Changes in ovarian oestrogens and in plasma gonadotrophins in female rabbits from birth to adulthood

Abstract

Plasma oestrogens (E1, E2) and gonadotrophins, and ovarian oestrogens, were determined in female rabbits from birth to 6 months. Increases in ovarian weight followed a curvilinear pattern, with a phase of slow growth (from 1 to 60 days) preceding a phase of rapid growth (from 60 to 90 days). At birth, E2 was already quantifiable in ovaries; it remained at very low levels up to 50 days. Ovarian E2 content increased until 6 months with two sharp rises between 50 days (46 \ m=+-\4 pg/2 ovaries) and 60 days (365 \m=+-\ 53 pg/2 ovaries) and between 80 days (326 \ m=+-\77 pg/2 ovaries) and 90 days (1118 \ m=+-\307 pg/2 ovaries). E1 appeared in ovaries at 50 days and then followed a pattern similar to that of E2. Oestrogens were never detected in plasma.At birth FSH and LH levels were similar to those measured in adult females but from 10 days the secretion of both gonadotrophins showed a clear dissociation. LH concentrations varied little during the period studied (between 1077 \m=+-\106 pg/ml to 2030 \ m=+-\466 pg/ml). Plasma FSH levels were considerably higher between 10 and 50 days than those measured thereafter, particularly in adulthood. The decline in FSH levels occurred simultaneously with the rise in ovarian oestrogens. The pubertal development involves many different maturational events including maturation of the hypothalamic-pituitary-gonadal axis and secondary sexual development which culminates in fertility.rabbit. The aim of the present prospective study was to measure longitudinally, from birth to adult¬ hood, ovarian and plasma oestrogens and circula¬ ting gonadotrophins. Materials and MethodsRabbits of the New Zealand strain were raised in the laboratory under identical conditions of temperature, lighting (daylight) and nutrition (complete pelleted chow and water given freely). Newborns of both sexes were raised by their mothers. When 30 day old, females were isolated 2-4 per cage until sacrifice and were housed in a room containing males and females of different ages. Under our breeding conditions, female rabbits first con¬ ceived at 110-120 days and first fertile matings occurred in males at the mean age of 146 ± 13 days (Berger et al. 1982). Females were killed, without anaesthesia, by sec¬ tion of the jugular and carotid vessels, every 10 days from birth to 90 days and at 4, 5 and 6 months. The blood plasma and both ovaries were frozen at -25°C until assayed.Oestrone (E^a nd oestradiol-17ß (E2) were determined in plasma and ovaries by radioimmunoassay. After addi¬ tion of 2000 DPM of tritiated Et and 2000 dpm of tritiated E2 to monitor procedural losses, plasma (1 to 5 ml) and ovaries (homogenized in 3 ml distilled water) were alkalinized with 0.1 ml 0.1 NaOH and extracted twice with 5-10 ml of freshly distilled diethylether. Ej and E2 were separated by chromatography on a celite column (Ro¬ bertson et al. 1972). After incubation overnight at 4°C, antibody-bound and free hormone were separated using dextran-charcoal.The recovery of the added radioactive standards was 80 ± 13% (mean ± SD) for E, a...

Impact of Sex and Gonadal Steroids on Prolongation of Ventricular Repolarization and Arrhythmias Induced by I K -Blocking Drugs

“…23,24 That extragonadal or nonestrogenic factors may contribute to sex differences in repolarization is suggested by the persistence of sex-related differences in AP after gonadectomy. Consistent with other reports, 7,8 however, our results demonstrate that gonadal steroids modulate proarrhythmic responses to I Kr blockers.…”

“…Their serum estradiol levels remain constant and low (Ͻ100 pg/mL) and are unchanged by oophorectomy. 23 In women, normal estradiol levels range from 130 to 400 pg/mL. 30 Thus, the oophorectomized rabbit model fails to replicate the differences in estradiol levels between normal premenopausal and postmenopausal women.…”

Effects of in-vivo administration of GnRH on the release of gonadotrophins in the female rabbit

“…As part of our continuing studies to elucidate the mechanisms by which female rabbits become sexually mature, we have observed that there is a large increase in circulating gonadotrophin concentrations between Days 30 and 50 of life (YoungLai, 1986), which is several weeks before the rabbit becomes sexually receptive (Hulot et ai, 1982;DeTurckheim et al, 1983;Kamwanja & Hauser, 1983). A similar elevation in gonadotrophin concentrations is seen in the prepubertal female rat before the onset of puberty (Ramaley, 1979).…”

WITHDRAWN: Sex-differences in sodium/calcium exchange expression is a determinant of the arrhythmia phenotype in pre-pubertal rabbit hearts with Long QT type 2

“…An interesting aspect of LQT2 is the reversal of TdP risk in pre-pubertal rabbits, before the surge of sex hormones (in 42-day old rabbits)12, 13 where male hearts are more likely to have E4031-induced TdP than female hearts even though females have longer APDs 14. The reversal of TdP-risk in pre-pubertal rabbits is similar in humans where boys (< 14 years old) with inherited LQT2 are more likely to fall victim of lethal arrhythmias than girls 15.…”