The relationship between ovulation and the changes in thyroid gland activity that occur during the oestrous cycle in rats, mice and hamsters

Abstract

SUMMARY1. When ovulation is prevented by the injection of pentobarbitone on the day of pro-oestrus in female rats, the expected increases in thyroidserum concentration ratio (T/S ratio) for 131I and in the uptake of 113I by the thyroid on the day of oestrus do not occur.2. Ovulation induced by human chorionic gonadotrophin or ovine luteinizing hormone in rats treated with pentobarbitone at pro-oestrus is not associated with an increase in T/S ratio or 131I uptake at oestrus.3. These results support the view that it is the neuro-endocrine changes at the hypothalamic or pituitary level that lead to ovulation rather than changes in the pattern of ovarian steroid secretion before or at ovulation that are responsible for the increased thyroid activity at oestrus in the female rat.4. Experimental evidence of an increase in thyroid activity after ovulation in mice and hamsters also supports this view.

Influence of oestrogen on thyroid function in the ewe

“…The significance of oestrogen as a normal stimulator of thyroid activity in the oestrus rat is however still in doubt. The experiments of Brown-Grant (1966) support the view that it is the neuro-endocrine changes at the hypothalamic or pituitary level which lead to ovulation that are responsible for the increased thyroid activity at oestrus in the rat, and not changes in ovarian IAN B. FALCONER steroid secretion. An increase in blood TSH at the beginning of oestrus in the rat was observed by Boccabella & Alger (1967), demonstrating that the activation of the thyroid at normal oestrus was due to a pituitary release of TSH.…”

“…The work of Brown-Grant (1966) demonstrated this phenomenon in rats, mice and golden hamsters, and also established that pentobarbitone blockade of ovulation prevented the normal increase in thyroid activity during oestrus in rats. A similar marked activation of the thyroid gland occurs at oestrus in the ewe (Robertson & Falconer, 1961), which is preceded by a rapid rise in the concentration of oestrogen in the blood (Moore, Barratt, Brown, Schindler, Smith & Smyth, 1969).…”

The effects of a single injection of progesterone on the oestrous cycle, thyroid gland activity and uterus‐plasma concentration ratio for radio‐iodide in the rat

“…During the normal oestrous cycle there is a. striking rise in the T/S ratio between pro-oestrus and oestrus ( (Brown-Grant, 1966a). The questions studied here were whether, when ovulation is delayed by progesterone, the rise in T/S ratio is also delayed and whether when delayed ovulation does occur, it is accompanied by the usual rise in T/S ratio.…”

“…The animals were adult virgin Wistar rats from the closed laboratory colony; conditionsa of housing, diet, etc., were as in earlier studies (Brown-Grant, 1966a). The animals were exposed to 14 hr of light (08.00 to 22.00 hr) and 10 hr of darkness.…”

“…Modification of the oestrous cycle of the rat by the administration of pentobarbitone to adult animals or of testosterone to new-born animals (Brown-Grant, 1965b;1966a) has been of value in the analysis of the relationship between ovulation and the changes in thyroid gland activity that occur during the cycle. Progesterone and other steroids with progestational properties are known to inhibit or delay ovulation but may also, under certain circumstances, advance the time of ovulation (Everett, 1964a).…”