Pattern Of Gonadotropin Release Research Articles

Effect of maternal fatness on fetal steroids and semi-quantitative real-time PCR expression of receptor genes in sheep

Sexual differentiation of the brain occurs between d 30 and 70 in the fetal lamb. The objective of this experiment was to determine if maternal fatness affects fetal steroid production and expression of their receptors which may ultimately alter endocrine systems postnatally. Fetuses were collected from ewes fed at either 100% (Control; n = 5) or 150% (Fat; n = 6) of NRC recommendations from 60 d prior to breeding until collection at 75 d of gestation. Hypothalamic and amygdala neural tissues were collected from twin male/female fetuses. Serum concentrations of testosterone were greater ( P < 0.001) in male fetuses compared to female fetuses. Further, male fetuses from Fat ewes had greater ( P < 0.05) serum concentrations of testosterone than male fetuses from Control ewes, but differences in testicular steroidogenic enzyme mRNA were not detected ( P = 0.18). Quantity of hypothalamic mRNA for estrogen receptor (ER) β tended ( P = 0.1) to be influenced by a sex by treatment interaction. Messenger RNA for ER-β was greater in female fetuses than male fetuses from Control ewes ( P = 0.05). Although amount of ER-β mRNA did not differ among male fetuses ( P = 0.7), amounts tended to be less ( P = 0.07) in female fetuses from Fat ewes compared to those from Control ewes, and did not differ ( P ≥ 0.8) from male fetuses. Hypothalamic ER-α mRNA tended ( P = 0.1) to be less in fetuses from Fat ewes compared to Control fetuses but was not influenced ( P = 0.3) by fetal sex or their interaction. Amount of mRNA for hypothalamic progesterone receptor tended ( P = 0.06) to be greater in male fetuses than female fetuses and tended to be less ( P = 0.06) in fetuses from Fat ewes than in Control fetuses, but did not differ by any sex by treatment interaction ( P = 0.6). Hypothalamic RNA for the androgen receptor did not differ by sex, dam nutritional treatment, or the interaction. Likewise, amygdala RNA for the estrogen or androgen receptor did not differ ( P ≥ 0.3) by sex, treatment, or their interaction. Dam fatness appears to decrease the expression of progesterone receptor, ER-α, and decrease amount of ER-β in the female fetuses while increasing circulating concentrations of testosterone in male fetuses. Altered expression of hypothalamic receptor genes by the uterine environment may affect adult responses to stress, sexual behavior and/or the pattern of gonadotropin release in response to gonadal steroids.

Effect of rabbit doe-litter separation on 24-hour changes of luteinizing hormone, follicle stimulating hormone and prolactin release in female and male suckling pups

BackgroundThe daily pattern of nursing of the rabbit pup by the doe is the most important event in the day for the newborn and is neatly anticipated by them. Such anticipation presumably needs a close correlation with changes in hormones that will allow the pups to develop an appropriate behavior. Although a number of circadian functions have been examined in newborn rabbits, there is no information on 24-h pattern of gonadotropin release or on possible sex-related differences in gonadotropin or prolactin (PRL) release of pups. This study examined the 24-h changes of plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) in 11 days old suckling female and male rabbits left with the mother or after short-term (i.e., 48 h) doe-litter separation.MethodsAnimals were kept under controlled light-dark cycles (16 h – 8 h; lights on at 08:00 h). On day 9 post partum, groups of 6–7 female or male rabbit pups were separated from their mothers starting at 6 different time intervals in the 24 h cycle. Pups were killed 48 h after separation. At each time interval groups of male or female pups that stayed with the mother were killed as controls. Plasma, LH, FSH and PRL levels were measured by specific radioimmunoassays.ResultsIn pups kept with their mother plasma FSH and LH maxima occurred at the first and second part of the light phase (at 13:00 and 17:00 – 21:00 h, respectively) (females) or as two peaks for each of the hormones (at 13:00 and 01:00 h) (males). PRL release was similar in female and male rabbit pups kept with their mother, showing a 24-h pattern with two peaks, at 13:00 and 01:00 h, respectively. Mean 24-h values of gonadotropins and PRL did not differ between sexes. Isolation of pups for 48 h augmented circulating gonadotropin and PRL levels and distorted hormone 24-h pattern to a similar extent in both sexes.ConclusionSignificant sex differences in 24-h changes in LH and FSH, but not in PRL, release occurred in rabbit pups kept with the doe. Separation of newborn pups from their mother augmented circulating gonadotropin and PRL levels and disrupted 24-h rhythmicity of gonadotropin and PRL release similarly in both sexes. The effect of pups' isolation can be attributed either to a modification of the circadian pacemaker or to a masking effect on some of its output overt rhythms.

Effect of stage of development and sex on gonadotropin-releasing hormone secretion in in vitro hypothalamic perifusion.

