Changes in plasma kininogen levels in rats before ovulation, and after treatment with luteinizing hormone and oestradiol-17 beta

The pre-ovulatory fall in plasma kininogens in rats with 4 day oestrous cycles started between 12.00 and 15.00 h pro-oestrus, reached a maximum decline of 51% by 18.00 h pro-oestrus, and started to recover before ovulation. Because these changes appeared to correspond with the LH-surge, and to follow the peak in plasma oestradiol-17 beta levels, both of these hormones were tested for possible effects on plasma kininogens. Intracardiac injections of 110 IU of equine LH into dioestrous rats were followed by a decline of 30.8 +/- 6.7% in plasma kininogens, 6 h after injection (significant, P less than 0.01). Values were still depressed, but recovering, 12 h after treatment; the reduction was 21.3 +/- 5.8% (significant, P less than 0.01). Controls showed no decline. Injections of oestradiol-17 beta (1.0 micrograms/100 g body weight) produced no significant effects. It is suggested that the LH surge may be responsible, at least in part, for the decline in plasma kininogens seen before ovulation.     

Characterization of human ovarian oestradiol-17 beta oxidoreductase activity.

Oestradiol-17 beta oxidoreductase activity, which catalyzes the interconversion of oestrone and oestradiol, was investigated in preparations of human ovaries. The enzyme activities were localized primarily in the 105,000 X g supernatant fraction; dialyzed supernatant preparations were used in subsequent studies. The pH optima were 6.9 for reduction and 8.1 for 17 beta-dehydrogenation. The apparent Michaelis constants for oestrone and oestradiol were 1 X 10(-7) M and 5 X 10(-7) M, respectively. The enzyme activity was present with either NADP(H) or NAD(H), though (NADP(H) were the preferred cofactors. Non-aromatic steroids androstenedione, dehydroepiandrosterone, testosterone and 5-androstene-3beta,17beta-diol were poor substrates for the enzyme preparation. Methylation of the phenolic hydroxyl of oestrone and oestradiol resulted in slightly enhanced activities. The sulfhydryl reagent, N-ethylmaleimide, inhibited the reduction of oestrone. A dialyzed supernatant preparation retained approximately 79% of the original enzyme activity when stored at -20 degrees C for 6 weeks.     

Differential effects of catecholoestradiol-17 beta and oestradiol-17 beta on concentrations of plasma LH in the fetal pig

The effects of 2-hydroxyoestradiol-17 beta and oestradiol-17 beta on the concentration of serum LH was studied in fetal pigs. 2-Hydroxyoestradiol-17 beta (5 micrograms/fetus; n = 6), oestradiol-17 beta (5 micrograms/fetus; n = 7) or vehicle (n = 6) were injected i.v. into chronically catheterized fetal pigs at gestational ages of 105-108 days. Seven additional fetuses at the same age served as untreated controls. 2-Hydroxyoestradiol-17 beta but not oestradiol-17 beta resulted in a rapid decline in plasma LH levels from 0.82 +/- 0.21 (S.E.M.) to 0.21 +/- 0.05 micrograms/l within 20 min of injection. Baseline concentrations of plasma LH in the mothers were low (0.72 +/- 0.2 microgram/l) and were not affected by catecholoestrogen or oestrogen treatment of fetuses. The results suggest that catecholoestrogens do not modulate LH secretion in fetal pigs through an oestrogenic action. It is possible that they act by modifying catecholamine metabolism or neurotransmission.     

Metabolism of oestradiol-17 beta and oestrone in the human uterus.

A study of the metabolism of oestradiol in the human endometrium and myometrium of the proliferative and secretory phases of the cycle showed that the conversion of oestradiol to oestrone by endometrium in the proliferative phase was higher than that in the secretory phase. The decreased metabolic activity of the secretory phase endometrium was attributed to the influence of progesterone on the endometrium. The metabolic conversion of oestradiol to oestrone was enhanced when pyridine nucleotides were added to the system. The conversion of oestradiol to oestrone was maximum in the cytoplasmic and nuclear fractions of the endometrium. Furthermore, the conversion of oestradiol was low in all the subcellular fractions of the myometrium as compared with the endometrial subcellular fractions. The presence of co-factors increased the metabolic conversion of oestradiol to oestrone in the subcellular fractions of the endometrium. The presence of 17 beta-hydroxysteroid oxidoreductase was indicated in all the subcellular fractions. A correlation was found between the amount of oestradiol and oestrone bound to the receptors in the uterus and the rate of metabolism of oestradiol in the uterus. The physiological significance of metabolism of oestradiol and the hormone action are discussed.     

