Responses of the three-toed sloth, Bradypus tridactylus, to some commonly used pharmacologic agents. I. Autonomic drugs

1. Sloths are very responsive to epinephrine and norepinephrine; i.v. injection of 1 microgram/kg elevates systolic pressure 80 and 90% respectively. 2. Doses as low as 0.01 microgram/kg of epinephrine as well as norepinephrine raise diastolic pressure. 3. Similarity of effects of these catecholamines can be explained on the basis of the low proportion of skeletal muscle (35 vs 45% in most mammals) and a small liver which reduces the proportion of beta 2 dilators to alpha constrictors responding to epinephrine. 4. Slowness of reflexes allows clear separation of early (0-20 sec), direct accelerating heart rate effect (up 15% with 1 microgram/kg of norepinephrine) and later (20-60 sec), reflex bradycardia (down 30% from control level). 5. Sloths are more sensitive to the vasodilating effects of isoproterenol or less sensitive to beta 1 cardiac stimulating effects than most laboratory mammals; doses as low as 0.1 microgram/kg cause a fall in mean arterial pressure not overcome by increased heart rate.     

Characterization of the blood volume and iron kinetics in the three-toed sloth,Bradypus tridactylus

• 1.1. Blood volume and iron kinetics were determined in three specimens of Bradypus tridactylus which were obtained in the coastal north-east regions of Brazil.
• 2.2. The average blood volume, circulating red cell volume and plasma volume were 54.9, 19.5 and 35.4 ml/kg body weight, respectively.
• 3.3. The average plasma iron disappearance half-time was 150.6min; the red cell radioiron uptake was 62% and the serum iron was 74.3 μg/100 ml.
• 4.4. From these figures the plasma iron turnover rate was calculated to be 165.6 μg/kg per day and the red cell iron turnover rate 102.7 μg/kg per day.

     

The primary structure of pale-throated three-toed sloth (Bradypus tridactylus, Xenarthra) hemoglobin

The hemoglobin of the Pale-Throated Three-Toed Sloth (Bradypus tridactylus, Xenarthra) was separated into two components (ratio 4:1) with identical amino-acid analyses for the alpha- and beta-chains. The primary structures of both chains from the major component are given. They could be isolated by chromatography on carboxymethyl cellulose CM-52. The sequences have been determined by automatic Edman degradation of the native chains and their tryptic peptides. The comparison with human hemoglobin showed 27 substitutions in the alpha-chains and 33 in the beta-chains. In the alpha-chains one amino-acid exchange involves an alpha 1/beta 1-contact. In the beta-chains two heme- and four alpha 1/beta 1-contacts are substituted. The hemoglobin of the Sloth is compared to that of the Nine-Banded Armadillo (Dasypus novemcinctus), another representative of the order Xenerthra.     

Collection and evaluation of semen from the three-toed sloth (Bradypus tridactylus)

Sloths (Bradypus sp.) are extremely sensitive animals that suffer with the destruction and fragmentation of forests. They present a low population growth rate and need to be further studied for the preservation of the specie. Thus, the aim of this study was to establish an efficient semen collection protocol as well as characterize sperm concentration, motility and morphology in order to contribute with information about the reproductive traits of this specie, which has never been described in the literature before. For that, nine Bradypus tridactylus males were captured during the wet season and six during the dry season, in Manaus (AM), located in the north region of Brazil, semen was collected by electroejaculation with shocks given in sequences of progressive intensities (minimum 20 mA and maximum 60 mA). All animals ejaculated small volumes of semen and in some of them, the volume ejaculated was not enough for a complete spermiogram. Physical characteristics observed on the collections of the wet season were different from those seen in the specimen collected in the dry season. Motility an vigor was very low and did not show forward progression, only oscillatory movement. After Spermac stain, spermatozoa presented a wide variety of defects; however, the differences in morphology were not significant between seasons. The morphology assessed by scanning electron microscopy shows that the head in both groups could be elongated, short or could have a base narrower than the apex and the midpiece narrowed abruptly, forming a nip in its transition to the tail. Although further studies are necessary to verify our preliminary findings concerning seasonal variation in sperm quality, these results demonstrate that semen can be safely collected from sloths by electroejaculation and provide the first reports of semen characteristics in this species.     

