Inhibitor Synthesis

Other drugs may also have an inhibitory effect on cytokine synthesis. Elevation of cyclic AMP has an inhibitory effect on ID2 release from lymphocytes in vitro (Didier et al., 1987) and this may be achieved by theophylline at high plasma concentrations. Selective phosphodiesterase inhibitors may also be effective and recently phosphodiesterase IV inhibitors have been demonstrated to inhibit the release of IL-4 and IL-5 from T lymphocytes in vitro (Essayan et al., 1993). 

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Most of the GA-synthesis inhibitors characterized so far affect two segments of the compHcated pathway from MVA to the many different GAs identified. The cycHzation reactions that produce / Akaurene are inhibited by the onium growth retardants, and the oxidations of /-kaurene to /-kaurenoic acid are sensitive to heterocycHc triazoles such as paclobutrazol and similar compounds. Other enzymes in the pathway are points for pathway dismption by as yet undeveloped GA biosynthesis inhibitors (236). 

Another approach to pregnancy termination has been the utilization of progesterone synthesis inhibitors. These compounds block production of progesterone by the corpus luteum and the early placenta. When adrninistered with a prostaglandin, their use can result in medically induced abortions. 

Lactam Antibiotics Ribosomal Protein Synthesis Inhibitors... 

L-NAME (N-nitro-L-arginine methyl ester), like L-NMMA, is a structural analogue of L-arginine and competes with L-arginine for NO-synthase, which uses L-arginine as a substrate for the formation of NO. L-NMMA and L-NAME are very effective NO-synthesis inhibitors, both in vitro and in vivo. 

Ribosomal Protein Synthesis Inhibitors. Figure 3 The chemical structure of tetracycline and possible interactions with 16S rRNA in the primary binding site. Arrows with numbers indicate distances (in A) between functional groups. There are no interactions obseived between the upper portion of the molecule and 16S rRNA consistent with data that these positions can be modified without affecting inhibitory action (from Brodersen et al. [4] with copynght permission). 

Ribosomal Protein Synthesis Inhibitors. Figure 4 The binding site of pactamycin on the 30S subunit. The positions of mRNA, the RNA elements H28, H23b, H24a, and the C-terminus of protein S7 are depicted in the E-site of the native 30S structure (left) and in the 30S-pactamycin complex (right). In the complex with pactamycin, the position of mRNA is altered (from Brodersen etal. [4] with copyright permission). 

Ribosomal Protein Synthesis Inhibitors. Figure 5 Nucleotides at the binding sites of chloramphenicol, erythromycin and clindamycin at the peptidyl transferase center. The nucleotides that are within 4.4 A of the antibiotics chloramphenicol, erythromycin and clindamycin in 50S-antibiotic complexes are indicated with the letters C, E, and L, respectively, on the secondary structure of the peptidyl transferase loop region of 23S rRNA (the sequence shown is that of E. coll). The sites of drug resistance in one or more peptidyl transferase antibiotics due to base changes (solid circles) and lack of modification (solid square) are indicated. Nucleotides that display altered chemical reactivity in the presence of one or more peptidyl transferase antibiotics are boxed. 

There are few reports on the effects of nitrous oxide on dopaminergic neurotransmission. A study in mice showed that nitrous oxide inhalation produced a significant increase in locomotor activity that was antagonized in a dose-dependent fashion by the dopamine synthesis inhibitor a-methyl-/)-tyrosine (Hynes and Berkowitz 1983). Moreover, administration of the D2 antagonist haloperidol also reduced the locomotor activity induced by nitrous oxide (Hynes and Berkowitz 1983). These results suggest that excitatory effects induced by nitrous oxide may be also mediated by dopaminergic neurotransmission. However, other studies have reported that exposure to nitrous oxide resulted in decreased dopamine release by neurons in the striatum (Balon et al. 2002 Turle et al. 1998). 

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