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.
Methods for the study of axons involve whole nerve preparations, teased preparations of axons that are excised from their proximal and distal connections, and tissue culture models. As a complement to these, it would be advantageous to study separated, isolated axons in vivo, still in continuity with the end organ distally and the spinal cord central nervous system neuron proximally. This would allow the study of axon function, normal or pathological, in a close relationship to its biological environment. To achieve this, we have passed the surgically isolated sciatic nerve of a rat through a chamber specially designed for enzymatic dissociation. This was based on principles derived from a prior in vitro method for dissociating nerve into axons. The chamber has controlled temperature and flow and is on an inverted microscope stage, allowing observation of the process. We perfused the chamber with a calcium-free solution followed by a series of enzymes: collagenase, trypsin, and hyaluronidase. This dissociates that part of the extracellular matrix external to the Schwann cells, leaving free, myelinated axons with their Schwann cells. In this acute preparation, the axons continue to conduct action potentials for at least 8 hours. Furthermore, an in vitro study of the axon after the in vivo dissociation demonstrated that axonal transport was maintained in over 90% of the axons, directly visualized on an AVEC-DIC type of microscope system. Properties of axonal transport or active spike propagation can thus be studied individually in an in vivo axon preparation.(ABSTRACT TRUNCATED AT 250 WORDS)
The qualitative and quantitative temporal effects of a 2-min handling stress, both with and without pretreatment with tubocurarine, and the intraaortic infusion of epinephrine, both with and without pretreatment with a combination of phentolamine and propranolol, on plasma lactate, glucose, and hematocrit levels were compared in the American alligator (Alligator mississippiensis). The drugs and epinephrine were administered, and serial blood samples were collected, via a nonocclusive cannula chronically placed in the left aortic arch. Plasma lactate and glucose were measured by standard enzymatic procedures. Plasma lactate rose approximately 92% by the end of the 2-min handling period and to maxima of 1,091 -i-476% greater than the timezero levels by 15 min. The hematocrit also increased rapidly to maxima of 11 * 3.1% greater than the time-zero levels by 5 min. Plasma glucose levels did not change significantly. The handlinginduced lactate and hematocrit increases were prevented by pretreatment with tubocurarine that blocks acetylcholine receptors at the skeletal muscle neuroeffector junction. Epinephrine infusion resulted in delayed, comparatively slow increases in plasma lactate, glucose, and the hematocrit.The peak levels for lactate were 334 * 92% by 6 hr, €or glucose were 135 ? 8% by 90 min, and for hematocrit were 10.9 ? 5.6% by 90 min. Pretreatment with the combination of phentolamine and propranolol that blocks mammalian "alpha" and "beta" adrenergic receptors, respectively, prevented the epinephrine-induced increases in glucose and hematocrit levels, but not the plasma lactate increases. The results support the conclusion that the immediate responses of the alligator to a sudden threat are mediated by the synergistic effects of the somatic nervous system neurotransmitter acetylcholine, released at the skeletal muscle neuroeffector junction, and the sympathetic nervous system neurotransmitter (presumably norepinephrine), released at the neuroeffector junctions of the relevant visceral tissues and organs. In contrast, the participation of adrenal chromaffin tissue epinephrine secretion in the immediate responses is precluded by the long circulation and response times.
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.