Increase In LH Release Research Articles

Differential Involvement of 5-Hydroxytryptamine (5HT) in Specific Hypothalamic Areas in the Mediation of Steroid-Induced Changes in Gonadotrophin Release and Sexual Behaviour in Female Rats

Ovariectomised rats were treated with either oestradiol benzoate (OB) alone or OB followed by progesterone (P). The effects of the steroid treatments were noted on plasma LH concentration, lordosis quotient and concentration of 5-hydroxytryptamine (5HT) and 5-hydroxyindole acetic acid (5HIAA) in microdissected hypothalamic areas, i.e. the preoptic area (POA), arcuate nucleus (ARC), median eminence (ME), ventromedial nucleus (VMN), suprachiasmatic nucleus (SCN) and zona incerta (ZI). The ratio of 5HIAA:5HT or parallel changes in the concentrations of 5HT and 5HIAA were taken as indices of 5HT neuronal activity. 5 micrograms OB alone reduced LH release and had no effect on receptivity. This treatment reduced 5HT activity in the SCN and raised it in the ZI. After 5 micrograms OB plus 0.5 mg P, all the rats exhibited an LH surge and full sexual receptivity. 5HT activity was significantly raised in the ME and reduced in the ARC, VMN and ZI. By using submaximal steroid regimes (2 micrograms OB plus 0.05 mg P, or 50 micrograms OB alone) correlations could be made between sexual behaviour, LH release and 5HT activity. There was no correlation between LH release and receptivity indicating that the two functions are controlled by different systems. Correlating 5HT activity in the various sites with the two physiological parameters indicated whether the changes seen after the maximal steroid treatment were concerned with behaviour, LH release or both. The results indicate that the changes seen in the VMN, ARC and ME are correlated with sex behaviour and those in the VMN and ZI with increased LH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Posterior hypothalamic lesions advance the time of the pubertal changes in luteinizing hormone release in ovariectomized female rhesus monkeys.

To examine further the relationship between developmental changes in LH release and the onset of puberty, effects of posterior hypothalamic lesions were tested in ovariectomized (OVX), sexually immature female monkeys. In OVX females (n = 3) with sham hypothalamic lesions basal LH levels were suppressed during the prepubertal period until 25 months of age, when LH levels started to increase. The increase in basal LH continued; a 100% elevation from prepubertal levels was attained at 26.0 +/- 0 months of age, and a 200% elevation was attained at 31.0 +/- 3.2 months of age. A consistent appearance of LH circadian fluctuation (nocturnal LH increase) with a large amplitude accompanied the initial LH increase. Lesions of the posterior hypothalamus (PH) in OVX animals (n = 6) at 17-18 months of age, which we previously reported to be effective in advancing the onset of puberty by several months in ovarian intact monkeys, resulted in an early 100% increase in basal LH levels and the circadian LH fluctuation (19.5 +/- 1.0 months of age). Basal LH levels in these animals further increased, reaching a 200% elevation of prelesion levels at 24.2 +/- 0.7 months of age. All of these LH changes with PH lesions occurred significantly (P less than 0.01) earlier than those in sham-lesioned animals. Lesion of the PH in OVX animals (n = 4) at 13-14 months of age resulted in an increase in LH and the circadian LH fluctuation within 1 month postoperatively. However, 100% and 200% LH elevations did not occur until 20.8 +/- 1.0 and 24.8 +/- 1.4 months of age, respectively. These ages were similar to those of animals receiving lesions at 17-18 months of age, but much younger than those of sham controls (P less than 0.01). PH lesions in animals at 13-14 months of age also advanced the time of the first positive feedback effects of estrogen. In animals (n = 4) with PH lesions, estradiol benzoate induced a first LH response at 21.5 +/- 1.6 months of age, when basal LH was 276 +/- 83% increased from prelesion levels. This age was significantly (P less than 0.05) younger than that (29.3 +/- 1.9 months; n = 6) of the first LH surge induced by estrogen in control animals when basal LH levels attained 248 +/- 18% of prepubertal levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Detection of a LAG phase in gonadotropin-releasing hormone stimulated synthesis of lutropin peptide chains in cultured rat anterior pituitary cells