Marked sexual and ontogenic differences have been described in gonadotropin regulation in the rat. These could arise from events occurring both at the hypothalamic or hypophyseal levels. The present experiments were designed to evaluate the capacity of the hypothalamus in releasing GnRH in vitro, basally and in response to depolarization with KCl, during ontogeny in the rat. To that end we chose two well-defined developmental ages that differ markedly in sexual and ontogenic characteristics of gonadotropin regulation, 15 and 30 days. We compared GnRH release from hypothalami of females, neonatal androgenized females and males. Mediobasal hypothalami were perifused in vitro, and GnRH measured in the effluent. Basal secretion of the decapeptide increased with age in the three groups with no sexual differences encountered. When studying GnRH release induced by membrane depolarization, no differences within sex or age were encountered. On the other hand FSH serum levels decreased with age in females and increased in males, and in neonatal androgenized females followed a similar pattern to that of females. LH levels were higher in infantile females than in age-matched males or androgenized females. Such patterns of gonadotropin release were therefore not correlated to either basal or K+-induced GnRH release from the hypothalamus. We conclude that sexual and ontogenic differences in gonadotropin secretion in the developing rat are not dependent on the intrinsic capability of the hypothalamus to release GnRH in response to membrane depolarization. The hormonal differences observed during development and between sexes are probably related to differences in the sensitivity of the GnRH neuron to specific secretagogue and neurotransmitter regulation, and/or to differences in hypophyseal GnRH receptors and gonadotrope sensitivity.

Ovarian follicular populations, steroidogenic capacity and physiological status in post-partum suckling beef cows in high and low body condition

Recent evidence indicates that body condition at calving has an important effect on the length of the post-partum anoestrous period in beef cows being longer in cows calving in low body condition (Richards et al, 1986, Wright et al, 1987). It is known that body condition affects baseline concentrations of LH (Rutter and Randel, 1984) and LH pulse frequency (Wright et al, 1987). However, the effect of body condition on ovarian follicles has not been studied.An experiment was designed to examine the effect of body condition score (BCS) at calving on follicle populations, follicular steroidogenic capacity, follicular histology and patterns of gonadotropin release at two different stages of the post-partum period (5 and 9 weeks after calving) in suckling beef cows.Thirty-eight suckling Blue-Grey cows with a mean live-weight of 567 ± 9.4 kg and mean BCS of 3.0 ± 0.05 at 110 days before calving to a synchronized insemination were differentially fed so that they achieved BCS of 2.83 ± 0.05 and 2.30 ± 0.05 for cows on a high (H) and low (L) plane of nutrition, respectively. After calving cows were fed a live-weight maintenance ration according to individual requirements. Cows of each BCS were ovariectomized at either 5 (w5) or 9 (w9) weeks after calving and follicles &gt; 3mm in diameter were dissected from the ovaries and incubated for 2 h in culture medium (Medium 199) at 37°C. Follicles were then kept in Bouin's solution until histological examination. Follicle incubates were assayed for progesterone, testosterone and oestradiol. Blood samples were taken 2 days before ovariectomy for 10 h every 15 minutes and were later assayed for LH (all the samples) and FSH (every third sample).

Abolishment of the positive feedback mechanism: a criterion for temporary medical hypophysectomy by LH-RH agonist.

The hypothalamic pituitary axis was studied in patients with an abnormal pattern of gonadotropin release during chronic treatment with LH-RH agonist. Two patients had PCOD and the third demonstrated the early luteinization phenomenon. Following a well-defined gonadotropin rise with initiation of LH-RH treatment, no further response was noted. Stabilization of the LH:FSH ratio in PCOD patients was noted after 4 weeks of treatment. Administration of both native LH-RH (100 micrograms) and intravenous pulsatile LH-RH did not evoke any rise in LH. In addition to the above LH-RH challenges, the positive feedback was examined by administration of estradiol benzoate (EB). The study demonstrated that, although the pituitary did not respond to any LH-RH challenge, it may still respond by a rise in LH following EB administration. Both functions of the hypothalamic pituitary axis should be examined in order to determine the state of medical hypophysectomy.

Puberty without Gonadotropins

Abstract Recent evidence suggests that a group of children exists in whom premature sexual maturation occurs in the absence of pubertal levels of gonadotropins; that is, they have gonadotropin-independent precocious puberty. We compared six boys and one girl with this disorder with four boys and five girls with central precocious puberty, in which there is a pubertal pattern of gonadotropin release. The two groups were similar in age of onset, degree of sexual development, growth velocity, and rate of skeletal maturation. A family history of precocity was noted in four of the boys with gonadotropin-independent precocity, and the girl had McCune–Albright syndrome. Children with central precocious puberty demonstrated a pulsatile release of gonadotropins, pubertal responses to luteinizing hormone–releasing hormone, and complete suppression of gonadarche after exposure to an analogue of luteinizing hormone–releasing hormone (LHRHa). In contrast, children with gonadotropin-independent precocity demonstrated a...

Regulation of tonic gonadotropin release in prepubertal female hamsters.

