Central nervous system peptide and amino acid modulation of luteinizing hormone and prolactin secretion in the pig

We recently demonstrated that pulsatile LH secretion is associated with pulsatile gonadotropin releasing hormone (GnRH) in the pig. Endogenous opioid peptide (EOP) inhibition of pulsatile LH and prolactin (PRL) secretion is dependent on reproductive status and development of this EOP system is a brain maturational process independent of the ovary. Once sexual maturation has occurred, EOP then become part of a progesterone dependent system and EOP inhibit a noradrenergic component of this system. During lactation, EOP also inhibit pulsatile LH, but stimulate PRL secretion. N-methyl-d,l-aspartate (NMA), an agonist of the excitatory amino acids (EAA), aspartate and glutamate, suppressed LH secretion in gilts pretreated with progesterone or vehicle. Both the EOP agonist, morphine (MOR), and the EOP antagonist, naloxone (NAL), delayed emergence and time to maximum serum LH concentration of the estradiol-induced LH surge in prepuberal and mature gilts, respectively. Therefore, EOP may normally have both a permissive as well as an inhibitory role in the LH surge mechanism. Although a norepinephrine synthesis inhibitor failed to alter basal PRL secretion, the PRL increase after NAL was suppressed in progesterone-treated ovariectomized (OVX) gilts. NAL suppressed the PRL response to NMA in OVX gilts pretreated with oil vehicle or progesterone, indicating that NMA stimulation of PRL secretion is mediated through the EOP system.

Influence of opioids on LH secretion in gilts during the estrous cycle

The effect of endogenous opioid peptides (EOP) on LH secretion is variable during different physiological states. A series of experiments concerning the role of EOP on LH secretion in cyclic gilts was performed. They were comprised of (1) an administration of an opioid antagonist or agonist in gilts during the estrous cycle and in ovariectomized (OVX) gilts in which the LH surge was induced with estradiol benzoate (EB) and (2) in vitro studies on GnRH release from the stalk median eminence (SME) of cyclic gilts and OVX estrogen and progesterone primed gilts in response to naloxone (NAL). Naloxone and met-enkephalin analogue (FK 33-824) administration as a single independent injections did not affect LH secretion during the early (Day 16) or late (Day 19 or 20) follicular phase. However, continuous infusion of FK 33-824 for 4 h decreased LH secretion during the infusion period on Day 19 of the estrous cycle. Morphine also exerts an inhibitory effect on the EB-induced LH surge during the positive feedback phase (60-64 h after EB administration) in OVX gilts. On the contrary, NAL infusion in OVX gilts during the negative feedback phase (30-34 h after EB administration) did not alter LH secretion. A single injection of FK 33-824 in luteal phase gilts decreased the number of LH pulses for a 3 h period. This allows to hypothesize that EOP participates in the regulation of pulsatile LH secretion in pigs during the luteal phase. In vitro studies indicate that influence of EOP on LH secretion also takes place at the SME level. GnRH efflux from the SME of gilts during the luteal and late follicular phases was augmented in the presence of NAL. Unexpectedly, the priming of OVX gilts with estrogens caused the highest increase in GnRH release from the SME in vitro in response to NAL. These results confirm the variety of functional links between the opioid system and LH secretion in gilts during different stages of the estrous cycle.

Control of the LH surge mechanism in the female pig

The functionality of the oestrogen-positive feedback mechanism is the basis for the preovulatory LH surge and thus for regular cyclic activity in the sow. The LH surge mechanism (LH SM) gradually matures as a function of age, immature gilts display delayed, low amplitude LH surges in response to oestradiol benzoate (OB). The maturation of the LH SM apparently is ovarian oestrogen-dependent. Continuous ovarian secretions, probably oestrogens, also appear to be necessary for the final peripubertal maturation of the LH SM and to maintain the functionality of this mechanism in the sexually mature gilt. Superphysiological levels of oestrogens are, however, detrimental to the development of the LH SM. Failure of various infusions of the opioid antagonist naloxone during the surge period to enhance the magnitude of OB-induced LH surges in immature gilts does not support the idea, that central opioidergic systems are of major importance in preventing mature LH surge response at this age. However, opioids could be involved in the termination of the LH surge. Experiments using the opioid agonist morphine and the antagonist naloxone to demonstrate that opioids are involved in the generation of the LH surge in the mature gilt have so far provided equivocal data. Studies using pulsatile infusions of LHRH or of a potent LHRH-agonist during the surge period in OB-treated immature gilts, in which endogenous LHRH release was blocked by methallibure, suggest that oestradiol fails to generate mature LH surges because the gonadotrophs of the immature gilt are unable to respond to enhanced LHRH secretion during the surge period in an adult-like manner. During early lactation the LH SM cannot be activated by OB, while during late lactation a partial recovery of the LH SM occurs. Minor breed differences exist in the functionality of the LH SM during lactation between LW sows and highly fertile Chinese Meishan sows, in which lactational anoestrus is not obligatory.

