Biomedical subjects

R G Jarrett

Publications and source records attributed to R G Jarrett.

22 records · Page 2Linked to original sources

PubMed1983

Neoplasia and chronic disease associated with the prolonged administration of dehydroheliotridine to rats.

When dehydroheliotridine (DHH), a pyrrolizidine alkaloid metabolite with bifunctional alkylating and antimitotic activities, was administered to a hooded strain of rats by ip injection, the incidence of tumors, excluding interstitial cell tumors, was significantly greater than that in saline-injected controls. The number of tumors was not further increased when thioacetamide (TA) was co-administered for its mitosis-stimulating effect. The life-span of the rats was significantly shortened by DHH and more so by combined DHH and TA treatment, but not by TA alone. The results indicate that DHH is responsible for some, possibly most, of the carcinogenicity of the parent pyrrolizidine alkaloids and also stimulates the earlier and more rapid development of renal and vascular diseases normally associated with aging in rats.

Age Factors↗

PubMed1982

Effects of a preventive and suppressive control scheme on the development of thiabendazole-resistance in Ostertagia spp.

Three years after the start of an experiment to assess the merits of thiabendazole (TBZ) treatment of trichostrongylid parasites in weaner sheep, field isolates of Ostertagia spp and Trichostrongylus spp were made from weaner sheep treated under one of three treatment schemes. Treatment frequencies were "nil", "planned" (5 or 6/year) and "regular" (every 3 weeks). In addition an isolate was taken from a group of "tracer" sheep drenched with TBZ every 10 days. Resistance to TBZ was assessed using an in vitro egg hatch assay, pre- and post-treatment faecal egg counts and a controlled anthelmintic efficiency test. Pre- and post-treatment egg counts revealed the presence of TBZ-resistance in field isolates of mixed species. Egg hatch assays indicated a level of resistance for Ostertagia spp which was proportional to the frequency of TBZ treatment. The "planned", "regular" and "tracer" strains of Ostertagia spp had resistance ratios for eggs of 4, 13 and 15 respectively when compared to the "nil" strain. In the anthelmintic efficiency assay treatment with 44 mg kg-1 and 88 mg kg-1 of TBZ removed 82 and 96% respectively of the total Ostertagia burden (adults and larvae) from the "nil" strain and 30 and 75% respectively from the "planned" strain. The same dose rates against the "regular" and "tracer" strains and additional rates of 132 or 176 mg kg-1 against the "tracer" strain failed to reduce the Ostertagia burden significantly. Intestinal Trichostrongylus spp from all isolates were fully susceptible to TBZ at 44 mg kg-1. Levamisole at 7.0 mg kg-1 was highly effective (99% reduction) against the "tracer" strain of Ostertagia.

Animals↗

PubMed1982

The protective effect of ipratropium bromide aerosol against bronchospasm induced by hyperventilation and the inhalation of allergen, methacholine and histamine.

The ability of the anticholinergic agent, ipratropium bromide, Atrovent, (40 mcg from a metered dose inhaler) to prevent bronchoconstriction produced by four different provocation tests was compared with placebo in 12 asthmatic patients. The provocation tests used were hyperventilation and inhalations of histamine, methacholine and an allergen to which the subject was known to be sensitive. The order in which each patient received the tests was determined according to a Latin-square design and remained the same on both test days. Pretreatment with ipratropium bromide and placebo was allocated randomly and administered in double-blind fashion. Ipratropium bromide provided significant protection at the 5% level against all four types of challenge. The average number of breaths required to produce a fall of at least 20% in FEV1 (forced expiratory volume in one second) was doubled for both histamine and allergen and increased by a factor of six for methacholine. The fall in FEV1 induced by hyperventilation was approximately halved. No side effects were noted with ipratropium bromide.

Adolescent↗

PubMed1982

Comparison of changes in resistance of Haemonchus contortus eggs following withdrawal of thiabendazole selection.

Two strains of Haemonchus contortus with different levels of thiabendazole resistance were developed from the same parent strains by being subjected to different selection intensities. These two strains were each subdivided into two; one selected by thiabendazole in each generation, the other unselected for four generations. Levels of thiabendazole resistance were monitored in each generation by an in vitro egg hatch technique. During this time the unselected strain with the higher level of resistance maintained an LC50 similar to its selected control. The LC50 of the unselected strain with the lower level of resistance actually increased until at the end of the fourth generation it had an LC50 similar to the thiabendazole selected strains.

Animals↗