The effects of posture on blood pressure and heart rate in the three-toed sloth, Bradypus tridactylus

1. In unanesthetized, minimally restrained three-toed sloths, Bradypus tridactylus, the mean arterial pressure was 125/85 mmHg and the heart rate was 83.6 beats/min. There was no significant difference between these parameters whether the animal was erect or supine in the experimental chair. 2. Animals without any restraint had a mean blood pressure of 133/87 mmHg and a heart rate of 78.1 beats/min. There was no significant difference between these parameters whether the animal was seated or suspended from a horizontal bar and there was no significant difference between the minimally restrained and the unrestrained animals. 3. Tilting from the erect to the supine position produced large increases in blood pressure parameters, 37% in systolic and 21% in diastolic, reaching the maximum effect in a mean time of 38 sec. Tilting from the supine to the erect position caused even greater increases in pressure, 43% and 38% respectively, and reaching the maximum also in a mean time of 38 sec. 4. Tilting initially increased the heart rate, in going from erect to supine by 21% in 16 sec and from supine to erect by 23% in 20 sec. 5. In going from erect to supine there was a reflex bradycardia later, 15% below control level with a maximum at 40 sec, and to a lesser degree in going from supine to erect, 9% with maximum at 50 sec.     

Ultrastructural study of crystalloids in Sertoli cells of the three-toed sloth (Bradypus tridactylus)

Summary Crystalloids were found in Sertoli cells of the testis of the three-toed sloth by examination at the lightand electron-microscopic levels. Needle-, or spindle-shaped crystalloids, varying in length, were located in the basal part of the Sertoli cells. They consisted of bundles of filaments each measuring ~ 11 nm in diameter. Several filaments were packed hexagonally to form a bundle. The center-to-center distance between individual filaments of a bundle was ~ 17 nm. Periodical lateral projections emanated from the filaments. Cross sections of crystalloids showed that the projections radiated from each filament in three directions, forming an equilateral triangle with a side length of ~ 15 nm. Scattered polyribosomes were found between and around the bundles.     

Blood pressure regulation in the three-toed sloth, Bradypus variegatus

The aim of this study was to elucidate the role of the baroreflex in blood pressure control in sloths, Bradypus variegatus, since these animals show labile levels in this parameter. Unanesthetized cannulated sloths were positioned in an experimental chair and the arterial catheter was coupled to a strain gauge pressure transducer. Blood pressure was monitored before, during and after the administration of phenylephrine (0.0625 to 4 microg/kg) and sodium nitroprusside (0.0625 to 2 microg/kg), bringing about changes in mean blood pressure from +/-30 mmHg in relation to control values. The relation between heart rate changes due to blood pressure variation was estimated by linear regression analysis. The slope was considered the reflex baroreceptor gain. The results (means+/-SD) showed that the reflex baroreceptor gain was -0.3+/-0.1 bpm/mmHg (r=0.88) to phenylephrine and -0.5+/-0.1 bpm/mmHg (r=0.92) to sodium nitroprusside, denoting a reduced reflex baroreceptor gain when compared with other mammals, suggesting that in sloths the baroreceptors are minimally involved in the buffering reflex response to these drugs. These findings suggest that the labile blood pressure could be influenced or be a result of this lowering in the reflex baroreceptor gain.     

The passage of digesta, particle size, and in vitro fermentation rate in the three-toed sloth Bradypus tridactylus (Edentata: Bradypodidae)

The digestive physiology of six three-toed sloths ( Bradypus tridactylus ) fed exclusively on Cecropia palmata foliage was studied. The mass of digesta in the gut was between 17 and 37% of body mass. This was between 133 and 282% of that expected in an animal of this size, based on published allometric equations. The concentration of total short chain fatty acids in the stomach was similar to that in the fermentative regions of other foregut fermenting herbivores but the rate of fermentation measured in vitro was very slow (6–12 mmol.l^-1.h^-1) and substantially lower than that observed using similar techniques in other small foregut fermenters.
The overall (dose to excretion) mean retention time of particulate and solute digesta markers was about 150 h. Most of this (73%) occurred in the stomach but a substantial proportion (17%) could be attributed to the storage of faeces in the rectum.
The slow rate of passage of digesta through the gut together with the slow rate of fermentation in the stomach is not typical of small foregut fermenting herbivores. However, such a pattern is feasible in Bradypus tridactylus because of the large volume of digesta retained in the gut and the very low metabolic rate of these mammals.     