Central administration of neuropeptide Y induces precocious puberty in female rats

To examine the role of neuropeptide Y (NPY) in the regulation of puberty, the effects of various doses of NPY or saline injected into the 3rd ventricle of peripubertal female rats were determined. A single injection of NPY at a dose range of 10-20 micrograms into the 3rd ventricle of 30-day-old female rats advanced the time of vaginal opening (VO) and first ovulation by 4 days, as compared to saline-treated controls. Ova number and ovarian, adrenal and uterine weights at first estrous were similar in all animals regardless of treatment. The NPY-treated precocious animals showed lower body weight than did the VO-matched controls, but showed similar body weight as that of age-matched controls. Determination of plasma luteinizing hormone (LH) levels in the peripubertal female rats revealed that plasma LH was increased transiently immediately after NPY administration. Also, NPY-treated rats which had precocious puberty showed elevated pituitary and plasma LH levels on the day of VO. These results suggest that NPY can activate the hypothalamic-pituitary-gonadal axis to precociously initiate puberty.

Opioid inhibition of luteinizing hormone secretion compared in developing male and female sheep

The sheep exhibits a marked sex difference in the timing of the pubertal increase in luteinizing hormone (LH). Male lambs undergo a reduction in sensitivity to inhibitory steroid feedback, leading to an increase in LH by 10 weeks of age, but females remain hypersensitive until 30 weeks of age. Endogenous opioids suppress LH secretion in the female lamb prepubertally and in adult male and female sheep. It has been suggested that a reduction in opioid inhibition of LH secretion is the signal to time puberty. Therefore, if a decrease in opioid tone occurs during sexual maturation, it should begin earlier in the male lamb than in the female. The objective of this study was to compare opioid inhibition of LH secretion in male and female lambs in relation to the timing of puberty. Our approach was to examine the response to the opioid antagonist naloxone at various ages in both sexes. To determine the timing of the pubertal LH rise in the presence of constant inhibitory steroid feedback, male and female lambs (n = 5 each) were gonadectomized at 3 weeks of age and implanted with a Silastic capsule of estradiol. They were then challenged with naloxone at 5, 11, and 23 weeks of age; blood samples were collected every 12 min for 8 hours, and lambs received naloxone (1 mg/kg i.v.) at hours 4, 5, 6, and 7. Mean LH before and during naloxone treatment was compared at each age.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of the new bombesin receptor antagonist RC-3095 on the luteinizing hormone release in rats

The effects of bombesin receptor antagonist RC-3095 and gastrin-releasing peptide [GRP (14-27)] on basal luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone levels, as well as on the release of LH and FSH in response to LH-releasing hormone, were studied in normal and castrated male rats. We also examined the release of LH and FSH after intracerebroventricular injection of RC-3095 under different types of anesthesia (urethane, sodium pentobarbital, Metofane). Following injection of 10 micrograms RC-3095 into the lateral brain ventricle, serum LH levels were rapidly and significantly (p < 0.001) lowered. This effect lasted for at least 60 min and was not affected by the type of anesthetic used. Serum FSH levels were not affected by intracerebroventricular administration of RC-3095 or GRP (14-27), indicating different central control mechanisms between LH and FSH release. The suppressive effect of RC-3095 on LH release could be completely prevented by prior intracerebroventricular administration of GRP (14-27) at a dose of 1 micrograms, but intravenous administration of either peptide RC-3095 or GRP (14-27) did not change the basal levels of LH, FSH, and testosterone. The pituitary LH response to LH-releasing hormone was also not modified by intravenous administration of RC-3095. These results indicate that bombesin-like peptides might be involved in control of LH release from the pituitary by an action on the CNS which is mediated by specific bombesin receptors.

