The uptake of (6,7-3H) 17beta-oestradiol by tissues of the domestic fowl during an ovulation cycle

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

Effects of early tamoxifen treatment on hormonal content of 15-day quail embryo gonads

An early treatment of quail eggs with an antiestrogen (Tamoxifen = TAM) modifies the female gonads morphologically. In the left ovary, the proliferation of the germinal epithelium and formation of a cortex is markedly inhibited, while the medulla on both sides becomes more developed and keeps a cordal organization. The effects of TAM on the hormonal potentialities of 15-day embryo gonads have been investigated by radioimmunoassay. The data have been compared with those of normal gonads. The results indicate that the TAM treatment does not mainly modify the hormonal levels and patterns in the gonads of both sexes and does not inhibit the function of the hypothalamo-hypophyseal-gonadal axis. The reduced cortical development is thus not linked to an estrogen decrease but to competitive effects on receptors at the level of this tissue.

Pharmacokinetics of estradiol-17 beta in the laying hen

The plasma metabolic clearance rate (MCR), production rate (PR), and half-life (T 1/2) of estradiol-17 beta (E2) were determined in 5 laying hens at a time 2 to 4 hr after oviposition of the second egg in the clutch. Pharmacokinetic parameters were calculated from data obtained after a single injection of 3H-E2. Results indicate that the disappearance of 3H-E2 from the plasma best fits a two compartment model. The MCR was calculated to be 77.3 +/- 14.2 (mean +/- SE) ml plasma/min/kg and the PR 6.36 +/- 1.46 ng/min. The T 1/2 for the distribution (or alpha) phase was 1.1 +/- .2 min and for the storage, metabolism, and excretory (or beta) phase was 27.5 +/- 6.5 min. We conclude that the MCR and T 1/2 alpha of E2 are similar to previously published values for progesterone (P4) but that the PR is substantially lower. This difference can account for the lower circulating basal levels of E2, compared to P4, in the laying hen.