Esters of apomorphine and N,N-dimethyldopamine as agonists of dopamine receptors in the rat brain in vivo.

Subcutaneous injections of O,O'-diacetylapomorphine, at doses of 0.1 to 10.0 $\text{mg}\text{kg}$, produced stereotyped gnawing behaviour in the rat, indistinguishable from that induced by apomorphine. The dose-response relationship and time course of this effect were similar for the two drugs, although the ester appeared to be somewhat more potent and longer-lasting at higher doses. While apomorphine had no behavioural effects when given orally at doses up to 100 $\text{mg}\text{kg}$, diacetylapomorphine produced discernible stereotypy at oral doses as low as 10 $\text{mg}\text{kg}$. The injection of diacetylapomorphine into animals previously lesioned electrothermally in the left nigro-striatal tract provoked turning behaviour toward the side contralateral to the lesions, with an effectiveness similar to that of apomorphine. Apomorphine, but not diacetylapomorphine, stimulated the production of cyclic AMP when incubated with homogenates of corpus striatum. In analogous experiments, N,N-dimethyldopamine, but not its ester, O,O'-diacetyl-N,N-dimethyldopamine (another apparent agonist of central dopamine receptors in vivo), also stimulated the production of cyclic AMP in homogenates, and a similar failure to stimulate the production of cyclic AMP was obtained with O,O'-dibenzylapomorphine, which had prolonged behavioural effects in vivo. These results are compatible with the conclusion that catechol esters of certain structural analogues of dopamine can be hydrolysed in vivo to yield free catechols capable of stimulating central dopamine receptors.     

A conditioned taste aversion induced by alpha-methyl-p-tyrosine

Rats treated with either four 50 $\text{mg}\text{kg}$ or 100 $\text{mg}\text{kg}$ injections of alpha methyl-p-tyrosine (α-MPT) spaced 12 hr apart acquired an aversion to a 0.1% saccharin solution in a two-bottle choice with water. Rats treated with either saline or four injections of 100 $\text{mg}\text{kg}$ of α-MPT without saccharin present exhibited a complete preference for the saccharin solution. In a subsequent experiment, the saccharin aversion induced by the four 100 $\text{mg}\text{kg}$ α-MPT injection procedure was found to persist after telencephalic norepinephrine had returned to normal levels. Thus, α-MPT was found to be a highly effective drug for inducing a taste aversion at dose levels which did not produce obvious signs of toxicity.     

Drug interactions with misonidazole: Effects of dexamethasone and its derivatives on the pharmacokinetics and toxicity of misonidazole in mice

Misonidazole [1-(2-nitroimidazol-1-yl)-3-methoxypropan-2-ol; Ro 07-0582] selectively sensitizes hypoxic cells to radiation and is undergoing clinical trial in the radiation treatment of solid tumours. It has been suggested that the glucocorticoid hormone dexamethasone may reduce the incidence of neurotoxicity, the dose-limiting side effect of misonidazole in man. Here it is shown that the absorption and elimination of misonidazole (1 $\text{g}\text{kg}$ i.p.) in C3H mice are unaffected by pretreatment (i.p. for 5 days) with dexamethasone (10$\text{mg}\text{kg}$/day), dexamethasone acetate (10 $\text{mg}\text{kg}\text{day}$) and dexamethasone phosphate (0.5, 10, 25 and lOO $\text{mg}\text{kg}\text{day}$). The apparent half-life of misonidazole in blood and area under the curve (AUC) of misonidazole concentration × time were unaltered. Likewise O-demethylation was unaffected. In contrast, phenobarbitone pretreatment (80 $\text{mg}\text{kg}\text{day}$) increased misonidazole clearance through induction of demethylation. Dexamethasone phosphate pretreatment increased pentobarbitone sleeping-time and slightly decreased liver weight, whereas phenobarbitone did the opposite. Dexamethasone phosphate (25 $\text{mg}\text{kg}$) given as an i.v. bolus injection immediately before misonidazole also had no effect on the systemic pharmacokinetics of misonidazole. Broadly, pretreatment with dexamethasone derivatives had little effect on brain misonidazole and desmethylmisonidazole. But after 100 $\text{mg}\text{kg}\text{day}$ dexamethasone phosphate the 6 hr misonidazole concentration was reduced 36 per cent. Simultaneous dexamethasone phosphate (25 $\text{mg}\text{kg}$) reduced the concentration at 1 hr by 15 per cent and the brain AUC_(0–6hr) by 14 per cent. Dexamethasone phosphate pretreatment reduced the acute LD₅₀ for misonidazole by up to 19 per cent whereas phenobarbitone increased it by 16 per cent. Simultaneous dexamethasone phosphate had no effect. The drug had little effect on misonidazole-induced hypothermia. The significance of these findings for the putative role of dexamethasone in the protection of misonidazole neurotoxicity is discussed.     

