LH Increments Research Articles

15 RELEASABLE INTRAGONADOTROPE POOLS IN NORMAL AND AGONADAL CHILDREN

LHRH evokes biphasic LH release in mature subjects but not in prepubertal children. To further examine the nature of pituitary LH and FSH secretion and sex steroid (E2, T) modulation of early (I) and later (II) releasable gonadotropin pools, 100 μg synthetic LHRH was infused for 3 hr into 51 prepubertal (PRE) and 44 pubertal (PUB) children and 8 agonadal (Ag) girls (>11 yrs). A maturity-related LH increment (no sex difference) occurred. The ratios of I to basal (B) period increased from 2.2 in PRE to 4.8 in PUB (p < .001) while II/B increased from 4.8 in PRE to 10.6 in PUB (p < .001), suggesting a puberty-associated augmentation of the early and especially the late releasable LH pool. In contrast, for FSH, I and II are greater in the PRE than PUB with significantly more secretion in girls than boys. In girls, I/B fell from 5.6 in PRE to 2.6 in PUB and II/B from 15 in PRE to 3.4 in PUB (p < .001). Pool sizes and ratios to B correlated positively for LH and negatively for FSH with basal levels of E2 in girls and of T in boys. In Ag, basal LH and FSH secretion was 10-20 fold greater than in PUB, with parallel LHRH-evoked responses. In contrast to normal children, a relatively greater increment occurred in pool I in Ag after LHRH. Conclusions: 1) Biphasic LH secretion, with a greater increment of II than I, was more apparent in PUB than PRE; 2) LHRH-evoked FSH secretion is greatest in PRE girls with a large pool II; 3) E2 and T levels correlate with the releasable LH and FSH pools; 4) Ag have preferential augmentation of basal and pool I secretion.

The Effect of Systemic Administration of Dopamine and Apomorphine on Plasma LH and Prolactin Concentrations in Conscious Rats

The effect of systemic administration of various doses of dopamine (DA) and apomorphine (APM) on plasma gonadotropin and prolactin (Prl) concentrations in ovariectomized (OVX) as well as in ovariectomized, estrogen-progesterone (OEP)-primed rats bearing indwelling jugular venous catheters was evaluated. Intravenous (i.v.) infusion or pulse injection of 0.9% NaCl had no significant effect on plasma titers of LH or Prl. I.v. infusion of DA at 4 micrograms/kg-b.w./min induced a progressive increase in circulating LH concentration in OEP rats while infusion at a similar dose in OVX animals had no effect on plasma LH. I.v. injection of 100 micrograms DA or APM significantly increased LH at 15 min in OVX rats. Similarly, in OEP rats 100 micrograms of DA elevated plasma LH at 30 and 90 min while APM induced a significant elevation of plasma LH at 15 min after injection. In OVX rats injection of DA i.p. at a dose of 5 mg/kg-b.w. did not alter plasma LH levels, but a dose of 50 mg/kg-b.w. produced a significant reduction in plasma LH concentration. APM injected i.p. at either 5 or 50 mg/kg-b.w. doses was nearly equally effective in lowering plasma LH and the suppressive effect was significantly greater than with similar doses of DA. A single injection of LH-RH (100 ng in 0.2 ml of 0.9% NaCl) in animals pretreated 15 min earlier with an effective dose of APM (5 mg/kg-b.w.) produced a peak increase in LH titers 15 min after injection. The increment in plasma LH following LH-RH in APM-treated rats was comparable to that in rats which had received saline instead of APM. Prl levels were significantly lowered by each dose of DA and APM in OVX as well as in OEP rats. There was no significant change in plasma FSH titers induced by either drug in any of the experiments. It is concluded that DA may have different actions depending upon the dose and the endocrine state of the animal. Thus, i.v. infusion of low doses of DA in OEP animals or by pulse injection in both OVX and OEP rats can elevate plasma LH by activating the release of LH-RH from the hypothalamus, while large doses of DA in OVX animals may suppress the release of LH-RH.

