A series of experiments were conducted to investigate the elimination of swainsonine in the milk of lactating ruminants following a single dose oral exposure to swainsonine (locoweed; Oxytropis sericea) and to assess subsequent subclinical effects on the mothers and their nursing young. In a preliminary experiment, lactating ewes were gavaged with locoweed providing 0.8 mg swainsonine/kg BW (n = 4; BW = 75.8 +/- 3.6 kg; lactation = d 45) and lactating cows were offered up to 2.0 mg swainsonine/kg BW free choice (n = 16; BW = 389.6 +/- 20.9 kg; lactation = d 90). Serum and milk were collected at h 0 (before treatment), 3, 6, 12, and 24 for ewes, and h 0 (before treatment), 6, 12, 18, and 24 for cows. Swainsonine was highest (P < 0.05) by h 6 in the serum and milk of ewes. Consumption of at least 0.61 mg swainsonine/kg BW induced consistent (> 0.025 microg/mL) appearance of swainsonine in cow serum and milk. In response to the results obtained in the preliminary experiment, a subsequent experiment utilizing lactating ewes (n = 13; BW = 74.8 +/- 6.4 kg; lactation = d 30) and cows (n = 13; BW = 460.8 +/- 51.9 kg; lactation = d 90) was conducted. Each lactating ruminant was gavaged with a locoweed extract to provide 0 (control), 0.2, or 0.8 mg swainsonine/kg BW and individually penned with her nursing young. Serum and milk from the mothers and serum from the nursing young were collected at h 0 (before treatment), 3, 6, 9, 12, 24 and 48 (an additional sample was obtained at h 72 for ewes and lambs). Serum and milk swainsonine was higher (P < 0.05) in the 0.8 mg treated groups and maximal (P < 0.05) concentrations occurred from h 3 to 6 for ewes and h 6 to 12 h for cows (P < 0.05). Rises in alkaline phosphatase activity indicated subclinical toxicity in the treated ewes (P < 0.05). Following a single dose oral exposure to 0.2 and 0.8 mg swainsonine/kg BW provided by a locoweed extract, swainsonine was detected in the serum and milk of lactating ewes and cows, and rises in serum alkaline phosphatase activity were observed in the ewes. Neither swainsonine nor changes in alkaline phosphatase activity was detected in the serum of the lambs and calves nursing the ewes and cows dosed with swainsonine.

We used two dierent experimental approaches to test the hypothesis that thyroid hormone receptor (TR) variation is associated with alternate life cycles modes in ambystomatid salamanders. In the ®rst experiment, the inheritance of TRa and TRb genotypes was determined for metamorphic and non metamorphic ospring from backcrosses between Ambystoma mexicanum (an obligate metamorphicfailure species) and metamorphic F 1 hybrids (A. mexicanum´A. tigrinum tigrinum). The segregation of TR genotype was independent of the expression of life cycle mode phenotype, and neither TR locus was linked to DNA markers that¯ank a major-eect locus for life cycle mode. In the second experiment, a portion of the ligand-binding domain of TRa and TRb was cloned and sequenced for DNA samples from 14 dierent ambystomatid salamander populations, including obligate metamorphic, facultative metamorphic, and obligate metamorphic-failure taxa. Nucleotide sequence variation was found for both TRa and TRb, with several nonsynonomous substitutions that presumably code for nonconservative amino acid replacements. However, no general relationship was found between TR allelic variation and life cycle mode among populations or species. These data do not implicate TRs as candidate loci involved in the current maintenance or past evolution of alternate life cycle modes in members of the tiger salamander complex.

A study was conducted to evaluate the effects of acute and subacute locoweed exposure on serum swainsonine concentrations and selected serum constituents in sheep. Thirteen mixed-breed wethers (BW = 47.5 +/- 9.3 kg) were assigned randomly to 0.2, 0.4, or 0.8 mg of swainsonine x kg BW(-1) x d(-1) treatments. During acute (24 h) and subacute (19 d) exposure, serum swainsonine was detected in all treatments and was greatest (P < 0.03) in the 0.8 mg treatment. Serum alkaline phosphate (ALK-P) activity was increased (P < 0.01) for the 0.8 mg treatment compared with baseline (0 h) by 7 h and continued to increase throughout the initial 22 h following acute exposure to locoweed. A linear increase (P < 0.01) in serum ALK-P activity was noted, with the rate being 3.00 +/- 0.56 U x L(-1) x h(-1). Serum ALK-P activity was increased (P < 0.05) across treatments on d 7 over d -19, -12, 0, 1, 21, and 26; on d 14 over d -19, -12, 0, and 26; and on d 19 over d -19, -12, 0, 1, 21, and 26. By d 20, approximately 48 h after last exposure to swainsonine, serum ALK-P activities were no longer different (P = 0.13) than baseline (d -19, -12, and 0), and by d 26 values had generally returned to baseline. No linear (P = 0.98), quadratic (P = 0.63), or cubic effects of swainsonine with time from exposure were noted for serum aspartate aminotransferase. Similar to serum ALK-P activities, serum aspartate aminotransferase activities were increased (P < 0.05) across treatment levels on d 7, 14, 19, 20, 21, and 26 over those on d -19, -12, 0, and 1. Total serum Fe was decreased (P < 0.05) within the initial 22 h following the swainsonine exposure. On d 21 (48 h after swainsonine feeding ended), serum Fe increased to 472 mg/L. Concentrations of ceruloplasmin were lower (P < 0.10) on d 14 and 19 following exposure to locoweed. Recovery of ceruloplasmin levels coincided with similar changes in serum Fe. There was a linear (slope = 0.33 mg x dL(-1) x d(-1); P < 0.01) effect with time of exposure to locoweed (i.e., swainsonine) on serum triglyceride concentrations. Rapid changes in serum ALK-P and Fe concentrations without parallel changes in other damage markers indicate that acute exposure to swainsonine induces metabolic changes that may impair animal production and health before events of cytotoxicity thought to induce clinical manifestation of locoism.

