Endocrine modulation of gamma-aminobutyric acidergic innervation in the rat fallopian tube

The present study investigates the effect of different endocrine manipulations on the gamma-aminobutyric acid (GABA)-ergic system in the rat fallopian tube. Either hypophysectomy or ovariectomy induced a significant decrease of glutamic acid decarboxylase (GAD) activity and of GABA levels in in situ tubes. This effect was completely reversed by either gonadotropins or combined estrogen-progesterone administration, respectively. Estrogen or progesterone alone proved less effective than the administration of both steroids in counteracting the effect of ovariectomy on GAD activity. The in vitro incubation of ovariectomized rat fallopian tubes with estrogen-progesterone for 1 h failed to counteract the reduction of the GAd activity induced by surgical manipulation. The in vivo effect of estrogen-progesterone administration on the GABA-ergic system seems to be specific since steroid treatment induced the synthesis of an enzyme which was immunologically identical to the GAD present in the fallopian tube and brain of normal diestrous rat. Autotransplantation of the fallopian tube under the skin brought about a decrease of GAD activity similar to that obtained after ovariectomy. In this situation, however, estrogen-progesterone administration did not counteract the decrease of GAD activity induced by fallopian tube deafferentation. The present results demonstrate that an interaction between the GABA-ergic system and the hypothalamo-pituitary-gonadal axis seems to be operative at the level of the rat fallopian tube. However, the physiological meaning of this interrelationship between the endocrine and the peripheral nervous systems remains to be clarified.     

Effects of age on GABA turnover rates in specific hypothalamic areas in female rats.

During aging in female rats the estrous cycle ceases and the animals develop phases of constant estrous (CE) or constant diestrous (CD) prior to the irreversible transition into anestrous. In young rats, gamma-aminobutyric acid (GABA) is of pivotal importance for the release of GnRH. In the medial-preoptic area (MPO) where the majority of the GnRH perikarya are located in the rat, GABA release decreases at the time of the preovulatory LH surge. The suprachiasmatic nucleus (SCN) contains numerous GABA neurons. Neurochemical signals from this hypothalamic nucleus provide temporal information to GnRH neurons and thereby influence the preovulatory LH surge and the length of estrous cycles. To investigate aging-related changes of the activity of hypothalamic GABAergic neurons, we determined GABA turnover rates in various hypothalamic nuclei of CE and CD rats and compared them to those determined in young estrous (E) or diestrous rats (D1). In old female rats, GABA activity in the MPO was significantly decreased compared to E and D1 rats. A selective increase of GABA turnover rates was observed in the SCN of CE animals. No age-related changes were observed in the other examined brain areas. These data provide the first evidence for alterations in GABAergic activity in specific hypothalamic areas that depend on age and reproductive status. These may cause changes in ability to induce preovulatory LH surges and to maintain regular estrous cyclicity.     

Relationship of age, sex, and reproductive status to the quantity of tyrosine hydroxylase in the median eminence and superior cervical ganglion of the rat

Tyrosine hydroxylase (TH) in the median eminence (ME) and superior cervical ganglion (SCG) of the rat was quantified by means of an immunoblot procedure, using highly purified rat TH as the standard. Antibodies against rat TH were produced in the rabbit. The assay was linear from 0-100 ng TH and had a correlation coefficient of 0.990 +/- 0.0014 (mean +/- SE: n = 22). The interassay coefficient of variation was 8.65% (n = 17). In young female rats (12-16 weeks old) with regular 4-day estrous cycles, the quantity of TH in the ME on various days of the cycle was as follows: estrus, 42 +/- 2.9 ng; diestrous day 1, 61 +/- 2.8 ng; diestrous day 2, 75 +/- 4.2 ng; and proestrus, 84 +/- 3.3 ng. In ovariectomized rats (15-16 weeks old), the ME contained 24 +/- 1.6 ng TH. In prepubertal rats (5-5.5 weeks old), the ME of females contained 25 +/- 2.0 ng TH, and that of males contained 24 +/- 2.1 ng. The amount of TH in the ME of young mature males (15-16 weeks old) was 34 +/- 3.3 ng, and that of old males (17-20 months old) was 37 +/- 1.6 ng TH. In aged female rats (22-24 months old), the MEs of diestrous and estrous animals contained 71 +/- 2.8 and 63 +/- 4.2 ng TH, respectively. In cycling females (12-16 weeks old), the quantity of TH per SCG was as follows: estrus, 41 +/- 3.2 ng, diestrous day 1, 64 +/- 1.2 ng; diestrous day 2, 82 +/- 4.4 ng; and proestrus, 101 +/- 4.9 ng. In ovariectomized rats (15-16 weeks old), there was 34 +/- 2.0 ng TH/SCG. In prepubertal rats (5-5.5 weeks old), the SCG of females contained 33 +/- 4.1 ng TH, and that of males contained 32 +/- 2.3 ng. The amount of TH in SCG of mature males (15-16 weeks old) was 47 +/- 3.0 ng, and that in old males (17-20 months old) was 58 +/- 4.6 ng. In aged female rats (22-24 months old), the SCG of diestrous animals contained 152 +/- 6.3 ng TH, and that of constant estrous animals contained 139 +/- 8.8 ng TH. It is concluded that before puberty, the amounts of TH in the ME and SCG of female rats are similar to those in male rats. After puberty, the amount of TH in these structures is greater in females than in males.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sedative and GABAergic effects of ethanol on male and female rats

