectomy significantly inhibited cold-induced TSH secretion in SHR as in control rats.