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Serial blood samples were collected from the adult American bullfrog (Rana catesbeiana) via a non-occlusive cannula chronically placed in the systemic subdivision (aortic) of the right truncus arteriosus. Plasma glucose, alanine, lactate, and 0-hydroxybutyrate levels were estimated by standard enzymatic procedures. The metabolites remained relatively stable in the control animals during the $day experiments. A single infusion of mammalian insulin (5, 15, or 45 ITJkg body weight) via the cannula depressed plasma glucose and alanine to near or below detectable levels that required a minimum of 3 days to return to approximately the time-zero levels. Plasma lactate also fell severely after the infusion, but subsequently displayed precipitous surges followed by sharp declines on days 1 and 3, and also in some animals on day 5. In contrast, plasma P-hydroxybutyrate levels were not significantly altered by insulin. Despite the severe depressions of plasma glucose, alanine, and initially lactate, no symptoms were observed in the bullfrogs infused with 5 or 15 IU of insulin. The carnivorous adult bullfrog consumes abundant protein and lipid, but little carbohydrate, and is adapted to periods of food scarcity. The results are consistent with the hypothesis that the bullfrog may rely on non-esterified fatty acids and ketone bodies as primary energy sources.
Serial blood samples were collected from the adult American bullfrog (Rana catesbeiana) via a non-occlusive cannula chronically placed in the systemic subdivision (aortic) of the right truncus arteriosus. Plasma glucose, alanine, lactate, and 0-hydroxybutyrate levels were estimated by standard enzymatic procedures. The metabolites remained relatively stable in the control animals during the $day experiments. A single infusion of mammalian insulin (5, 15, or 45 ITJkg body weight) via the cannula depressed plasma glucose and alanine to near or below detectable levels that required a minimum of 3 days to return to approximately the time-zero levels. Plasma lactate also fell severely after the infusion, but subsequently displayed precipitous surges followed by sharp declines on days 1 and 3, and also in some animals on day 5. In contrast, plasma P-hydroxybutyrate levels were not significantly altered by insulin. Despite the severe depressions of plasma glucose, alanine, and initially lactate, no symptoms were observed in the bullfrogs infused with 5 or 15 IU of insulin. The carnivorous adult bullfrog consumes abundant protein and lipid, but little carbohydrate, and is adapted to periods of food scarcity. The results are consistent with the hypothesis that the bullfrog may rely on non-esterified fatty acids and ketone bodies as primary energy sources.
The effects of several hormones on intestinal brush border membrane enzymatic activities have been investigated in intestinal explants taken from the amphibian midwife toad at different developmental stages. Explants were treated for at least 2 days with thyroxine (0.1 microgram/ml of culture medium) or for 2 days with cortisol (25 micrograms/ml) or insulin (6 mU/ml). The hydrolases examined were maltase, trehalase, glucoamylase, and alkaline phosphatase. In the explants from tadpoles in prometamorphosis, thyroxine had no effect on hydrolase activities; cortisol increased the activity of only glucoamylase, and insulin increased activity of maltase, glucoamylase, and alkaline phosphatase. When the explants were taken from tadpoles at the beginning of climax, cortisol and insulin generally stimulated the enzyme activities studied. When taken from tadpoles at the end of climax, at the moment when the embryonic cells under the degenerating epithelium divide, cortisol and insulin had little effect on these activities. When the animals terminate their metamorphosis, the intestinal epithelium of the explants is totally newly formed (secondary epithelium). At this time, cortisol stimulated the activities of maltase, glucoamylase, and alkaline phosphatase, while insulin decreased the activities of maltase and glucoamylase.
The hormonal control of ontogeny in fish and amphibians is reviewed. Neuroendocrine regulation and actions of metabolic and osmoregulatory hormones (thyroid, interrenal, pituitary, pancreas, and gut) during amphibian and fish metamorphosis and the parr-smolt transformation of juvenile salmon are considered. The developmental significance of hormones in egg yolk is discussed. It is concluded that the transitions between life-history stages provide many unique opportunities for studying basic endocrine phenomena.The study of hormones in ontogeny is particularly interesting and challenging because the endocrinology of the animals under investigation is continually changing through time, e.g., the embryo progresses to larva, juvenile, and adult. The transitions between life-history stages provide many unique opportunities for studying basic endocrine phenomena. For example, during development a tissue can gain or lose status as an endocrine target, and such events can be exploited to investigate mechanisms and control of cellular responses to hormones. The endocrine system not only influences and directs development, but also is itself a subject of a developmental program. Complex neuroendocrine systems evolve from simpler ones, and this can also present valuable opportunities for research. Studies in developmental endocrinology can focus on the appearance of hormones in endocrine tissue, the appearance and disappearance of hormone receptors in endocrine targets, changes in the functions of hormones during development, the ontogeny of hormone feedback mechanisms, and other regulatory processes. In contrast, endocrine studies of adult animals are usually conducted with the assumption that the basic function and control of the endocrine glands and their relationships with the target tissues are unchanging.As alternates to mammalian models, there are numerous examples in fish and amphibian ontogeny that are appealing to the endocrinologist. The best known and most utilized of these are metamorphoses. Fish and amphibian metamorphoses include many dramatic and quantifiable developmental changes that are under hormone control. The metamorphosis of the tadpole into the adult frog, and its control by thyroid hormones, have been a long-standing subject of investigation. It was perhaps the first "model" used to study hormonal control of ontogeny (Gudernatsch, '12). Generations of developmental endocrinologists have been trained with this model and its investigation continues to yield important insights into the actions, interactions, and mechanisms of action of hormones in development. Several parallels to amphibian metamorphosis and its hormonal control occur in fish, including flounder metamorphosis and the parr-smolt transformation of migratory salmonids. The more recent investigations of fish and amphibians emphasize the multihormonal nature of developmental control mechanisms.With respect to the earliest stages of development, fish and amphibians have been less well studied. Thyroid hormones have long been known t...
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