Growth rates of Chinese and American alligators.

Growth rates in two closely related species, Alligator mississippiensis (American alligator) and Alligator sinensis (Chinese alligator), were compared under identical conditions for at least 1 year after hatching. When hatched, Chinese alligators were approximately 2/3 the length and approximately 1/2 the weight of American alligator hatchlings. At the end of 1 year of growth in captivity in heated chambers, the Chinese alligators were approximately 1/2 as long and weighed approximately 1/10 as much as American alligator yearlings. When the animals were maintained at 31 degrees C, Chinese alligator food consumption and length gain rates dropped to near zero during autumn and winter and body weights decreased slightly, apparently in response to the change in day length. At constant temperature (31 degrees C), food consumption by American alligators remained high throughout the year. Length gain rates in American alligators decreased slowly as size increased, but were not affected by photoperiod. Daily weight gains in American alligators increased steadily throughout the year. In autumn, provision of artificial light for 18 h a day initially stimulated both length and weight gain in Chinese alligators, but did not affect growth in American alligators. Continuation of the artificial light regimen seemed to cause deleterious effects in the Chinese alligators after several months, however, so that animals exposed to the normal light cycle caught up to and then surpassed the extra-light group in size. Even after removal of the artificial light, it was several months before these extra-light animals reverted to a normal growth pattern. These findings may be of interest to those institutions engaged in captive growth programs intended to provide animals for reintroduction to the wild or to protected habitat.

The flow theory of enzyme kinetics: role of solid geometry in the control of reaction velocity in live animals.

1. When blood flows, membranes are bombarded with ions etc., whose entry creates an ATP demand proportional to flow rate. Also proportional to flow rate is ATP production from oxidation of substrates [S] from the same blood volume. 2. O2 is limiting and reaction velocity at rest (metabolic rate) is determined by flow rate, F, but not by [S]. 3. Since resting blood O2 A-V difference is about 5 vol%, 11 circulated produces about 0.25 kcal in mammals, birds or warm reptiles. 4. Where O2 is not limiting, as in most amino acid deaminations, V = K F[S] with K a constant unrelated to Km. 5. At equal blood vol/kg, solid geometry dictates that the average cross-sectional area of major vessels/kg will be an inverse function of body mass. The smaller the animal, the shorter the vessels, the "thicker" the vessels/kg body wt, and at any one blood pressure, the higher the flow/kg/hr. If a man's major vessels were equal in cross-section/kg to those of a shrew, it would take 224 l of blood to fill them. 6. Growth decreases flow/kg (and therefore metabolic rate), by decreasing vessel cross-section/kg without changing blood pressure or linear velocity of flow. 7. Surface area/g, body wt to some power, average vessel length/kg, circulation time and average major vessel cross-sectional area are all related mathematically.

Biological activity of alligator, avian, and mammalian insulin in juvenile alligators: plasma glucose and amino acids.

The biological activity of alligator, turkey, and bovine insulin on plasma glucose and plasma amino acids was tested in fasted juvenile alligators. Preliminary experiments showed that the stress associated with taking the initial blood sample resulted in a hyperglycemic response lasting more than 24 hr. Despite repeated bleedings no additional hyperglycemic events occurred, and blood glucose declined slowly over the next 7 days. Under these conditions the smallest dose of insulin eliciting a hypoglycemic response was 40 micrograms/kg body wt. A dose of 400 micrograms/kg body wt of either alligator or bovine insulin caused a pronounced hypoglycemia by 12 hr postinjection. Maximum decline in plasma glucose occurred at 24 to 36 hr with a slow return to control levels by 120 hr. There were no significant differences in the hypoglycemic responses to any of the three insulins tested. The decline in plasma amino acids was much more rapid than the decline in plasma glucose in response to insulin. Even at the 40 micrograms/kg body wt dose a significant difference from saline-injected control was seen at 2 hr postinjection. Maximum decline in plasma amino acids occurred at 8 to 12 hr with a return to baseline by 36 hr. These results show that the relatively conservative changes in the sequence of alligator insulin (three amino acid substitutions in the B-chain compared with that of chicken) have little effect on biological activity and that alligator insulin receptors do not appear to discriminate among the three insulins.

Protein nutrition in the alligator.

1. Fourteen different protein-containing diets were fed to small alligators. Their rates of digestion and their nutritional values were determined by following changes in free amino acids in the plasma. 2. Fish, chicken and nutria were digested rapidly and all their component essential amino acids disappeared quickly and at the same rate. When given in the dry, fat-free form the amino acids were released and assimilated about 50% faster than when fat was included. 3. None of the isolated proteins tested (casein, gelatin, edestin, gliadin, corn gluten and soy) proved nutritionally adequate and all but gelatin digested slowly and incompletely. 4. One diet compounded of salts, vitamins and mixed commercial animal products was tested. It showed promise but it was lacking in methionine and isoleucine. 5. It was concluded that dry, powdered, preparations from whole animals could prove a satisfactory, stable diet for alligator husbandry. 6. Prolonged force-feeding of an animal diet increased the percent of nitrogen excreted as NH3 over that excreted in urates.

Decreased oxygen consumption after catecholamine-induced glycolysis in the alligator.

Anaerobic glycolysis was stimulated by forcing alligators to work to exhaustion, or by injecting them with epinephrine or norepinephrine. In all three groups, plasma lactate increased to above 20 mM. In the work group, oxygen consumption increased three-fold. In the catecholamine experiments, oxygen consumption dropped almost to zero immediately and stayed at zero from 45 min to over 2 hr. Gradually oxygen consumption resumed, finally exceeding the control value, but only by 50%. It was concluded that catecholamine-induced glycolysis produced phosphate-bond energy greatly in excess of immediate need, and that this energy was stored until it was used by the tissue. No oxygen was used until the store was depleted.

