Development of chick embryo liver during organ culture: requirement for zinc-insulin

A hundred years of the hepatotrophic controversy

Venous blood returning from the splanchnic viscera has liver-supporting (hepatotrophic) qualities not found to the same degree in other kinds of arterial or venous blood. The effects of portal blood have been noted in animals with two livers (or a differential portal blood supply to different regions of one liver) to include hypertrophy, glycogen storage, hyperplasia, capacity for regeneration, increase of several synthetic functions, and maintenance of normal structure. The main splanchnic venous hepatotrophic factors are endogenous hormones of which the single most important is insulin. Thus, the foregoing portal hepatotrophic effects are largely eliminated with the diabetes produced by alloxan or total pancreatectomy. The injury of portacaval shunt is caused by the diversion of the hormones around the liver. Accordingly, the atrophy, injury to the organelles, and loss of the capacity for cell renewal is minimized if insulin is infused into the portally deprived liver. In these and other experiments, exogenous glucagon alone or the addition of glucagon to insulin has had no effect, but this may be because of the masking presence of gut glucagon and other hormonal or non-hormonal substances in our models. At present, the effects on the liver of exogenous insulin, glucagon, epidermal growth factor, and numerous other hormones are being determined by their intraportal infusion into eviscerated dogs in which other endogenous splanchnic factors have been eliminated.

Estrogen receptor and the development of estrogenic responses in embryonic chick liver

We have examined the development of responsiveness to estrogen by embryonic chick liver with a view to determining common and unique factors involved in the establishment of different genomic responses to th e hormone. The major apoproteins of chick VLDL, apo VLDL-B and apo VLDL-II, both appear to be estrogen inducible at an earlier stage of of embryonic development than is vitellogenin. Apo VLDL-B, but not vitellogenin, exhibits a significant level of hepatic synthesis in the absence of estrogen treatment. This basal synthesis in the absence of estrogen treatment. This basal synthesis is tamoxifen-resistant and is detectable at very early stages of hepatic development, well before estrogen responsiveness is seen. Immunological cross-reactivity, electrophoretic behavior and the results of limited proteolysis mapping suggest that the apo VLDL-B synthesized under basal and estrogen-stimulated conditions is the same (or a very similar) protein. Inducibility of the VLDL apoproteins appears to parallel the appearance of the hepatic estrogen receptor system at days 10-12 while vitellogenin induction is delayed by several days. Cytosol receptor concentration undergoes a gradual increase up to the 19th day of development and thereafter declines. The properties of the 19-day receptor are very similar to those of cytosol receptor in hatched chickens, but the fall in concentration does not appear to be proportionately related to inducibility of estrogenic responses, as measured by the relative rates of synthesis in vitro.

Functional differentiation of the chick endocrine pancreas. II. The alpha cells and glucagon

A radioimmunoassay for glucagon, together with electron microscopic observations of early embryonic alpha cells were utilized to examine developmental aspects of glucagon accumulation and release in the chick embryo. Immunoreactive glucagon was detected in both the pancreas and blood plasma from the fifth embryonic day onwards. In addition, emiocytotic events were observed in alpha cells as early as the fifth embryonic day. The early appearance of glucagon and its subsequent developmental profile correlate well with major events in carbohydrate metabolism occurring in the embryonic chick, and are discussed in relation to a functionally responding system, the developing liver. The present data show that glucagon is secreted at earlier embryonic stages than hitherto demonstrated, and suggest a developmental role for glucagon in hepatic glycogen metabolism.

Proliferation of endoplasmic reticulum with its enzyme, UDP-glucuronyltransferase, in chick embryo liver during culture. Effects of phenobarbital

UDP-Glucuronyltransferase (GT) activity increases in chick embryo liver during culture from zero to a steady-state level at or above adult values. The GT activity (o-aminophenol as acceptor) is located entirely in the membranes of the endoplasmic reticulum (ER) and the question arises whether ER increases along with GT. Earlier work showed that the synthesis and degradation rates of GT can be varied in culture over wide ranges by choosing embryo livers of different ages and both phenobarbital. In the present study we measured the GT activities and the concentrations of ER (using stereologic methods) in 5- and 11-day embryo liver during culture with and without phenobarbital. We found that GT and ER always increased in a constant ratio of 2.2 X 10(-9) U of GR activity per square micrometer of membrane, suggesting that the synthesis and degradation of GT are coupled to the synthesis and degradation of ER. A general structure for ER is proposed to explain this finding.

Radioimmunological evidence for early functional activity in chick embryonic alpha cells

A radioimmunoassay for glucagon was utilized to investigate early developmental aspects of glucagon synthesis and release in the chick embryo. Immunoreactive glucagon was detected in both the pancreas and blood plasma from the fifth embryonic day onwards. The present data show that the chick embryonic alpha cell has the potential for secretory activity very early in development, and suggest a developmental role for glucagon in hepatic glycogen metabolism.