Morphine Inhibition of the Preovulatory Surges of Plasma Luteinizing Hormone and Follicle Stimulating Hormone in the Rat

A study was made of the effects on the preovulatory surges of LH and FSH exerted by morphine sulfate (M) administered at 1400 h on proestrus, the beginning of the critical period for gonadotropin release in cycling rats in our colony. Various doses of M were given ip and jugular venous blood was collected under ether anesthesia for radioimmunoassay of plasma levels of LH and FSH. To verify ovulation, oviducts were examined the following day for the presence of ova. A high dose of M (60 mg/kg) totally abolished the LH surge and partially prevented the FSH surge while completely blocking ovulation. With intermediate doses of M (20-30 mg/kg) about half of the rats showed undiminished elevations of plasma LH at 1800 h and complete ovulation the next morning, whereas the other half revealed almost total blockade of LH release and no ovulation. Following a low dose of M (10 mg/kg) a small but significant (P < 0.05) augmentation of LH levels was observed in two of three experiments and all animals receiving this dose ovulated. Pretreatment with naloxone (10 mg/kg) did not itself affect LH or FSH release or ovulation but reversed the effect of the high dose of M and permitted complete ovulation. At 1800 h the pituitaries of control and Mblocked rats responded about equally to exogenous LHRH (100 ng iv) in 15 min increments of plasma LH and FSH and all of the rats ovulated. A timecourse study indicates that the onset of the LH surge may be somewhat delayed but the amplitude was undiminished following administration of a low dose of M. These findings indicate that M exerts dose-dependent effects on the preovulatory discharge of pituitary gonadotropins in the cycling rat.

A Medial Basal Hypothalamic Site of Synergistic Action of Estrogen and Progesterone on the Inhibition of Pituitary Luteinizing Hormone Release1

Plasma LH concentrations were measured by radioimmunoassay in blood withdrawn from indwelling atrial cannulas in long-term ovariectomized (OVX) rats. Subcutaneous injection of 50 μg of estradiol benzoate (EB) in oil depressed the plasma LH concentration to about one-third within 2 h. In other rats, sc injection of 25 mg of progesterone (P) in oil at the time of EB injection did not alter this response. Plasma LH remained suppressed at that level until at least 8 h after injection in both groups, but fell an additional 50% within 24 h after injection only in the rats treated with both EB and P. In additional rats, P, but not the oil vehicle alone, when administered 18 h after the injection of EB, caused plasma LH to decline by about 50% within 60 min. Under these latter conditions, 5, 20 or 100 ng of LHRH was injected through the cannula at 1 h after the injection of P or oil. Progesterone did not inhibit pituitary LH release in response to LHRH as determined by comparison of plasma LH concentrations and increments at 3, 10 and 30 min after LHRH in the two groups. In OVX rats which still exhibited pulsatile LH release after surgical interruption of all of the neural connections to their medial basal hypothalami, injection of EB followed 18 h later by injection of P produced results similar to those seen in control OVX rats. The results suggest that P acts synergistically with estrogen at the level of the medial basal hypothalamus in long-term OVX rats to lower plasma LH concentrations to levels which approach but do not reach basal plasma LH levels in cyclic rats and that, under the conditions of this study, P does not lower plasma LH concentration in EB-treated OVX rats until estrogen has exerted its effect for >8 h but ≤18 h.

ANTERIOR PITUITARY SENSITIVITY IN IMMATURE FEMALE RATS STIMULATED WITH GONADOTROPHIN RELEASING HORMONE IN VIVO: EFFECT OF PRIMING WITH OESTROGEN, PREGNANT MARE SERUM GONADOTROPHIN OR BRAIN LESION