Some morphological and histochemical studies on the intestinal tract of the Brazilian sloth (Bradypus tridactylus)

The intestinal of the 3-toed sloth, Bradypus tridactylus, was studied macroscopically, with light microscope and with histochemical methods for mucosubstances. Macroscopically, the inner surface of the duodenum shows longitudinal and circular folds. There is no caecum, nor appendix. The large intestine consists of a short colon and a large rectal pouch, which has a thick wall. The mucosa of the small intestine has long leaf-shaped villi covered with columnar epithelium having a well developed striated border, and the goblet cells are scattered among the columnar cells. An association between neutral and acidic mucosubstances was detected in the goblet cells. The duodenal (Brunner's) glands are confined exclusively in the lamina propria of the duodenum. No Paneth cells were observed in the crypt lining. Argyrophil and argentaffin cells were found in the entire length of the intestine. The large intestine does not possess villi, but many goblet cells were observed in its mucosa.     

Myocardial ultrastructure and electrocardiograms of the sloth (Bradypus tridactylus) under normal and experimental conditions

Adult sloths (Bradypus tridactylus) were studied by electrocardiography and by light and electron microscopy under normal conditions and under experimental conditions as provided for by injection of 2,4-dinitrophenol (DNP) and ether anesthesia. ECG's of the animals indicated heart rates of 45–71/min, which can be considered as the normal heart rate of the sloth under laboratory conditions. Under normal conditions, the contracted ventricular myocardium of the sloth exhibited (a) a wrinkled sarcolemma, (b) the usual pattern of myofibrils and of sarcoplasmic reticulum, (c) small mitochondria with spiked and branched, often anastomosed cristae, including a few small intramitochondrial dark bodies, (d) an amount of sacrcosomes smaller than the amount of myofibrils, (e) many glycogen granules, isolated, in the form of a chain, or as clusters, in subsarcolemmal, intermyofilamentous and perimitochondrial positions, (f) few multivesicular bodies and (g) large flat sections of the transverse tubular system. Injection of DNP (1 mg/kg) caused tachycardia. With ether anesthesia, the ECG showed monophasic action potential of myocardial injury and prolongation of inter or intraventricular condition. Electrically, the sloth's heart responded to hypoxia as do other mammalian hearts. The administration of DNP produced (a) derangement and reduction in number and length of the mitochondrial cristae, (b) disappearance of spikes, connections between the cristae and, consequently, the honeycombed arrangement, (c) increased matricial space in the center of mitochondria which was often filled with a grayish substance, (d) disappearance of small dark intramitochondrial granules, (e) depletion of glycogen particles and (f) few dilations in the sarcoplasmic reticulum.     

Stomach lysozymes of the three-toed sloth (Bradypus variegatus), an arboreal folivore from the Neotropics

Lysozymes are antimicrobial defences that act as digestive enzymes when expressed in the stomach of herbivores with pre-gastric fermentation. We studied this enzyme in the complex stomach of the three-toed sloth (Bradypus variegatus), a folivore with pre-gastric fermentation. Lysozymes were identified by SDS-PAGE and immunoblotting in all portions: diverticulum, pouch, glandular and muscular prepyloric area with 14.3 kDa of molecular mass. Purified lysozymes from all areas but the diverticulum were characterized by MALDI-TOF, optimal pH, optimal ionic strength, and specific activity. The differences observed suggested at least three isoforms. The optimal pHs were similar to the pH of the stomach portion where the enzymes were isolated. The lysozyme from the pouch (fermentation chamber) exhibited higher specific activity and concentration than the others. The specific activity of the enzyme from the acid muscular prepyloric portion was comparable to that reported in the cow abomasums; however, its concentration was lower than that observed in cow. This distinctive pattern of secretion/specific activity and overall low concentration suggests different roles for the lysozymes in this herbivore compared to Artiodactyla. We postulate that sloth stomach lysozymes may still be antimicrobial defences by protecting the microbial flora of the fermentation chamber against foreign bacteria.     

Histological and histochemical study on the ependyma of Bradypus tridactylus.

