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Biomedical subjects

R Bloch

Publications and source records attributed to R Bloch.

At least 109 records · Page 6Linked to original sources
PubMed1975

Composite membrane estradiol implant.

The diffusion and permeability of large organic molecules through polymeric films were investigated, specifically the passage of estrogen through films of polyethylene, silicone, or a composite of these two films. Such systems are of interest because of the possibility of constructing a biocompatible implant that releases a hormone at a controlled and desired rate. Diffusion and permeability coefficients through implants of a desirable size-successfully tested in rats-were measured by the "time lag" method of diffusion, and solubility coefficients were determined by the method of sorption kinetics. Independently derived values were in good agreement. An interesting observation was made with implications for the controlled release from membrane-based drug delivery systems. Permeability coefficients of estrogen are orders of magnitude higher when estrogen is present as a solid rather than in a dilute solution, while diffusion coefficients are equal. This finding is explained by the considerably higher partial vapor pressure of estrogen in the former case. In fact, control of the partial vapor pressure of the encapsulated drug is a powerful method for controlling its release rate.

Adsorption↗
PubMed1975

Role of the ventral surface of the brain stem in the hypotensive action of clonidine.

The areas S of the ventral surface of the brain stem and the immediately surrounding zone were superficially destroyed by the means of electro-coagulation, in 14 cats. This destruction produced a drop in blood pressure, which was transient in 9 and definitive in 4 animals; in one cat only the arterial pressure did not change after the destruction. In 6 animals which have been sham-operated, clonidine (15 mug/kg, i.v.) always induced a marked fall in blood pressure whereas in 10 animals which had maintained or recovered a normal blood pressure after the destruction of the area S, clonidine (15 mug/kg) injected intravenously no longer produced any decrease of the arterial pressure. These results suggest that the integrity of the areas S is necessary for the development of the hypotensive action of clonidine. This hypotensive drug may act, at least at the level of the ventral surface of the brain stem, through inhibition of a vasopressive structure.

Animals↗
PubMed1975

Laeve-[1-3H]Methadone disposition in tolerant dogs.

1. Following a subcutaneous dose (4mg/kg) of [3H]methadone, peak levels of drug occurred in plasma, tissues and selected areas of the central nervous system (CNS) 2h after injection in both non-tolerant and tolerant dogs. Highest concentrations of methadone were attained in bile and lung compared to other tissues. 2. Levels of methadone in plasma, tissue and CNS of tolerant and non-tolerant animals were not markedly different up to 8h after injection, but a much faster rate of egression of free drug (lower t1/2) was observed subsequently in tolerant dogs. 3. Peak levels of methadone in various areas of the CNS ranged between 2-7 (spinal cord) to 3-6 (thalamus) mug/g in non-tolerant and 3-0 -rebellum) to 4-1 (thalamus) mug/g in tolerant dogs 2h after injection. No marked accumulation of methadone occurred in selected areas of the CNS in spite of the persistence of drug in these areas. 4. The plasma protein electrophoretic profiles did not differ between control, non-tolerant and tolerant dogs. 5. Similar qualitative patterns of metabolites were observed in non-tolerant and tolerant dogs and the development of tolerance did not appear to modify the metabolic pathways of methadone.

Animals↗
PubMed1975

[Role of ventral surface of brain stem in control of arterial pressure and in hypotensive action of clonidine].

Superficial destructions of the brain stem have been performed in cats at the level of the chemosensitive areas "S". These destructions produced a drop in blood pressure, which was transient in 9 and definitive in 4 animals. In 6 sham-operated animals, clonidine (15 mug/kg), injected intravenously, always induced a marked fall in blood pressure, whereas in the 10 animals which have maintained or regained normal blood pressure after the destruction of the areas S, clonidine no longer induced any decrease in blood pressure. These results suggest that the integrity of the areas S is necessary for the development of the hypotensive action of clonidine. This hypotensive drug may act, at least at that level of the ventral surface of the brain stem, through an inhibition of a vasopressive structure.

Animals↗