Background: Women consume less alcohol than men, and yet they are more susceptible than men to the negative medical consequences of alcohol use, such as cirrhosis of the liver, cardiac disease, and cognitive impairments. This sex difference is also reflected in animal studies, in which male and female rats differ on both behavioral and electrophysiological measures. Given that one significant difference between males and females is the cycling fluctuations of the sex hormones, this study aimed to compare the relative sensitivity of adolescent and adult rats of both sexes and varying estrous stages to the behavioral and electrophysiological effects of ethanol. Methods: Adult female rats were lavaged daily for estrous cycle assessment. Following administration of 5 g/kg ethanol, adolescent and adult male and female animals were observed for loss of the righting reflex. Then, using whole‐cell recording, we tested the response of spontaneous, gamma‐aminobutyric acid (GABA_A) receptor‐mediated inhibitory postsynaptic currents (sIPSCs) in hippocampal slices from drug‐naïve adult male and female rats. Results: Consistent with previous findings, adolescent animals were less sensitive than adults to the effect of ethanol on the righting reflex. In addition, adult proestrous and diestrous female rats were less sensitive than male rats to the sedative effects of ethanol. Finally, ethanol increased the frequency of sIPSCs in hippocampal pyramidal neurons and did so more potently in cells from male rats than in those from female rats. Conclusions: Female animals are less sensitive to the behavioral sedative effects of ethanol than adult male rats, and the effect is pronounced in the proestrous and diestrous states. This sex difference may be related to differential sensitivity of GABA receptor–mediated central nervous system function to ethanol in females.     

Neonatal Melatonin Administration Advances Rat Vaginal Opening and Disrupts Estrous Cyclicity and Estrogen-Dependent Regulatory Mechanisms of Luteinizing Hormone and Prolactin

Melatonin (100 micrograms/rat) was administered to female rats on day 5 of life, 3 hours prior to the onset of darkness or at 12:00 hours. Melatonin administration induced precocious puberty in both cases, as indicated by the advance of the time of the vaginal opening and the appearance of the first estrous smear as compared with controls (P less than 0.01), together with an increase in the number of estrous smears (P less than 0.05) and a reduction in the number of diestrous smears (P less than 0.05). Decreased serum prolactin levels were observed on day 21 of age (P less than 0.05) in melatonin-treated rats with both of the melatonin injection times as compared with controls. No differences were apparent in basal luteinizing hormone (LH) levels either at 30 or at 60 days of age comparing melatonin- and vehicle-treated rats with either of the scheduled melatonin injection times. As to serum follicle-stimulating levels (FSH) levels, there was a marked decrease in circulating FSH levels in melatonin-treated rats in both cases on days 21, 30, and 45 (P less than 0.05) as compared with controls. A marked increase of serum prolactin at both 48 and 55 hours after estradiol benzoate (EB) administration was detected in 30-day-old melatonin-treated rats as compared with controls (P less than 0.05 for both points). Also, an increased responsiveness of prolactin to EB was found on the first day post-administration. At 60 days of age, an increase in prolactin responses to EB was observed on the first day post-administration (31 and 48 hours after, (P less than 0.01), whereas no differences were detected at any other studied time. The LH burst that occurs 31 hours after EB administration in 30-day-old rats was decreased in melatonin-treated animals as compared with controls (P less than 0.05). In 60-day-old melatonin-treated rats, a marked increase in the LH response to EB administration, 31 hours after injection (P less than 0.01), was observed. These data suggest that neonatal melatonin administration in pharmacological amounts induces precocious puberty as measured by vaginal opening and, furthermore, it advances the appearance of the first estrous smear with age-dependent modifications of estrous cyclicity and prolactin and LH responses to EB.     

