Injection Of Luteinizing Hormone Releasing Factor Research Articles

Correlation between integrated LH and FSH levels and the response to luteinizing hormone relasing factor (LRF).

Integrated blood plasma levels of LH and FSH and their response to the iv administration of 100 mug synthetic LRF were studied in 29 normal subjects, 12 women with Stein-Leventhal syndrome, 8 subjects with primary gonadal failure, 7 women with Sheehan's syndrome, 20 subjects with pituitary tumors, 10 subjects with idiopathic gonadotropin deficiency and 5 subjects with hypothalamic tumors. Within each group there was considerable variation in the response of LH and FSH levels to LRF. In each group there was a statistically significant positive correlation between basal integrated gonadotropin levels and the response of the levels to LRF. Both within groups and between groups, the best indicator of the response to LRF was the basal levels of FSH and LH. In subjects with hypogonadotropic hypogonadism there was no significant difference in mean basal LH levels and mean response to LRF between patients with primarily pituitary disease (pituitary tumors or Sheehan's syndrome) and conditions which might represent hypothalamic disease (hypothalamic tumors or idiopathic gonadotropin deficiency). The response to an acute, single, injection of LRF appears to more directly reflect basal gonadotropin levels rather than disease category.

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.

Action of luteinizing hormone-releasing factor (lrf) in the initiation of lordosis behavior in the estrone-primed ovariectomized female rat.

In order to evaluate the precise role of luteinizing hormone-releasing factor (LRF) in mediating the onset of sexual behavior, the specificity, time-course, and dose-response relationship of LRF-facilitated lordosis behavior were determined. Ovariectomized female rats, pretreated with estrone and LRF, displayed a pattern of lordosis behavior which differed little from that produced by estrone-progesterone. Little if any lordosis behavior was observed in response to LRF alone, estrone alone, or estrone in combination with luteinizing hormone (LH), follicle-stimulating hormone (FSH), or thyrotropin-releasing factor (TRF). Furthermore, LRF-induced lordosis behavior occurred in the absence of the adrenals, thus eliminating adrenal progesterone as a factor in facilitating the appearnce of lordosis behavior. The LRF-facilitated lordosis behavior was seen 2 h after the injection of LRF and was maintained for a total of 8 h. A minimal dose of 150 ng LRF was required to initiate the first consistent appearance of lordosis behavior; the maximum response was obtained with 500 ng. It is thus suggested that LRF is not only responsible for the ovulatory discharge of LH and subsequent ovulation, but may also play a role in the initiation of the onset of mating behavior in the female rat.

A priming effect of luteinizing hormone releasing factor on the anterior pituitary gland in the female rat.

SUMMARY The possibility that luteinizing hormone releasing factor (LH-RF) not only stimulates the secretion of luteinizing hormone (LH) but also has the ability to prime the anterior pituitary gland so that further exposure to LH-RF enhances the responsiveness of the gonadotrophs has been investigated. The effect of two successive i.v. injections of the same dose of LH-RF (50 ng/100 g body weight) on the concentration of LH in plasma was determined in rats anaesthetized with sodium pentobarbitone. Blood samples were collected from the external jugular vein immediately before and at frequent intervals after the injections of LH-RF, and plasma concentrations of LH and, in some samples, follicle-stimulating hormone (FSH) were measured by radioimmunoassay. In rats anaesthetized with sodium pentobarbitone at 13.30 h of pro-oestrus and injected i.v. with two successive doses of LH-RF, separated by an interval of 30, 60, 120 or 240 min, the LH response to the second injection was significantly greater than that to the first. The LH response was greatest when the two doses were separated by an interval of 60 min. The FSH response to the second injection of LH-RF given 60 min after the first was not significantly different from that to the first injection. Compared with pro-oestrus, the priming effect of LH-RF was much less at metoestrus and dioestrus, and could not be demonstrated at oestrus. Ovariectomy on the morning of dioestrus reduced the LH responses to the first and second injections of LH-RF given 60 min apart on the afternoon of pro-oestrus, an effect which was partially reversed by administration of oestradiol benzoate shortly after ovariectomy. These findings together with the fact that administration of oestradiol benzoate at metoestrus increased the magnitude of the priming effect of LH-RF at dioestrus suggest that the response at pro-oestrus is dependent upon the rise in plasma oestradiol-17β which reaches a peak on the morning of pro-oestrus. Although oestrogen plays an important role in determining the magnitude of the priming effect of LH-RF, it appears that none of the steroids secreted by either the ovaries or the adrenal glands mediates this effect since the profile and magnitude of the LH responses to the two doses of LH-RF injected at pro-oestrus into rats adrenalectomized and ovariectomized before the first injection of LH-RF were comparable to those in control animals. The possible role which the priming effect of LH-RF may play in the development of the preovulatory surge of LH in the rat and man is discussed.