We have studied the time course (0-5h) of the stimulatory effect of the hypothalamic gonadotropin-releasing hormone (GnRH) on the biosynthesis of lutropin (LH) polypeptide chains, as measured by the incorporation of [35S] methionine into proteins synthesized in cultured rat anterior pituitary cells in the absence or presence of 10nM GnRH. Labeled polypeptides, immunologically related to LH subunits alpha and beta, were isolated by specific immunoprecipitation, analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, then revealed by fluorography and quantified by counting the excised bands. This methodology allowed us to detect the radioactivity incorporated into LH subunits after less than 15 min of incubation. During first 1h of the time-course the quantity of [35S]Met incorporated into both alpha and LH beta subunits was not increased by the presence of GnRH in the incubation medium. A significant increase in the incorporation of radioactivity into LH subunits was observed after 2h of GnRH treatment. However, the increase in LH release into the medium in response to GnRH, as measured by RIA, was immediate. These data demonstrate that GnRH-stimulated synthesis of LH polypeptide chains occurs after a lag of approximately 1h and involves mechanisms different from those governing the stimulation of LH release.

Effects of treatment with the opioid antagonists naloxone and naltrexone on LH secretion and on sexual maturation in immature female rats.

The effects on sexual maturation of the opioid receptor antagonists naloxone and naltrexone were studied in the female rat. Neonatal treatment (days 1-10) with either naloxone (2.5 mg/kg at 6-h intervals) or naltrexone (20 or 50 mg/kg per day) did not advance sexual maturation as judged by age and body weight at vaginal opening and first ovulation. After treatment with naltrexone (20 mg/kg) first ovulation occurred 2.3 days earlier than in saline-treated control rats but this could be attributed to a growth-stimulating effect of naltrexone; the effect was not observed with 50 mg/kg. An effect of neonatal treatment with naloxone on serum LH levels was seen at 23 days of age (155 +/- 36 (S.E.M.) vs 14 +/- 4 micrograms LH/l in controls, P less than 0.01), but not at 29 or 33 days of age, at 2 days before first ovulation nor at first pro-oestrus. There were no differences in the number of ova released at first oestrus, nor in the length of the first cycle. Neonatal treatment with naltrexone (50 mg/kg per day) did not alter the response to treatment with human chorionic gonadotrophin at 28-31 days of age: ovulation of a mean of 7.3 ova was induced on day 32 in both naltrexone- and saline-treated rats. Naltrexone treatment (four daily injections of 20 mg/kg at 2-h intervals) at 28-32 days of age advanced first ovulation by 4.4 days in about 40% of the rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Estradiol Sensitization of Cultured Human Fetal Pituitary Cells to Gonadotropin-Releasing Hormone*

In adult women, estradiol (E2) sensitizes the pituitary to GnRH. To assess whether this effect develops during intrauterine life, dispersed pituitary cells from second trimester male and female fetuses were cultured on extracellular matrix-coated plates. E2 (10(-8) mol/L) exposure for 72 h resulted in a significant increase in LH release when cells were stimulated with GnRH and caused a significant shift to the left of the dose-response curve for GnRH-stimulated LH release [relative potency ratio, 0.33 +/- 0.05 (+/- SE)]. E2-enhanced LH release was not associated with an increase in cell number, total LH content, or percentage of LH-containing cells (immunocytochemistry). The EC50 of GnRH-stimulated LH release and the degree of E2 sensitization were not sex dependent, although female fetal pituitary cells in the absence of E2 had significantly greater LH content and released more LH under basal and GnRH-stimulated conditions than cells from male fetuses. Therefore, E2 sensitization of second trimester human fetal gonadotrophs to GnRH does occur, is not influenced by sex, and may involve an acutely releasable LH pool. At these gestational ages, basal and maximal GnRH-stimulated LH release as well as total LH content are greater in the female than the male. Thus, E2 sensitization of GnRH responsiveness appears to have its origins during intrauterine fetal life.

