Effect of Thyroid Activity Upon Delayed Implantation of Blastocysts in the Rat

Abstract

The effects of l-thyroxine and of surgical thyroidectomy upon the survival of blastocysts have been studied in 200 albino rats. These rats were ovariectomized on the 3rd day of pregnancy, and maintained on progesterone in order to delay implantation. Delay of implantation was confirmed by laparotomy on the 8th day of pregnancy. Subsequent implantation was accomplished by giving 1 \ g=m\ g oestrone daily from the 9th day of pregnancy. At autopsy on the 14th day of pregnancy hyperthyroid rats and hypothyroid rats which had been maintained on daily injections of 2\m=.\0 mg progesterone did not differ from their respective control groups in the number of surviving blastocysts. However, hyperthyroid rats which had been maintained on daily injections of 0\m=.\4mg progesterone possessed more implantation sites than controls. Similarly, the hypothyroid rats maintained on daily injections of 0\m=.\3 mg progesterone had fewer implantation sites than controls. The experiments suggest that the level of hyperthyroidism tested is beneficial to the maintenance of implantation of delayed blastocysts when low amounts of progesterone are available, while hypothyroidism tends to be detrimental to this process during low progesterone availability.

Uterine Alkaline Phosphatase and Blastocyst Implantation During Altered Thyroid Activity

“…oviduct flushings in other experiments.) These findings are discussed in detail elsewhere (Holland et al 1967). Immediately above the bar graphs of Fig.…”

“…The procedure for obtaining the delayed implantation of blastocysts has been described in detail elsewhere (Holland et al 1967). Briefly, it is based upon the method of Cochrane 8c Meyer (1957) and involves ovariectomy on Day 3 of pregnancy, daily injection of progesterone through Day 8, verification of delay by laparotomy on Day 8, and supplementing the progesterone with oestrone on Days 9 through 14 to obtain implantation and development of the blastocysts.…”

Progesterone-Dependent Blastocyst Survival During Altered Thyroid Activity in the Rat

“…A daily dosage of 15 /¿g was highly effective and 8^g daily has also proved to be quite effective in counteracting progesterone deficiency. In earlier studies of delayed implantation, it was reported (Holland et al, 1967) (1956) reported that thyroid activity increases by 100% during normal oestrus as compared with di-oestrus in the rat, while Grosvenor & Turner (1958) reported that lactation may also produce a two-fold increase in thyroid secretion in the rat. Thyroxine secretion rate in the rat has been reported (Grosvenor & Turner, 1958) to be 1-24 to 1-75 µg/100 g body wt/day or about 2-8 to 4-0 /ig/day in rats of the size used in our experiments.…”

“…Investigators have reported beneficial effects, disadvantageous effects and some have reported that it exerts no effect. Exam¬ ples of these investigations and possible reasons for the conflicting results were presented in an earlier publication (Holland, Dorsey, Harris & Johnson, 1967 (Holland et al, 1967) (Meyer & Nutting, 1964) of Days 3 to 8 rather than influencing the effectiveness of the oestrogen-dependent implanta¬ tion process (Prasad, Mohla & Rajalakshmi, 1969).…”

“…Seventy-nine Holtzman, albino, virgin rats of between 90 and 120 days of age were housed, maintained and ovariectomized as described earlier (Holland et al, 1967). These rats were ovariectomized on Day 3 of pregnancy and treated Since 48 µ% L-thyroxine exceeds the hyperthyroid secretory levels in the rat, lower thyroxine dosages were investigated.…”