Estrus synchronization

The estrus-synchronizing effect of adult male urine described for female rats has puzzled investigators. Recent experiments and more sophisticated statistical analysis have indicated that apparent synchronization may be actually chance (Schank, 2001). 

Elantrine, 418 Elucaine, 44 Encyprate, 27 Endorphins, 317 Endrysone, 200 Enkephalins, 316 Ephedrine, 39 Epimestrol, 13 Epinephrine, 38, 105 Eprozinol, 44 Eryonovine, 475 Ergotism, 475 Eritadenine, 467 Eschweiler-Clark methyla-tion, 29, 162, 210, 28( Esproquin, 373 Estradiol, 136 Estrazinol, 142 Estriols, 138 Estrofurate, 137 Estrogenic activity, 9 Estrogens, 137 Estrone, 137 Estrus synchronization,... 

Estrus synchronization may be used in management situations where there is limited stallion availability (e.g. the stallion is often away at horse shows) or the stallion is subfertile. Synchronization may also be used to facilitate the coordination of estrus, ovulation and insemination in mares imdergoing artificial insemination or embryo transfer. There are many methods of synchronizing estrus in single mares or in groups of mares. 

Ball B A 2000a Hormonal management of transitional estrus. In Proceedings of the Bluegrass Equine Reproduction Symposium, Lexington, KY, 2000 Ball B A 2000b Estrus synchronization in mares. 

In 1984, 3,4-dehydro-exo-brevicomin (99, Figure 4.50) and 2-sec -butyl-4,5-dihydrothiazole (100) were isolated by Novotny and coworkers from the urine of the male house mouse (Mus musculus) as pheromone components.92 They act, synergistically, in promoting intermale aggression, sex attraction, and estrus synchronization in female mice. It was later found that the natural components are ( R,5S,lR)-99 and (S)-100. Additional achiral compounds 101 and 102 were also identified as possible pheromone components. 

Wilson (3) and Wilson and Bossert (4) divided pheromones into release pheromones (if the stimulus triggers an immediate behavioral response in the receiving organism) and primer pheromones (if the response is a long lasting one). Substances involved in alarm, territorial marking, trail, social status, sexual attraction and reproductive isolation are release pheromones while the odors involved in puberty acceleration, pregnancy block, estrus synchronization or suppression are primer pheromones. 

The urine of the mouse is the source of estrus synchronization, pregnancy block, group and individual recognition, sexual attraction, aggregation, histocompatibility-related mating preference, fear and stress (293). 

Artificial Insemination. Artificial insemination is a reproductive technology that has been used for a long time. Semen is collected from males and is used to breed females. Because semen can be frozen, it can be used to eventually sire thousands of offspring. This expanded use of superior males can markedly increase the rate of genetic change. Estrus synchronization facilitates artificial insemination by ensuring that a group of females come into estrus at the same time. 

D. Estrus Synchronization - Megestrol acetate (12 mg/kg/day for 7 days) synchronized ovulation in 50% of the treated rats. Both medroxyprogesterone acetate and chlorpromazlne were also able to delay ovulation in rats, presumably by a similar mechanism to that of megestrol acetate. 

Bovine estrus synchronization is an important field for the veterinary pharmaceutical industry. A description of the natural bovine cycle and methods to cycle control are presented. In addition, commercially available silicone devices for bovine estrus synchronization are listed. The mathematical modeling of progestagens release from such devices is a crucial tool in the development of novel and/ or optimized delivery systems. For this purpose, several in vitro models, approaches to explain the ADME processes and overall models are described. This type of mathematical modeling could help in the future to customize drug delivery systems to specific animals and/ or situations. 

Keywords Silicone, drug delivery, mathematical modeling, controlled release, bovine estrus synchronization... 

The understanding of the estrous cycle and the effects of various hormone treatments on follicular dynamics leads to the development of protocols that efficiently handle the estrous cycle and ovulation [16]. These protocols involve the use of hormones that mimic the physiological release during the estrous cycle, allowing estrus synchronization [16]. Hence, hormone therapy for synchronization of estrus and ovulation is the key tool for responding to the need for more and better calves per year. 

Estrus synchronization therapy requires a specific release rate from silicone devices to maintain the plasmatic level of progestagens between the therapeutic values. Due to this requirement, the initial load of progestagens in the devices is always higher than progestagens solubility in the polymeric matrix. Following are the most important sihcone devices used for the previously mentioned administration of progesterone and norgestomet... 

Table 15.4 presents some of the intravaginal veterinary drug delivery systems for bovine estrus synchronization. These devices contain progesterone uniformly distributed throughout the silicone matrix. As mentioned before, the initial progesterone load is higher than hormone solubility in the matrix to meet the therapeutic requirements. 

Table 15.4 Intravaginal silicone devices for bovine estrus synchronization.

The possibihty of dehvering sufficient quantities of norg-estomet from subcutaneous implants inserted under the skin of the ear has been investigated. The norgestomet prevents the release of LH, ovulation, and the formation and maintenance of the CL [143]. As a result, two implantable devices have been developed to use in estrus synchronization... 

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