Oral AAS compounds, such as metandienone (Dianabol), oxandrolone (Anavar), and stanozolol (Winstrol) are commonly used in conjunction with injectable AAS during steroid cycles for added muscle size and strength benefits.42 These agents gained popularity in the 1970s and continue to be common additions to user-designed AAS cycles.27
Ultimate Steroid Cycles Free Download Pdf
Milk is synthesized by mammary epithelial cells of lactating mammals. The synthetic capacity of the mammary gland depends largely on the number and efficiency of functional mammary epithelial cells. Structural development of the mammary gland occurs during fetal growth, prepubertal and post-pubertal periods, pregnancy, and lactation under the control of various hormones (particularly estrogen, growth hormone, insulin-like growth factor-I, progesterone, placental lactogen, and prolactin) in a species- and stage-dependent manner. Milk is essential for the growth, development, and health of neonates. Amino acids (AA), present in both free and peptide-bound forms, are the most abundant organic nutrients in the milk of farm animals. Uptake of AA from the arterial blood of the lactating dam is the ultimate source of proteins (primarily β-casein and α-lactalbumin) and bioactive nitrogenous metabolites in milk. Results of recent studies indicate extensive catabolism of branched-chain AA (leucine, isoleucine and valine) and arginine to synthesize glutamate, glutamine, alanine, aspartate, asparagine, proline, and polyamines. The formation of polypeptides from AA is regulated not only by hormones (e.g., prolactin, insulin and glucocorticoids) and the rate of blood flow across the lactating mammary gland, but also by concentrations of AA, lipids, glucose, vitamins and minerals in the maternal plasma, as well as the activation of the mechanistic (mammalian) target rapamycin signaling by certain AA (e.g., arginine, branched-chain AA, and glutamine). Knowledge of AA utilization (including metabolism) by mammary epithelial cells will enhance our fundamental understanding of lactation biology and has important implications for improving the efficiency of livestock production worldwide.
The growth of mammary tissue during estrus is related to ovarian steroid hormones [64]. Estrogen receptors and progesterone receptors both appear in cells of the mammary gland around the time of puberty. However, the exact roles of estrogen and progesterone are not completely understood. Mammogenic hormones establish the conditions for specific growth patterns in mammary tissue [63]. For example, concurrently elevated concentrations of estrogen and progesterone in plasma during late gestation result in an exponential increase in parenchymal growth and in the formation of alveoli. In contrast, cyclic changes in those hormones associated with estrous cycles result primarily in duct elongation and formation of some lobular tissue, but not in formation of alveoli. Thus, mammary gland development is usually driven by a complex of hormones acting in concert.
Progesterone is another ovarian steroid hormone that plays a key role in mammary gland development. While progesterone receptors have been difficult to identify in the mammary fat pad, administration of progesterone stimulates proliferation of stromal cells under physiological conditions [63]. The stimulatory effect of progesterone on DNA synthesis in ductal epithelium is probably mediated indirectly through its effects on stromal cells. The major mammogenic effects of progesterone require its receptors in MEC and include ductal side branching or alveolar bud formation, which are the hallmarks of post-pubertal mammary gland development. Estrogen stimulation of progesterone receptor expression in MEC is necessary for progesterone to exert its effects. Therefore, progesterone has a major role in alveolar morphogenesis but a lesser role in ductal morphogenesis. During estrous cycles, duct elongation and expansion of the parenchymal tissue into the fat pad occur when the circulating concentrations of estrogen are high. During the luteal phase when concentrations of progesterone in plasma are greatest, little growth of the mammary gland occurs in ruminants, but the formation and maintenance of lobular structures in the mammary gland may be stimulated by progesterone, with little regression of the mammary ductal system occurring between estrous cycles [64].
2ff7e9595c
Commenti