Carbonic anhydrase (CA) plays an important role in the secretion of aqueous humor. The orally administered CA inhibitor acetazolamide lowers the intraocular pressure (IOP) of patients with glaucoma. However, approximately 50% of patients stop treatment with acetazolamide as a consequence of intolerable side effects due to the extraocular inhibition of the enzyme. This prompted attempts to develop a topically active CA inhibitor. Merck Research Laboratories focused on developing a water- and solvent-soluble compound to penetrate the cornea. Dorzolamide hydrochloride is a potent inhibitor of human CA isoenzyme II, with an IC₅₀ value of 0.18 nM in vitro. In contrast, its inhibitory activity against human CA isozyme I is much weaker (IC₅₀ value of 600 nM). Topically administered dorzolamide penetrated the ciliary body, inhibited its CA activity and had a hypotensive effect in rabbits; in contrast, topical administration of acetazolamide or methazolamide did not decrease IOP. In clinical trials, dorzolamide administered 3 times daily was effective in lowering IOP in patients with open-angle glaucoma or ocular hypertension. The hypotensive effect of dorzolamide 0.5% was similar to that of oral CA inhibitors or timolol (0.25%) twice daily. Dorzolamide did not induce the severe systemic adverse events associated with oral CA inhibitors. Dorzolamide was as effective as pilocarpine or dipivefrine as an adjunctive therapy in patients receiving β-adrenergic antagonists. Dorzolamide also reduced IOP and accelerated retinal arteriovenous passage time in addition to improving visual function in patients with normal-tension glaucoma.

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Insulin is the only ‘hypoglycemic’ hormone synthesized in and secreted from the pancreatic beta cell. Type 2 diabetes results from both secretory failure in the beta cell and insulin resistance in the target tissues for insulin. Attempts to develop anti-diabetic drugs that induce insulin secretion from residual beta cells in type 2 diabetic patients originate from the serendipitous discovery of sulphonylureas as hypoglycemic agents 60 years ago. Generally, secretion is carried out by sequential processes such as granule formation, intracellular traffic, granule docking/ priming and the final step, exocytosis (secretory cascade). In the beta cell, recent progress in cell biology enables us to analyze each step in the secretory cascade and to reveal controlling mechanisms. This review describes regulatory mechanisms of insulin release by distinct nutrients, hormones and neurotransmitters, and roles of second messengers and protein phosphorylation in the insulin secretory cascade. Possible development of insulinotropic drugs for the treatment of type 2 diabetes has been also discussed.

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In the recent decade, remarkable progress has been made in the field of cardiac development through the use of molecular, biological and genetic techniques. Several genes that regulate this process have been cloned, and their functions have been analyzed in vivo and in vitro. Cardiac-specific transcription factors, including Csx/Nkx-2.5, GATA4, MEF2 and dHAND eHAND, play central roles in cardiac development. Loss-of-function and gain-of-function studies have revealed that these factors regulate heart morphogenesis and cardiac-specific gene expressions. Cardiac-specific genes, including MLC2v, cardiac α-actin and ANP, have specific binding sequences for transcription factors in their promoter regions and expressions of these genes are regulated by binding of transcription factors. In addition to the transcription factors, growth factors secreted from ectoderm and endoderm play important roles in induction of cardiomyocytes. Decapentaplegic and bone morphogenetic proteins, members of the transforming growth factor-β superfamily, induce the expression of cardiac-specific transcription factors in the precardiac mesodrem and are indispensable to cardiomyocyte differentiation. We think that understanding the genetic cascade of cardiomyocyte differentiation will open the gate for cardiomyogenesis from non-cardiac cells.

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A novel analgesic test using neonatal rats was developed. In neonatal rats, body movement was induced by bolus, subcutaneous (s.c.) injection of algesic substances. The body movement was quantified by using a device composed of an audio speaker as a detector. Capsaicin, injected s.c., induced the body movement including scratching and struggling responses. The response peaked at 0-1 min and then decayed during the next 1-3 min. Furthermore, this method also detected that the magnitude of the response increased dosedependently up to the maximum dose of 3000 ng. Endogenous algesic substances such as bradykinin, serotonin and histamine induced responses similar to those induced by capsaicin. Exogenous algesic substances such as formalin and acetic acid evoked more prolonged responses than those induced by capsaicin and endogenous substances. The effects of drugs on the capsaicin-induced response were examined in the following experiments. Opioid analgesics, morphine, buprenorphine and pentazocine, inhibited the response. Non-steroidal anti-inflammatory drugs, indomethacin, ibuprofen and acetaminophen, did not exert any effect on the response. Non-steroidal ani-inflammatory drugs, indomethacin, ibuprofen and acetaminophen, did not exert any effect on the response. Neither the sedative diazepam nor the sedative chlorpromazine inhibited the response. It is concluded that this method is useful to quantify the body movement induced by noxious stimulation and is suitable for screening centrally acting analgesics with μ-opioid receptor agonist activity.

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In this study, we investigated the hypothesis that mexiletine has an inhibitory action on spontaneous sensory afferent activity caused by small fiber neuropathy in diabetic rats (WBN/Kob rats). Gastric administrations of mexiletine (10 mg in 0.3 ml saline) and the local anesthetic agent lidocaine (10 mg in 0.3 ml saline) were made in urethane-anesthetized rats. In 6 of 7 WBN/Kob rats (57-62 weeks of age), spontaneous afferent activity was observed and was significantly inhibited after administration of mexiletine, whereas it was not seen in either WBN/Kob rats (54 weeks of age) or Wistar SLC rats (31 and 35 weeks of age). This inhibitory action of mexiletine was sustained for more than 2 h after the administration. In contrast, lidocaine administration also inhibited the spontaneous nerve activity, but the magnitude of the inhibitory action was less than that of mexiletine. In another experiment, the afferent conductance velocity of the sural nerve was not affected after mexiletine was administrated in the WBN/Kob rats (62 weeks of age). The results suggest that pain mitigation of a diabetic prescribed with mexiletine may depend on the inhibitory effect of mexiletine on the generation of the spontaneous afferent action potentials by mexiletine in aged WBN/Kob rats, whereas mexiletine has no effect on the autonomic function of the afferent nerve.

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