A conditional tetracycline-regulated increase in Gamma amino butyric acid production near luteinizing hormone-releasing hormone nerve terminals disrupts estrous cyclicity in the rat

Gamma amino butyric acid (GABA) is the main inhibitory neurotransmitter controlling LH-releasing hormone (LHRH) secretion in the mammalian hypothalamus. Whether alterations in GABA homeostasis within discrete regions of the neuroendocrine brain known to be targets of GABA action, such as the median eminence, can disrupt the ability of the LHRH releasing system to maintain reproductive cyclicity is not known but amenable to experimental scrutiny. The present experiments were undertaken to examine this issue. Immortalized BAS-8.1 astroglial cells were genetically modified by infection with a regulatable retroviral vector to express the gene encoding the GABA synthesizing enzyme glutamic acid decarboxylase-67 (GAD-67) under the control of a tetracycline (tet) controlled gene expression system. In this system, expression of the gene of interest is repressed by tet and activated in the absence of the antibiotic. BAS-8.1 cells carrying this regulatory cassette, and cultured in the absence of tet ("GAD on"), expressed abundant levels of GAD-67 messenger RNA and GAD enzymatic activity, and released GABA when challenged with glutamate. All of these responses were inhibited within 24 h of exposure to tet ("GAD off"). Grafting "GAD on" cells into the median eminence of late juvenile female rats, near LHRH nerve terminals, did not affect the age at vaginal opening, but greatly disrupted subsequent estrous cyclicity. These animals exhibiting long periods of persistent estrus, interrupted by occasional days in proestrus and diestrus, suggesting the occurrence of irregular ovulatory episodes. Administration of the tetracycline analog doxycycline (DOXY) in the drinking water inhibited GAD-67synthesis and restored estrous cyclicity to a pattern indistinguishable from that of control rats grafted with native BAS-8.1 cells. Animals carrying "GAD on" cells showed a small increase in serum LH and estradiol levels, and a marked elevation in serum androstenedione, all of which were obliterated by turning GAD-67 synthesis off in the grafted cells. Morphometric analysis of the ovaries revealed that both groups grafted with GABA-producing cells had an increased incidence of large antral follicles (>500 micrometer) compared with animals grafted with native BAS-8.1 cells, but that within this category the incidence of steroidogenically more active follicles (i.e. larger than 600 micrometer) was greater in "GAD on" than in "GAD off" rats. These results indicate that a regionally discrete, temporally controlled increase in GABA availability to LHRH nerve terminals in the median eminence of the hypothalamus suffices to disrupt estrous cyclicity in the rat, and raise the possibility that similar local alterations in GABA homeostasis may contribute to the pathology of hypothalamic amenorrhea/oligomenorrhea in humans.     

The effect of transient dopamine antagonism on thyrotropin-releasing hormone-induced prolactin release in ovariectomized rats treated with estradiol and/or progesterone

