The vertebral column of diabetic sand rats (Psammomys obesus)

Intervertebral discs and vertebral spongiosa of diabetic and nondiabetic sand rats were investigated histologically and morphometrically. In diabetic animals, degeneration of the intervertebral discs was accelerated. Morphometrically, there was a consistent trend in the diabetics toward an attenuated bone turnover, which was, however, statistically significant only in regard to the length of the trabecular surface covered by osteoblasts. In the vertebral column of the sand rat, the tendency to osteoporosis - age-linked or diabetes-related - is reduced apparently due to the influence of local forces which promote osteogenesis.     

Diabetes mellitus in sand rats (Psammomys obesus): microangiopathy during development of the diabetic syndrome.

The purpose of the study was to investigate the development of microangiopathic complications in North African sand rats with diabetes induced by a long-term standard laboratory diet. Hyperinsulinaemic rats, whether non-diabetic obese or diabetic, developed capillary basement membrane (CBM) thickening in the skin; in insulin-dependent animals, this change was diffuse. Many PAS positive areas were demonstrated in skeletal muscle and myocardium, together with evidence of microangiopathy; the primary myocardial lesion in insulin-dependent disease was ischaemic fibrosis. The kidney was also affected with marked basement membrane thickening in Bowman's capsule and glomerular capillaries; glomerulosclerosis and tubular changes were found in insulin-dependent disease. No evidence of diabetic retinopathy was found, and there was a high incidence of cataract.     

The innervation of the thyroid gland of the sand rat (Psammomys obesus)

It has been reported on the occurence of vegetative neurons in the stroma of the sand rat (Psammomys obesus) thyroid gland. The cells show all the typical signs of autonomic nerve cells. In contrast to neurons appearing in the pancreas of the sand rat, the neurons in the thyroid gland occur in most cases as singular neurons. The importance of the sympathetic innervation for the thyroid function has been discussed and the close relationship between thyroid hormone secretion and biogenic amines localized in the thyroid mast cells has been described as well.     

Occurrence of biogenic amines in the pancreatic islets of sand rats (Psammomys obesus).

The islets of Langerhans of sand rats (Psammomys obesus) have been investigated ultrahistochemically in order to demonstrate biogenic amines. It could be found that amine-containing vesicles with a diameter of 600-700 nm from the type of catecholamine-granules exist in A-cells as well as in B-cells. It can be stated that the sand rat belongs to the species containing amines in A- and B-cells. The importance of the amines for the regulation of the hormone secretion of the islets of Langerhans is discussed and the connections to diabetes mellitus are referred too.     

Elimination of oxalate by fat sand rats (Psammomys obesus): wild and laboratory-bred animals compared

Wild fat sand rats (Psammomys obesus) can feed exclusively on plants containing much oxalate, but little calcium; oxalate intake may exceed 300 mg/d, while calcium intake is approximately 30 mg/day. By contrast, for generations, laboratory bred P. obesus have been fed a low-oxalate (<100 mg/day), high-calcium (approximately 150 mg/day) rodent chow. We compared oxalate intake and excretion between wild and laboratory-bred animals, both fed the natural high-oxalate diet, to determine whether these different dietary histories are reflected in the animal's ability to eliminate dietary oxalate. Since both wild and laboratory-bred P. obesus harbor intestinal oxalate-degrading bacteria, we predicted that their oxalate intake and excretion would be similar. Indeed, we found no significant differences in oxalate intake or excretion between the groups fed either saltbush or alfalfa (p>0.05). However, due to the differences in dietary calcium intake between the two diets, in both groups only part (23-25%) of the ingested oxalate was excreted when the animals were fed the oxalate-rich saltbush, yet most (87-90%) was excreted when feeding on calcium-rich alfalfa. Thus, even after generations of feeding on a commercial low-oxalate diet, fat sand rats maintain intestinal oxalate-degrading bacteria that appear to increase in number and activity when presented with their natural diet.     

Studies on the (pro) insulin biosynthesis of islets of Langerhans of sand rats (Psammomys obesus).