Effects of body condition and estradiol on luteinizing hormone secretion in post-partum beef cows

An experiment was conducted to test the hypothesis that the effect of body fatness on LH pulsatility in post-partum cows is entirely independent of the negative feedback effects of ovarian steroids. Forty beef cows were fed in the last 100 d of gestation so that they achieved either a thin (mean score 1.97) or fat (mean score 2.79) body condition (0 to 5 scale) at calving and were fed after calving to maintain live weight and body condition. At 15 (sd 3.7) d post partum all cows were ovariectomised and half from each body condition score treatment group received a subcutaneous estradiol implant (+EST) while the remainder received no implant (-EST). At weeks 5 and 9 post-partum blood samples were collected via jugular catheter every 20 minutes for 10 hr on two consecutive d and on the third d cows were injected via the jugular vein with 2.5 micrograms GnRH. Blood samples were collected every 15 minutes for 1 hr before and 2 hr after GnRH injection. At 5 and 9 weeks the fatter cows had significantly higher mean LH concentrations, baseline LH concentrations, LH pulse amplitudes and pulse frequencies (P < 0.01). Implantation with estradiol in both fat and thin cows reduced mean LH concentrations, baseline LH concentrations, LH pulse amplitudes and pulse frequencies (P < 0.001). The lack of interaction between body condition and the presence or absence of estradiol implies that the effect of body condition on LH release is independent of ovarian steroid feedback mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of long-term hemodialysis on luliberin-induced lutropin secretion in patients with chronic renal failure]

The purpose of the work was to answer the question whether time of haemodialysis treatment affects the secretion of lutropin (LH) in patients with chronic renal failure. The study was carried out in 41 men with chronic renal failure and 15 healthy controls. There were three groups of hemodialyzed patients. The first one comprised 17 patients dialyzed up to 50 months, the second one 14 patients treated during 51-100 months and the third one 10 patients hemodialyzed for more than 100 months. In all these subjects the test of stimulation with luliberin (LH-RH) was done. Significantly higher serum levels of LH were found in patients as compared to controls. No significant alterations in LH levels were observed in the groups of patients. After administration of LH-RH the reactivity of LH secretion was significantly lower in patients dialyzed longer than 50 months then in men dialyzed shorter and in controls. These facts suggest an influence of long-term dialysis treatment on the secretion of LH in men with chronic renal failure.

New trends in combined use of gonadotropin-releasing hormone antagonists with gonadotropins or pulsatile gonadotropin-releasing hormone in ovulation induction and assisted reproductive technologies

The use of gonadotropin-releasing hormone agonists as adjunctive therapy with gonadotropins for ovulation induction in in vitro fertilization and other assisted reproductive technologies has become common clinical practice. With the recent advent of potent gonadotropin-releasing hormone antagonists free from the marked histamine-release effects that stymied earlier compounds, an attractive alternative method may be available. We have established the feasibility of combining gonadotropin-releasing hormone antagonist-induced inhibition of endogenous gonadotropins with exogenous gonadotropin therapy for ovulation induction in a nonhuman primate model. Here, the principal benefits to be gained from using the gonadotropin-releasing hormone antagonist rather than the gonadotropin-releasing hormone agonist are the immediate inhibition of pituitary gonadotropin secretion without the "flare effect," which brings greater safety and convenience for patients and the medical team and saves time and money. We have also recently demonstrated the feasibility of combining gonadotropin-releasing hormone antagonist with pulsatile gonadotropin-releasing hormone therapy for the controlled restoration of gonadotropin secretion and gonadal steroidogenesis culminating in apparently normal (singleton) ovulatory cycles. This is feasible only with gonadotropin-releasing hormone antagonists because, unlike gonadotropin-releasing hormone agonists, they achieve control of the pituitary-ovarian axis without down regulation of the gonadotropin-releasing hormone receptor system. This capacity to override gonadotropin-releasing hormone antagonist-induced suppression of pituitary-ovarian function may allow new treatment modalities to be employed for women who suffer from chronic hyperandrogenemia with polycystic ovarian disease.

