Changes in Plasma Levels of Oestradiol, Progesterone and Luteinizing Hormone in Immature Rats Treated With Pregnant Mare Serum Gonadotrophin

Abstract

The pattern of hormonal changes just before ovulation was investigated in immature rats induced to ovulate with pregnant mare serum gonadotrophin (PMSG). Oestradiol levels in the blood reached a maximum 42\p=n-\52h after PMSG treatment and then decreased dramatically. Pituitary luteinizing hormone (LH) levels remained constant until the time of the critical period (50\p=n-\52h) and then fell significantly. Plasma LH levels started to rise at 52 h, reached a peak at 54 h and fell to undetectable levels by 58 h. Plasma progesterone also reached a peak at 54 h and then fell slowly over the following dark period. The timing and pattern of changes in plasma and pituitary hormone levels were very similar to those seen in adult rats before ovulation. There was a positive correlation between the dose of PMSG, the peak concentration of plasma oestradiol and the average number of ova shed.

Pituitary and Plasma Levels of Luteinizing Hormone and Prolactin in the Immature Female Rat Following Administration of Pregnant Mares’ Serum

“…The pattern of change in pituitary LH levels found in this study was somewhat more difficult to analyze with reference to the literature. Direct comparisons of pituitary LH levels as a function of time were com plicated by differences in lighting conditions [Wagner and Brown-G rant, 1965], time of injections and differences in the strain of rats used for the study [Wilson et al, 1974]. Most important, the choice of discrete points in time at which measurements were made determined the pattern of hormonal change seen in each study.…”

“…The increase in pituitary weight on the afternoon preceding ovulation (tables I, II), also described and discussed by Rennels and O'Steen [1967], may have been due to the increased level of plasma estrogen associated with the preovulatory hormonal surge found in the PMS-treated immature rat [Wilson et al, 1974], As well as playing an integral role in gonadotrophin feedback mechanisms affecting pituitary synthesizing and releasing activity, estrogen can act directly to cause glandular hypertrophy [Saunders, 1964].…”

Action of gonadotrophic hormones on cholesterol side-chain cleavage and cholesterol ester hydrolase in the ovary of the immature rat

“…The ultrastructural changes induced by PMSG and by hCG resemble changes occurring in granulosa cells during luteinization (Bramley, Ryan, Kang, Perotti & Anderson, 1980), and PMSG and hCG have been shown to increase oestrogen and progesterone output, respectively, from the immature rat ovary (Wilson, Horth, Endersby & McDonald, 1974;Parker, Costoff, Moldoon & Mahesh, 1976;Shashida & Johnson, 1976;Tan & Robinson, 1976, 1977. The corpus luteum of PMSG-hCG-treated rats resembles the corpus luteum of pregnancy in its steroidogenic output and the modulation of this output by LH.…”

Hormonal control of ovarian phospholipase A2 activity in rats

“…However, as mentioned earlier, the rate-limiting step for prostaglandin syn¬ thesis is the availability of arachidonic acid and it is possible that LH might also act to enhance PLA2. Thyroid-stimulating hormone can increase PLA2 activity and thence prostaglandin production in the thyroid (Haye et al, 1973) (Wilson et al, 1974 …”