By feeding a regular laboratory chow, sand rats (Psammomys obesus) from our breeding colony gained different body weights, though they received approximately the same quantity of calories. Sand rats, reaching a body weight above 160 g (group B) showed significantly increased blood glucose values in contrast to the animals with a body weight under 160 g (group A). Isolated pancreatic islets of these two groups of sand rats were incubated with [3H]-leucine to study the incorporation of this amino acid into proinsulin and insulin. The incorporation into proteins of pancreatic islets of sand rats of group B was stimulated by 0.45 mg and 3.0 mg/ml glucose. In group A there was no further stimulation from 0.45 mg to 3.0 mg/ml glucose. Insulin secretion could be stimulated by glucose in both groups, but the stimulation was stronger in group B than in group A.     

Morphologic features of spontaneous annular tears and disc degeneration in the aging sand rat (Psammomys obesus obesus)

The sand rat, a member of the gerbil family, is a valuable small animal model in which intervertebral disc degeneration occurs spontaneously as the animal ages. Radiographic features of cervical and lumbar degeneration resemble those in human spines. We conducted a retrospective analysis of spines of 140 animals 3?41 months old focusing specifically on the presence of annular tears that are not visible by radiography and have not been described previously in the sand rat disc. During degeneration of the nucleus pulposus, notochordal cell death occurs and granular material, which stains with Alcian blue for proteoglycans, accumulates. Lamellar architecture also deteriorates and annular tears occur that are morphologically similar to the concentric, radiating and transdiscal annular tears in human discs. These tears contain granular material that provides a “marker” that can be used to distinguish the annular tears from artefactual separations during sectioning. We observed lamellar degeneration and separation in the annulus fibrosus at 4 months with associated tears that contained granular material in the nucleus. Tears that contained granular material and displacement of the degenerating nucleus were common in cervical and lumbar discs of animals older than 9 months; some specimens showed tears at 4 and 5 months. With advanced degeneration, granular globules were displaced dorsally adjacent to and into the spinal cord area and also ventrally into regions where osteophytes formed. We present morphologic data that expand the utility of this rodent model of spontaneous age-related disc degeneration and provide novel information on annular tears and disc degeneration.     

Fiber digestion and energy utilization of fat sand rats (Psammomys obesus) consuming the chenopod Anabasis articulata

Most herbivorous rodents consume a variety of plants and, when available, select ones low in fiber content. In contrast, the fat sand rat (Psammomys obesus), a diurnal gerbillid rodent that is wholly herbivorous, is able to survive while consuming only the halophytic chenopod Anabasis articulata. We hypothesized that these gerbils are able to digest chenopods efficiently and that fiber digestion contributes substantially to their energy budget. Digestibility of total fibers (NDF), hemicellulose, and cellulose was 51.6%, 66.4%, and 44.0%, respectively. Energy derived from fiber digestion was 211.7 kJ kg(-0.75) d(-1) and resulted mostly from hemicellulose digestion. Average daily metabolic rate was 658.4 kJ kg(-0.75) d(-1), and basal metabolic rate (BMR) was determined to be close to 192.6 kJ kg(-0.75) d(-1). Therefore, fiber digestion provided 32% of maintenance requirements and 110% of BMR requirements, one of the highest values reported thus far for placental mammals. The efficiency of utilization of the chenopod was 0.29, a low value compared to other dietary items. We concluded that A. articulata fulfills all the energy and nutrient requirements of fat sand rats, even though energy yields and efficiency of utilization of its energy is low.     

Age-related changes in fibronectin in annulus fibrosus of the sand rat (Psammomys obesus)

Fibronectin stains were carried out and evaluated by microspectrophotometric techniques in annuli fibrosi of vertebral discs of sand rats (Psammomys obesus) of both sexes and two age groups, 13-18 months and over 2 years of age. The distribution of fibronectin in the annulus shows a centripetal gradient from the outer to the inner laminae. Fibronectin was significantly more abundant in the annuli of old than of young animals of corresponding sex. Sex differences were not significant. The dorsal segment contained more fibronectin than the ventral, but the difference was statistically significant only in the aged females. The outer laminae of the annuli appeared consistently higher in fibronectin content than the inner laminae.     