The role of sex steroid hormones in modulating the responsiveness of the anterior pituitary gland to luteinizing hormone releasing factor in the female rat.

SUMMARY The role of ovarian hormones in the development of increased sensitivity of the anterior pituitary gland to synthetic luteinizing hormone releasing factor (LH-RF) which occurs before and during the preovulatory surge of luteinizing hormone (LH) in the rat has been examined. The response of the pituitary gland was determined, with respect to the secretion of LH and follicle-stimulating hormone (FSH), after the intravenous injection of 50 ng LH-RF/100 g body weight. The LH-RF was injected 30–60 min after the administration of sodium pentobarbitone at either 13.30 h or 18.80 h of pro-oestrus. Blood samples were collected immediately before and at frequent intervals after the injection of LH-RF, and the concentration of LH and FSH in these samples was measured by radioimmunoassay. Ovariectomy at 10.00–11.00 h of dioestrus reduced the LH response to LH-RF injected at 14.00 h of pro-oestrus, while oestradiol benzoate administered immediately after ovariectomy restored and even augmented this response. These data together with the finding that administration of the antioestrogen, ICI 46 474, at 17.00 h of dioestrus reduced the LH response to LH-RF injected on the afternoon of pro-oestrus indicates that the initial phase of increased pituitary sensitivity to LH-RF is dependent upon the marked rise in the concentration of oestradiol-17β in plasma which precedes the preovulatory surge of LH. The abrupt, marked increase in pituitary sensitivity to LH-RF, which, in the normal cycle, occurs between 14.00 and 18.30 h of pro-oestrus, failed to develop in rats ovariectomized on the morning of dioestrus whether or not oestradiol benzoate was administered after the operation. However, the LH response to LH-RF injected on the evening of pro-oestrus increased significantly when progesterone was administered at 13.00 h of pro-oestrus in rats ovariectomized and treated with oestradiol benzoate at 10.00–11.00 h of dioestrus. This suggests that the development of the second phase of increased pituitary sensitivity to LH-RF depends, at least partially, on progesterone acting on an oestrogen-primed pituitary gland. The concentrations of FSH in blood samples taken before injection of LH-RF at either 14.00 or 18.30 h of pro-oestrus were significantly greater in ovariectomized compared with those in sham-operated rats. In contrast the FSH responses, in terms of the mean maximal increments, were not significantly different in the various groups irrespective of the nature or time of operation or the time of injection of LH-RF. The FSH response to LH-RF was not appreciably altered by treatment with either oestradiol benzoate or progesterone immediately after ovariectomy although it was increased significantly by the sequential administration of oestrogen and progesterone. The significance of the findings that under certain conditions there were considerable differences between the LH and FSH responses to synthetic LH-RF is discussed with respect to the hypothesis that there is a common releasing factor for both gonadotrophins.

Changes in the sensitivity of the pituitary gland to luteinizing hormone releasing factor during the oestrous cycle of the rat.

SUMMARY The responsiveness of the anterior pituitary gland to synthetic luteinizing hormone releasing factor (LH-RF) was tested at various times of the oestrous cycle of the rat in order to assess the relative importance of changes in pituitary sensitivity in the timing and magnitude of the preovulatory surge of luteinizing and follicle-stimulating hormones (LH and FSH). The minimal dosage of LH-RF which consistently induced ovulation in rats anaesthetized with sodium pentobarbitone (Nembutal) immediately before the critical period of pro-oestrus was 50 ng/100 g body weight, and this was used as the standard dose throughout the study. The LH-RF was injected either intravenously into animals anaesthetized with Nembutal 30 min to 1 h before, or into conscious animals through a cardiac catheter which had been inserted several days before. Most experiments were carried out on rats which had exhibited regular 4-day oestrous cycles, although results from animals with 5-day cycles are also presented and discussed. Blood samples were taken immediately before and at frequent intervals after the injection of LH-RF, and the concentrations of LH and FSH in these samples were determined by radioimmunoassay. With respect to the secretion of LH, in both anaesthetized and conscious animals with regular 4-day cycles a tenfold increase in pituitary sensitivity occurred between the early afternoon of dioestrus and pro-oestrus. This was followed by a marked (50-fold) increase which reached a peak at 17.00–18.00 h of pro-oestrus. The phase of marked increase in sensitivity appeared to commence at about the time of the onset of the pre-ovulatory surge of LH and continued for some hours after. Pituitary sensitivity then declined through oestrus and metoestrus, reaching a nadir at 14.00 h of dioestrus. From 15.00 to 22.30 h of pro-oestrus there was a significant positive correlation between the pre-injection levels of and maximal increments in plasma LH, and this, together with the fact that the marked increase in sensitivity could be abolished by administering Nembutal before the critical period, raised the possibility that endogenous LH-RF, presumably secreted in greater amounts during the early afternoon of pro-oestrus, may exert a priming effect on the anterior pituitary gland. Pituitary responsiveness to LH-RF with respect to the secretion of FSH was also at its highest at 17.00–18.00 h of pro-oestrus. However, in contrast to LH, the mean level of FSH before injection reached a peak at 05.00 h of oestrus, 11 h after the maximum FSH response to LH-RF. These results suggest that a change in pituitary sensitivity to LH-RF may play an important role in determining the magnitude of the pre-ovulatory surge of LH, but it would appear that the timing and duration of the surge depend on other factors as well. The relationship between the secretion of LH and ovulation is discussed with respect to the finding that there appeared to be no correlation between the number of ova shed and the maximal levels of plasma LH after injection.