Delta sleep inducing peptide (DSIP) stimulates the release of LH but not FSH via a hypothalamic site of action in the rat

Long term ovariectomized (OVX) Sprague-Dawley rats were injected intraventricularly (3rd ventricle) with 5 μg (2 μl) of DSIP. This caused a significant elevation ( p=0.01) of LH levels within 30 min. The values remained elevated for 2 hr; however, FSH levels remained unchanged. The minimal effective dose of DSIP to evoke this effect was 1 μg. If plasma LH was lowered by pretreatment of the animals with estradiol, the 5 μg dose evoked an even greater effect to elevate LH significantly at 30 and 60 min following its intraventricular injection. To determine the site of action of DSIP, dispersed, overnight cultured pituitary cells from OVX rats were incubated with varying concentrations (10 −7 to 10 −12 M) of DSIP in an in vitro system. There was no response to DSIP from the cells in the above system. To evaluate its possible action on the hypothalamus, median eminence (ME) fragments from male rats were incubated in vitro with DSIP in varying concentrations from 10 −7 to 10 −10 M. There was a significant ( p<0.001) increase in LHRH released from the ME at a concentration of DSIP of 10 −7 M. A sleep-related increase in LH release is seen during puberty in man. It is possible that DSIP released within the hypothalamus may play a physiological role in sleep-related LH release.

Substance P stimulates gonadotropin-releasing hormone release from rat hypothalamus in vitro with involvement of oestrogen

The effects of substance P on the release of LH and GnRH were examined in a sequential double-chamber perifusion system by perfusing the medio-basal hypothalamus and/or pituitary excised from normal female rats in dioestrus or ovariectomized rats. When the medio-basal hypothalamus and pituitary from normal rats were perifused in series with substance P (10(-6) mol/l), the concentration of LH in the efflux was significantly (P less than 0.05) increased by 70-120% compared with that before the injection, but substance P had no effect on LH release from the pituitary perifused alone. This LH release by substance P increased in a dose-dependent manner and was blocked by substance P antagonist. Administration of 10(-6) mol/l substance P induced a significant release (40-80% increase, P less than 0.05) of GnRH from the medio-basal hypothalamus. Infusion of 10(-6) mol/l substance P induced significant release (50-100% increase, P less than 0.05) of LH and GnRH in ovariectomized rats with an implanted oestradiol capsule, but caused no significant increase in LH release in ovariectomized rats without an oestradiol capsule. Progesterone injection to both ovariectomized rats and ovariectomized rats with an implanted oestradiol capsule had no significant effect on the response of LH to substance P. These findings suggest that substance P induces GnRH release from the medio-basal hypothalamus, resulting in LH release from the pituitary, and that oestrogen may be involved in these processes.

Desensitization to Gonadotropin-Releasing Hormone in Perifused Chicken Anterior Pituitary Cells*

A perifusion method consisting of dispersed chicken anterior pituitary cells suspended in columns of Bio-Gel was developed to monitor the dynamics of LH release. The perifused cells responded to chicken I GnRH (Gln8-GnRH) in a dose-dependent manner. The ED50 was 3 X 10(-10) M, and maximal LH release occurred in response to 4 X 10(-9) M Gln8-GnRH. Continuous administration of 10(-7) M Gln8-GnRH and agonist stimulated an initial 8- to 10-fold increase in LH release within minutes. LH release then declined rapidly, reaching basal levels within 100 min. A biphasic response was noted. Calcium ionophore A23187 was effective in releasing additional LH from cells desensitized to 10(-7) Gln8-GnRH and agonist, indicating that total cellular LH was not depleted. In contrast, delivery of 2-min pulses of 10(-7) M and 10(-9) M Gln8-GnRH at a frequency of one pulse every 30 or 60 min for 3-5 h maintained pituitary responsiveness. Exposure to 10(-7) M Gln8-GnRH for 20 min was sufficient to desensitize pituitary cells to subsequent Gln8-GnRH stimulation. However, 20-min exposure to 10(-7) M GnRH antagonist neither evoked LH release nor had a desensitizing effect on subsequent stimulation by 10(-7) M Gln8-GnRH, indicating that receptor activation, not merely receptor binding, is necessary for Gln8-GnRH-mediated homologous desensitization. Pituitary cells desensitized by 20-min exposure to 10(-8) M Gln8-GnRH maintained responsiveness to a higher dose (10(-6 M) of Gln8-GnRH, suggesting that down-regulation of pituitary GnRH receptors might play a part in desensitization. Calcium ionophore A23187 partially desensitized pituitary cells to subsequent stimulation with Gln8-GnRH, probably due to depletion of releasable LH or desensitization of calcium-coupled secretory mechanisms. In calcium-free medium, 10(-7) M Gln8-GnRH did not evoke LH release, but nevertheless partially desensitized cells to subsequent 10(-7) M Gln8-GnRH stimulation. Thus desensitization is partially calcium-dependent. These findings demonstrate that the GnRH-mediated desensitization of gonadotrophs is a characteristic of chicken pituitary cells as in the mammal. However, chicken pituitary cells differ from mammalian cells in that desensitization is more rapid and partially dependent on extracellular calcium.

