A Benakis’s research while affiliated with University of Geneva and other places

Substituted benzamides have been the object of numerous metabolic studies including many by whole body autoradiography of rats and mice. The present study reports autoradiographic data concerning14C-labelled Sulpuride in monkey. The Study was limited to the brain in order to elucidate the controversial question as to whether the drug can cross the blood-brain barrier. The results showed that in monkey, as in rat and mouse, there is no localization in the brain as can be clearly seen on the autoradiograms. In view of these results and of the undeniable neuroleptic properties of Sulpiride, an indirect mode of action through the release of endogenous mediators is proposed.

Sulpiride (SU), a widelyused benzamide neuroleptic, is known to promote rapid prolactin release. Sulpiride plasmalevel and the prolactin response to the most commonly used dose, i.e., 50 and 200 mg sulpiride (ad-ministered orally), were studied inten male volunteers. The design of this study permitted the simultaneous measurement of the sulpiride plasma level for 48 hours, by means of a new HPLC-electrochemical detection method, and of the prolactin level, by means of RIA. Pharmacokinetic study of sulpiride showed that the mean concentration and time of peak plasma level of the two doses were different: 77 ng/ml SU at 2.3h for the 50 mg dose and 243 ng/ml at 3.5 h for the 200 mg dose. The absorption and elimination rateconstants were similar regardless of the dose. (ka: 1.05–1.9 h−1; t1/2β: 25 h).. A linear relationship of the area underthe plasmatic concentration versus time curve with the dose was observed. Mean plasma leveldecreased for both doses to about 14%of peak value at48 hours. Prolactin serum levels increased from the basal value after SU administration with marked individual differences. The 200 mg dose resulted in earlier prolactin peak levels (54 ng/ml between 30 min and 1 h) than the 50 mg dose (50 ng/ml between 1 and 2 h). The prolactin level then decreased and remained constant at about 15 ng/ml for 11 to 48 h. Prolactin levels returned to basal values (mean: 5 ng/ml) after one week. It is concludedthat therapeutic doses of sulpiride induce prolactin secretion thatis dose-dependent in a first phase and stimulated independently of the sulpiride concentration in a second phase. A mechanism of indirect action mediated by PRL is suggested to explainthe neurolepticactivityofthe drug. Key wordssulpiride-prolactin-pharmacokinetics-man

The binding of 14C-fenpentadiol to plasma proteins of different species in vivo and in vitro was studied using equilibrium dialysis. In vivo, the binding rate, in rat, was found to be 30%. In the pig, this rate varied as a function of time from 10.8% 15 minutes after drug administration to 20.4% 6 hours later. In vitro, the binding rate was found to be a function of the drug concentration and ranged from 57 to 36% at concentrations of from 0.4 to 11 micrograms/ml. No significant differences were observed between the two species. In human plasma, the in vitro binding rate was found to range from 34 to 18.4% for concentrations of 11 to 200 micrograms/ml. Under the same conditions, but using 10 mg of human albumin incubated in varying concentrations of the drug (50 to 800 micrograms/ml), the binding rate ranged from 8.4 to 4%. The binding rate seemed also to be a function of the pH of the medium with the pH of 11 yielding a maximum binding rate. Scatchard analysis of the in vitro human albumin data gave the following values: K = 4.7 X 10(3) M-1, n = 1.5. When human alpha-globulin was used, the protein binding values varied from 9.1 to 4.3% at drug concentrations from 50 to 40 micrograms/ml. When human beta- and gamma-globulins were used, no binding was found to occur. In vitro, incubation of the drug in whole blood of either rat or pig gave a value of 20% drug fixed in erythrocytes. In vivo, in the rat, this value was found to be 60%.

Summary The binding of tienilic acid [2,3-dichloro-4-(2-tienylcarbonyl)-phenoxy acetic acid] (TA), a new anti-hypertensive agent with diuretic and uricosuric properties, to human plasma proteins, pure protein fractions, erythrocytes, as well as the effect of heparin on the degree of protein binding were measured by means of ultrafiltration and equilibrium dialysis. Different amounts of TA (1 to 1000 μg) were incubated with 1 ml of either human plasma or phosphate buffer M/15 (pH 7.4), containing 47 mg of albumin, at 37°C for 2 hrs. The degree of binding of TA to plasma proteins and albumin, at plasma concentration (1–30 μg/ml) of the drug at therapeutic doses, was 99.4–98.5 and 95.8–94.2% respectively. In the case of albumin, a Scatchard plot showed two classes of binding sites (M1=0.5, K1=6.3 × 104 M−1; M2=8, K2=2.8 × 103 M−1). After incubation of 10 μg of drug with 8 mg of α-globulins, 8 mg of β-globulins or 7.4 mg of γ-globulins at 37°C, pH 7.4 and ultrafiltration, the degree of binding was 83%, 44% and 44% respectively. The distribution of TA between erythrocytes and plasma ranges between 0.11–0.17 for concentrations of 1 to 15 μg/ml and between 0.17–0.10 for concentrations of 15 to 30 μg/ml under different experimental conditions, heparin had no effect on the degree of binding of TA to plasma proteins.

The reduction of the hypermotility and stereotyped behaviour induced by amphetamine and apomorphine was used as a criterion for the effectiveness of neuroleptics. Considering the impact of neuroleptics on the hypophysis as well as the relationship between the hypophysis and the thyroid, motility and stereotyped behaviour induced by amphetamine and apomorphine was studied in both hypophysectomized and thyroidectomized rats. In the hypophysectomized rat, amphetamine-induced hypermotility, observed between 1 and 3 hours after administration, was almost 3 times greater than in normal animals. Thyroidectomy resulted in a reversal of the motility effect induced by amphetamine. The stereotyped behaviour induced by apomorphine was practically abolished in both hypophysectomized and thyroidectomized animals.

Tetrabamate (Atrium) and Complexe 1656, two psychosedative drugs, are complexes formed by phenobarbital with its N-substituted derivatives. We have studied the induction effect of all these compounds on the microsomal liver enzymes in male rats. Tetrabamate and Complexe 1656 were found to be equally effective in increasing the amount of microsomal proteins, cytochrome P-450 and the in vitro aniline p-hydroxylation and amino-pyrine N-demethylation activity. These effects were similar to those obtained after a treatment with an equivalent dose of phenobarbital. Febarbamate and difebarbamate had no significanteffect on microsomal enzymes. The inductive effect of tetrabamate and of its analogue seems essentially due to the phenobarbital content of these complexes.

A vast fund of published information on the use of mass spectrometry and associated techniques for the study of drug metabolism has accumulated in recent years. The annual “Specialist Periodical Reports” on mass spectrometry of the London Chemical Society is particularly worthy of mention. This publication reviews all the literature in the field. In the issue covering the two year period from 1972 to 1974 (1), there are more than one hundred and forty reviews of papers devoted to mass spectrometry applications for drug metabolism. From 1974 to 1976 (2), there were a hundred and twenty.

1.1. Hypophysectomized rats exhibited an enhancement in locomotor stimulation induced by amphetamine in comparison with normal animals.2.2. It is suggested that the hypophysis would play an important role in the mechanism of action of this sympathomimetic amine.