PRL release was studied in ovariectomized (OVX) rats pretreated with estradiol benzoate (EB), progesterone (P), or a combination of both steroids using a protocol that was selected to mimic ovarian steroid changes that have been observed during the female rat 4-day estrous cycle and early pregnancy. On the morning of the experiment, the animals received injections of either the dopamine (DA) antagonist domperidone (0.01 mg/rat iv) or vehicle (acetic acid in saline). Five minutes later, all animals received injections of the DA agonist 2-bromo-alpha-ergocryptine (CB-154; 0.5 mg/rat, iv) followed 60 min later by the administration of TRH (1.0 microgram/rat, iv). Plasma obtained from blood samples taken during the experiment was assayed for PRL by RIA. In OVX or P-treated OVX rats, a transient blockade of DA by domperidone did not alter the sensitivity of the pituitary to TRH administration, as measured by an increase in plasma PRL. However, such an effect of DA blockade was induced by 2 days of EB treatment and was maintained and amplified by P administration after EB injections. We conclude that enhancement of the PRL-releasing effect of TRH by DA antagonism, a mechanism we previously observed in female rats during midlactation, proestrus, estrus, and metestrus using the present drug protocol, can be induced by estrogen and maintained by P. Further, our data suggest that the previously observed loss of this secretory mechanism on the morning of diestrus may be due to the decrease in plasma P that takes place between metestrus and diestrus.     

Age-, sex-, and gonadal steroid-related changes in immunoreactive substance P in the rat anterior pituitary gland

The interrelationship of anterior pituitary lobe (AP) immunoreactive substance P (I-SP) concentrations with age, sex, gonadal steroids, and estrous cyclicity in rats was examined. There was no difference between male and female AP I-SP levels at 0.5 month of age. At 2.0 and 5.0 months of age, a sex-linked difference in AP I-SP concentrations was evident, inasmuch as male APs contained approximately 3 and 8 times greater concentrations of I-SP, respectively, than APs from age-matched females. Long term (6 weeks) gonadectomy of adult rats resulted in an increase in I-SP concentrations in female APs and a decrease in the concentrations of the peptide in male APs compared to values in their respective sham-operated controls. Treatment of gonadectomized animals for the same length of time with gonadal steroid-filled Silastic capsule implants resulted in qualitatively identical responses in males and females; that is, estradiol benzoate decreased and 5 alpha-dihydrotestosterone propionate increased AP I-SP levels compared to the respective control values in castrates. Testosterone propionate treatment had no effect on AP I-SP levels compared with the respective gonadectomy control values. Short term (8 days) gonadectomy of adult males did not affect the AP concentration of I-SP. Likewise, gonadectomy of adult females was ineffective in altering the AP I-SP concentration compared with concentrations in females on diestrous day 1, diestrous day 2, proestrous, or estrous stages of the vaginal cycle. These data suggest that gonadal steroids are physiologically important in the regulation of I-SP concentrations in the AP. We hypothesize that I-SP is indigenous to the AP and that gonadal steroids act directly at the level of the AP to affect the synthesis and/or release of the peptide.     

Actions of pregnant mare serum gonadotropin in the immature female rat: correlative changes in blood steroids, gonadotropins, and cytoplasmic estradiol receptors of the anterior pituitary and hypothalamus.

Several blood steroids, serum gonadotropins and cytosol estradiol receptors of the anterior pituitary and hypothalamus were quantified in immature female rats which were induced to ovulate with pregnant mare's serum gonadotropin (PMSG). Studies revealed that serum levels of progesterone, 17-hydroxyprogesterone, testosterone, androstenedione and estradiol were initially elevated at 6 PM (day 30) after administration of 8 IU of PMSG at 10 AM day 30. Serum levels of estradiol and testosterone rose progressively from day 30 through the AM of day 32. A further increase in serum concentrations of progesterone, 17-hydroxyprogesterone, androstenedione, testosterone, and dehydroepiandrosterone occurred on the PM of day 32 whereas serum estradiol levels declined. Serum levels of all steroids declined on the day of estrus (33) and only progesterone levels were further elevated on day 34 (diestrus). Dihydrotestosterone concentrations were minimally altered by PMSG treatment. Saline administration resulted in no significant alterations in levels of any steroid quantified from day 29 to 34 in control animals. A progressive decline in cytosol estradiol receptor content of the anterior pituitary and hypothalamus was documented following PMSG treatment of intact female rats; there was no depletion of receptors following PMSG administration to ovariectomized immature rats. Maximal depletion of cytosol estradiol receptors occurred on day 32 with replenishment of cytosol estradiol receptor levels on estrus (day 33). The preovulatory gonadotropin surge was found to occur on the PM of day 32 after maximal receptor depletion. The cycle of depletion and replenishment of receptors was repeated during a second spontaneous estrous cycle four days later which coincided with a rise and fall in serum estradiol levels. It is suggested that the depletion of cytosol estradiol receptors of the anterior pituitary/hypothalamic unit may be causally related to the preovulatory gonadotropin surge resulting from PMSG administration to immature female rats. In addition, changes in blood steroids and gonadotropins after PMSG treatment are similar to those reported for proestrus-estrus-diestrus I of the normal adult estrous cycle. These findings further demonstrate the validity of the PMSG-primed immature female rat preparation as a model for the estrous cycle of the adult rat.     