An investigation of pituitary sensitivity, assessed in terms of increments in plasma LH and FSH concentrations, to stimulation with one or two injections of gonadotrophin releasing hormone (GnRH) was carried out on 26-day-old immature female rats which had received one of the following priming treatments: 10 μg oestradiol benzoate (OB) as a single injection on day 23 or day 25, or on both days; 10 i.u. pregnant mare serum gonadotrophin (PMSG) on day 24; an electrochemical brain lesion placed in the mediobasal hypothalamus on day 23; control animals received either vehicle alone or a sham lesion. Pituitary sensitivity assessed at 10.00 h on day 26, after one or two injections of GnRH (100 ng/100 g body weight, s.c.), was enhanced to a similar degree in the three groups treated with OB in terms of LH (P &lt; 0-01). The FSH response also increased after OB treatment but was not statistically significant. In contrast, 48 h after the injection of PMSG (i.e. when the rats were in a 'pro-oestrous-like' condition) pituitary sensitivity in terms of both LH and FSH dropped sharply (P &lt; 0·001). In lesioned animals, pituitary sensitivity to one injection of GnRH was unchanged. A second GnRH injection administered after a 60 min interval induced a slightly larger LH response in control animals. In contrast, the ratio of the second response to the first increased in animals treated with PMSG, despite the state of overall decrease in sensitivity, being 4·5:1 in PMSG-treated rats versus 1·4:1 in controls. In a second set of experiments, we investigated the variation of pituitary sensitivity in conjunction with an experimentally induced gonadotrophin surge. In animals treated with OB on day 23 and with 1 mg progesterone at 12·00 h on day 26, pituitary sensitivity was increased at both 14.00 and 17.00 h as compared with that in the day 23 OB-treated group at 10.00 h. The PMSG-treated animals maintained their state of decreased responsiveness at 14.00 h, but exhibited increased pituitary sensitivity at the time of the gonadotrophin surge (17.00 h). These results show that OB increases pituitary sensitivity to GnRH in 26-day-old female rats and that the induction of a gonadotrophin surge further increases this sensitivity. In contrast, PMSG-treated rats displayed a state of decreased responsiveness 48 and 52 h, but not 55 h, after the injection. Pituitary sensitivity on the second day after PMSG treatment thus clearly differs from that observed during pro-oestrus in the adult cyclic female rat.

HORMONAL EFFECTS OF TAMOXIFEN IN OLIGOSPERMIC MEN

The hormonal effects of tamoxifen (10 mg daily for 6 months) have been studied in nine men with oligospermia. Basal concentrations of serum LH (1-7 +/- 0-1 (S.E.M.) i.u./l) increased to a maximum of 4-1 +/- 1-3 i.u./l (P less than 0-001) after 6 months, and FSH rose from 4-9 +/- 1-0 to a maximum of 7-7 +/- 1-3 i.u./l after 4 months of treatment (P less than 0-01). The response to luteinizing hormone releasing hormone (LH-RH) was studied at monthly intervals. Sums of increments of serum LH increased from 35 +/- 4 to 92 +/- 17 i.u./l at 4 months (P less than 0-001) and of FSH from 14 +/- 3-4 to 23 +/- 3-5 i.u./l at 4 months (P less than 0-01). Basal serum androgens rose from 25 +/- 2-7 to 38 +/- 2-4 nmol/l after 4 months of treatment (P less than 0-05), and serum oestradiol-17beta increased from 185 +/- 25 to 631 +/- 90 pmol/l by 6 months (P less than 0-001). No significant changes occurred in sperm counts. Five normal men acted as controls: they were given tamoxifen for 1 week. No significant changes were observed in serum LH, FSH or release of these hormones following administration of LH-RH. Serum androgens and oestrogens however, increased significantly by day 4 of treatment (P less than 0-05).

Increased Responsiveness to LH-Releasing Hormone (LHRH) in Rats with Median Eminence Lesions

SummaryResponsiveness to synthetic LHRH, as measured by increments in plasma LH following its sc injection, was evaluated in castrated rats with median eminence lesions and compared to that in sham-operated controls and controls with intact brains. Median eminence lesions in castrates were followed by a decline in plasma LH to approximately 30% of control values at 1, 7, and 14 days postlesions. This was associated with an increase in responsiveness to LHRH at 1 day, followed by a return to normal responsiveness at 7 and 14 days postlesions. Even though plasma LH was lowered in the animals with lesions, pituitary LH was little changed, which indicates that these lesions, although effective to inhibit LH release, were probably incomplete.It is concluded that LH release is inhibited by lesions in the median eminence in the face of normal or even increased responsiveness to LHRH. The cause of the increased responsiveness to LHRH which appeared at 1 day after lesions remains to be elucidated.