Evidence of three cell types in the islets of Langerhans in sand rats (Psammomys obesus).

The islets of Langerhans of sand rats were examined light- and electron microscopically with respect to the presence of various cell types. Apart from A- and B-cells, already known in sand rats, the presence of the third type of cells was established in the islet organ. According to their topography, argyrophilia (Hellman and Hellerstr?m technique) and electron microscopical appearance of their granules they should be considered as D-cells.     

Variations of glucose utilization in muscle and adipose tissue of sand rats (Psammomys obesus) during adaptation to laboratory holding

Sand rats, captured in Egypt and fed with a low caloric vegetable diet during adaptation, were investigated before and after 2.5 and 8 weeks diet treatment (30 and 40 kcal/100 g body weight daily). In hexobarbital anaesthesia the sand rats were loaded with 1 g glucose/kg body weight in a single dose intravenously. After a rapid increase the content of glucose in blood remained at a level of about 600 mg glucose/100 ml blood. The insulin immunoreactivity in blood did not change uniformly after application of glucose and remained in a physiologic range. In the islets of Langerhans a degranulation was found during diet treatment. The sensitivity of the epididymal adipose tissue towards insulin in vitro decreased to a nearly complete resistance in the course of diet treatment. A diminution of insulin sensitivity was also found in the m. soleus in vitro. The content of glucose-6-phosphate in the m. semimembranosus was found enhanced after the preparation of the animal. It was found progressively increased up to the five-fold at the end of diet treatment. In the corresponding muscle the glucose distribution volume was increased to about double the extracellular volume. An accumulation of free glucose within the muscle cell must be taken into account. In conclusion the treatment of sand rats with a diabetogenic diet results very quickly in a loss of insulin sensitivity of adipose tissue. The progressively increased stress-mediated accumulation of glucose-6-phosphate and free glucose refers to an inhibition of glucose utilization in the phosphorylation step of glucose in skeletal muscle.     

Water, electrolyte and nitrogen balances of fat sand rats (Psammomys obesus) when consuming the saltbush Atriplex halimus

The fat sand rat (Psammomys obesus), a diurnal gerbillid rodent, is able to thrive while consuming only the saltbush Atriplex halimus. This plant has a high ash, nitrogen and water content but low energy yield. We measured the electrolyte, nitrogen (N) and water balances of fat sand rats in captivity when they were offered only A. halimus.
The fat sand rats scraped the outer layers of A. halimus leaves before consuming them. This removed 14.3% to 19.6% of the ash content of the leaves, and thus substantially reduced the electrolyte intake of the fat sand rats. Total urine osmolality ranged between 2739 and 3098 mOsm/kg, with Na+, K+ and CI - comprising 74.3% to 82.5% of the total osmolytes, percentages much higher than those usually found in desert rodents. Water intake was relatively high compared to other rodents because of the high water content of A. halimus. Evaporative water loss averaged approximately 50% of the total water output. Nitrogen requirements were easily fulfilled, even when the fat sand rats did not meet their energy requirements because of the high N content of the plant. Metabolic faecal nitrogen was 70.5 mg-kg-' 75.d-', endogenous urinary nitrogen was 171.9 mg. kg-0'75 d-' and minimal N requirements were 242.3 mg.k g-75d -1 . Minimal N requirements for the fat sand rats were approximately 98% of that expected for a eutherian mammal of its body mass.
It was concluded that fat sand rats can maintain water, electrolyte and nitrogen balances when consuming only A. halimus without producing highly concentrated urine. This is due, in part, to their ability to remove much of the electrolytes before consuming the plant and by producing urine of which Na+, K+ and C1- comprise a large percentage of the total osmolytes.     

