A Calcium Agonist, Bay k 8644, Suppresses the Embryotoxic Effects Induced by Dihydropyridines Calcium Channel Blockers in Cultured Rat Embryos.

Abstract

ABSTRACT. Day 9 rat embryos were exposed to 1,4-dihydropyridine calcium channel blockers; nifedipine (NIF), nicardipine (NIC) or nitrendipine (NIT), for 48 hr in the whole embryo culture system. There were dose-dependent growth retardation and abnormalities, predominantly in cardiovascular system. The three compounds exhibited very similar pattern of dysmorphogenic effects, but the potency of these compounds were quantitatively different. The incidences of embryos with the abnormalities were 100%, 100% and 85% following either exposure of NIF, NIC or NIT at concentration of 300, 8 and 15 µM, respectively. This study was to investigate whether these blocker-induced embryotoxicity was due to calcium channel blocking properties themselves in the embryos. Day 9 rat embryos were co-exposed to 1,4-dihydropyridine calcium channel agonist, Bay k 8644 (BAY) and each calcium channel blocker under the same culture condition. The retarded embryonic growth induced by 200 or 300 µM of NIF, 8 µM of NIC and 15 µM of NIT nearly or completely ameliorated when embryos were co-exposed with BAY at one-third or half concentration of each calcium channel blocker. Supplementation of BAY reduced the incidence of abnormalities by NIF-, NIC-and NIT-alone. These results suggested that one of mechanisms for embryotoxicity induced by calcium channel blocker was directly related to channel blocking property of the chemicals. -KEY WORDS: Bay k 8644, calcium channel blocker, culture, embryo, rat.J. Vet. Med. Sci. 60(10): 1067-1072, 1998 (NIT) were also investigated whether the observed embryotoxicities were basically class effects for dihydropyridines calcium channel blockers. The whole embryo culture system [13] was employed since the method allows observation of the direct effects of drug on the embryonic morphogenesis, and it also eliminates maternal factors as well as environmental influences [5]. Embryos were co-exposed to either NIF, NIC or NIT and BAY, and examined whether the embryotoxic effects of each calcium channel blocker are suppressed. BAY has positive inotropic and vasoconstrictor actions through the activation of voltagedependent calcium channel in contrast to the negative inotropic and vasodilator effects of NIF, even though BAY belongs to the dihydropyridines and is similar in structure to NIF [19,20]. MATERIALS AND METHODS Animals:Sprague-Dawley rats of the Crj: CD(SD) strain at approximately 11 weeks of age purchased from Charles River Japan Inc. were kept in an animal room where the temperature (22 ± 2°C), the relative humidity (55 ± 10%) and the light and dark cycle (12 hr each) were controlled. They were allowed to have free access to Purina Rodent Chow and tap water. Females were mated overnight with mature male breeders of the same strain. The day on which a vaginal plugs were found was designated as gestational day (GD) 0.Embryo culture: Females were euthanized by carbon dioxide asphyxiation on GD 9. The uterus was excised and all individual implantation sites were placed in a sterile dish containing Hank's balanced s...