Peripheral blood lymphocytes (PBL) were obtained from heifers and wethers to assess the in vitro effects of swainsonine. Stimulated and unstimulated PBL (2x10(5)/well; 96 well plates) were incubated in the presence of swainsonine (2, .2, .02, .002, and 0 microg/mL; n = 32) for 72 h. Mitogens used to stimulate PBL were concanavalin A (ConA; 5 microg/mL), phytohemagglutinin-P (PHA-P; 5 microg/mL), phytohemagglutinin-M (PHA-M; 5 microg/mL), pokeweed mitogen (PWM; 5 microg/mL), and lipopolysaccharide (LPS; 10 microg/mL). Controls received no swainsonine or mitogen. Effects of swainsonine are expressed as a percentage of stimulation relative to control (stimulation index; SI). Unstimulated bovine PBL treated with 2 microg/mL of swainsonine exhibited a depressed (P<.001; SI of 87 and 100 for 2 microg/mL and control, respectively; SE = 2.7) SI. At concentrations of .2 and 2 microg/mL, swainsonine inhibited (P<.001; SI of 351, 310, and 464 for .2, 2, and 0 microg/mL, respectively; SE = 27.1) bovine PBL proliferative response to PHA-P. Swainsonine had a mitogenic effect on unstimulated ovine PBL at .2 and 2 microg/mL (P<.05; SI of 118, 113, and 100 for .2 and 2 microg/mL and control, respectively; SE = 4.4). Swainsonine inhibited ovine proliferative responses to PHA-P at .2 and 2 microg/mL (P<.005; SI of 190, 178, and 228 for .2, 2, and 0 microg/mL, respectively; SE = 9.4) and to PHA-M at .002 and 2 microg/mL (P<.03; SI of 165, 167, and 192 for .002, 2, and 0 microg/mL, respectively; SE = 7.9). The opposing responses of unstimulated ovine (mitogenic) and bovine (antiproliferative) PBL to swainsonine indicates a differential species response. Swainsonine suppression of PHA-P-induced proliferation would indicate a negative effect on ovine and bovine T-cell function.

A series of experiments were conducted to investigate the elimination of swainsonine in the milk of lactating ruminants following a single dose oral exposure to swainsonine (locoweed; Oxytropis sericea) and to assess subsequent subclinical effects on the mothers and their nursing young. In a preliminary experiment, lactating ewes were gavaged with locoweed providing 0.8 mg swainsonine/kg BW (n = 4; BW = 75.8 +/- 3.6 kg; lactation = d 45) and lactating cows were offered up to 2.0 mg swainsonine/kg BW free choice (n = 16; BW = 389.6 +/- 20.9 kg; lactation = d 90). Serum and milk were collected at h 0 (before treatment), 3, 6, 12, and 24 for ewes, and h 0 (before treatment), 6, 12, 18, and 24 for cows. Swainsonine was highest (P < 0.05) by h 6 in the serum and milk of ewes. Consumption of at least 0.61 mg swainsonine/kg BW induced consistent (> 0.025 microg/mL) appearance of swainsonine in cow serum and milk. In response to the results obtained in the preliminary experiment, a subsequent experiment utilizing lactating ewes (n = 13; BW = 74.8 +/- 6.4 kg; lactation = d 30) and cows (n = 13; BW = 460.8 +/- 51.9 kg; lactation = d 90) was conducted. Each lactating ruminant was gavaged with a locoweed extract to provide 0 (control), 0.2, or 0.8 mg swainsonine/kg BW and individually penned with her nursing young. Serum and milk from the mothers and serum from the nursing young were collected at h 0 (before treatment), 3, 6, 9, 12, 24 and 48 (an additional sample was obtained at h 72 for ewes and lambs). Serum and milk swainsonine was higher (P < 0.05) in the 0.8 mg treated groups and maximal (P < 0.05) concentrations occurred from h 3 to 6 for ewes and h 6 to 12 h for cows (P < 0.05). Rises in alkaline phosphatase activity indicated subclinical toxicity in the treated ewes (P < 0.05). Following a single dose oral exposure to 0.2 and 0.8 mg swainsonine/kg BW provided by a locoweed extract, swainsonine was detected in the serum and milk of lactating ewes and cows, and rises in serum alkaline phosphatase activity were observed in the ewes. Neither swainsonine nor changes in alkaline phosphatase activity was detected in the serum of the lambs and calves nursing the ewes and cows dosed with swainsonine.