LH and FSH Levels in Urine and Serum of Prepubertal and Pubertal Children Receiving a 3 Hour Infusion of LH-RH

LH-RH was administered to 17 normal prepubertal and 14 pubertal children as well as to 6 GH deficient prepubertal patients. Urinary immunoreactive LH and FSH were measured in acetone extracts of 3 h collections prior to, during, and immediately after a 3 h infusion of 100 mug LH-RH. Peak LH excretion in response to LH-RH was higher in pubertal than prepubertal children. Girls excreted larger quantities of FSH after LH-RH than did boys. Serum LH and FSH increments evoked by LH-RH correlated significantly (P less than 0.01) with peak urinary gonadotropin excretion. These data suggest that measurement of urinary immunoreactive LH and FSH prior to and after LH-RH administration is clinically useful in evaluation of the reproductive endocrine system of young children and of individuals with low basal levels of gonadotropin.

The LH and FSH responses to LH-releasing hormone (LH-RH) in girls with true precocious puberty treated with cyproterone acetate

Ten girls with precocious puberty ranging in age from 7 to 10 7/12 years who were treated with oral cyproterone acetate on a long term basis, were subjected to LH-RH tests, prior to and 3 to 16 months after the institution of therapy. Cyproterone acetate was given in doses from 60 to 153 mg/m2, which proved to be clinically effective, as evidenced by the slowing down of sexual maturation. The basal levels of LH were found to be unaffected by therapy and corresponded to the pubertal stages of the individual girls. The peak increment of LH after LH-RH stimulation was markedly suppressed by the therapy. FSH secretion and its responsiveness to LH-RH was not affected by cyprotereone acetate. The basal levels of FSH were higher during therapy than before, but the peak FSH increment remained the same. An escape phenomenon in the LH peak response was evident in 2 patients upon retesting after prolonged therapy. It is possible that the antigonadotrophic action of cyproterone acetate is due to its progestational nature.

Spironolactone stimulation of gonadotropin secretion in boys with delayed adolescence.

Spironolactone (Aldactone) acts as an antiandrogen by blocking testosterone synthesis and competing with testosterone for the androgen receptor. These properties of the mineralcorticoid antagonist were used in an attempt to interrupt the gonadal-pituitary-hypothalamic negative feedback axis and thereby stimulate LH and FSH in 7 boys with delayed puberty. Following administration of aldactone (5 mg/kg) daily for one week, there was a significant (P less than .01) mean increase in serum LH of 60%. In all 7 boys an absolute rise in LH was observed, but these changes were statistically significant in only 5 individuals. While mean FSH levels increased by 60% in this group of boys, the individual responses were variable. No rise in gonadotropin levels occurred in 2 patients with Kallmann's syndrome, who also received 5 mg/kg of spironolactone daily for 1 week. Large doses of the drug appeared necessary to stimulate gonadotropin secretion since a dose of 3 mg/kg per day did not cause LH or FSH increments in 2 additional patients with delayed puberty. Progesterone and 17alpha-hydeoxyprogesterone levels increased to a greater extent than LH and FSH in response to spironolactone, reflecting either adrenal or testicular enzyme inhibition. Spiornolactone is the first drug shown to be capable of stimulating gonadotropin secretion by interrupting negative feedback inhibition in boys with delayed puberty.