Mechanisms of hyperglycemic response to chlorpromazine administered into lateral ventricle in rats. I. Possible role of dopaminergic nervous system

Injection of a chlorpromazine(CPZ) dose of 0.5 $\text{mg}\text{kg}$ into the lateral ventricle caused a transient rise of about 50 per cent of the initial level in blood glucose of rat. The induced hyperglycemia was reduced by simultaneous injection of dopamine (0.02 $\text{mg}\text{kg}$) with CPZ into the ventricle or by pretreatment with l-DOPA (150 $\text{mg}\text{kg}$, i.p.) and diethyldithiocarbamate (DDC, 1 $\text{mg}\text{kg}$, intraventricularly). An increase of dopamine in brain per se did not significantly change the glucose levels. The inhibitory effect of dopamine injected into the ventricle was blocked by pretreatment withalpha-blockers(tolazoline, dibenamine, 0–05 $\text{mg}\text{rat}$) injected into the ventricle. Alpha-blockers per se did not cause any hyperglycemia. These results suggest that the sites of action of dopamine and alpha-blockers are similar and that of CPZ is different. An effect of beta-blockers on the inhibitory effect of dopamine was not obvious, because intraventricularly injected propranolol blocked the hyperglycemia induced by systemically administered epinephrine probably owing to a leak into extracerebral tissues. On the other hand, the combined administration of reserpine (1 $\text{mg}\text{kg}$, i.p.) and α-methyltyrosine (0.1 $\text{mg}\text{rat}$, intraventricularly) partially reduced the CPZ-induced hyperglycemia. 6-hydroxydopamine (6-OHDA) which caused a selective destruction of catecholamine-containing neurones, also reduced the CPZ-induced hyperglycemia, but this reduction was partially reversed after injecting simultaneously dopamine and CPZ.     

Hematin toxicity in rats

The toxicity of intravenously administered hematin (3.4 and 6 $\text{mg}\text{100 g}$) was investigated in rats, where an LD₅₀ of 4.32 $\text{mg}\text{100 g}$ was computed, with 95% confidence limits of 5.40 and 3.46 $\text{mg}\text{100 g}$. At toxic levels (4 $\text{mg}\text{100 g}$) the rats showed a drop of blood pressure, hemorrhages and renal failure, whereas lower doses were well tolerated. This study indicates a possibly wide therapeutic margin of safety, when compared to the therapeutic use of hematin on porphyric patients.     

Cadmium and zinc toxicity to an aquatic insect, Ranatra elongata (Fabr.)

Cadmium chloride and zinc chloride were used to measure their short-term toxicity to an aquatic insect Ranatra elongata (Fabr.). The LC₅₀ values were 0.497, 0.438, 0.355 and 0.288 $\text{mg}\text{l}$ for cadmium chloride and 2.853, 2.456, 1.934 and 1.658 $\text{mg}\text{1}$ for zinc chloride after 24, 48, 72 and 96 h, respectively. Cadmium chloride was found to be more toxic than zinc chloride.     