Effects of progesterone on gonadotropin-releasing hormone receptor concentration in cultured estrogen-primed female rat pituitary cells

Acute (0.5-4 h) treatment of estradiol (E)-primed female rat pituitary cells with progesterone (P) augments gonadotropin-releasing hormone (GnRH)-induced LH release, whereas chronic (48 h) P-treatment reduces pituitary responsiveness to the hypothalamic decapeptide. Dispersed E-primed (48 h, 1 nM) rat pituitary cells were cultured for 4 or 48 h in the presence of 100 nM P to assess the effects of the progestagen on GnRH receptors and on gonadotrope responsiveness to the decapeptide. P-treatment (4 h) significantly augmented GnRH-receptor concentrations (4.44 +/- 0.6 fmol/10(6) cells) as compared to cells treated only with E (2.6 +/- 0.5 fmol/10(6) cells). Parallel significant changes in GnRH-induced LH secretion were observed. The acute increase in GnRH-receptor number was nearly maximal (180% of receptor number in cells treated with E alone) within 30 min of P addition. Chronic P-treatment (48 h) significantly reduced pituitary responsiveness to GnRH as compared to E-treatment. The GnRH-receptor concentrations (3.9 +/- 0.6 fmol/10(6) cells), however, remained elevated above those in E-primed cells. GnRH-receptor affinity was not influenced by any of the different treatments. These results indicate that the acute facilitatory P-effect on GnRH-induced LH release is at least chronologically closely related to an increase in GnRH-receptor concentration. The chronic negative P-effect on pituitary responsiveness to GnRH, however, shows no relation to changes in available GnRH receptors.

N-methyl-d,l-aspartate stimulates growth hormone and prolactin but inhibits luteinizing hormone secretion in the pig

The effects of n-methyl-d,l-aspartate (NMA), a neuroexcitatory amino acid agonist, on luteinizing hormone (LH), prolactin (PRL) and growth hormone (GH) secretion in gilts treated with ovarian steroids was studied. Mature gilts which had displayed one or more estrous cycles of 18 to 22 d were ovariectomized and assigned to one of three treatments administered i.m.: corn oil vehicle (V; n = 6); 10 micrograms estradiol-17 b/kg BW given 33 hr before NMA (E; n = 6); .85 mg progesterone/kg BW given twice daily for 6 d prior to NMA (P4; n = 6). Blood was collected via jugular cannulae every 15 min for 6 hr. Pigs received 10 mg NMA/kg BW i.v. 2 hr after blood collection began and a combined synthetic [Ala15]-h GH releasing factor (1-29)-NH2 (GRF; 1 micrograms/kg BW) and gonadotropin releasing hormone (GnRH; .2 micrograms/kg BW) challenge given i.v. 3 hr after NMA. NMA did not alter LH secretion in E gilts. However, NMA decreased (P < .02) serum LH concentrations in V and P4 gilts. Serum LH concentrations increased (P < .01) after GnRH in all gilts. NMA did not alter PRL secretion in P4 pigs, but increased (P < .01) serum PRL concentrations in V and E animals. Treatment with NMA increased (P < .01) GH secretion in all animals while the GRF challenge increased (P < .01) serum GH concentrations in all animals except in V treated pigs. NMA increased (P < .05) cortisol secretion in all treatment groups. These results indicate that NMA inhibits LH secretion and is a secretagogue of PRL, GH and cortisol secretion with ovarian steroids modulating the LH and PRL response to NMA.

The effects of a dopamine antagonist on luteinizing hormone and prolactin release in women with anorexia nervosa and in normal controls

To evaluate the possible role of central dopaminergic suppression of gonadotropin secretion in the genesis of amenorrhea associated with anorexia nervosa (A.N.), a central D-2 dopamine receptor blocker was administered to 10 women with A.N. and 10 regularly menstruating age-matched controls. Serum prolactin and luteinizing hormone (LH) levels were measured at -15, 0, 30, 60, 120, and 180 min after administration of metoclopramide (10 mg orally). Mean basal prolactin (p less than 0.001) and estradiol levels (p less than 0.02) were significantly lower in women with A.N. The prolactin response to metoclopramide was significantly impaired in women with anorexia nervosa. No correlation was found between the prolactin response and percentage ideal body weight. Basal and post-stimulation prolactin levels were correlated with estradiol levels. After adjusting for the effects of estradiol, significant differences between patients with A.N. and controls remained in prolactin levels at baseline (p less than 0.01), 120 min (p less than 0.02) and 180 min (p less than 0.05). Metoclopramide did not induce a significant rise in LH levels in either the A.N. or control groups. These data are consistent with central dopaminergic inhibition of prolactin secretion in anorexia nervosa but do not support the hypothesis that central dopaminergic inhibition is related to diminished LH release in this state.

