Swimming ability in three Costa Rican dry forest rodents.

We investigated the swimming abilities of three Costa Rican dry forest rodents (Coues' rice rat. Oryzomys couesi, hispid cotton rat, Sigmodon hispidus, and spiny pocket mouse, Liomys salvini) associated with a large marsh, Laguna Palo Verde, using 90 s swim trials in a plastic container. Swimming ability was evaluated by observing the use of limbs and tail in the water, inclination to the surface, and diving and floating behavior. Rice rats could float, swim and dive, suggesting that they can exploit surface and underwater resources. Cotton rats swam at the water's surface, but were less skilled swimmers than rice rats. Spiny pocket mice tired quickly and had difficulty staying at the water's surface. Results suggest that differential swimming ability is related to the distribution of the three sympatric species within the marsh and adjacent forest habitats.

A 28-day feeding study with ethyl acetoacetate in rats.

Ethyl acetoacetate encapsulated in gum arabic was administered in rodent diet for a minimum of 28 consecutive days to groups of 16 male and 16 female rats (Sprague-Dawley strain) at levels of approximately 100, 300 and 1000 mg/kg body weight/day. A further group of 16 male and 16 female rats was given rodent diet containing gum arabic as a control. The administration of ethyl acetoacetate in the diet did not adversely affect the growth or general health of the animals or their food intakes. None of the minor variations observed in the haematology, serum chemical analyses or urine analyses are considered to be indicative of a treatment-related toxic effect. Caecal enlargement was seen in male rats treated with the top dose of ethyl acetoacetate, but this was accompanied by a normal histopathology. Few histopathological abnormalities were observed. Proteinaceous casts were found in the bladder of approximately half the male rats given 1000 mg ethyl acetoacetate/kg, and nephrocalcinosis was a common occurrence in female rats in this dose group. Renal function was unimpaired in treated male and female rats, and the histopathological findings are common in the strain of rats chosen for this study. Although the caecal enlargement and the changes in kidney and bladder of rats given 1000 mg ethyl acetoacetate/kg are noted, it is considered that ethyl acetoacetate did not produce treatment-related adverse effects in rats during this study.

The role of gut micro-organisms in the metabolism of deoxynivalenol administered to rats.

1. Oral administration of deoxynivalenol (DON) to control rats resulted in the appearance of a de-epoxy metabolite in urine and faeces. 2. When DON was administered to rats treated with antibiotics to deplete their gut microflora there was very little excretion of radioactivity as the de-epoxy metabolite in faeces or urine. 3. Incubation of DON with a strictly anaerobic preparation of gut contents resulted in the progressive appearance of de-epoxy DON during a 24 h incubation period. 4. Incubation of DON with liver homogenate did not result in the appearance of the de-epoxy DON metabolite. 5. These results indicate that the presence of de-epoxy DON in rat excreta, following the oral administration of DON, is the result of metabolism by micro-organisms in the gut.

Effect of mono-(2-ethylhexyl) phthalate on the metabolism of energy-yielding substrates in rat sertoli cell-enriched cultures.

The effect of the testicular toxin mono-(2-ethylhexyl) phthalate (MEHP) on the metabolism of energy-yielding substrates in Sertoli cell-enriched cultures has been studied. MEHP stimulated glucose utilization and oxidation. Stimulation of (14)CO(2) production was greater with [1-(14)C]- than with [6-(14)C]glucose. Oxidation of [1-(14)C]pyruvate and [U-(14)C]acetate to (14)CO(2) was reduced by MEHP treatment in the presence but unaffected in the absence of glucose. MEHP increased the incorporation of radioactivity from [1-(14)C]- and [6-(14)C]glucose but not from [U-(14)C]acetate into fatty acids. MEHP markedly increased the production of lactate by Sertoli cells cultured in the presence of 5.5 mm-glucose and 0.5 mm-pyruvate. Decreasing the glucose concentration reduced this stimulatory effect. In glucose-free medium containing 0.5 or 2.5 mm-pyruvate MEHP had no effect on Sertoli cell lactate production. Thus, MEHP appears to stimulate the utilization of glucose by the Sertoli cell but does not appear to have a direct effect on the conversion of pyruvate to lactate, on the conversion of pyruvate to acetyl CoA or a direct effect on the metabolism of acetyl CoA through the Krebs cycle. Increased glucose utilization appears to be a consequence of the increased metabolism of glucose that occurs through the glycolytic and pentose phosphate pathways. These results suggest that in contrast to its effects on the liver, MEHP does not exert a primary effect on the Sertoli cell mitochondrion.