In vitro, greenhouse and field assessments of cassava lines for resistance to anthracnose disease caused by Colletotrichum gloeosporioides f.sp. manihotis.

Fifty-three cassava lines were selected from breeding populations at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria and screened in vitro for resistance to cassava anthracnose disease (CAD). The in vitro inoculation of stem cuttings with the fungus Colletotrichum gloeosporioides f.sp. manihotis showed significant differences (p +/- 0.05) in acervuli production and in the sensitivity of the cassava lines to the fungal infection after 7 days of incubation at 25 degrees C. Cassava lines 88/01084, 91/00595, 91/00475, 91/00344, 91/00684, 91/00313, 91/00422, and 91/00344 were highly resistant, with necrotic lesion sizes less than 7 mm. In contrast pedigree lines 88/02549, 89/0008, 91/00390 and 91/00402 were highly susceptible with the largest necrotic lesion size being greater than 20 mm. Ten cassava lines from the in vitro screening that showed varying levels of resistance to CAD were selected, based on their flowering abilities for diallel hydridization trials, and were further screened in greenhouse and field trials for CAD resistance. The greenhouse and field screening showed significant varietal differences (p +/- 0.05) in sensitivity to the fungus. In all cases, the progeny lines showed correlated levels of resistance irrespective of the type of screening or assessments. Correlation analysis of the in vitro, greenhouse and field assessments showed that there was a good correspondence among all three methods of evaluating for CAD.

All-trans-retinoic acid in maternal plasma and teratogenicity in rats and rabbits.

The teratogenicity of all-trans-retinoic acid, 13-cis-retinoic acid, and retinol was investigated in pregnant Wistar rats given a single oral dose on Day 10 of gestation. External malformations showed dose-dependent increases and the order of potency was all-trans-retinoic acid > retinol > 13-cis-retinoic acid. The metabolites in maternal plasma were determined following a single oral dose on Day 10 of gestation. Equipotent teratogenic doses of all-trans-retinoic acid and 13-cis-retinoic acid had similar plasma levels of all-trans-retinoic acid; however, retinol teratogenicity could not be accounted for by circulating all-trans-retinoic acid or its metabolites. The teratogenicity and maternal pharmacokinetics of all-trans-retinoic were compared in pregnant Wistar rats when given as a single dose (50 mg/kg) and as three equal doses (16.66 mg/kg) over 6 hr. Divided doses were of slightly greater potency than the single dose but the maximum observed concentration (Cmax) and area under the plasma concentration-time curve (AUC) values for the second and third doses were greatly attenuated compared with the first dose; in consequence, both the total AUC and Cmax were reduced compared with the single dose. The altered profile could not be explained by increased formation of all-trans-retinoic acid glucuronide or increased isomerisation to 13-cis-retinoic acid. The maternal plasma levels of all-trans-retinoic acid in pregnant rabbits were reduced by a dose given 24 hr earlier. These data show that all-trans-retinoic acid in maternal plasma is a poor indicator of fetal exposure to teratogenic risk.

The teratogenic metabolites of vitamin A in women following supplements and liver.

Ten healthy female volunteers were given 5 doses of retinol as the palmitate; 50 and 150 mg retinol as an oral supplement, 50 and 150 mg as fried calf liver (50 and 150 g) and 3, 9 or 30 mg by intra-muscular injection. Plasma concentrations of retinyl palmitate were higher after 50 mg retinol given as an oral supplement compared with 50 mg as liver; there was no significant difference between the 150 mg doses. Plasma concentrations of retinol showed only small increases. The peak plasma concentrations (Cmax) of all-transretinoic acid, the principal teratogenic metabolite of retinol, and the area under the concentration-time curve (AUC) were up to 20-times higher after supplements compared to the same dose as liver. Plasma concentrations of all-trans-4-oxo-retinoic acid, 13-cis-retinoic acid and 13-cis-4-oxo-retinoic acid showed smaller differences between supplements and liver. Intra-muscular administration of 30 mg retinol gave retinyl palmitate concentrations similar to those found after the oral doses but did not increase circulating concentrations of the acid metabolites. Based on the formation of all-trans-retinoic acid, liver and supplements are not of equivalent teratogenic potential. Advice to pregnant women on the consumption of liver based on the reported teratogenicity of vitamin A supplements should be reconsidered.

Pharmacological profile of the 5-hydroxytryptamine receptor of Fasciola hepatica body wall muscle.

5-HT is a candidate for the excitatory transmitter at the neuromuscular junction in trematodes including Fasciola hepatica. This study has determined the response of a muscle strip preparation from Fasciola hepatica to 5-HT and a range of agonists that distinguish between the vertebrate receptor 5-HT subtypes. 5-HT increased the resting tone and the rhythmic activity of the muscle strip. Of the 19 compounds tested, only 10 had an effect similar to 5-HT and all but 2 of these were tryptamine compounds. 5-HT was more potent than tryptamine whilst 4-OH-tryptamine had no effect, suggesting that the response is mediated by a 5-HT rather than a tryptamine receptor. 5-Fluorotryptamine and 5-carboxyamidotryptamine were the most potent agonists. 8-OH-DPAT also mimicked the effect of 5-HT, though less potently. Assuming that these agents elicit their response through a common receptor, this suggests the presence of a 5-HT receptor with similar properties in terms of agonist recognition as the vertebrate 5-HT1 class of receptor involved in controlling Fasciola muscle motility.