| Abstract: | Thyroxine and progesterone levels were studied in cows and heifers in the luteal stage of the cycle after the application of the synthetic analogue of prostaglandine of group F2 alpha: Oestrophan Spofa. The preparation was administered at a rate of 0.5 mg in 2 ml per animal. The thyroxine and progesterone levels were determined radioimmunologically. The administration of Oestrophan led to a reduction in the progesterone level from the initial value of 17.33 +/- 2.73 nmol/l of serum to 7.69 +/- 1.17 nmol/l of serum an hour after the application, followed by slow decrease below the value 1.59 +/- 0.22 nmol/l of serum at the 24th hour. The initial levels of thyroxine with the average values of 122.11 +/- 23.41 nmol/l of serum were comparatively high. An hour from application of the preparation, a significant decrease to the average levels of 88.14 +/- 16.26 nmol/l of serum (P less than 0.05) was recorded with a significant negative correlation. The correlation coefficient r = -83316, P less than 0.01. The thyroxine level decreases to the values of 24.20 +/- 9.26 nmol/l of serum and 24.12 +/- 6.68 nmol/l of serum, P less than 0.01, at the 52nd to 56th hour, i. e. at the time when the pre-ovulation peak of oestrogens can be expected. A statistically significant correlation--even despite the fact that a highly significant decline in thyroxine and progesterone had been observed--was recorded in none of the cases in the subsequent period of study, except the first hour. It can be assumed from the results that the thyroid hormones are among the links acting at more levels of the regulatory biological circuit responsible for the physiological course of ovulation and reproduction process. |