The effect of testosterone on the responsiveness of the quail's pituitary to luteinizing hormone-releasing hormone (LH-RH) during photoperiodically induced testicular growth

Experiments were undertaken to determine whether the responsiveness of the pituitary to luteinizing hormone-releasing hormone (LH-RH) changed during photoperiodically induced testicular growth in the Japanese quail ( Coturnix coturnix japonica). LH release from the pituitary was induced either by the intravenous administration of 0.5 μg LH-RH/100 g body weight, or by elevating the animal's own level of endogenous LH-RH by electrical stimulation in the posterior basal hypothalamus. Groups of both intact and castrated males were tested while still on short days and on the seventh, twenty-eighth, fifty-sixth day following transfer to long daylengths. Pituitary responsiveness to LH-RH was increased by the seventh long day in the intact birds (max. incremental LH change: 11.6 ± 2.2 (20) ng/ml and 25.8 ± 4.0 (20) ng/ml, respectively) but this heightened sensitivity had disappeared by the twenty-eighth and fifty-sixth long day (max. incremental LH change: 17.5 ± 1.9 (19) ng/ml and 12.6 ± 1.3 (18) ng/ml, respectively). No significant changes were observed in the responsiveness of the castrates during photostimulation. The role of testosterone in modifying pituitary responsiveness was investigated by implanting Silastic capsules containing testosterone into castrated males. After 7 long days it was observed that in the group of birds where testosterone had very little negative feedback effect on resting plasma LH levels the incremental change induced by LH-RH was significantly augmented compared with the untreated castrates (27.6 ± 6.2 (7) ng/ml versus 15.0 ± 1.6 (13) ng/ml), suggesting a positive sensitizing effect of testosterone on the pituitary. In addition to this positive effect testosterone also causes negative feedback, which operates to maintain a low plasma LH concentration throughout the life of the animal both under short days, when the birds are immature, and when they are sexually mature on long days. It would appear, therefore, that testosterone has a dual role in modifying plasma LH concentration. A negative feedback, probably acting at the level of hypothalamus dampens LH secretion while superimposed upon, but independent of this negative effect, there is a transient positive feedback action on the pituitary to increase its responsiveness to LH-RH.

Effect of clomiphene on basal and LRH-induced gonadotropin secretion in postmenopausal women.

LRH tests were performed in 11 postmenopausal women before and after the administration of 200 mg of clomiphene citrate daily by mouth for 7 consecutive days. The basal levels and the maximum increments of serum LH (deltaLH) and the area under the response curve from basal level (deltaarea) after LRH administration, significantly (P less than 0.005) decreased after consecutive administration of this compound. Serum FSH levels were significantly (P less than 0.025) decreased but deltaFSH and deltaarea in LRH test were statistically unchanged. These results suggest that clomiphene citrate in postmenopausal women inhibits the pituitary gonadotropin response to exogenous LRH by its estrogenic effects.

Parameters of electrical stimulation of the medial preoptic area for release of gonadotrophins in male rats.

The release of LH and FSH after the application of an electrical stimulus to the anterior diencephalon of male rats has been studied. The stimulus was applied through either platinum or steel electrodes implanted stereotaxically in animals anaesthetized with urethane. The efficacy of various parameters of stimulation by means of a current consisting of balanced biphasic square waves, was tested by systematically changing the frequency, amplitude and duration of the pulses. The effect of direct current (d.c.) stimulation on hormone release was also examined. The concentrations of the hormones in blood withdrawn from the femoral vein before and at frequent intervals up to 80 min after application of the stimulus were determined by radioimmunoassay. The optimal parameters for the release of LH by square wave stimulation of the medial preoptic area were: frequency, 60 Hz; pulse amplitude, 0-50 mA; pulse duration, 1-00 ms. This stimulus was more effective when applied through steel than through platinum electrodes. Direct current stimulation (15 muA for 10 s) through steel electrodes was most effective of all. When applied through platinum electrodes to the medial preoptic and anterior hypothalamic areas, the optimal square wave stimulus produced significant increases in the concentration of LH after 5 and 10 min respectively. The concentration of plasma FSH in these animals also increased, but the increments were much less than the increments in LH. The magnitude of the respective increases of the gonadotrophins after stimulation of the two brain areas did not differ significantly. Measurement of the milk ejection response to stimulation of the hypothalamo-hypophysial tract in the lactating rat indicated that the spread of the square wave stimulus was no more than 1-5 mm from the electrode tip. The significance of these findings is discussed with respect to the importance of the medial preoptic area in the male rat, the neurones which may be involved in the regulation of gonadotrophin secretion, and the parameters of stimulation used in studying the hypothalamo-hypophysial system.