Failure of dexamphetamine to antagonise a cholinomimetic-induced hyperactivity

Rats that were treated with physostigmine (0.05 $\text{mg}\text{kg}$) manifested marked hyperactive behaviour. A subsequent injection of dexamphetamine (2.0 $\text{mg}\text{kg}$) did not antagonise the physostigmineinduced locomotor hyperactivity, whereas atropine (10 $\text{mg}\text{kg}$) attenuated the hyperactive behaviour. Higher dosages of physostigmine depressed the locomotory behaviour of rats. Carbachol and (±)-α-methyl-p-tyrosine did not significantly affect rats' locomotory behaviour. Implications of the results are discussed in terms of the aetiology of hyperkinesia.     

The concentration of 5-methoxytryptamine in rat brain and its effects on behaviour following its peripheral injection.

The concentration of 5-methoxytryptamine in the rat brain, increased linearly with time over 30 min following its injection intraperitoneally (12.5 $\text{mg}\text{kg}$), tranylcypromine (20 $\text{mg}\text{kg}$) having been given 30 min previously. Injection of 5-methoxytryptamine (12.5 $\text{mg}\text{kg}$) caused transient behavioural changes. However, when this dose was given following tranylcypromine pretreatment, these behavioural changes were considerably enhanced. All doses (2.5–50 $\text{mg}\text{kg}$) of 5-methoxytryptamine injected intraperitoneally after tranylcypromine pretreatment, produced these behavioural changes. Pretreatment of the rats with p-chlorophenylalanine or tetrabenazine did not alter the behavioural responses to 5-methoxytryptamine. In general, the behavioural Changes were similar to those seen following tranylcypromine and l-tryptophan, which increases 5-hydroxytryptamine synthesis in the brain. Intraperitoneal injection of 5-hydroxytryptamine, which produces similar effects to 5-methoxytryptamine in isolated tissue preparations but does not enter the brain, did not cause behavioural changes, nor did intraperitoneal injection of melatonin.     

Effect of vitamin D3 derivatives on calcium concentrations in the serum of rats treated with stannous chloride

Calcium concentrations in the serum of rats were significantly increased by treatment with vitamin D₃ (frsol|25 μg/100 g), but this increase was prevented by a single intraperitoneal administration of tin (Sn²⁺, $\text{3.0 mg}\text{100 g}$). The decrease in serum calcium levels after the administration of Sn²⁺ was reversed by treatment with synthetic 1α-hydroxyvitamin D₃ ($\text{0.25 μg}\text{100 g}$) or 1α,25-dihydroxyvitamin D₃ ($\text{0.25 μg}\text{100 g}$). These results suggest that the decrease in serum calcium levels produced by the administration of Sn²⁺ may be caused by inhibition of metabolism of 25-hydroxyvitamin D₃ to 1α,25-dihydroxyvitamin D₃ in the kidneys.     

Effect of oil of nutmeg on the fertility and induction of meiotic chromosome rearrangements in mice and their first generation

The dose-dependent effects of oil of nutmeg on the fertility and induction of chromosomal translocations in treated mice and their F₁ males were examined. C3H male mice were treated with oil of nutmeg for 8 successive weeks at 60, 80, 100 and 400 $\text{mg}\text{kg}$ body weight. The greatest reduction of fertility occurred in the group treated with 400 $\text{mg}\text{kg}$; chromosomal translocation in directly treated animals was not found. The chromosomal translocations in F₁ males, derived from males treated with oil of nutmeg occurred at dose levels of 60, 80 and 100 $\text{mg}\text{kg}$.     

EEG-synchronizing effect of gamma-hydroxybutyrate and 1-hydroxy-3-amino-pyrrolidone-2 (HA-966) in relation to dopaminergic brain function.