Blood acid-base status, whole blood and whole body buffer values in sand rats (Psammomys obesus) exposed to hypercapnia

Arterial blood acid-base status of unanesthetized sand rats (Psammomys obesus) were studied under normocapnic and hypercapnic conditions, and compared to those obtained for the albino rat (Rattus norvegicus). The average control blood pH: 7.396 +/- 0.034; PaCO2: 30.5 +/- 2.9 mmHg; HCO-3: 18.8 +/- 2.5 mM/l; and HCO-3 std: 20.9 +/- 2.1 (N = 15) obtained here for the sand rat are in the lower range of values found in other mammals and indicate a status of partially compensated metabolic acidosis. The blood buffer values of the sand rat, delta log PCO2/delta pH = -2.32 +/- 0.35 (N = 25) are significantly higher than those found here for the rat, delta log PCO2/delta pH = -1.51 +/- 0.10 (N = 39), and those reported for other mammals. This high blood buffer value may be related to the natural high mineral diet of the sand rat. The in vivo (whole body) buffer value delta log PaCO2/delta pH = -1.41 and -1.65 for the sand rat and the rat found here are higher than those reported for the man and dog and may represent a physiological adaptation to the hypercapnic conditions prevailing in underground burrows.     

Studies on (pro)insulin biosynthesis and secretion of pancreatic islets of sand rats (Psammomys obesus) after different feeding conditions.

It was possible to induce different metabolic states in sand rats of our breeding colony or in newly caught Egyptian sand rats, respectively, by feeding a pellet diet or vegetable diet (green cabbage). Newly captured sand rats fed only on native food were used as reference group (group C). Plasma IRI-level and glucose in vivo and [3H]-leucine incorporation into proinsulin and insulin, insulin secretion and insulin content in vitro were investigated. Sand rats fed on pellet chow and ad libitum (group B) developed a hyperinsulinism and showed higher sensitivity of [3H]-leucine incorporation into proinsulin and insulin to glucose (maximal stimulation at 3 mM) and increased incorporation rates in vitro. Restriction of pellet food to 35-40 kcal/animal/day (group A) lead to changes of all parameters, which were investigated in the same direction as in group B, but to a much smaller extent. Newly captured sand rats, which were fed green cabbage for 4 to 6 weeks divided into two groups: One group (group D1) was comparable to the normal group (C) in IRI levels, glucose levels, glucose sensitivity and amount of [3H]-leucine incorporation. The other group (group D2) tended to group A. Marked changes in insulin content and insulin secretion of isolated pancreatic islets could not be found in any group.     

Oxalate, calcium and ash intake and excretion balances in fat sand rats (Psammomys obesus) feeding on two different diets

Fat sand rats Psammomys obesus feed exclusively on plants of the family Chenopodiaceae, which contain high concentrations of chloride salts (NaCl, KCl) and oxalate salts. Ingestion of large quantities of oxalate is challenging for mammals because oxalate chelates Ca(2+) cations, reducing Ca(2+) availability. Oxalate is a metabolic end-point in mammalian metabolism, however it can be broken-down by intestinal bacteria. We predicted that in fat sand rats microbial breakdown of oxalate will be substantial due to the high dietary load. In addition, since a high concentration of soluble chloride salts increases the solubility of calcium oxalate in solution, we examined whether a change in the intake of chloride salts affects microbial oxalate breakdown and calcium excretion in fat sand rats. We measured oxalate, calcium and other inorganic matter (ash) intake and excretion in fat sand rats feeding on two different diets: saltbush (Atriplex halimus), their natural diet, and goose-foot (Chenopodium album), a non-native chenopod on which fat sand rats will readily feed and that has a similar oxalate content to saltbush but only 2/3 of the ash content. In animals feeding on both diets, 65-80% of the oxalate ingested did not appear in urine or faeces. In animals consuming the more saline saltbush, significantly more oxalate was apparently degraded (p<0.001), while significantly less oxalate was excreted in urine (p<0.01) and in faeces (p<0.05). We propose, therefore, that fat sand rats rely on symbiotic bacteria to remove a large portion of the oxalates ingested with their diet, and that the high dietary salt intake may play a beneficial role in their oxalate and calcium metabolism.