Gonadotropin secretion in prepubertal and pubertal primary hypogonadism: response to LHRH.

Plasma LH and FSH were measured before and after LHRH administration in 10 patients with Turner's syndrome, in 7 with anorchia, in 2 castrates, in 18 with Klinefelter's syndrome, and in 11 prepubertal subjects with unilateral cryptochidism used as a control group. Basal LH was elevated in 4 and basal FSH in 8 of 10 patients with Turner's syndrome. Four patients with anorchia showed elevations of LH while FSH had increased in all of them. The two castrates had normal or slightly increased basal LH and definite elevations of FSH. Prepubertal subjects with Klinefelter's syndrome had normal plasma LH and FSH levels, but showed a marked elevation when they developed puberty. After LHRH administration, mean LH increased by 297% and FSH by 81% in Turner's syndrome, while in anorchia LH increased 757% and FSH 104%. After LHRH administration, patients with unilateral cryptorchidism had an LH increment of 316% and a FSH increment of 164%. Patients with prepubertal Klinefelter's syndrome showed elevations of 261% for LH and 221% for FSH after LHRH treatment. Adolescent subjects with Klinefelter's syndrome had an increment of 352% for LH and only 13% for FSH after LHRH administration. We have concluded that patients without functioning gonads fail to suppress gonadotropin secretion even before puberty while the gonads of the prepubertal Klinefelter's syndrome are able to control LH and FSH release. After puberty, in spite of the hypersection of LH and FSH observed in all subjects with agonadism there is a large pituitary reserve of the gonadotropins. We suggest that the relative inability of pubertal patients with Klinefelter's syndrome to increase FSH after LHRH treatment might be due to the presence of an abnormal compound secreted by the gonads.

The effects of estrogen and progesterone on the functional capacity of the gonadotrophs.

The functional capacity of the gonadotrophs under the influence of exogenous estrogen and progesterone was assessed by repeated stimulation with submaximal doses of LH-releasing factor (LRF) (10 mug at 2-h intervals) of subjects during the early follicular phase of the cycle and of hypogonadal women. The initial increment of peak serum LH and FSH concentrations after the first administration of LRF, was used to describe the pituitary sensitivity, and the integrated release during the 10 hours of LRF-stimulated pulses was utilized to approximate the pituitary gonadotropin reserve. During the early follicular phase, response to LRF stimulations was relatively stable with corresponding release of LH and FSH. An augmentation of sensitivity, as well as the reserve, for both LH and FSH was elicited by an incremental change in circulating estradiol levels, a change imposed by daily administration of estradiol benzoate for 4 days during the early follicular phase. Under the same conditions, the addition of progesterone (10 mg, im) at the end of the estradiol benzoate treatment induced a marked amplification of the estrogen-augmented pituitary gonadotropin sensitivity and reserve. The pituitary sensitivity, relatively higher than the reserve in hypogonadal subjects, was reversed by the administration of ethinyl estradiol (20-50 mug/day) for 7 days. These data indicate that the functional capacity of the gondotrophs is profoundly modulated by estrogen through relative changes in pituitary sensitivity and reserve, and that progesterone in low doses exhibited an amplifying effect on estrogen-primed gonadotrophs in both the pituitary sensitivity and the reserve.

Interaction of estradiol and LHRH on LH release in rhesus females: evidence for a neural site of action.