Effects of opioid antagonism with naltrexone on pulsatile luteinizing hormone secretion in women with hypothalamic amenorrhea in basal conditions and after discontinuation of treatment with pulsatile LHRH

Although endogenous opioids seem to play an important role in the inhibition of luteinizing hormone releasing hormone (LHRH) secretion in women with hypothalamic amenorrhea, opioid antagonism does not always cause an increase of pituitary luteinizing hormone (LH) secretion. The effect of the long-acting oral opiate antagonist naltrexone on pulsatile LH secretion was studied in eight women with weight loss and exercise-related hypothalamic amenorrhea. LH pulse studies and LHRH tests were performed in basal conditions and after 4 days of naltrexone treatment, 50 mg q.d. Naltrexone caused a slight, but significant increase of LH pulse frequency. Six weeks later, a second experiment was performed. The response to naltrexone was studied after enhancement of the pituitary sensitivity. Patients were pretreated with pulsatile LHRH during 4 days, followed by naltrexone 50 mg q.d. during 4 days. An increased LH response to LHRH, but no response to naltrexone, were seen after discontinuation of pulsatile LHRH. It is concluded that the limited pituitary response to opioid antagonism, observed in weight loss-related forms of hypothalamic amenorrhea, is not caused by pituitary insensitivity to LHRH.

Blockade of the LH response induced by the agonist D-Trp-6-LHRH in rats by a highly potent LH-RH antagonist SB-75

During treatment of prostate cancer patients with luteinizing hormone-releasing hormone agonist, a transient LH and sex steroid release, which precedes the secretion blockade, may result in a flare-up of the disease, whereas the antagonists induce an immediate suppression. The administration of the modern, superactive LHRH antagonist SB-75 before or together with the agonist D-Trp-6-LHRH should prevent the "flare-up" phenomena. In order to demonstrate that the LHRH antagonist can prevent the initial stimulation of gonadotropins in response to LHRH agonists, groups of 5-7 male rats were injected s.c. with the antagonist SB-75 in doses in 100, 500, and 1,000 micrograms/rat 1 hour prior to or 1, 2, and 3 days before administration of D-Trp-6-LHRH agonist (50 micrograms/rat). Supraphysiological doses of the agonist were used in order to obtain prolonged stimulation of LH release, which was necessary to study the duration and the extent of LH release inhibition. Blood samples were taken before and 2, 6, 24, 48, and 72 hours after D-Trp-6-LHRH stimulation for measurement of LH levels. The administration of SB-75 in doses of 500 and 1,000 micrograms/rat 3 days prior to administration of the agonist significantly lowered LH response (P less than 0.01), as compared to animals injected with D-Trp-6-LHRH alone. The D-Trp-6-LHRH-stimulated LH secretion was markedly more suppressed by all 3 doses of the antagonist in rats pretreated with SB-75 2 days prior to the stimulation with the agonist. An even greater reduction in LH response could be observed in rats injected with SB-75 1 day prior to the agonist, the magnitude of LH response being decreased by 75% with 500 micrograms/rat SB-75 and by 90% with 1 mg/rat SB-75. The LH response was virtually abolished when the antagonist, SB-75 was given in doses of 500 or 1,000 micrograms/rat 1 hour prior to the D-Trp-6-LHRH injection. Under these conditions, the agonist-induced LH and testosterone secretion was completely suppressed during the whole period of the experiment. The antagonist to agonist dose ratio of 2 to 1 produced a 90% decrease in the LH response to D-Trp-6-LHRH at 2 hours and 75% at 5 hours after agonist administration. The effects of LHRH decapeptide itself (500 micrograms/rat) on LH secretion could be totally suppressed by an injection of 50 micrograms/rat of SB-75 1 hour beforehand.(ABSTRACT TRUNCATED AT 400 WORDS)