The earlier finding that γ-hydroxybutyrate and HA-966-induced depression of the central nervous system was associated with the increase of dopamine concentration and block of its release, prompted this study of the influence which the monoaminergic system may have upon the electrocorticogram in rats.The synchronization induced by α-methyl-p-tyrosine began earlier than the decrease of the duration of arousal, indicating different sensitivities to the depressive drug action of structures responsible for synchronizing and for arousal.Five $\text{mg}\text{kg}$ HA-966 in diethyldithiocarbamate desynchronized animals increased the amplitude but the duration of arousal was unchanged. p-Chlorophenylalanine treatment of rats did not influence the synchronizing effect of HA-966 (10–20 $\text{mg}\text{kg}$) or the inhibitory effect upon the duration of arousal. Haloperidol (100 μg-4 $\text{mg}\text{kg}$) potentiated the synchronizing effect of y-hydroxybutyrate and HA-966. The number of phasic discharges in the electrocorticogram induced by treatment with anaesthetic doses of γ-hydroxybutyrate were increased by the low dose of haloperidol (100 $\text{μg}\text{kg}$), while the higher dose (4 $\text{mg}\text{kg}$) was ineffective.Animals with intact and lesioned substantia nigra compacta responded equally to the synchronizing activity of HA-966 and γ-hydroxybutyrate. Therefore, it is concluded that their effect is not due to the accumulation of dopamine in the nigrostriatal system.     

Active transport of foreign amino acids by rat lung slices

Uptake of amino acids by rat lung slices was investigated using the ¹⁴C-labeled nonmetabolized foreign compounds 1-aminocyclopentanecarboxylic acid (cycloleucine) and α-aminoisobutyric acid (AIB). When incubated with slices suspended in oxygenated Krebs-Ringer phosphate-glucose solution (pH 7.4) at 37°, cycloleucine was accumulated in the tissue against a concentration gradient by a saturable process that was inhibited by anaerobic conditions, low temperature, ouabain, iodoacetic acid, 2,4-dinitrophenol and N-ethylmaleimide. Uptake was depressed by AIB, glycine and l-methionine but not by d-ornithine, $\text{3-O-}\text{methyl}\text{-}\text{d}\text{-}\text{glucose}$, phenol red or disodium cromoglycate. Phenol red enhanced cycloleucine accumulation. AIB was taken up by lung slices by a process similar to that seen with cycloleucine, and uptake was depressed by cycloleucine, glycine and l-methionine but not by d-ornithine. From the initial rates of saturable transport of cycloleucine and AIB, V_max and K_m values were calculated. l-Methionine was a competitive inhibitor of the transport of both cycloleucine and AIB.     

The blockade of bulbospinal inhibition by imipramine, desipramine and pargyline

Bulbospinal inhibition of the spinal cord monosynaptic reflex was antagonized by im-ipramine HCl (5 $\text{mg}\text{kg}$), desipramine HCl (4.8 $\text{mg}\text{kg}$) and pargyline HCl (30.0 $\text{mg}\text{kg}$) in unanaesthetized, decerebrate cats. The blocking action of imipramine was prevented in animals pretreated for three consecutive days with dl-p-chlorophenylalanine (300 $\text{mg}\text{kg}$) but not in animals pretreated with dl-α-methyl-p-tyrosine methyl ester HCl (125 $\text{mg}\text{kg}$) 16 and 4 hr prior to recording. These results do not support the proposal of Clineschmidt and Anderson (1970) that the bulbospinal inhibitory pathway contains a 5-hydroxytryptamine (5-HT) link. Rather, the findings suggest that 5-HT is involved in antagonizing bulbospinal inhibition of the monosynaptic reflex.     