The development of afternoon minisurges of luteinizing hormone secretion in prepubertal female rats is ovary dependent.

We have recently disclosed sustained episodes of LH release (minisurges) during the afternoons of the juvenile-peripubertal transition period in the female rat. To determine if these LH minisurges are gonad independent, i.e. develop in the absence of the ovaries, animals were ovariectomized when neonates, and the mode of LH release was examined using a 5-min blood-sampling regimen at one of three ages corresponding to the juvenile, peripubertal, or adult phase of development. In no instance was a minisurge of LH secretion detected. We were concerned, however, that LH minisurges may have been obscured by the exceedingly high level of LH secretion in these long term ovariectomized rats and, therefore, decided to pursue the study employing a short term (48-h) ovariectomy paradigm. Late juvenile rats which had been ovariectomized for 48 h exhibited conspicuous LH pulses, but, again, LH minisurges were not detected, further suggesting that these sustained secretory episodes do not occur in the absence of the ovaries. Next, plasma estradiol (E2) levels were differentially raised in 48-h ovariectomized juvenile rats via sc implantation of Silastic capsules containing the steroid (dissolved in corn oil at various concentrations), and plasma LH was measured at 1-h intervals. The highest E2 concentration elicited a midafternoon LH increase of preovulatory magnitude in all cases, whereas the lowest E2 concentrations consistently suppressed plasma LH. However, intermediate E2 concentrations (producing plasma E2 levels 20-30% greater than those found in intact controls) elicited, in several instances, an increase in LH release of intermediate magnitude. To clarify the nature of these LH responses, we examined, using a 5-min blood-sampling regimen, the afternoon pulsatile pattern of LH release after treatment with appropriate doses of E2. As expected from the results of the infrequent blood-sampling paradigm, the highest E2 dose induced proestrus-like surges of LH secretion, while the lowest dose suppressed pulsatile LH release. Moreover, an intermediate E2 dose which raised plasma E2 levels just above those of intact animals, was again able to cause suppression of LH pulses, a proestrus-like surges of LH secretion, while the lowest dose suppressed pulsatile LH release. Moreover, an intermediate E2 dose which raised plasma E2 levels just above those of intact animals, was again able to cause suppression of LH pulses, a proestrus-like increase in LH output, or, more importantly, a minisurge of LH secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Estrogen exposure affects the post-ovariectomy increases in both LH and FSH release in female rats.

In female rats ovariectomy (OVX) on the morning of diestrus day 2 resulted in a prompt (within 8 h) and gradual increase in LH release, whereas a similar operation on estrus did not raise serum LH until 24 h later. In proestrous females, OVX in the morning neither prevented the anticipated LH surge on that evening, nor increased LH release on the next morning. Since circulating concentrations of estradiol (E2) are progressively increased during diestrus day 2 and proestrus, this pattern of E2 secretion may affect the acute increase in LH secretion following OVX. To test such a hypothesis, we examined the effects of large, sustained or large, transient increases in circulating estrogen on the subsequent increase in gonadotropin secretion after OVX. On the morning of diestrus day 1 a subcutaneous injection of 20 micrograms estradiol benzoate (EB) produced prompt and large increases in both serum E2 and estrone (E1) for about 2 days, despite OVX of females at 24 h after the EB injection. An injection of 20 micrograms 17 beta-estradiol (E2) also promptly increased both serum E2 and E1. micrograms E2 injection were twice that observed after 20 micrograms EB, and both E2 and E1 returned to low baseline values within 24 h after the E2 injection. In contrast, administration of 1 microgram EB only produced small and transient rises in serum E2 and E1.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of beta-endorphin on gonadotropin-releasing hormone and thyrotropin-releasing hormone releasing activity in cultured rat anterior pituitary cells.

