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Biomedical subjects

D J Back

Publications and source records attributed to D J Back.

At least 235 records · Page 13Linked to original sources
PubMed1978

The pharmacokinetics of tritiated ethinylestradiol in the rabbit.

The disappearance of ethinylestradiol from the blood of rabbits has been studied, following the intravenous administration of this steroid. The disappearance followed two exponentials, the first having a half life (t1/2) of 5.5 min and the second, apparently terminal exponential was also rapid (t1/2-69 min). The plasma clearance was 150 ml/min which suggests almost total clearance of this steroid during a single passage through the liver. Bile contained a significant concentration of EE conjugates and thus this steroid could undergo enterophepatic recirculations. A large oral dose of unlabelled EE, given prior to intravenous administration of tritiated EE, considerably altered the pharmacokinetics of the latter by saturating both phase one metabolism (changes of the steroid nucleus) and the secretion of conjugates into bile. It was not clear whether phase two metabolism (conjugation) was also saturated.

Animals↗
PubMed1978

First-pass effect of norethindrone in rabbits and rats.

The influence of the route of administration on the pharmacokinetics of the synthetic progestogen norethindrone was studied in the rabbit and rat. In the rabbit, the area under the curve (AUC) after oral administration was 54% of that after i.v. administration. In the rat, the AUC after administration into the hepatic portal vein was 32% of AUCi.v.; after oral administration the AUCoral was 13.7% of AUCi.v. and 57.6% of AUCportal. Therefore, in both the rabbit and rat norethindrone is subject to a first-pass effect. Using the technique of constant withdrawal of blood from the hepatic portal vein after drug administration into the gastrointestinal tract, it was shown the norethindrone is metabolized in the gut wall. Hence, in the rat at least, there are both intestinal and hepatic components of the overall first-pass effect. In addition, increasing the time of intraportal injection from 15 sec to 2 min (thereby reducing the rate of drug delivery to the liver) resulted in the AUC being reduced by 40%. Dose-dependent kinetics were observed with doses of norethindrone greater than 500 microgram/kg.

Administration, Oral↗
PubMed1977

Some effects of cyproterone and cyproterone acetate on the reproductive physiology of the male rat.

Male rats were treated with 5 or 20 mg cyproterone acetate/kg/day or 20 mg cyproterone/rat/day for 1, 2, 3, 4, or 5 weeks. There was some reduction in fertility with both compounds, the maximum effect occurring after 5 weeks with the higher dose of cyproterone acetate and after 2 weeks with cyproterone. A significant increase in testosterone levels was found after treatment with the high dose of cyproterone acetate by 1 week and with cyproterone by 2 weeks. Dose-dependent atrophy of the seminal vesicles occurred after treatment with cyproterone acetate; with cyproterone atrophy occurred at 1 and 2 weeks but approximated to control values at 3, 4 and 5 weeks. Epididymal weights were reduced with the high dose of cyproterone acetate but the low dose had little effect. Reduction in the weight of the testes was only observed after 5 weeks of treatment with the high dose of cyproterone acetate. Since plasma testosterone levels were not depressed below normal values, accessory sex organ regression evidently resulted from the local antiandrogenic action of the drugs. There was some indication of interference with the secretory and absorptive activity of the lining cells of the epididymis but in general treatment with either steroid caused only relatively small and variable changes in the composition of epididymal plasma.

Animals↗
PubMed1975

The presence of metabolites of 3-H-testosterone in the lumen of the cauda epididymidis of the rat.

Following the administration of 3-H-testosterone to adult male rats radioactivity appeared in epididymal fluid and at 60 minutes was in excess of the level in tissue of the cauda epididymidis and blood plasma. Ligation of the arterial blood supply to this region caused a significant decline in the radioactive content of epididymal fluid and cauda tissue. It is concluded that direct transfer occurs from the systemic circulation into the cells of the cauda epididymidis and thence into the lumen of the duct. The major radiometabolite of 3-H-testosterone identified in chloroform extracts of epididymal tissue (60.6%) and epididymal fluid (72.8%) was 17-beta-hydroxy-5-alpha-androstan-3-one.

Animals↗
PubMed1975

The effects of alpha-chlorohydrin on the composition of rat and rabbit epididymal plasma: a possible explanation of species difference.

The relationship between the antifertility effect of alpha-chlorohydrin and changes in composition of luminal plasma from the cauda epididymidis of rats and rabbits has been investigated. At each dose regimen studied, the fertilizing capacity of rats treated with alpha-chlorohydrin was reduced to zero. The levels of sodium, potassium, glycerylphosphorylcholine (GPC), acid phosphatase and alkaline phosphatase in epididymal plasma were not markedly affected by drug treatment. The most noticeable change was a considerable increase in the concentration of lactic dehydrogenase (LDH) at all dose levels and of glutamic-oxaloacetic transaminase (GOT) after 7 days of treatment with 8 and 16 mg/kg. The effect of cold shock on the composition of epididymal plasma showed that LDH and GOT are, at least in part, derived from spermatozoa. In contrast, alpha-chlorohydrin did not have an antifertility action in the rabbit, and the only notable change in the compositon of epididymal plasma was an increase in the level of GPC. These results provide evidence that, in the rat, alpha-chlorohydrin or a metabolite primarily exerts its antifertility effect by a direct action on the spermatozoa, whilst in the rabbit a barrier may exist to the entrance of the drug into the lumen of the epididymal duct.

Acid Phosphatase↗
PubMed1974

The pharmacokinetics of (14C)-edrophonium in normal wistar rats and homozygous Gunn rats with ligated renal pedicles.

1 The distribution kinetics of [(14)C]-edrophonium were studied in both normal Wistar and homozygous Gunn rats with ligated renal pedicles.2 After intravenous injection the plasma concentration-time curve of [(14)C]-edrophonium was adequately fitted by a triexponential function in both species of rat and interpreted in terms of a three compartment model.3 The influence of the route of administration (i.e., systemic venous versus hepatic portal) of [(14)C]-edrophonium on its concentration in plasma was studied in normal Wistar rats with ligated renal pedicles. There was a marked difference in the area under the plasma concentration-time curve depending on the route of administration.4 The parameters of the model were determined and compared.5 The value of the metabolism rate constant was approximately the same in both species of rat. This suggests that the rate of conjugation of [(14)C]-edrophonium is unaltered in the homozygous Gunn rat despite the genetic lesion in UDP-glucuronyltransferase.

Animals↗