Benign symptomatic hyperandrogenism in a postmenopausal woman

Hyperandrogenemia in postmenopausal women requires an evaluation to exclude pathologic ovarian or adrenal causes. Our patient exhibited no signs of hypercortisolism, congenital adrenal hyperplasia, or adrenal or ovarian neoplasia based on biochemical testing and pelvic sonography. We hypothesized that unexplained androgen excess in our patient was due to the development of gonadotropin-dependent excess ovarian stromal androgen production. This syndrome may be comparable to gestational hyperreactio luteinalis where elevated gonadotropins stimulate ovarian stromal androgen production. If tumor can confidently be excluded, such women may benefit from gonadotropin suppression with long-acting GnRH-a.

[The contraceptive efficacy and mechanism of action of combinations of ethinyl estradiol and norethisterone acetate]

The purpose of the study was to establish the optimal combinations of ethynilestradiol and norethysterone acetate exhibiting a high contraceptive activity. It was shown that the ratio of 1:20 (ethynilestradiol 0.04 mg/kg and norethysterone acetate 0.8 mg/kg) is characterized by a high contraceptive efficacy. The inhibitory effect on the incretion of lutropin and follitropin leading to the change of the process of oogenesis and gravidary reorganization of the endometrium underlies probably the mechanism of action.

Triggering ovulation with endogenous luteinizing hormone may prevent the ovarian hyperstimulation syndrome

In a series of 126 therapeutic cycles in 48 patients with primary infertility and treated with HMG for anovulation or preparation to insemination, ovulation was triggered by endogenous LH instead of HCG when the patient was considered to be at high risk for ovarian hyperstimulation syndrome (OHS), (plasma oestradiol greater than 1200 pg/ml) and/or multiple pregnancy (greater than 3 follicles greater than 17 mm in diameter). The endogenous LH surge was provoked and maintained by intranasal buserelin 200 micrograms three times at 8-hourly intervals. In the 37 cycles with buserelin, no OHS occurred despite high preovulatory levels of oestradiol; a single twin pregnancy was recorded despite the presence of numerous mature preovulatory follicles. Conception results (21.6% pregnancy per therapeutic cycle) compared favourably with HCG administration (16.8%). It is concluded that, when ovulation must be triggered in a hazardous situation, the use of endogenous LH through the administration of a short-acting GnRH analogue prevents the complications of exaggerated follicular stimulation.

The effects of aging on the secretion of the common alpha-subunit of the glycoprotein hormones in men

To investigate the effects of aging on the secretion of the common alpha-subunit of the glycoprotein hormones, we measured basal levels of luteinizing hormone (LH), testosterone (T) and alpha-subunit in 176 normal men aged 19 to 89 years. In addition, in two groups of young (less than 65 years; n = 25) and old (greater than 65 years; n = 15) subjects, the effects of luteinizing hormone-releasing hormone (LHRH) on LH and alpha-subunit secretion were determined. Age-related increases in serum alpha-subunit and LH were noted only in the oldest men while T levels decreased progressively with advancing age. LHRH stimulation resulted in significantly greater secretion of alpha-subunit in the old subjects while no difference in LH release between young and old men was observed. Moreover, there was a delay to peak LH and alpha-subunit levels after LHRH in the old subjects. These data suggest that the aging process in males involves deficits in both testicular and gonadotroph functions as demonstrated by (1) the relative hypogonadotropic hypogonadism seen until the ninth decade; (2) the hypergonadotropic hypogonadism apparent in men greater than 80 years; (3) the delay in the timing of peak responses of LH and alpha-subunit after LHRH administration; and (4) the disproportionate increase in the secretion of alpha subunit relative to intact LH.

