Plasma and Pituitary Luteinizing Hormone and Peripheral Plasma Oestradiol Concentrations in the Normal Oestrous Cycle of the Rat and After Experimental Manipulation of the Cycle

Abstract

SUMMARY Plasma and pituitary luteinizing hormone (LH) concentrations were measured by radioimmunoassay at different stages of the normal 4- and 5-day oestrous cycle of rats. Plasma levels were low except between the afternoon of pro-oestrus and the morning of oestrus when levels were high but variable. Pituitary LH content and concentration were less consistent but averaged values showed a steady rise from a low level after ovulation to a peak on the afternoon of pro-oestrus, and a rapid fall that evening when plasma levels rose rapidly. No significant differences were observed in plasma LH between 4- and 5-day cycles; in particular there was no reduction at metoestrus or dioestrus-1 or increase on the evening of dioestrus-2. Plasma oestradiol was already high on the morning of dioestrus-2 in some rats and in all rats by that evening. On the morning of pro-oestrus in the 5-day cycle, plasma oestradiol was still high but somewhat lower than at the corresponding stage in the 4-day cycle. Blocking ovulation by administration of sodium pentobarbitone at prooestrus in a 4-day cycle prevented the rise in plasma LH and the fall in pituitary content. Blocking generally failed in animals whose plasma LH had reached the level of 20 ng/ml or more at the time of injection. Plasma oestradiol levels on the morning of the expected day of oestrus were higher than normal in animals in which ovulation was blocked by pentobarbitone but were below pro-oestrous values. In the anovulatory state induced by exposure to constant light no major increase in plasma LH was detected after 24 days of illumination or after 3 months exposure. Animals rendered anovulatory by injection of testosterone propionate on the 4th day of postnatal life had low plasma LH levels as adults. All three groups had a low pituitary LH content. The animals exposed to long-term light and those treated with androgen generally had plasma oestradiol concentrations below the peak levels seen on the morning of pro-oestrus in the normal cycle.

Effects of Progesterone on the Pituitary Responsiveness to, and Priming Effect of Luteinizing Hormone Releasing Hormone in Female Rats Exposed to Constant Light

“…In LD females, progesterone can only increase pituitary responsiveness to LHRH when act ing on a hypothalamic-pituitary system that has been ex posed to E2 [1,15]. The efficacy of progesterone in increas ing pituitary responsiveness in LL rats may be due to the higher plasma concentrations of E2 which were in between the concentrations in LD females on the morning of diestrus and the morning of proestrus, a finding which agrees with those of Naftolin et al [26] and Takahashi et al [36] who measured E2 in ovarian vein plasma. The pattern of E2 concentrations in the plasma of LD animals (table I), with a peak during the morning of proestrus, was similar to that reported by Naftolin et al [26], Shaikh and Shaikh [32] and Henderson et al [20].…”

“…The efficacy of progesterone in increas ing pituitary responsiveness in LL rats may be due to the higher plasma concentrations of E2 which were in between the concentrations in LD females on the morning of diestrus and the morning of proestrus, a finding which agrees with those of Naftolin et al [26] and Takahashi et al [36] who measured E2 in ovarian vein plasma. The pattern of E2 concentrations in the plasma of LD animals (table I), with a peak during the morning of proestrus, was similar to that reported by Naftolin et al [26], Shaikh and Shaikh [32] and Henderson et al [20]. The plasma concentration of E2 was not significantly increased 2 h after mating (table I) and this suggests that E2 is not involved in triggering the LH surge induced by mating.…”

A Priming Effect of Luteinizing Hormone Releasing Factor on the Anterior Pituitary Gland in the Female Rat

“…In the rats in which ovulation was advanced, the maximal concen¬ trations of LH after injection (16-0, 40-0, 35-5, 40-0 and 25-6 ng/ml) were not much greater than that suggested as the lowest ovulatory concentration of plasma LH Priming effect of during the LH surge (Naftolin, Brown-Grant & Corker, 1972). This reinforces pre¬ vious suggestions (Greig & Weisz, 1973 ; that the ovulatory threshold level of LH may be related to the total amount of the hormone reaching the ovaries rather than to the peak concentration of LH in plasma alone.…”

Limbic Seizures Alter Reproductive Function in the Female Rat

“…Human PCOD is characterized by (a) increased basal concentrations of LH and normal or low-normal basal levels of FSH (30), (b) chronic anovulation (39), (c) enlarged ovaries containing follicular cysts at different stages of growth and atresia (40), (d) elevated plasma concentrations of estrone and estradiol, and (e) elevated levels of circulating androgens (41). A number of previous studies attempted to develop the hypothesis that conditions of anovulatory sterility in female rodents may provide models for human PCOD (33,(42)(43)(44)(45). However, although these different rodent models all have polyfollicular ovaries, none exhibit the combination of elevated T, E,, and LH levels that is a common feature of human PCOD.…”