Seinosuke Iwata

Antisympathetic and hemodynamic property of a dual L/N-type Ca2+ channel blocker cilnidipine in rats

The in vivo antisympathetic property of a dual L/N-type Ca(2+) channel blocker cilnidipine compared with that of typical N-type Ca(2+) channel blockers has never been clarified. We investigated the effects of the drug on a sympathetic nerve-mediated vascular response and vasodilating action in rats in comparison with those of an N-type Ca(2+) channel blocker omega-conotoxin MVIIA. In pithed rats, omega-conotoxin MVIIA preferentially suppressed the sympathetic nerve stimulation-induced pressor response, whereas cilnidipine suppressed the pressor response induced by sympathetic nerve stimulation and angiotensin II. In anesthetized rats, cilnidipine or omega-conotoxin MVIIA decreased mean blood pressure, while heart rate was decreased by omega-conotoxin MVIIA, but slightly increased by cilnidipine. These results suggest that cilnidipine can affect sympathetic N-type Ca(2+) channels in addition to vascular L-type Ca(2+) channels in antihypertensive doses in the rat in vivo. The antisympathetic activity of cilnidipine is not excessive for an antihypertensive drug in comparison with that of omega-conotoxin MVIIA.

The structure–activity relationship study on 2-, 5-, and 6-position of the water soluble 1,4-dihydropyridine derivatives blocking N-type calcium channels

In order to find an injectable and selective N-type calcium channel blocker, we have performed the structure-activity relationship (SAR) study on the 2-, 5-, and 6-position of 1,4-dihydropyridine-3-carboxylate derivative APJ2708 (2), which is a derivative of Cilnidipine and has L/N-type calcium channel dual inhibitory activities. As a consequence of the optimization, 6-dimethylacetal derivative 7 was found to have an effective inhibitory activity against N-type calcium channels with more than 170-fold lower activity for L-type channel compared to that of APJ2708.

Behavioural studies in rats treated with monosodium l-glutamate during the early stages of life

Abstract Behavioural observations were made on rats given repeated high, subneurotoxic doses of monosodium l -glutamate (MSG), or large amounts of MSG in the diet, during the early stages of life. Multiple injections of 4 g/kg MSG to neonates caused low grip strength, hypoactivity, changes of spontaneous motor activity pattern in a day, deficit of learning ability and tail mutilation. The same treatment at the infant stage resulted in only slight behavioural abnormalities at a later stage of life, or yielded nothing at all. Administration of subneurotoxic doses either by s.c. injection or forced intubation, or at high levels in a diet provided ad libitum, were without behavioural effect. Adverse behavioural effects were not induced when the brains were free from histological evidence of damage.

Asymmetric synthesis and biological evaluations of (+)- and (−)-6-dimethoxymethyl-1,4-dihydropyridine-3-carboxylic acid derivatives blocking N-type calcium channels

An efficient asymmetric synthesis of 1,4-dihydropyridine derivatives is described. The key step is the stereoselective Michael addition using t-butyl ester of L-valine as a chiral auxiliary to achieve good ee (>95% for all the tested experiments) and moderate yield. With this method, (+)-4-(3-chlorophenyl)-6-dimethoxymethyl-2-methyl-1,4-dihydropyridine-3,5-dicarboxylic acid cinnamyl ester was obtained and was characterized as a promising N-type calcium channel blocker with improved selectivity over L-type compared to its (-)- and racemic isomers.

Ca2+ handling mechanisms underlying neuropeptide Y-induced contraction in canine basilar artery

The effects of neuropeptide Y on isometric tension simultaneously measured with cytosolic Ca2+ concentration ([Ca2+]cyt) and Ca2+ sensitivity of contractile elements were studied in isolated canine basilar arteries. Neuropeptide Y (1-100 nM) increased [Ca2+]cyt and tension in a concentration-dependent and parallel manner, whereas 9,11-dideoxy-11 alpha,9 alpha-epoxymethano prostaglandin F2 alpha (U46619) (10-100 nM), a thromboxane A2 mimetic, produced a large contraction with a small increase in [Ca2+]cyt. Ca2+ channel antagonists such as d-cis-diltiazem (10 mM) abolished both [Ca2+]cyt and tension augmented by neuropeptide Y. In Ca(2+)-free solution containing 0.2 mM EGTA, neuropeptide Y did not change [Ca2+]cyt and tension, whereas U46619 transiently increased both of them. Furthermore, neuropeptide Y apparently did not affect the Ca2+ sensitivity when assessed in the artery permeabilized with Staphylococcus aureus alpha-toxin, whereas U46619 augmented it. These findings suggest that neuropeptide Y-induced contraction in the canine basilar artery is produced mainly by Ca2+ influx through L-type Ca2+ channels.

Effects of parenteral and oral administration of monosodium l-glutamate (MSG) on somatic growth in rats

Abstract The effects of parenterally and orally administered monosodium l -glutamate (MSG) on somatic growth were studied in rats. Neonatal rats receiving 10 s.c. injections of 4 g/kg body wt. showed hyperphagia only in the postweaning stage: at maturity they were obese, hyperlipidaemic and stunted, with reduced nasoanal and tail length, reduced endocrine and other organ weights and almost complete absence of neurons of the arcuate nucleus (AN). Low blood pressure and high heart rate were recorded in males. Infant rats receiving 10 injections of 4 g/kg of MSG showed milder disturbances. Neonatal or infant rats given repetitive doses of 0.2 or 0.5 g/kg showed parallel weight gains to those of controls. Weanling rats fed a diet containing 5% MSG for 10 days, following earlier intubation, consumed 7 g/kg body wt. per day of MSG without effect, their AN remaining normal. These data indicate that an adverse effect from MSG on somatic growth is not induced in so far as the AN neurons are not injured following any route of administration.

Discovery and evaluation of selective N-type calcium channel blockers: 6-Unsubstituted-1,4-dihydropyridine-5-carboxylic acid derivatives

A structure-activity relationship study of 6-unsubstituted-1,4-dihydropyridine and 2,6-unsubstituted-1,4-dihydropyridine derivatives was conducted in an attempt to discover N-type calcium channel blockers that were highly selective over L-type calcium channel blockers. Among the tested compounds, (+)-4-(3,5-dichloro-4-methoxy-phenyl)-1,4-dihydro-pyridine-3,5-dicarboxylic acid 3-cinnamyl ester was found to be an effective and selective N-type calcium channel blocker with oral analgesic potential.

Studies on reproductive endocrine function in rats treated with monosodium l-glutamate early in life

Abstract Repeated s.c. injections of high doses of monosodium- l -glutamate (MSG) to neonatal female rats caused precocious puberty, disturbed oestrous cycle and small ovaries and pituitary. Pituitary LH and FSH were low but the basal serum levels were unchanged from control values. Serum E 2 level was significantly low in the early stages. Cyclic regulation of gonadotrophin release and follicular maturation was inadequate. Pituitary-gonadal function in males was less affected. Females treated with high doses of MSG as infants showed normal onset of puberty and regular oestrous cycles, but subsequent earlier oestrous cycle irregularity was observed than in controls. Gonadal weights in both sexes were slightly reduced. Serum hormone levels and the pituitary contents were not changed from those of controls except for reduced FSH. Males and females, given subneurotoxic doses of MSG, or fed large amounts of MSG ad libitum, presented no abnormalities. MSG administration therefore induces marked abnormalities in reproductive endocrine function after maturation only when injected parenterally, early in postnatal life, in repeated, very large doses.