Prolactin in cerebrospinal fluid increases the synthesis and release of hypothalamic gamma-aminobutyric acid

The effect of intracerebroventricularly (i.v.t.)-injected rat prolactin (2 micrograms/rat) on the function of tuberoinfundibular gamma-aminobutyric acid (GABA)ergic neurones was assessed in adult male rats by measuring the activity of glutamic acid decarboxylase (GAD) in the mediobasal hypothalamus (MBH) and the concentrations of GABA in hypophysial portal plasma and in the anterior pituitary gland. Fourteen hours after i.v.t. injection of rat prolactin the activity of GAD in the MBH was significantly (P less than 0.05) increased and it remained elevated for at least 16 h after injection. The mean concentrations of GABA in hypophysial portal plasma and in the anterior pituitary were twice those found in vehicle-treated controls 16 h after administration of rat prolactin; no significant effects were observed at earlier time-periods. A significant (P less than 0.01) and long-lasting decrease in endogenous plasma prolactin concentrations was detected 2 h after the i.v.t. injection of rat prolactin and the concentrations remained suppressed for up to 16 h. The present results are consistent with the concept that the activity of tuberoinfundibular GABAergic neurones is regulated, at least in part, by circulating prolactin. The ability of prolactin to accelerate the synthesis and release of GABA in the MBH might constitute a short loop feedback system by which the hormone regulates its own secretion.     

Estrogenic effects on urinary 6-sulphatoxymelatonin excretion in the female rat

ABSTRACT: The pattern of melatonin production during the estrous cycle of the rat was measured by monitoring urinary 6-sulphatoxymelatonin (aMT.6S) excretion. Adult rats were maintained under a 14L: 10D photoperiod and urine was collected at hourly intervals over a 5-day period using an automated collection system; the concentration of aMT.6S was assayed by RIA and hourly outputs were calculated. Each nightly collection of urine was assigned to an estrous cycle stage as determined by the vaginal smear of the preceding morning. Total aMT.6S excretions (mean ± SEM) during estrous, metestrous, diestrous, and proestrous stages were 493 ± 49, 539 ± 44, 562 ± 40, and 646 ±51 pmol/night, respectively (n = 7). The excretion of aMT.6S was significantly higher on the night of proestrus compared to each of the other stages ( P < 0.05). To determine whether estrogen was responsible for the increased aMT.6S excretion during proestrus, rats were studied before and after ovariectomy and following implantation with estradiol implants. Total overnight aMT.6S excretion was reduced by 31 % in ovariectomized animals relative to the intact state ( P < 0.05) and restored to the intact levels by administration of estradiol ( P < 0.05). It was concluded that estradiol can modulate melatonin production in adult rats, and that the changing pattern of aMT.6S excretion throughout the estrous cycle may provide a basis for a functional relationship between pineal activity and reproduction in this species.     

Development of gonadal feedback regulation of gonadotropin gene expression and secretion in female rats.

The postnatal development of the gonadal negative feedback control of gonadotropins was studied in female rats. Neonatal (5-day-old) and randomly cycling young (60-day-old) and more mature (180-day-old) adult rats were ovariectomized, and half of them received Silastic implants containing the synthetic estrogen, diethylstilbestrol. The neonatal rats were killed 5, 10 or 15 days, and the adult rats 7 days after the operation. Age-matched and sham-operated animals served as controls. There were no statistically significant responses of serum LH or FSH concentrations or of the pituitary gonadotropin subunit mRNA levels to ovariectomy at any of the neonatal ages. A marked increase (p < 0.01) after ovariectomy was seen in serum gonadotropins and in the cognate mRNA levels at both adult ages. In spite of the weak feedback response of the neonatal rats to ovariectomy, diethylstilbestrol suppressed the basal pituitary gonadotropin concentrations and the specific LH and FSH beta-chain mRNAs (p < 0.01-0.05). These results demonstrate that the gonadal negative feedback regulation of gonadotropin synthesis and secretion is not fully developed in neonatal and prepubertal female rats before 20 days of age. This is probably due to the steroidogenic quiescence of the ovaries in early life. However, the capability of the pituitary to respond to negative estrogen feedback has developed in the neonatal female, as demonstrated by the suppressive effects of diethylstilbestrol treatment on gonadotropin secretion.     