Delayed protein digestion in the alligator following carbonic anhydrase inhibition.

Small alligators were injected with a carbonic anhydrase (CA) inhibitor (dichlorphenamide) and a day later they were fed large amounts of lean beef. The rate of protein digestion was determined and compared with that in controls fed the same amount. The controls began digestion at once, while in the CA-inhibited ones, digestion was blocked for over 10 hr. The inhibitor decreased gastric HCl production to one-third that in controls and delayed activation of pancreatic and intestinal proteases. After 15 hr, digestion began in the inhibited group and proceeded to completion. Once digestion began, further injections of the inhibitor could not block it. It seems that CA inhibition blocks digestion (for a time) by reducing HCl synthesis. NaHCO3 to neutralize the acid chyme in the intestine, was derived from that in the plasma.

Energy production per circulatory cycle: a constant in resting land vertebrates?

Correcting for differences in blood flow, resting alligators, caimans, lizards, turtles, rats and dogs deaminated amino acids at the same rate. Each produced about 21 calories/kg during one complete circulatory revolution, irrespective of body temperature, size or species. Uniform O2 and substrate A-V differences are responsible for the phenomenon.

Amino acid transport in the intestine of the caiman.

Seventeen amino acids were fed singly to small caimans and the rates of their disappearance from the gut lumen, and of their appearance in intestinal mucosa, whole intestine, whole stomach, and plasma were determined. The results were compared with those in which massive amounts of protein were fed. When single amino acids were fed, only traces of arginine, ornithine, lysine, aspartate and asparagine were absorbed intact. Glycine, alanine and serine were absorbed rapidly reaching mucosal concentrations as high as 40 mM. The others were not concentrated as highly and most were absorbed by the mucosa more slowly than the glycine group. Protein feeding did not result in high amino acid concentrations in the mucosa. Whether amino acids were ingested as protein or in the free state, glycine, alanine and glutamine increased in the mucosa, suggesting these three incorporate nitrogen released from the others. It appeared that several transport systems operate if amino acids are given singly, and that a different more efficient transport system operates during protein digestion.

Reaction velocities in vivo: standardization of kinetic "constants" by correction for blood flow.

1. The results of kinetic studies in vitro are difficult to apply to metabolic reactions in vivo. 2. In living vertebrates reaction rates are usually first-order and for a particular reaction the rate "constant", k, varies with the several thousand-fold variations in metabolic rate. 3. Therefore, in the kinetic equation (formula: see text) since K varies with metabolic rate, Vmax and/or Km will aslo vary. 4. However, reaction rates for a series of different substrates were similar in animals varying widely in metabolic rate if corrections were made for differences in blood flow. 5. The observation that metabolic rate (reaction rate) is directly dependent on blood flow (Coulson et al., 1977) allowed derivation of new kinetic constants which were valid in vivo. 6. Introduction of a flow term into the observed first-order equations yields an "affinity constant", K, or a "flow constant", KF, somewhat analogous to Km, which allows one to predict reaction rates in animals of different metabolic rates. 7. The defining equations are (formula: see text) where V = reaction velocity in mmol/hr/kg tissue, [S] = millimolar substrate concentration in the blood, k = In 2/tau (tau the half-life) and F = blood flow in 1/hr/kg tissue. 8. Thus, K = k/F = 1/KF. The KF's for the initial step in the degradation of 17 amino acids in rats, dogs, lizards, turtles and alligators were similar, demonstrating the similarity of enzyme affinities in different species.

Possible polypeptide synthesis following injection of balanced but incomplete amino acid mixes into lizards.

The rate of disappearance of carcass-free amino acids following and injection of a mixture of the composition of fish muscle was compared with the rate seen after giving the same mix minus three essential amino acids in one series of experiments, and minus five amino acids in another series. The experimental animal was a 3.5 g lizard (Anolis carolinensis) whose metabolic rate is about equal to man's. Lizards were injected with one of the mixes, at intervals some were killed and homogenized, and the free amino acids were assayed on protein-free filtrates of the entire carcass. Amino acids disappeared from complete and incomplete mixes at the same rate, a rate several-fold greater than that at which they could be catabolized. When three or five essential amino acids (as defined for the growing rat) were injected by themselves, they were removed only one-third as fast as when accompanied by a balanced mix of the rest of the protein components. I concluded that if the amino acids were in proper ratio and if they were sufficient in number, they were removed rapidly even though as many as five essential amino acids are missing. For want of a better explanation, some type of macromolecule synthesis from balanced incomplete mixes was postulated.

Increase in metabolic rate of the alligator fed proteins or amino acids.

Energy required for protein digestion, amino acid absorption and transport, and for protein synthesis in the alligator was estimated by determining oxygen consumption following feeding of single amino acids, various amino acid mixtures, fish, casein, gelatin, zein, and a gelatin hydrolysate. Results suggested a low energy requirement for protein digestion, for absorption of the released amino acids, and for amino acid transport, and a high energy requirement for protein synthesis. Little energy was needed for absorption and transport of neutral single amino acids but absorption of single ionic amino acids appeared to require energy. The alligator's metabolic rate is so low that processes requiring extra energy increased oxygen consumption as much as 300%. Peptide bond synthesis seems to have been responsible for the 3-fold increase in metabolic rate after feeding protein. Whether that phenomenon should be called "specific dynamic action" is problematical.