To study the effect of human beta-endorphin (beta h-End) on pituitary response to gonadotropin-releasing hormone (LH-RH) and thyrotropin-releasing hormone (TRH) in vitro, we used dispersed rat pituitary cells. When beta h-End (10(-7) M) was simultaneously added along with LH-RH, its stimulatory effect was blocked and naloxone (NAL, 10(-5) M) did not reverse the beta h-End inhibitory effect. NAL alone elicited an increase in LH release, but in the presence of both stimulants (LH-RH and NAL), LH secretion was lower than that observed with LH-RH alone. TRH stimulatory activity of TSH and PRL secretion was blunted by the presence of beta h-End (10(-7) M) and was not reversed by NAL (10(-5) and 10(-3) M). These data suggest that beta h-End directly blocks the LH, TSH- and PRL-secreting activity of both LH-RH and TRH at the pituitary level. This beta h-End effect is not reversed by the specific opiate receptor blocker NAL.

Developmental changes in the positive feedback effect of estrogen on luteinizing hormone release in ovariectomized female rhesus monkeys.

To examine developmental changes in the LH response to estrogen, eight neonatally ovariectomized monkeys received repeated injections (sc) of 50 micrograms/kg estradiol benzoate (EB) at approximately 4-month intervals starting at age 8-12 months and ending at 49-52 months. Serum samples were obtained 24 before and 0, 6, 12, 24, 36, 48, 60, 72, 94, 108, and 120 h after each EB injection. Serum LH and estradiol levels were measured by RIA. The baseline LH level before EB injection during the prepubertal period (greater than 20 months of age) was 14.4 +/- 2.2 ng/ml, and it increased progressively to 115.3 +/- 13.5 ng/ml at 41-44 months, the age shortly before the first ovulation in our intact colony animals, then declined slightly. EB first induced a typical LH response, which consisted of a negative phase (suppression) followed by a positive phase (surge), at the average age of 29.3 +/- 1.9 months (n = 8). This is similar to the age of menarche in our colony animals. The baseline LH level before EB injection at the time of the first typical response (with negative and positive phases) was 36.7 +/- 6.7 ng/ml, a level 2.5 times higher than that of the prepubertal age. The magnitude of LH suppression by EB was significantly correlated with the baseline level of LH; the higher the baseline LH before EB injection, the greater the degree of LH decrease (r = 0.968; P less than 0.001). Similarly, the amplitude of the LH peak from the trough of the negative phase was significantly correlated with the baseline LH; the higher the LH level before EB injection, the higher the LH increase (r = 0.863; P less than 0.001). The latency to the LH peak was shortest when baseline LH was highest; the peak latency (34.4 +/- 1.6 h) of the LH surge at 41-44 months of age was significantly shorter than the latency (46.5 +/- 2.7 h) of the first LH response occurring at 29.3 +/- 1.9 months of age (P less than 0.001). Finally, the pattern of circulating levels of estradiol after EB injection did not differ across the developmental stages examined. These results are interpreted to mean that an increase in LH release, presumably LHRH release, starts at the onset of puberty and continues until the age of first ovulation, and that the levels of LHRH release during the pubertal period may determine the effectiveness of estrogen on the LH surge.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of pretreatment of long-term ovariectomized rats with an LRH antagonist on LH release in vitro by LRH, elevated K+ or N6-monobutyryl adenosine 3',5'-monophosphate (mbcAMP) plus theophylline.

The effect of the LRH antagonist (Ac-D-p-Cl-Phe1,2,D-Trp3,D-Phe6-D-Ala10)LRH (Org 30093) on pituitary LH release was studied, using pituitary glands of ovariectomized rats. In vitro, the antagonist had no detectable agonist activity in the concentration used, had no effect on the maximal LH release which can be induced by LRH and shifted the dose-response line of LRH to the right, without changing its slope. By this the antagonist fulfilled the conditions of purely competitive antagonist. Also, when present in vitro, the antagonist had no effect on LH release induced by raised K+, whether alone or in combination with mbcAMP plus theophylline. A single injection of Org 30093 decreased serum LH without inducing a change of pituitary LH content measured 24 h later. Twenty-four h after the sc injection of the agonist, LH release in vitro induced by LRH was affected differently, depending on the concentration of LRH used: the effect of low concentrations of LRH was inhibited, whereas the effect of high concentrations of LRH was augmented. Pretreatment with the agonist had no effect on LH release by raised K+ combined with mbcAMP plus theophylline, but slightly increased LH release by raised K+.