The effects on LH release of infusing luteinizing hormone-releasing hormone (LHRH 80 mug/20 min) into the third ventricle, the pituitary, and the peripheral circulation were compared in spayed rhesus monkeys. Within 30 min after iv administration, serum LH concentrations increased to twice to preinfusion levels, and by 120 min declined to original values. Intraventricular or intrapituitary infusions of LHRH resulted in similar LH increments, but the peaks occurred somewhat later (70 to 90 min) and the elevations persisted beyond 200 min. Estradiol-17beta (E2) administered by a sc silastic capsule caused a 5-fold increase in serum E2 within 1 h and reduced serum LH levels by 65% within 4 h. The LH release caused by intrapituitary LHRH was significantly suppressed by maintaining for 72 h E2 concentrations near 100 pg/ml, a level inadequate for stimulating an LH surge. A comparable E2 treatment before intraventricular infusion of LHRH, however, did not inhibit LH release. This difference between the effects of intrapituitary and intraventricular LHRH was demonstrable only in E2-treated monkeys. Moreover, the release of LH after intraventricular infusion of LHRH in E2-treated females was blocked (P less than 0.001) by a single iv injection (90 min before LHRH) of haloperidol (1 mg/kg BW) or phentolamine (5 mg/kg), but was not altered by phenoxybenzamine (3 mg/kg) or propranolol (5 mg/kg). Without E2 pretreatment, LH release after intraventricular LHRH was enhanced by each drug. Phentolamine, injected into both E2- and non-E2-treated monkeys 90 min before an intrapituitary infusion of LHRH had no demonstrable effects on the patterns of serum LH. Our interpretation of these data is that E2 at a concentration below the level that triggers an LH surge has a dual action on LHRH-induced LH release in monkeys: an inhibitory effect exerted directly on the pituitary and a stimulatory effect on the brain. Furthermore, the paradoxical effects of the drugs with and without E2 are due to the involvement of two distinct neuronal systems. The postulated neural effects of both E2 and these drugs can be explained either by an increase in the quantity of injected or secreted LHRH which ultimately binds to LH-secreting cells or by the release of additional endogenous LH-stimulating agents together with ventricular LHRH.

THE RESPONSIVENESS OF THE ANTERIOR PITUITARY GLAND TO LUTEINIZING HORMONE RELEASING FACTOR IN RATS EXPOSED TO CONSTANT LIGHT

The responsiveness of the anterior pituitary gland to synthetic luteinizing hormone releasing factor (LH-RF) was tested in rats exposed to constant light. At a dosage of 50 ng LH-RF/100 g body wt the mean maximal increments in plasma LH and FSH were similar to those at 10.00 h of pro-oestrus. The increments in the plasma gonadotrophins at dosages of 500 and 1000 ng LH-RF/100 g body wt did not differ significantly from those at 250 ng LH-RF/100 g body wt. These findings suggest that, in contrast to rats which exhibit regular oestrous cycles, the preovulatory (post-coital) release of LH in rats exposed to constant light may depend almost entirely on the release of a relatively large amount of LH-RF into hypophysial portal vessel blood. Whereas in pro-oestrous animals a relatively small fraction of the readily releasable pool of LH is released during the spontaneous preovulatory surge, in rats exposed to constant light most releasable LH appears to be discharged during the reflex preovulatory surge of this hormone. The concentrations of radioimmunoassayable FSH in blood samples withdrawn before the injection of LH-RF support the view that FSH secretion in the rat is increased by constant exposure to light.

Alterations during the estrous cycle in the responsiveness of the pituitary to subcutaneous administration of synthetic LH-releasing hormone (LHRH).