Effects of apomorphine,TL-99 and 3-PPP on yawning in rats

Dopaminergic agonists, apomorphine (APO) (0.025–0.25 $\text{mg}\text{kg}$, s.c.), TL-99 (0.5–3 $\text{mg}\text{kg}$, s.c.) and 3-PPP (0.15–10 $\text{mg}\text{kg}$, s.c.) elicited yawning in rats and the dose-response curves of all 3 compounds showed a bell-shaped form. Haloperidol (0.02 $\text{mg}\text{kg}$, s.c.) reduced the yawning induced by DA-agonists to about 50%. The potencies of the DA-agonists in inducing yawning were APO > TL-99 > 3-PPP (comparable to potencies obtained in other in vivo tests, determining DA-ergic activity). The findings support the validity of the yawning phenomenon as a screening test for DA-agonists.Additionally, it was found that apomorphine induced yawning was significantly and dose-dependently enhanced by the β-agonist, formoterol. This effect was counteracted by scopolamine, not changed by metergoline and further increased by l-propranolol. These data support the hypothesis of cholinergic involvement in yawning and indicate a role, though unclear at present, of β -receptors in this behaviour.     

Oxygen and chromium transfer in perfused gills of rainbow trout (salmo gairdneri) exposed to hexavalent chromium at two different pH levels

An in vitro study was performed on uptake and transfer of hexavalent chromium, Cr(VI), in gills of rainbow trout (Salmo gairdneri). Gills were perfused according to the isolated head perfusion technique, and externally exposed to Na₂CrO₄ solutions containing ⁵¹CrO₄². Experiments were conducted at a concentration of 10 $\text{mg}\text{l}$ Cr and at pH values of 8.1 and 6.5. The results show that the transfer of chromium is directly coupled with the transfer of oxygen from the external solution to the internal perfusion medium. Under similar conditions of oxygen transfer, however, chromium transfer was significantly more effective at pH 6.5 than at pH 8.1. In addition more chromium was accumulated by the gill tissue at the lower pH. Gill preparations of trout which had been pre-exposed in vivo for 4 days to 10 $\text{mg}\text{l}$ Cr(VI) at pH 6,5, exhibited an impaired oxygen transfer. This could be well explained by the structural alterations seen after histological examination of the perfused gills.     

Effects of thiamin antagonists on drug hydroxylation and properties of cytochrome P-450 in the rat

The administration of small amounts of thiamin (0.3 $\text{μg}\text{day}$ or more, i.p., for 21 days) depressed musomal cytochrome P-450 content and the V_max of aniline hydroxylase when compared to values obtained from rats fed a thiamin-deficient diet (approximately 0.1 μg of thiamine/day in basal diet). The concurrent administration of neopyrithiamin (50 $\text{μg}\text{day}$, i.p.) eliminated the depressant effect of 10.0 μig of thiamin/ day, but was without significant effect in rats receiving more than 100 μg of thiamin/ day. In contrast, 100 μg of oxythiamin/day had no thiamin-opposing effect on cytochrome P-450 content and only partially counteracted the effects of 1 μg of thiamin/day on aniline hydroxylase activity. These treatments were without significant effect on the K_m for this reaction. Using ethyl isocyanide as the ligand, there appears to be a qualitative change induced in the cytochrome P-450 from thiamin-deficient rats. The absorption peak height ratios indicate that cytochrome P₁-450 is increased in a manner analogous to that produced by the administration of 3-methylcholanthrene. This was supported by the fact that aniline binding, as evidenced by increased ΔA_max, is enchanced in musomes from thiamin-deficient animals, whereas the hexobarbital spectral shift was unaltered.     

Effects of dietary ascorbic acid supplementation on hepatic drug-metabolizing enzymes in the guinea pig.