Quantitative differences in goblet cells in the tracheal epithelium of male and female rats.

The cause of higher morbidity rates among men than women from diseases of the respiratory tract may be complex and involve several factors, one of which may be structural differences within airways. In an attempt to determine whether such differences exist, 13 male rats and 45 female rats (15 each in proestrous, estrous, and diestrous) were evaluated. Tracheas were fixed in situ by injection of a mixture of formaldehyde and glutaraldehyde. Longitudinal sections cut from paraffin blocks were stained and combined alcian blue (pH 2.5) and periodic acid-Schiff stain to count goblet cells, or with Weigert's hematoxylin and eosin stain to determine epithelial thickness. In the normal rat trachea, cells containing periodic acid-Schiff-positive granules at their apices constituted a major population of goblet cells. The number of these goblet cells present in the trachea was greater in female than in male rats at each stage of the estrous cycle, with the values in the diestrous females closest to the value in the males. Among females, estrous and proestrous rats contained significantly more of these goblet cells than did diestrous animals. The tracheal epithelium of male rats was significantly thicker than that of female rats. These studies demonstrate that the tracheal epithelium differs in male and female rats and varies in the female rat as a function of hormonal cycles. These results raise the question of whether similar differences might be important in the pathogenesis of human disease, and they deserve further clarification in man.     

Evidence for a physiological role of gonadotropin-releasing hormone (GnRH) or GnRH-like material in the ovary

The possibility that GnRH or a GnRH-like material of ovarian origin may play a physiological role in follicular development was explored in immature hypophysectomized rats by testing whether a potent synthetic antagonist of GnRH action [( N-acetyl-dehydro-Pro1,D-p-chloro-Phe2,D-Trp3,6]GnRH), would potentiate FSH-induced maturation of ovarian follicles to an ovulable stage. Rats were hypophysectomized on day 25 of their life and implanted with a Silastic capsule containing diethylstilbestrol. On day 30, they were started on injections of 10 micrograms NIH FSH-S12 twice daily alone (control) or in combination with 10 micrograms of either native GnRH or GnRH antagonist. On day 35, all rats received 30 IU hCG to trigger ovulation and luteinization of mature follicles. Rats were killed 25.5-28 h later and inspected for number of ova in Fallopian tubes, ovarian weight, number of corpora lutea (CL) on ovarian surface, and appearance of hematoxylin-eosin-stained ovarian slices. In control animals (n = 6), we found some ovulations (mean +/- SEM, 3.2 +/- 1.1/rat), many more CL (16.5 +/- 4.5/rat), and ovarian weights of 37.7 +/- 1.1 mg/rat. In GnRH-treated rats (n = 5), there were no CL formed, no ova were found, and ovarian weights were 16.0 +/- 1.5 mg/rat. In contrast, in GnRH antagonist-treated rats (n = 5), 16.4 +/- 1.6 ova/rat were recovered from the Fallopian tubes, and ovaries contained 20.8 +/- 2.5 CL/rat and weighed 52.7 +/- 3.2 mg/rat. All changes were statistically significant. We conclude that an antagonist of GnRH action is able to potentiate the action of FSH on ovarian follicle development and suggest that it does so by inhibiting the action of an endogenous GnRH or GnRH-like substance that may play a role as a physiological atretic signal.     

