The protective effect of vitamin E and reduced glutathione (GSH) against lipid peroxidation in boar semen plasma was studied. The lipid peroxidation, measured by the test for thiobarbituric acid reactive substances (TBARS), doubled in the presence of the lipid peroxidation Fe(2+)-sodium ascorbate-inducing system. The ascorbate-induced TBARS were inhibited by about 62% through the water-soluble vitamin E analog (TROLOX) and about 57% by GSH. In the in vivo experiments, 7 wk of oral DL-alpha-tocopherol acetate (1000 IU/d/animal) administration caused a significant fall in the level of the semen plasma TBARS, from 2.2 +/- 0.09 to 1.2 +/- 0.13 nmol MDA/mL. The semen plasma superoxide dismutase (SOD) and GSSG tended to increase with the time of vitamin E administration, but the increment did not reach a significant level by the seventh week. The vitamin E supplementation significantly increased the number of spermatozoa per 1 cm3 of ejaculate. The protective role of vitamin E and GSH with respect to boar semen against fatty acid peroxidation and a positive influence of vitamin E supplementation on semen quality have been evidenced.

No abstract

Principal serum iodothyronines, T₄, T₃ and rT₃, have been simultaneously measured by a specific radioimmunoassay in piglets kept for sequential observation with the mother from 1 to 21 days of age. During several hours postnatally, a high concentration of the hormone was noted as a result of an enhanced secretory activity of the thyroid gland. Later, a progressive decrease with a nadir at about day 3 was observed, followed by a second rise in the hormone level. Changes in T₃ and rT₃ levels from birth to the end of the 1st week, paralleled those for T₄. The T₃:rT₃ ratio of about 2 during the 1st week fell to about 1.5 during the 3rd week as a result of the progressive increase in rT₃ and decrease in T₃ concentrations. The T₄:rT₃ ratio fell with the progressing age to the level observed in post-weaned pigs. At birth, the newborn pig seems to possess a low capability of 5-deiodinase enzyme system thus the converting enzymes first work towards T₄–T₃ conversion while T₄–rT₃-converting ability progressively increases with age. The role of this variability for the neonatal thermogenic stability is discussed.

Utilizing the difference in pH optima between two distinct enzyme systems responsible for the thyroxine (T4) inner and outer ring monodeiodination, and a specific radioimmunoassay for iodothyronines, the net T4 conversion to 3, 3', 5'-tri-iodothyronine (rT3) and 3, 5', 3'-tri-iodothyronine (T3) in growing pigs kept under various food restrictions was determined in vitro. It has been found that fasting lowers deiodination of T4 to T3 by liver and kidney homogenates. The conversion of T4 to rT3 was reduced in the liver but not in the kidney, unless the animals were completely fasted. During food restriction serum T4 and T3 decreased whereas rT3 increased, which indicated that the serum rT3 level is not a good reflection of T4 to rT3 converting activity in the liver or kidney. The data suggest that a rise in rT3 reflects a lowered degradation rate of the hormone or an increased secretion by the thyroid gland rather than changes in rT3 neogenesis in the periphery.