That calcitonin (CT) at supraphysiological doses is hypocalcemic led to the mistaken conclusion that it was important for calcium homeostasis and this idea has persisted to this day. Despite these findings, there is no readily apparent pathology due to CT excess or deficiency and there is no evidence that circulating CT is of substantial benefit to any mammal. Mammalian CT at physiological doses is not essential and very likely the CT gene has survived because of the gene's alternate mRNA pathway to produce calcitonin-gene-related peptide found in neural tissues. CT is not involved in calcium homeostasis or any other important physiological function, except, possibly, as an adjunct to protection of the skeleton under conditions of calcium stress, and appears to be in the process of becoming vestigial. CT produced in other tissues has paracrine actions that modulate functions such as proton transport, acid-base balance, prolactin secretion, and gastrointestinal motility. C-cells in mammals evolved from the ultimobranchial body that secretes CT in all lower vertebrates. It is highly probable that changes in amino acid sequence during evolution are responsible for the loss of activity, as fish CT is about 40 times as potent as human CT. CT may have been very important to survival in seawater fish, but the presence of the parathyroid gland and other evolutionary changes occurring in tetrapods suggest that the function of CT is no longer important.
The present methods for determining lipide-C14 of tissues, in experiments in which slices are incubated with a C14-labeled precursor, are time-consuming, and suffer from tedious manipulations, such as prolonged extraction and hydrolysis and repeated transferring of extracts from one vessel to another. These disadvantages have been completely eliminated in the simplified procedure described here. The entire analysis can be completed in less than 2 hours.Procedure. The incubation flask is a 50-ml Erlenmeyer flask with a center well 10 mm in diameter and 2 0 mm high fused into the bottom. A self-sealing rubber cap is used as stopper. The general details of the incubation procedure have been described elsewhere ( 1 ) .At the end of the incubation period, 0.25 ml of 30% KOH is introduced into the center well for absorption of c102 and, immediately thereafter, 0.25 ml of 5 N H2S04 are added to the medium for inactivation of the tissue. Both alkali and acid are introduced by means of a syringe with a long hypodermic needle that is inserted through the rubber cap. Sufficient time (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) minutes at room temperature) is allowed for the absorption of C& by the alkali, and the rubber cap is then removed. The contents of the center well axe siphoned directly into a volumetric flask. The incuba-~ -~ ~ ~ ~~ *This work was supported by a contraot from t Present address: Research Specialties Co., 1148 the U. S. Atomic Energy Commission. Walnut St., Berkeley.tion medium is carefully filtered through Whatman No. 1 filter paper, so that the tissue slices are retained in the main compartment of the flask. The slices are thoroughly washed with several portions of distilled water, each of which is decanted onto the .same filter paper. To avoid disintegration of the slices, the above procedure should be carried out no later than one hour after the reaction is stopped. The medium and washings are discarded unless a component of this fraction, such as glucose, ketone bodies, or the like, is to be analyzed. The filter paper is then washed with 5-10 ml of an alcohol-ether (3: 1) mixture, and the washings are returned to the incubation flask. Two ml of 1 M sodium ethylate are then added to the tissue slices in the flask which is covered with a bubble TABLE I. Test Df Extraction Procedure.To 500 mg +-5 mg of liver slices w m added one of the labeled compounds, and immediately thereafter the mixture was hydrolyzed. Extraction of the acidified hydrolysate was carried out as described in the text. Aliqeolts of the chloroform phase were directly mounted on aluminum discs and oounted in the usual manner.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.