Luteinizing Hormone-Releasing Factor Potentiates Lordosis Behavior in Hypophysectomized Ovariectomized Female Rats

Subcutaneous injection of luteinizing hormone-releasing factor (LRF) in estrogen-primed hypophysectomized, ovariectomized female rats facilitates the appearance of the lordosis response. The LRF effect on lordosis was seen 90, 180, and 360 minutes after injection. This effect could help to synchronize the female's mating behavior with the ovulatory discharge of luteinizing hormone.

THE EFFECT OF SYNTHETIC HYPOTHALAMIC RELEASING FACTORS ON PLASMA LEVELS OF LUTEINIZING HORMONE IN THE COCKEREL

SUMMARY The capacity of synthetic luteinizing hormone releasing factor (LH-RF) to stimulate the release of luteinizing hormone (LH) from the pituitary gland of the cockerel has been examined. Administration of LH-RF to 21 intact and 12 castrated cockerels aged between 14 and 20 months resulted in a rapid increase in the levels of LH in the plasma within 5–10 min of injection in both groups of birds. Plasma LH then declined rapidly and returned to basal values within 1 h. The amount of LH released in the intact birds was dependent on the dose of LH-RF. Concentrations of LH in the plasma did not increase after injection of thyroid-stimulating hormone releasing factor but the response of the pituitary gland to a subsequent injection of LH-RF 2 h later was not altered. The pattern of release of LH in the cockerel is compared with that of some mammalian species.

Induction of mating behavior in rats by luteinizing hormone-releasing factor.

Ovariectomized female rats treated with estrogen, in dosages too low to provoke mating, displayed this behavior when given subcutaneous injections of synthetic luteinizing hormone-releasing factor (LRF) 48 hours later. Two hours after the injection of LRF, components of female sexual behavior appeared. The lordosis reflex followed mounting by the male, and darting and hopping behavior was quite prevalent. On the other hand, treatment with estrogen followed by luteinizing hormone, follicle-stimulating hormone, or thyrotropin-releasing factor did not induce copulatory behavior. The results suggest that LRF may play a role in induction of mating behavior.

Induction of luteinizing hormone (LH) release and ovulation in rats, hamsters, and rabbits by synthetic luteinizing hormone-releasing factor (LRF).

The efficacy of synthetic LRF in inducing LH release in the estrogen progesteroneblocked, chronically ovariectomized rat and ovulation in the cycling rat, hamster, and rabbit was established. Synthetic LRF was highly effective by various modes of administration, but there were differences in the time course and magnitude of the LH release response depending on the route, and differences in the quantity of LRF required to induce ovulation depending on the species. Following the intracarotid injection of LRF, serum LH peaked at 10 min and a linear log dose—response relationship was obtained over the range of 1 to 5O ng per rat. After the oral administration of 1 mg of LRF, serum LH concentrations were increased to a maximum (27– fold) by 30 min, then steadily declined, reaching basal levels by 90 min. A sustained effect of LRF (10 or 100 μg/rat) on LH secretion was noted following intravaginal dosing using a repository vehicle; serum LH was significantly increased by 10 min, maximal at 30 min, and remained elevated for at least an additional 90 min. LRF, given sc in μg quantities or orally in mg amounts, induced ovulation in chlorpromazine (CPZ)—blocked proestrous rats. The lowest sc dose of LRF yielding 100% ovulation (MED100) in the CPZ—blocked proestrous rat was 1 μg (3.7 μg/kg body wt) whereas in the phenobarbital—blocked proestrus hamster the MED100 was 0.01 μg (0.11 μg/kg body wt). In estrous rabbits, an iv dose of 2.5 μg of LRF (0.88 μg/kg body wt) was the MED100 for induction of ovulation, a value intermediate to that of the rat and hamster. The administration of pharmacological doses (1000 times or more the MED100) to cycling rats, hamsters, or rabbits at a time coincident with the endogenous surge of ovulating hormone failed to induce superovulation. These results demonstrate that synthetic LRF is highly efficacious by several routes of administration in stimulating LH release and ovulation in three rodent species. (Endocrinology92: 1515, 1973)