Droloxifene, a new antiestrogen. Hormonal influences in postmenopausal breast cancer patients

Hormonal influences and pharmacokinetic aspects of the new antiestrogen droloxifene (3-hydroxytamoxifen) have been studied in a total of 148 postmenopausal patients with breast cancer. A negligible decrease in the gonadotropins LH and FSH was observed in patients treated with 20 mg (34 patients) and 40 mg (43 patients) of droloxifene (once daily). Serum concentrations of the gonadotropins obviously decreased (71 patients) with the highest dose of droloxifene (100 mg, once daily) given in this study. Sex hormone binding globulin rose only marginally in the 20- and 40-mg dose group. However, with 100 mg of droloxifene, a moderate increase was found, indicating some estrogenicity at higher doses. Rapid pharmacokinetic characteristics have been confirmed. The time to peak concentration ranges from 2 to 4 h, and the terminal half life is about 24 h, allowing interesting new schedules in endocrine therapy.

Effects of intracerebroventricular administration of opiate receptor antagonists on the suppressed pulsatile LH release during acute fasting in ovariectomized estradiol-treated rats

The involvement of specific opiate receptors in the suppression of LH release during acute fasting in ovariectomized estradiol-treated rats was examined by intracerebroventricular (i.c.v.) administration of opiate receptor antagonists that exert a specificity directed mainly, although not absolutely, towards the delta-, kappa- or mu-opiate receptors. Fasting for 48 h significantly decreased mean plasma LH levels in estradiol-treated animals by increasing sensitivity to the negative feedback effect of estradiol. Injecting i.c.v. the mu-opiate receptor antagonist naloxone (10 or 100 nmol in 2 microliters of saline) blocked the inhibitory effect of fasting on pulsatile LH release and reinstated LH pulses. On the other hand, i.c.v. administration of the same dosages of a delta-opiate receptor antagonist ICI 174,864 or a kappa-opiate receptor antagonist WIN 44441-3 did not have any effect. These results suggest that the increased sensitivity of the LH-releasing mechanism to the negative feedback effect of estradiol during fasting involves the endogenous opioids mainly through the selective activation of the mu-opiate receptors.

[The role of testosterone metabolism in the hypothalamus in regulating the gonadotropic function of the hypophysis in male pre- and postpubertal rats]

Experiments were staged on immature (21 days) and mature (3.5 mos.) Wistar male rats to investigate the influence of the aromatase inhibitor 1, 4, 6-androstatriene-3, 17-dione on the activity of the aromatase and 5 alpha-reductase enzymatic complexes of the hypothalamus and the blood levels of LH and testosterone (T). The formation of 5 alpha-dehydrotestosterone against a background of aromatase activity inhibition was increased in mature rats and was unchanged in immature animals. The blood levels of LH and T were increased, the reaction of LH in immature animals being more marked. A conclusion has been made of a role of T aromatic transformations in the hypothalamus in tonic inhibition of LH secretion by endogenous T and a possible involvement of this mechanism in the maturation of male rats.

Paternity in idiopathic hypothalamic hypogonadism during testosterone therapy in two unrelated patients

When fertility is desired, idiopathic hypothalamic hypogonadism is amenable to treatment with pulsatile low dosage GnRH administration or injections of gonadotrophins. Patients with this disorder are hypogonadal and require therapy with androgens or oestrogens/progestagens. This would presumably lower pituitary gonadotrophin production even further. However, fertility occurring spontaneously during testosterone substitution, as proven by paternity testing, has been described twice. The present report adds two more cases. It is unwise to make a definite statement about infertility in male patients with this condition.

[The effect of tefestrol on the secretion of luteinizing hormone from the hypophysis]

The effect of tefestrol on the content of luteinising hormone in blood and hypophysis in female and male rats was studied on the basis of the radioimmunological assays. It was shown that administration of tefestrol to the female rats depending on the preparation dose and the time of administration during the estrous cycle can produce an increase and a decrease of luteinising hormone content in the material under study. In the male rats tefestrol induced a stable elevation of blood gonadotropine level. The results obtained suggest that tefestrol may be used as a stimulant of the reproductive function and also as a contraceptive depending on the dose and the functional state of the reproductive system during the treatment.

[The dynamics of pulsatile LHRH (GnRH) secretion]

A review of the features of RHLH, especially of the pulsating secretion, which is very important to the correct function of the reproduction system, is presented. Now it is accepted that this pulsating secretion is the producer of the episodic release of gonadotrophins, the gonadal steroids being the modulator of the frequency and the extent of the LHRH pulses. Several experiences showed that changes in the pulse frequency of GnRH, can dynamically modify the seric concentration of LH and FSH.