Plasma luteinizing hormone (LH) concentrations and the numerical density (Nv) of gonadal LH-binding (LH-positive) cells were determined in intact male and female chick embryos from Days 10.5 through 18.5 of incubation for plasma LH and from Days 6.5 through 19.5 for LH-binding cells, as well as in Day 15.5 decapitated (“hypophysectomized”) embryos with pituitary transplants for both plasma LH and LH-binding cells. The data demonstrate that LH is already present in the plasma of male and female embryos as early as Day 10.5, the first day examined. Plasma LH levels in hypophysectomized embryos were statistically significantly lower than those of intact embryos, while pituitary transplants to the chorioallantoic membrane of hypophysectomized embryos elevated plasma LH concentrations to levels not statistically different from those of intacts. The “role(s)” of plasma LH levels and changes in form and numerical density (Nv) of gonadal LH-binding cells in the maturation of the pituitary-gonadal axes of the chick embryo are discussed and evaluated.

The Ets gene family codes for transcription factors containing a conserved DNA binding domain. The proto-oncogene c-ets1 is highly expressed in lymphoid organs and in developing mesodermal-originating structures. We studied c-ets1 gene expression in the developing rat hypothalamo-hypophyseal system, using in situ hybridization on paraformaldehyde-fixed frozen sections. At embryonic day 12 (E12) and E13, cells synthesizing c-ets1 mRNA are found in the neural tube where they form small, heavily labeled strand-like and punctate structures; positive mesenchymatous cells, corresponding to the surface capillary network, surround the brain and hypophysis. C-ets1 mRNA is synthesized from E14 in the neural pituitary and E15 in the adenohypophysis, during angiogenesis; no c-ets1 mRNA is detected in the avascular intermediate pituitary at any stage. Strand-like c-ets 1 mRNA labeling is intense from E14 to E21 in the diencephalon. This labeling is also detected during perinatal stages in the hypothalamic magnocellular nuclei, one of the most richly vascularized brain areas. In the rat hypothalamo-hypophyseal system, c-ets1 gene expression is maximal during fetal and perinatal stages and progressively decreases thereafter until adulthood. The spatio-temporal correlation observed between c-ets1 gene expression and blood vessel formation in the rat hypothalamus and pituitary suggests a role for c-ets 1 in angiogenesis in this system.

This study aimed at elucidating the effects of thermal manipulation (TM) during different periods of embryogenesis on hatchability, body weight, and thermoregulation of Ross chicks at hatch, and on the chick's ability to cope with thermal challenge (TC) at 3 d of age. Control embryos were incubated at 37.8 degrees C and 56% RH, whereas the TM embryos were treated for 3 h at 39.5 (1) or 41.0 degrees C (2) and 65% RH, during early embryogenesis (EE), E8 to E10, and late embryogenesis (LE) at E16 to E18. At hatch, after feather drying, BW and body temperature (Tb) were measured, blood was drawn from the jugular vein to measure plasma concentrations of thyroxine (T4), triiodothyronine (T3), and corticosterone. These parameters were also measured in 3-d-old chicks during exposure to TC at 41 degrees C for 6 h. Hatchability was significantly higher in the LE1-treated group than in the other treatments. EE1- and LE1-treated embryos exhibited significantly lower Tb at hatch than the LE2 chicks. Significant hyperthermia was noted in the control chicks during 6 h of TC; it coincided with a higher plasma T3 concentration (P = 0.074). During TC, the LE1-treated chicks exhibited the lowest T3 to T4 ratio and a significantly reduced plasma corticosterone concentration. It can be concluded that TM at 39.5 degrees C for 3 h during E16 to E18 of incubation improved chick's thermotolerance acquisition and reduced the corticosterone level of chicks exposed to TC at the age of 3 d.

After thiourea administration to chick embryos on Day 5.5, total plasma thyroxine concentrations were significantly decreased on Days 7.5, 9.5, 10.5, and 11.5 of incubation. Also, radioiodide uptake in normal and thiourea-treated embryos was measured at 1.0, 3.0, and 5.0 hr post-treatment on all days studied. There was no statistically significant difference in radioiodide uptake between normal and goitrogen-treated embryos on Days 7.5 and 9.5. However, on Days 10.5 and 11.5, a statistically significant increase in radioiodide uptake was observed in thiourea-treated individuals as compared to nontreated embryos. Thyroid wet weights were compared between normal and thiourea-treated embryos on all days studied. There were no statistically significant differences in wet weights between normal and goitrogen-treated individuals on the days assayed. The data indicate that on Day 10.5 of incubation, the pituitary and/or hypothalamus of the chick embryo first responds to decreases in circulating T4 levels. Thus, the maturation of the hypothalamo-adenohypophyseal-thyroid axis during Days 10.0–13.0 of development in the chick embryo may be similar to that found in sheep and humans at midgestation.

The effect of hypophysectomy upon glycogen accumulation by the yolk sac membrane of the developing chick embryo has been studied. Animals were hypophysectomized at 33- to 38-hours of incubation by the “partial decapitation” method of Fugo (1940), Yolk sac membranes were collected at 24-hour intervals from day 9,5 through 19.5 of incubation. Glycogen levels were determined by the anthrone method (Carroll et al., 1956). Although hypophysectomy produces no change in glycogen levels of yolk sac membranes of 9.5-, 10.5-, and 11.5-day embryos, by day 12.5 of incubation a statistically significant reduction in rate of glycogen accumulation has occurred. Glycogen levels of operated animals on days 13.5, 14.5, 15.5, 16.5, and 17.5 of incubation remain at the 12.5-day level. The period of 15.5 to 19.5 days of incubation is characterized by a sharp increase and decline in yolk sac membrane glycogen levels in normal animals. This increase and reduction is reflected in hypophysectomized animals, however it is out of phase by 1 day. A single administration of cortisone acetate on day 13.5 to pituoprivic embryos raises glycogen levels above normal on days 14.5 and 15.5 of incubation. The data demonstrate that the developing chick embryo does exert hormonal control over metabolic events within this membrane.