Steroid release

The rate and duration of steroid release is affected by (1) polymer composition, (2) drug/polymer ratio (3) microsphere size distribution, and (4) microsphere quality (75). The ratio of glycolide to lactide in the copolymer has been found to be more dominant than the polymer molecular weight in the design of controlled release formulations. Microspheres of smaller size provide in vivo drug profiles of higher levels and shorter durations because of greater surface area. 

Ho, N.F.H., et al. 1976. Systems approach to vaginal delivery of drugs III Simulation studies interfacing steroid release from silicone matrix and vaginal absorption in rabbits. J Pharm Sci 65 1576. 

The Ocusert system illustrated in Figure 12.7 is one example of a diffusion-controlled reservoir device. Another is the steroid-releasing intrauterine device (IUD) shown in Figure 12.9. Inert IUDs of various shapes were widely used for... 

Sorensen, P. W. and Scott, A. P., The evolution of hormonal sex pheromones in teleost fish. Poor correlation between the pattern of steroid release by goldfish and olfactory sensitivity suggests that these cues evolved as a result of chemical spying rather than signal specialization, ActaScand. Physiol., 152, 191, 1994. 

Once the various steroids have been formed in paticular subcellular compartments, they must be released into the peripheral blood circulation. There is evidence that some steroids are released by passive diffusion, as in the case of corticosterone, but for 18-hydroxylated corticosteroids, Na+/K+-ATPase activity is necessary [6,109]. The situation is more complicated, however, because the presence of proteins in the adrenal cortex, which act as non-classical receptors, may bind C2i steroids to different extents, thus reducing rates of steroid release (see Ref. 6). So far as pregnenolone is concerned, there is no barrier to its efflux from the mitochondria where it is formed from cholesterol [50], During incubation of rat testis [110], pregnenolone was found to travel from the mitochondria, through the ER and cytosol and then out into the medium. The release with time could be resolved into two components, one rapid and the second, much slower. More than 25% of the pregnenolone remained in the tissue after 150 min. incubation. This two-phase release may reflect the presence of two pools of steroid, the initial loss representing passive dif-... 

Gardner, D.L. Patanus, A.J. Fink, D.J. Steroid release from microcapsules. In Drug Delivery Systems Gabelnick, H.L., Ed. DHEW Publ. No. (NIH), 77-1238 Department of Health, Education, and Welfare Washington, 1977 265-278. 

Adrenal Y-1 Cells Role of microfilaments in steroid release Considine et a/., 1992 ... 

Considine RV, Simpson LL, Sherwin JR (1992) Botulinum C2 toxin and steroid production in adrenal Y-1 cells The role of microfilaments in the toxin-induced increase in steroid release. In J Pharmacol Exp Then 260 859-64... 

In bony fishes, corticosteroids are secreted from the interrenal tissues (analogous to the adrenal cortex) located in the head kidney region121 182. Cortisol is the major steroid released from these cells in response to neuroendocrine stimulation emanating from the hypothalamus and the pituitary (see Chapter 12). The release of cortisol in response to stress has been characterized in several species and also in response to different stressors and this topic has been extensively reviewed1011 70 182. Cortisol... 

The possible roles of 5-HT4-RS in emotional and rewarding processes are only suggested by their presence in limbic structures such as septum, nucleus accumbens, ventral pallidum, and frontal cortex in human (Table 4, Figure 5) [55, 56]. One has to take in account that steroid release elevates mood and consequently putative behavioural modifications induced by 5-HT4-R agonists could be complicated by these effects [98, 99, 137]. 

Haleblian J, Runkel R, Mueller N, Christopherson J, Ng K. Steroid release from silicone elastomer containing excess drug in suspension. Journal of Pharmaceutical Sciences. April 1971 60(4) 541-545. PubMed PMID 4108479. 

In another study, Pitt and others compared the steroidal release kinetics of caprolactone homopolymer, D,L-lactide homopolymer, and their related copolymers to silicone rubber. While the observed release rates from the poly (D,L-lactide) were much slower than any of the other materials studied,incorporation of a plasticizer such as tributy l citrate into the poly(D,Lrlactide) seemed to increase the release rates. The other caprolactone-based materials showed release kinetics similar to that of silicone rubber (Pitt et al, 1979b). 

Other novel combination devices on the market for targeted dmg delivery include resorbable dug-eluting stents, dmg-eluting balloons, and steroid-releasing nasal implants (Fig. 3). Dmg-eluting contact lenses are also under development for the treatment of glaucoma. ... 

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