Guinea pigs were maintained on four diets which varied only in ascorbic acid (AA), containing 0.3, 1.5, 3.5 and 7.0 mg $\text{AA}\text{g}$ of diet. The lowest diet contained sufficient AA to prevent scurvy, while the two diets highest in AA content produced liver saturation of the vitamin after 8 weeks. Several hepatic enzymes were measured after 1, 2, 3, 4 and 8 weeks. There were no significant differences among the four groups in the following parameters of microsomal mixed-function oxidation: cytochrome P-450 content, NADPH cytochrome c reductase and aminopyrine N-demethylase. Also, there were no differences in native and nucleotide-activated UDP-glucuronyl transferase activities. However, in the post-microsomal supernatant, overall glutathione S-aryl transferase activity was significantly lower in the group with the lowest supplementation of ascorbic acid, as compared to the three higher groups. Kinetic parameters of aminopyrine N-demethylation were studied in animals maintained for 21 days on a diet deficient in ascorbic acid (< 0.1 mg $\text{AA}\text{g}$), an intermediate control diet (1.5 mg $\text{AA}\text{g}$) and a high-dose AA diet (7.0 mg $\text{AA}\text{g}$). Curvilinear Lineweaver-Burk plots for N-demethylation were obtained in all three groups, and apparent K_m and V_max calculated separately for both low and high ranges of substrate concentrations. Apparent K_m values did not differ significantly among the three groups. Microsomes from AA-deficient animals had V_max values lower than the control and high-dose groups. There was no difference in kinetic parameters between microsomes from animals receiving control and high-dose AA diets.     

Effects of exposure to ozone on susceptibility to experimental tuberculosis

Exposure of mice to 1.96 $\text{mg}\text{m}{}^3$ ozone (O₃) 3 $\text{h}\text{day}$, 5 days/week, for up to 8 weeks beginning at 1 or 2 weeks after challenge with Mycobacterium tuberculosis R 1Rv resulted in significant enhancement of bacterial titers in the lungs at 5 through 8 weeks after challenge when compared to mice exposed to filtered air. Exposure to lower concentrations of O₃ did not produce any significant changes compared to controls.Exposure of guinea pigs to 2.9 $\text{mg}\text{m}{}^3$ O₃ for 3 h immediately after challenge with M. tuberculosis resulted in a suppression of the cutaneous delayed hypersensitivity response, without affecting the serum hemagglutination antibody titers. However, exposure of guinea pigs to 0.98 $\text{mg}\text{m}{}^3$ O³ 3 $\text{h}\text{day}$ for 5 days, initiated within 3 h after the infectious challenge, enhanced hemagglutination antibody titers initially, but the delayed hypersensitivity reaction did not differ from controls.     

Effects of phospholipids on the binding of [3H]dihydroalprenolol to the beta-adrenergic receptor of rabbit heart membranes

The specific binding of [³H]dihydroalprenolol (DHA) by rabbit heart membranes and by a solubilized Lubrol PX-free preparation amounted to 0.80 ± 0.06 $\text{pmoles}\text{mg}$ protein and 0.61 ± 0.07 $\text{solpmoles}\text{mg}$ protein, respectively. The binding was stereospecific. Optimal solubilization was achieved with 1% Lubrol PX. The addition of total rabbit brain phospholipids significantly enhanced the specific [³H]DHA binding of the solubilized Lubrol PX-free receptor fraction. Although the number of binding sites (B_max) increased in the presence of phospholipids, the dissociation and the K_D constant of [³H]DHA in the solubilized Lubrol PX-free receptor fraction did not change.     

Carbon disulphide tetratogenicity and postnatal effects in rat

Pregnant albino rats were exposed to carbon disulphide vapour in concentrations of 50, 100 or 200 $\text{mg}\text{m}{}^3$throughout gestation. Two successive generations (F₁ and F₂) were studied.Concentration levels of 100 and 200 $\text{mg}\text{m}{}^3$ produced marked dose-related impairment in the prenatal development of the F₁ progeny, with increase of early embryonal lethality, reduction in foetal weight and a high incidence of malformations affecting mostly the brain and limbs. Postnatal viability, body weight, lipid and energy metabolism and behaviour were also impaired. Behavioral deviations were observed even at 50 $\text{mg}\text{m}{}^3$.After reaching sexual maturity the F₁ rats were mated within their experimental groups, but no further carbon disulphide exposure was applied. The adverse effects on progeny were still detectable in the F₂ generation. Structural abnormalities of the same type as those found in the F₁ at 100 and 200 $\text{mg}\text{m}{}^3$ exposure were observed in their progeny and, postnatally, statistically significant behavioral changes were observed in the progeny of all test groups.