Modulation of luteinizing hormone release and catecholamine activity by opiates in the female rat.

Previous studies have shown that the stimulation of LH release by the opiate receptor blocker, naloxone, can be prevented by catecholamine synthesis inhibitors, suggesting opiate regulation of catecholamine release. The present study tested whether an opiate agonist and antagonist would affect the depletion of hypothalamic catecholamines observed after synthesis inhibition, as a measure of catecholamine activity, concomitant with changes in LH secretion. Administration of naloxone to estradiol-primed rats increased LH release and potentiated the depletion of norepinephrine in the preoptic-anterior hypothalamus and medial basal hypothalamus, and enhanced the decline of epinephrine and of dopamine in the medial basal hypothalamus, suggesting increased catecholamine activity in these regions. Administration of the opiate agonist, morphine, to estrogen/progesterone pretreated females decreased LH and decreased the depletion of the catecholamines in the above mentioned areas, suggesting reduced activity. In most cases, naloxone antagonized the inhibitory effect of morphine. These findings indicate that naloxone may stimulate LH release by enhancing hypothalamic catecholamine turnover, possibly by removing the inhibitory influence of an endogenous opioid neuropeptide.

Prostaglandin D2 induces release of luteinizing hormone from the rat pituitary gland without the modulation of hypothalamic luteinizing hormone releasing hormone.

The effect of prostaglandin D2 (PGD2) on release of LH and LH releasing hormone (LHRH) was studied in a sequential double-chamber superfusion system using the medial basal hypothalamus (MBH) and the pituitary gland from female rats at dioestrus. Infusion of PGD2 (5.7 or 57 mumol/l) caused a significant (P less than 0.05) increase in LH release to values 40-60% above the preinjection values from the pituitary gland superfused either alone or in series with the MBH. No release of LHRH in response to PGD2 was observed from the superfused MBH. These data demonstrate that PGD2 causes LH release from the pituitary gland not by inducing release of hypothalamic LHRH but by a direct action on the gland.

Modulation of endogenous opioid influence on luteinizing hormone secretion by progesterone and estrogen.

Studies were undertaken using the opiate receptor antagonist naloxone (NAL) to evaluate the relative influence of endogenous opioid peptides (EOP) on LH secretion in cycling and ovariectomized, steroid-treated adult rats. Intact animals received NAL (2 mg/kg, sc) or saline (control vehicle) at 0800 and 1400 h on estrus, 0800 h on diestrus day 1,2000 h on diestrus day 2, and before (at 0800, 1200, and 1400 h) and during the preovulatory LH surge (at 1600 and 1800 h) on proestrus. NAL stimulated LH release by 2- to 3-fold at all stages of the estrous cycle, including during the proestrous gonadotropin surge. Ovariectomized rats were treated with estradiol benzoate (EB; 7.5 micrograms/rat, sc) and 2 days later received NAL (2 mg/kg, sc) or saline at 1000, 1200, 1400, 1600, and 2000 h. NAL induced a relatively small (44-73%), but significant, increase in LH release before (1000, 1200, and 1400 h), during (1600 h), and after (2000 h) the afternoon LH rise. While progesterone (P) treatment (5 mg, sc, day 2 at 1000 h) of EB-primed ovariectomized rats augmented NAL-induced LH release before the LH surge (1200 h), it abolished the LH secretory response to NAL during the LH surge (1400, 1600, and 1800 h). The NAL-induced LH response returned after the LH surge at 2000 h. Likewise, administration of P on proestrus morning (0900 h) abolished the LH secretory response to NAL during the LH surge. These studies indicate that central opioid neurons participate in the tonic inhibition of LH secretion at all stages of the estrous cycle of the rat. The ability of exogenous P to advance and amplify the LH surge on proestrus and in EB-primed ovariectomized rats appears to result in part from a reduction in the EOP inhibitory influence on LH secretion and may indicate a role for EOP in mediating the stimulatory effects of endogenous steroids on LH secretion in the female rat.