Gonadotropic activity of the hypophysis of rats with continuous estrus induced by autotransplantation of the ovaries into the medium with low temperature

Gonadotropic activity of the adult rat hypophyses with continuous estrus (CE), induced by ovarian autotransplantation into the concha auriculae was studied. The "summary" gonadotropin content in the hypophyses of CE rats, determined on experimental infantile young rats, was higher than in intact estrous animals. LH level, examined by radioimmunoassay, was also higher than in intact estrous rats. LH content was lower in the blood of CE rats, as compared with that of intact estrual animals. In control female rats, prolonged reserpine administration led to the sexual cycle cessation and diestrus arising during 13 days Reserpine did not influence CE in the majority of rats. The drug interrupted CE in some animals not more than for 2 days, followed by CE recovery. The absence of a true reserpine effect upon CE was indicative of estrogenic insufficiency. A single subcutaneous estradiol benzoate injection (15 micrograms/rat) provoked a marked LH secretion in CE rats. It is concluded that CE, induced by ovarian autotransplantation into the concha auriculae is caused by estrogenic insufficiency leading to the absence of ovulation.     

Activation of growth hormone short loop negative feedback delays puberty in the female rat

Implantation of GH in the median eminence of the hypothalamus of 23-day-old female rats tonically inhibited serum GH levels throughout prepubertal development (days 23-36) and depressed GH diurnal pulsatile release. Puberty was significantly delayed in GH-deficient animals, a delay associated with a blunted in vitro ovarian steroidal responsiveness to gonadotropins (particularly estradiol) and a marked decrease in prepubertal uterine weight, as evaluated 4, 7, and 13 days after GH implantation. The prepubertal body weight increase was also depressed. Neither ovarian weight nor serum levels of LH, FSH, PRL, or TSH were consistently altered by the GH implant. In addition, evaluation of pulsatile PRL release in 33-day-old rats revealed no difference between control and GH-deficient animals. Ovarian LH receptor content was lower in GH-implanted rats than in controls, suggesting that a decrease in LH receptors may be one of the mechanisms by which a chronic decrease in serum gH depressed the prepubertal ovarian estradiol and, to a lesser extent, the progesterone response to gonadotropins. A direct ovarian site of action for GH was indicated by the results of experiments in which GH was administered to immature hypophysectomized estrogen-treated rats. The in vitro ovarian progesterone response of the GH-treated animals to both hCG and human FSH was distinctly increased by prior in vivo GH treatment. This effect of GH was not reproduced either by the in vivo administration of LH at a dose calculated by RIA to be contaminating the GH preparation or by FSH at a dose that induced a marked increase in aromatase activity in the same ovaries. GH treatment of hypophysectomized rats failed to affect either aromatase activity or hCG-induced estradiol release, indicating that GH does not directly facilitate the production of estradiol by the ovary. The fact that intact rats with GH implants did not actually show a decrease in the ovarian estradiol response to hCG but, rather, failed to show an increased response at the same time as control animals strongly suggests that ovarian maturation was delayed in GH-deficient rats. It is suggested that, in addition to PRL, GH may also play a role in the process of prepubertal reproductive development by enhancing the steroidal response of the ovary to gonadotropins.     

Progesterone-like effects of estradiol on reproductive behavior and hypothalamic progestin receptors in the female rat

During the rat estrous cycle, estradiol (E2) and progesterone (P) synergize to activate reproductive behavior. However, receptivity and proceptivity can be elicited by E2 alone in ovariectomized (OVX) animals, particularly when E2 doses are high. The purpose of this study was to determine the neuroendocrine mechanism by which E2 elicits P-dependent reproductive behavior. Adult OVX females received estrogen treatment for 72 h, which consisted of 5 mm Silastic capsules containing 100% E2 or 10% E2, or of 3 injections of estradiol benzoate (EB; 20 micrograms daily). At 72 h, animals were sacrificed for nuclear progestin receptor (NPR) measurements, while others were tested for reproductive behavior. The remaining animals received 1-mg injections of E2, P, moxestrol (Mox) or oil, and either were sacrificed 2 h later for NPR measurements or were tested 4 h later for reproductive behavior. A subset of the animals receiving 1 mg E2 received concurrent administration of the protein synthesis inhibitor, anisomycin (ANI; 100 mg/kg). Acute administration of 1 mg of E2 or P significantly elevated proceptivity, receptivity and NPRs in the mediobasal hypothalamus-preoptic area (MBH-POA) and pituitary (PIT) in females primed with 100% E2. An equivalent dose of Mox was without effect. ANI blocked the acute activation of feminine reproductive behavior by 1 mg of E2. In the absence of acute steroid administration, animals primed for 72 h with EB showed higher levels of reproductive behavior than animals primed with 100% E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diabetes-induced alterations of reproductive and adrenal function in the female rat