Basal serum gonadotropin levels were monitored weekly in female hamsters from birth to 10 weeks of age. Hamsters raised on three different photoperiods presented uniform pre- and postpubertal patterns of serum LH and FSH, suggesting that gonadotropin release in the young hamster occurs independently of ambient photoperiod. In all groups, serum LH levels increased gradually in animals up to 4 weeks of age, after which levels plateaued at 50--100 ng/ml. Serum FSH was markedly elevated in 2- and 3-week-old hamsters (800--1200 ng/ml), but remained at 200--400 ng/ml in all other groups. We next examined the change in the responsiveness of the pituitary to exogenous gonadotropin-releasing hormone (GnRH) challenge. Female hamsters 2 days of age failed to respond to any dose (0.025--1000 ng) of GnRH, while 10-day old females responded in typical dose-dependent fashion. GnRH-stimulated LH release first occurred in 6-day-old hamsters and was maximal by day 9, whereas FSH release first occurred on day 8 and was maximal by day 9. The prepubertal pattern of gonadotropin release can, in part, be explained on the basis of the development of pituitary GnRH sensitivity, which occurs independently of photoperiod.

Some Aspects of Pituitary Function in the Male Diabetic

In order to elucidate the hypothalamic—pituitary function in diabetes, the pituitary responsiveness of LH, FSH, prolactin (PRL), and growth hormone (GH) to a thyrotropin releasing hormone (TRH, 200 μg) plus gonadotropin releasing hormone (GnRH, 100 μg) intravenous bolus injection was studied in a group of 13 insulindependent male patients aged 23–47 years. The results obtained for gonadotropin secretion showed LH responses to be significantly higher than those obtained in a group of controls, while basal and stimulated FSH levels were not different from those in the controls. There were no significant differences in PRL secretion between diabetics and control subjects. However, most of the diabetic patients studied (nine out of 12) showed an unexpected but definite GH response to the combined TRH + GnRH test. In conclusion, the observed pattern of gonadotropin release is consistent with gonadal failure previously documented in diabetics. However, the paradoxical GH responses suggest that diabetes also affects the function of the hypothalamic—pituitary unit in a manner similar to that documented in other pathologic conditions.

Maturation of the Clock-Timed Gonadotropin Release Mechanism in Hamsters: A Key Event in the Pubertal Process*

Gonadotropin secretion patterns were monitored in 10, 14 to 21-, and 35-day-old prepubertal female hamsters by RIA. Blood samples were obtained between 1500-1900 h to coincide with the time when the adult female hamster experiences a clock-timed surge in gonadotropin release. Before 16 days of age, the female hamster appears to exhibit a tonic pattern of gonadotropin release. On day 16 and thereafter, the female hamster exhibits a daily surge of gonadotropin release. Around the clock sampling (every 3 h) has shown that this cyclic pattern of gonadotropin release is not present at any time studied in female hamsters younger than 16 days of age, appears to be clock timed, and occurs at the same time of day as the proestrus surge in cyclic adults. The maturation of the clock timed gonadotropin release mechanism may indicate maturation of the reproductive control system, a key event in the pubertal process.

Pituitary and gonadal desensitization after continuous luteinizing hormone-releasing hormone infusion in normal females.

Three normal females were studied during the early follicular phase of the menstrual cycle employing a continuous infusion of LHRH (1.4 micrograms/min) for 72 h. Blood samples were taken every 4 h. LH concentrations climbed from 9.3 mIU/ml basally to peak values of 120 mIU/ml at 12 h, then fell to a plateau between 23-31 mIU/ml from 36-72 h. FSH levels rose from 5.4 to 36 mIU/ml at 4 h of infusion and then returned to baseline. 17 beta-Estradiol increased from 48 to 184 pg/ml at 32 h, but subsequently fell toward basal concentrations. 17-Hydroxyprogesterone increased from 0.5 to 1.23 ng/ml at 12 h and remained elevated for the remainder of the infusion period. Serum progesterone levels remained constant. Three females with premature ovarian failure were studied, and the pattern of gonadotropin release was similar to that of normal subjects. Studies demonstrate that continuous LHRH infusion in normal females causes pituitary and gonadal desensitization. The desensitization of the pituitary is independent of gonadal activity.

Gonadotropin Output in Congenital Adrenal Hyperplasia before and after Adrenal Suppression

Basal release of gonadotropin and the response to an infusion of 100 mug of synthetic luteinizing hormone releasing hormone (LRH) were studied in a teenage girl with congenital adrenal hyperplasia (CAH). The initial study was done during a period of poor adrenal suppression, and second study was done after adequate adrenal suppression was achieved. To assess adrenal function, circulating levels of adrenal steroid hormones were evaluated continuously over a 24 h period. During the period increased production of adrenal androgens, the pattern of gonadotropin release was that of a prepubertal child. After 3 months of adrenal suppression the pattern of gonadotropin secretion was similar to that of a normal girl in mid-puberty. This demonstrates the rapid change from prepubertal to pubertal gonadotropin dynamics in a teenage patient following adequate suppression of androgens from the adrenal.