Evidence for noradrenergic involvement in naloxone-induced stimulation of luteinizing hormone release in prepubertal female rats

The effects of phenoxybenzamine an α-adrenergic blocker, propranolol a β-adrenergic blocker, and diethyldithiocarbamate a noradrenaline synthesis inhibitor, on the LH increase induced by naloxone an opiate antagonist, was investigated in 25 day old female rats. Pretreatment with phenoxybenzamine or diethyldithiocarbamate suppressed the LH increase induced by naloxone, whereas pretreatment with propranolol had no significant effects on the naloxone-induced LH release. These results suggest that naloxone-induced increase in LH release is mediated via a noradrenergic mechanism.

Altered Leydig cell function in patients with testicular cancer: evidence for bilateral testicular defect.

In search of an abnormality in Leydig cell function in patients with testicular cancer, serum levels of testosterone, oestradiol, LH and FSH were compared in 3 groups of men. Group I comprised 26 patients studied after recent orchidectomy for a testicular carcinoma, group II 8 patients operated for benign testicular lesions and group III 8 normal controls. In group II normal testosterone values were found as a result of increased LH release. In group I patients, however, testosterone levels often were low, despite elevated LH levels and increased LH capacity. Evidently, in these patients a partial Leydig cell insufficiency may be present, which does not recover within one year of orchidectomy. After removal of one testis for benign disease, normal testosterone levels are maintained by increased LH levels. After orchidectomy for testicular carcinoma a partial Leydig cell insufficiency may be revealed, which seems to have a permanent character. A pre-existent Leydig cell insufficiency of the remaining testis in patients with testicular cancer indicates a bilateral testicular defect.

Time-course of release and synthesis of luteinizing hormone, follicle-stimulating hormone and prolactin from rat pituitary glands in vitro.

To study the time-course of release and synthesis of LH, FSH and prolactin, anterior pituitary glands from ovariectomized rats were incubated for different time-intervals between 0 and 4 h. Comparable patterns of release and synthesis of LH and FSH as a function of the incubation time were observed. It was possible to distinguish two phases in the profiles of secretion of both gonadotrophins. During the first phase, from 0–2 h, release was associated with a corresponding decrease of the hormone concentrations within the gland but no overall changes in total LH and FSH production. During the second phase, between 2 and 4 h, a progressive reaccumulation of both gonadotrophins occurred in spite of the continuous release of hormones into the medium, reflecting formation of new immunoassayable material. These results suggest that the increased synthesis ensues as a secondary phenomenon arising from the release of the hormones from the tissue. The time-course of release and synthesis of prolactin showed different dynamics during the course of incubation. High levels of prolactin were released and synthesized when the adenohypophysis was incubated in vitro. Considerably larger amounts of this hormone were found in the medium than in the tissue from the first hour of incubation. After a lag of about 40 min synthesis of prolactin was increased in parallel with its release. This led to the assumption that both prolactin synthesizing and releasing processes occurred simultaneously from the early stages of the incubation. Comparatively, prolactin-secreting cells had a very fast and LH-secreting cells a low rate of turnover; FSH-secreting cells were intermediate between the two. These results indicate that (1) the increase in release of LH, FSH and prolactin into the medium precedes that of hormone synthesis and (2) the initial depletion of the pituitary gland as a result of hormone release could act as a stimulus for synthesis, leading to the reestablishment of hormonal storage levels.

Progesterone facilitates the LRH releasing action of oestrogen.

The effects of progesterone (P) on the release of LRH and LH were examined in a sequential double chamber superfusion system by superfusing the medial basal hypothalamus (MBH) and/or pituitaries excised randomly from cycling female rats. Addition of 10 microliters of 10(-6) M oestradiol (E2) to the first chamber resulted in a gradual and significant (60-160%) increase in LH release above the pre-injection level from the pituitary in series with MBH. Administration of 10(-8) M P after 10(-6) M E2 caused a prompt and marked increase (300%) of LH (P less than 0.05), whereas 10(-8) M P alone had no effect. Administration of 10(-6) M E2, 10(-8) M P or E2 plus P did not significantly change LH secretion from the pituitary superfused alone. The concentration of LRH in the efflux was significantly increased (150-200%) 150 min after 10(-6) M E2 administration. P administration after E2 injection produced a prompt and significant increase of LRH and the increase of LRH (300-600%) was 2-3-fold that produced by E2. P alone had no effect. These data clearly indicate that P enhances E2-induced LH release by increasing LRH secretion from the MBH.