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Sibutramine hydrochloride, a novel monoamine reuptake inhibitor antidepressant, has been studied to determine whether it alters dopaminergic function in the brain. Its effects have been compared with bupropion, a dopamine reuptake inhibitor, and methamphetamine, a dopamine reuptake inhibitor and releasing agent. Sibutramine (0.1-3 mg/kg PO) and methamphetamine (0.3-30 mg/kg PO) both prevented reserpine (0.75 mg/kg IV) ptosis in rats with ED50 values of 0.6 mg/kg and 4.2 mg/kg, respectively. Bupropion (10-100 mg/kg PO) was ineffective against reserpine ptosis. The efflux of [3H]-dopamine from preloaded rat striatal slices was not altered by 10(-7)-10(-5) M concentrations of sibutramine, BTS 54,354, BTS 54,505 (secondary and primary amine metabolites, respectively) or bupropion. In contrast, methamphetamine (10(-8)-10(-4) M) caused a significant concentration-dependent increase in [3H]-dopamine release. Sibutramine (3 mg/kg IP or 6 mg/kg PO) and bupropion (10 mg/kg IP or 30 mg/kg PO) did not alter 3-methoxytyramine (3-MT) levels in rat striatum. Striatal 3-MT concentrations were, however, dose-dependently increased by methamphetamine (0.3-10 mg/kg IP or 0.42-4.2 mg/kg PO). Sibutramine (6 mg/kg PO) did not induce circling in rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopaminergic neuronal tract. Bupropion (10-100 mg/kg PO) did not induce circling at the lowest dose, but caused increasing ipsilateral rotation at higher doses. Methamphetamine (0.42 or 4.2 mg/kg PO) induced ipsilateral circling with marked effects at the higher dose.(ABSTRACT TRUNCATED AT 250 WORDS)

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Sibutramine HCl, a monoamine reuptake inhibitor type of antidepressant, was administered to healthy male volunteers as either a single dose (12.5 or 50 mg) or repeated treatment (5-20 mg once daily or 15 mg twice daily). Plasma, obtained at regular intervals during and after sibutramine HCl or placebo treatment, was assayed in vitro for its ability to inhibit the uptake of [3H]-noradrenaline (NA) by rat cortical synaptosomes, [3H]-5-hydroxytryptamine (5HT) by human platelets and [14C]-dopamine (DA) by rat striatal synaptosomes. After both single and repeated sibutramine HCl administration, the rank order of uptake inhibition was [3H]-NA greater than [3H]-5HT greater than [14C]-DA. The level of monoamine uptake inhibition increased on daily administration to a plateau 4-6 days after initiation of treatment, for example, approximately 60% and 40% inhibition of [3H]-NA and [3H]-5HT, respectively, following 15 mg sibutramine HCl twice daily. The pattern of monoamine uptake inhibition following sibutramine HCl administration to man is similar to that observed in sibutramine HCl-treated rats, and probably at least partly reflects inhibition of uptake by drug metabolites in both species. The inhibition of monoamine uptake following sibutramine HCl administration to man is consistent with an antidepressant effect.

The incorporation of a biologically active group into a naturally occurring structure is an interesting approach to new pharmacological agents. For example, when an acetylcholine-like structure is incorporated in ring-A of 5a-androstane-17-one or 5a-pregnan-20-one, neuromuscular blocking agents of up to one-fifteenth the potency of tubocurarine are obtained (Lewis, Martin-Smith, Muir & Ross, 1967). Although of limited clinical value, such compounds present useful leads for further chemical exploration, particularly the synthesis of bisquaternary amino-steroidal salts. A series of 2,8,16,3-diamino-5a-androstane-3a,17p-diol dimethohalide derivatives was described by Buckett, Hewett & Savage (1967). One of them, 2ft,16,/-dipiperidino-5a-androstane3a,17,8-diol diacetate dimethobromide (code number Org.NA97; approved name pancuronium bromide), is a potent neuromuscular blocking agent and in the experiments described in this paper its actions were compared with those of tubocurarine chloride. Cats were anaesthetized with a mixture of chloralose (70 mg/kg) and sodium pentobarbitone (12 mg/kg) injected intraperitoneally; rabbits and dogs were anaesthetized with sodium pentobarbitone (45 mg/kg) injected intravenously, and hens with sodium barbitone (200 mg/kg) injected intravenously. In all species the trachea was intubated and artificial ventilation applied throughout each experiment Twitches and tetani of a gastrocnemius muscle were elicited by stimulating the peripheral portion of the crushed sciatic nerve in the popliteal space with rectangular shocks of

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