Corticotrophin releasing hormone levels in human plasma and amniotic fluid during gestation

OBJECTIVE Corticotrophin releasing hormone, a hypothalamic neuropeptide also made in placenta, may regulate fetal maturation in a stress-responsive manner. The objectives of this study were: (1) to determine if levels of corticotrophin releasing hormone in the amniotic fluid correlate with fetal lung maturation; (2) to confirm that third trimester plasma levels of corticotrophin releasing hormone are increased in patients with pregnancy-induced hypertension compared to normotensives, and (3) to increase the recovery of extracted corticotrophin releasing hormone from plasma and amniotic fluid. DESIGN (1) Levels of corticotrophin releasing hormone in amniotic fluid during the third trimester were compared with those of saturated phosphatidyl choline. (2) Corticotrophin releasing hormone levels were measured in a group of normotensive pregnant women during the entire gestation period. Corticotrophin releasing hormone levels during the third trimester were compared in normotensives and patients with pregnancy-induced hypertension. PATIENTS Twenty-one non-pregnant normal volunteers and 63 pregnant women. MEASUREMENTS Blood pressure, corticotrophin releasing hormone in plasma and amniotic fluid, and saturated phosphatidyl choline in amniotic fluid. RESULTS Corticotrophin releasing hormone levels in amniotic fluid samples during the third trimester ranged from 12 to 98 pmol/l and positively correlated with the saturated phosphatidyl choline levels, but not with gestational age. A significant difference existed in plasma corticotrophin releasing hormone concentration between gestational age-matched third trimester normotensive and hypertensive gravids: corticotrophin releasing hormone levels were significantly lower in normotensives (223 ± 65 pmol/l) than in patients with pregnancy-induced hypertension (544 ± 106 pmol/l, P= 0.001). Plasma corticotrophin releasing hormone increased with gestational age from 51 pmol/l (range 8.4–85) at 25–32 weeks to 375 pmol/l (range 35–1386) at 33–40 weeks. During the third trimester the rise in plasma corticotrophin releasing hormone conformed to an exponential mathematical model of a positive feedback loop between placental corticotrophin releasing hormone and fetal adrenal Cortisol. CONCLUSIONS During the third trimester of pregnancy there is a positive correlation between the level of amniotic fluid corticotrophin releasing hormone and that of saturated phosphatidyl choline. The positive correlation between amniotic fluid corticotrophin releasing hormone and saturated phosphatidyl choline, but not between amniotic fluid corticotrophin releasing hormone and gestational age, suggests that a factor(s), such as stress, may affect both amniotic fluid corticotrophin releasing hormone and saturated phosphatidyl choline in parallel. Furthermore, our data are consistent with the hypothesis that the rise in placental corticotrophin releasing hormone is coupled to an increase in fetal glucocorticoid and lung maturation, and that stresses such as pregnancy-induced hypertension may accelerate this process.     

Effect of pulsatile infusion of gonadotropin-releasing hormone on plasma oestradiol-17 beta concentrations and follicular development during naturally and artificially maintained high levels of plasma progesterone in heifers

To stimulate a follicular-phase pattern of pulsatile LH release, gonadotrophin-releasing hormone (GnRH; 5 micrograms) was infused (i.v.) hourly into heifers for periods of 5-11 days during the luteal phase of the oestrous cycle, and also when plasma progesterone levels were increased artificially by means of a progesterone-releasing intravaginal device. Plasma oestradiol-17 beta concentrations increased from basal (less than or equal to 2.5 pmol/l) to preovulatory peak levels (20-30 pmol/l) during the first 3 days of GnRH treatment. They were maintained at these values before returning to basal levels within 24 h of cessation of infusion. This response occurred regardless of the source of progesterone (endogenous or administered). Follicular development was observed by ovarian palpation (per rectum) in some heifers at the time of maximum secretion of oestradiol-17 beta. There was no detectable cervical mucus secretion or oestrous behaviour during these periods of high oestradiol-17 beta levels and ovulation did not occur. Treatment with GnRH did not affect plasma progesterone concentrations or oestrous cycle length. The study shows that oestradiol-17 beta secretion and follicular development (and the accompanying oestrus and ovulation) are suppressed during the luteal phase of the cycle by high concentrations of plasma progesterone, and provides strong indirect evidence that such inhibition is associated with a reduction in the pulse frequency of LH release.