The existence of an early effect of testosterone, prior to the effects dependent upon interaction between the hormone-citosolic receptor complex and the cellular nucleus, has been explored in the present paper, in 3-day old chickens. Liver glycogen phosphorylase activity is increased before protein synthesis activation, and furthermore this effect is not blocked by antibiotics (actinomicin D and cycloheximide) inhibitor of protein synthesis. When liver phosphorylase is activated, cAMP levels are not enhanced, as would be expected, but deeply depleted. The hypothesis of a phosphorylase-kinase activation due to an increase in the intracellular Ca++ concentration is considered.
Cortisol produces a glycogenogenic effect 5 hours after intraperitoneal injection to 3 day old chicks. This effect is dependent on protein synthesis because it can be blocked by antibiotics such as actinomycin D. On the other hand, there is a previous glycogenolytic effect 45 minutes after cortisol administration which is independent of protein synthesis. Thyroid hormones produce a similar early effect as has been previously shown. However, the observed glycogenolysis after cortisol injection is not correlated with an enhancement in the liver cAMP levels.
The effects of a single dose of 3,3'-5-triiodothyronine (T3) on the uptake of (methyl-14C) choline into liver phosphatidylcholine (PC) and lysophosphatidylcholine (LPC) were studied in chicks as a function of time up to 6 h after injection of the radioactive precursor. In all cases, chicks received the T3 dose intraperitoneally 5 h before injection of the labelled compound. T3 enhances the incorporation of 14C-choline into liver PC, showing a biphasic response; the main uptake occurs between 2 and 3 h after administering the precursor. A smaller but significant hormone-dependent increase in incorporation of the labelled compound is observed in the case of LPC. Lipid P associated to PC and LPC remains constant throughout the experiment, and does not vary with hormone treatment. It is suggested that T3-injection increases, either directly or through other metabolic processes, PC and LPC turnover in chick liver cells.
Activities of hepatic glycogen synthase a and glycogen phosphorylase a have been studied in mouse liver at different times after an acute intraperitoneal administration of hydrocortisone. It has been observed an increase of glycogen synthase a activity and a decrease of glycogen phosphorylase a between 2 and 3.5 hours after cortisol injection. An early effect, previous to the synthase activation has been discovered. Cortisol caused an increase of glycogen phosphorylase a activity in mice 45 min after injection. This early effect of cortisol is independent of protein synthesis and it does not imply an increase in cAMP levels.
Glycogen phosphorylase activity is increased before protein synthesis activation by progesterone. This effect is not blocked by antibiotics (actinomycin D and cycloheximide) that are known to inhibit mRNA or protein synthesis. At times similar to those of phosphorylase activation, cAMP are not enhanced, as would be expected considering the classical glycogenolytic cascade, but depleted with respect to control values. A little earlier, cGMP levels are significantly increased.
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