Histological and histochemical aspects of the whole encephalic ventricular system of eight specimens of Bradypus tridactylus were studied. After anesthesia and perfusion, the encephalons were obtained by craniotomy. Transverse serial sections of the encephalon, stained according to Azan (Heidenhain's method) or Kluver-Barrera for nerve cells and myelinated nerve fibers; silver impregnation was carried out according to Cajal-De Castro's or Palmgren's methods. The following histochemical reactions were used: PAS (McManus), metachromasia, acid phosphatase (Gomori), Brachet's and Gomori's trichromic reaction (modified by Bargmann for neurosecretion). Histologically, different characteristics of the ependymal cells in different areas were observed, which would be related to functional peculiarities of each area of the encephalic ventricles. The ependymal cells showed discrete apical basophilia due to the presence of RNA which disappears after treatment with crystalline ribonuclease. The PAS reaction indicated the presence of a small quantity of PAS-positive substances in the apical zone of the ependymal cells and the subependymal tissue. These substances disappeared after the salivary amylase test, indicating the presence of glycogen. The acid phosphatase reaction was negative.     

Ultrastructural study on topographical variations of the ependyma in Bradypus tridactylus.

An electron-microscopic study of ependymal cells in 24 different areas of the encephalic ventricular system of Bradypus tridactylus was made, with a view to making a comparative analysis, of a topographical kind, of various cell components: cilia, microvilli, plasma membrane, cytoplasmic protrusions, types of cellular junctions, ribosomes, Golgi apparatus, endoplasmic reticulum, microfilaments, microtubules, mitochondria, granules and dense bodies. There were differences in the distribution of all these cytologic elements, according to the topography, being a complement to a similar work done by the same authors with light-microscopy. By means of a morphofunctional analysis they draw the conclusion that even if one can admit the passage of substances by an intracellular route, on the other hand few facts support the idea the intracellular absorption or secretion could be considered as important phenomena in a great number of the ependymal areas studied.     

Mutagenicity testing of some commonly used dyes.

Seventeen commonly used dyes and 16 of their metabolites or derivatives were tested in the Salmonella-mammalian microsome mutagenicity test. Mutagens active with and without added Aroclor-induced rat liver microsome preparations (S9) were 3-aminopyrene, lithol red, methylene blue (USP), methyl yellow, neutral red, and phenol red. Those mutagenic only with S9 activation were 4-aminopyrazolone, 2,4-dimethylaniline, N,N-dimethyl-p-phenylenediamine, methyl red, and 4-phenyl-azo-1-naphthylamine. Orange II was mutagenic only without added S9. Nonmutagenic azo dyes were allura red, amaranth, ponceau R, ponceau SX, sunset yellow, and tartrazine. Miscellaneous dyes not mutagenic were methyl green, methyl violet 2B, and nigrosin. Metabolites of the azo dyes that were not mutagenic were 1-amino-2-naphthol hydrochloride, aniline, anthranilic acid, cresidine salt, pyrazolone T,R-amino salt (1-amino-2-naphthol-3,6-disulfonic disodium salt), R-salt, Schaeffer's salt (2-naphthol-6-sulfonic acid, sodium salt), sodium naphthionate, sulfanilamide, and sulfanilic acid. 4-Amino-1-naphthalenesulfonic acid sodium salt was also not mutagenic. Fusobacterium sp. 2 could reductively cleave methyl yellow to N,N-dimethyl-p-phenylenediamine which was then activated to a mutagen.     

The autonomic component in blood pressure and heart rate effects of tilting in the three-toed sloth

1. This study attempts to elucidate unique heart and blood pressure responses seen in sloths in response to tilting by blocking autonomics with atropine, propranolol, or a combination of these. 2. Atropine produces less heart rate increase in sloths than in other mammals but blocks reflex bradycardia as expected. 3. Propranolol reduces heart rate to about the same degree as in man and completely blocks all cardiac responses to tilting, both direct and reflex. 4. Atropine slightly diminishes blood pressure responses to tilting whereas propranolol tends to augment the already marked increases.     

Mu receptor binding of some commonly used opioids and their metabolites.

The binding affinity to the mu receptor of some opioids chemically related to morphine and some of their metabolites was examined in rat brain homogenates with 3H-DAMGO. The chemical group at position 6 of the molecule had little effect on binding (e.g. morphine-6-glucuronide Ki = 0.6 nM; morphine = 1.2 nM). Decreasing the length of the alkyl group at position 3 decreased the Ki values (morphine less than codeine less than ethylmorphine less than pholcodine). Analgesics with high clinical potency containing a methoxyl group at position 3 (e.g. hydrocodone, Ki = 19.8 nM) had relatively weak receptor binding, whilst their O-demethylated metabolites (e.g. hydromorphone, Ki = 0.6 nM) had much stronger binding. Many opioids may exert their pharmacological actions predominantly through metabolites.