To further evaluate the alterations in responsiveness of the pituitary to synthetic LHRH during the proestrous discharge of gonadotropins, LHRH was given SC in the hope of producing a release of FSH as well as LH, and blood samples were removed prior to and at various intervals after the injections of the neurohormone while the rats were anesthetized with tribromoethanol. The procedure of anesthesia and blood sampling produced small declines in both FSH and LH, but these only achieved significance in the case of FSH on the morning of estrus and diestrus day 2. An increase in plasma LH occurred in response to LHRH at all stages of the estrous cycle but was minimal during diestrus. The increment in plasma LH was already increased by 9 AM on proestrus and the titer remained elevated for 2 h. A further increase in response to LHRH occured at 2 PM associated with an increase in initial plasma LH. The maximum response occurred at 5 PM together with maximal initial plasma LH, and the characteristics of the response changed such that there was a much larger increase in plasma LH at 20 min and a rapid decline thereafter, so that the response became pulselike. Initial plasma LH had already declined significantly by 9 PM, and this was associated with a dimished pulselike release of LH in response to LHRH. By the morning of estrus, an even smaller pulse-like release occurred. Significant FSH release in response to LHRH occurred at all stages of the cycle as indicated by the increments in plasma FSH. The relative increase in plasma titers was much less than that for LH and responsiveness to LHRH did not increase until 5 PM on proestrus. Responsiveness had already begun to decline by 9 PM on proestrus and by the morning of estrus was similar to that obtained on diestrus. Initial plasma FSH titers were first elevated by 2 PM on proestrus and they remained elevated on the morning of estrus. The results indicate that maximal responsiveness to LHRH in terms of LH release is associated with the proestrous discharge of LH, but that the maximal responsiveness in terms of FSH release terminates long before the endogenous release of hormone ceases sometime on estrus. The increased responsiveness in terms of LH release may be related to prior estrogen secretion and to the priming action of endogenous LHRH. The continued release of FSH in the face of a return of responsiveness to LHRH to low levels indicates that release of FSH on late proestrus and early estrus is not caused by endogenous release to LHRH.

Role of adrenal steroids in the regulation of gonadotropin secretion at puberty

Plasma levels of androstenedione (Δ4), testosterone (T), estrone (E1), and estradiol (E2), were measured by specific radioimmunoassays in 109 normal subjects, 55 boys and 54 girls 3.5 to 16.3 years of age, and were correlated with maturational parameters such as bone age (BA) and Tanner's stage of sexual development (P). Plasma levels of Δ4 and E1 show a significant increment earlier in females than in males, and increase earlier than those of T or E2 in females. A better correlation was consistently found between plasma levels of Δ4 or T and BA or P both in males and females.Plasma levels of δ4, T, E1 and E2 were also measured in 8 boys and 10 girls undergoing testing with LH-RH for various disorders of sexual development, and were correlated with the maximum plasma LH increment (ALH) observed after LH-RH. In these patients a better correlation was found between ALH and plasma levels of Δ4 in males, and between ALH and plasma levels of Δ4 or T in females than between ΔLH and T in males and ALH and E2 in females.These data seem to indicate that the adrenal gland, through “adrenal” sex steroids such as Δ4 and E1, plays a role in the triggering and the maintaining of sexual maturation.

The effect of oestrogen pretreatment on subsequent response to luteinizing hormone releasing hormone in normal women.

Twenty-two normal, regularly menstruating female subjects had an LHRH test performed before and after pretreatment with 0.5 mg, 1 mg. or 2.5 mg of oestradiol benzoate during the follicular phase of their menstrual cyclees (days 4-8). Two further women acted as controls and received no oestrogen; they showed identical responses for both LH and FSH release when LHRH tests were performed at intervals of 48 h. Oestrogen pretreatment induced a biphasic effect upon subsequent LHRH response. Four subjects retested 20 h after 0.5 mg oestradiol benzoate showed either no change or a slight suppression of LH and FSH release. Fifteen of the eighteen women pretreated with oestradiol benzoate and retested 44 h later showed significantly increased LH release and fourteen significantly increased FSH release when compared to their control responses. The responses appeared to be dose related with a positive correlation between sum of LH increments and basal oestradiol levels (R = 0.61; P less than 0.001) and a similar correlation (r = 0.67; P less than 0.001) between sum of FSH increments and basal oestradiol levels. The physiological significance of this biphasic action of oestrogen upon pituitary sensitivity is discussed in relation to the control of the menstrual cycle.