Diabetes interferes with reproductive function in laboratory animals. Previous studies in female diabetic rats have not resolved if the reproductive abnormalities observed are at the hypothalamic, pituitary and/or ovarian level. The interaction of the gonadal and adrenal axes has not been studied in the diabetic female rat. The purpose of this study is twofold: first, to determine the level of dysfunction in the hypothalamic-pituitary axis caused by diabetes in the adult female rat controlling for stage of the estrous cycle, and, second, to evaluate basal corticosterone secretion in female diabetic rats. Sixty cycling 40-day-old female rats were randomly assigned to 3 groups; control (n = 32), diabetic (n = 14), and diabetic insulin-replaced animals (n = 14). The level of hyperglycemia in each group was documented by glycosylated hemoglobin levels and biweekly blood glucoses. Three weeks after induction of diabetes, pituitary luteinizing hormone (LH) responsiveness following an i.v. injection of gonadotropin-releasing hormone (GnRH) was assessed in representative diestrous rats from each group. All animals were sacrificed in either diestrus or proestrus for determination of GnRH concentration in the hypothalamus, LH and follicle-stimulating hormone (FSH) content in pituitary and LH, FSH, estradiol and corticosterone in serum. Uterine weight to body weight ratios (a bioassay for estrogen) were also calculated. Hypothalamic GnRH concentration was significantly lower in diabetic versus control diestrous rats. Basal pituitary and serum gonadotropin levels were not different between any groups. GnRH-stimulated serum LH levels were higher in diabetic vs. control and diabetic insulin-treated animals. LH surges occurred in the control and diabetic insulin-replaced but not the diabetic group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in the control of gonadotrophin secretion by neurotransmitters during sexual development in rats.

Gonadotrophin hormone releasing hormone (GnRH) is the primary messenger involved in sexual maturation and the onset of puberty. The activity of these neurons are controlled by several neurotransmitters systems. The onset of puberty implies changes from a prepubertal type of gonadotrophin secretion, characterized by a low activity of GnRH neurons, to an adult pattern of secretion with phasic and synchronous activation of GnRH neurons resulting in an increase in the amplitute and frequency of GnRH pulses. Neurotransmitter systems are involved in these changes of GnRH secretion during the onset of puberty by quantitative and qualitative modifications in the effect on GnRH secretion. Serotonin (5-HT), GABA and catecholamines (CA) have qualitative differences in the effects on GnRH and LH secretion in early prepubertal than in late prepubertal and adult female rats. The administration of 5-hydroxytryptophan a precursor of serotonin (5-HT) which increases 5-HT hypothalamic levels induces GnRH and LH release in early prepubertal female rats, these effects dissapear in late prepubertal stage having an inhibitory action in adult female rats. GABAergic system also stimulates GnRH and LH secretion in early prepubertal female rats and has an inhibitory action on this axis in late prepubertal period and in adult female rats. On the contrary the inhibition of catecholamines synthesis by alpha-methyl-p-tyrosine induced an increase of LH secretion in early prepubertal female rats and inhibitory effect in late prepubertal and adult stage. These effects indicate tha CA has an inhibitory effects on GnRH-LH secretion in early prepubertal female rats changing to an stimulatory action in the late puberty and adult rats. These qualitative modifications were observed only in female rats and are probably connected with the hypothalamic differentiation into a female type of gonadotrophin control. Opiadergic and excitatory amino acid systems have quantitative differences on GnRH-LH secretion during prepubertal and peripubertal and adult stages. Opiates has an high inhibitory tone in early prepubertal rats that is decreasing during sexual maturation to reach puberty. On the contrary EAA increases its stimulatory activity on GnRH-LH secretion during sexual maturation by increasing the hypothalamic release of aspartate and glutamate, the excitatory amino acids involved in GnRH release, and the sensibility of NMDA receptors to these amino acids. In conclusion sexual maturation and the onset of puberty in the female rats involve qualitative and quantitative modifications in the effects of neurotrasmitters system on GnRH secretion.