E. Pedroza

Binding capacity of luteinizing hormone-releasing hormone and its analogues for pituitary receptor sites

Abstract Competition for luteinizing hormone-releasing hormone (LH-RH) receptor sites by the inhibitory analog [D-Phe 2 , D-Trp 3 , D-Phe 6 ]-LH-RH and by the superactive stimulatory analog [D-Trp 6 ]-LH-RH was observed in adenohypophysial homogenates incubated at 4°C. Competition for LH-RH binding sites was less evident with adenohypophysial plasma membranes. The binding affinities of these analogues to LH-RH pituitary receptors can explain at least in part their respective action in blocking ovulation and in inducing a greater release of luteinizing hormone and follicle stimulating hormone than the parent hormone.

Paradoxical effects of D-Trp6-luteinizing hormone-releasing hormone on the hypothalamic-pituitary-gonadal axis in immature female rats

The effect of administration of a superactive and long-acting analog of luteinizing hormone-releasing hormone (LH-RH), D-Trp6-LH-RH, in doses of 0.05 or 1 microgram/day for 10 days on the hypothalamic-pituitary-gonadal axis was studied in immature female rats. Treatment with a 0.05-microgram dose of analog produced few changes as compared with the control group. Treatment with 1 microgram of D-Trp6-LH-RH did not affect the body weight or the pituitary weight, but increased ovarian weight and decreased uterine weight; elevated serum gonadotropin levels; and lowered the pituitary LH content. This depletion of pituitary LH content was associated with a low pituitary responsiveness to LH-RH. Serum estradiol levels were not modified, suggesting that decreased uterine weight reflects a direct and extrapituitary effect of this analog. The hypothalamic LH-RH content was higher, indicating a possible inhibition of the release of endogenous LH-RH. A delay in vaginal opening was also observed. This indicates that large doses of D-Trp6-LH-RH may interfere with the process of puberty in rats. These findings extend other reports about the paradoxical antifertility effects of large doses of stimulatory analogs of LH-RH.

Prevention of Implantation by [D-Trp6]-LH-RH IN the Rat: Comparative Study with the Effects of Large Doses of Hcg on Pregnancy

Effect of large doses of [D-Trp6]-LH-RH and HCG on implantation of fertilized ova was examined in the rat. Subcutaneous administration of 6ug[D-Trp6]-LH-RH per day from days 1 to 5 of pregnancy by an implanted minipump completely prevented the implantation of fertilized ova associated with a dramatic reduction of plasma progesterone on days 4 and 8, with a slight reduction of estradiol on day 4. There was no balooning of the uterus in the exploratory laparatomy on days 8 and 14. Administration of 1000 U of HCG daily from days 1 to 5 partially prevented implantation and completely terminated gestation. However, plasma progesterone and estradiol levels did not differ from those in the control animals. Ovaries in the [D-Trp6]-LH-RH treated rats appeared to be the same in size as those of the control pregnant rats, whereas the ovaries of the HCG-treated rats were hypertrophied. The results suggest that [D-Trp6]-LH-RH prevents nidation through a mechanism different from that for the adverse effect of excess of HCG on pregnancy.

Danazol effects on gowadotrop in basal levels and pituitary responsiveness to lh-rn in immature male rats

Abstract The effects of acute administration of Danazol on the basal serum levels and pituitary content of LH and FSH and on the release of gonadotropins induced by LH-RH in immature male rats were studied. The basal serum levels of LH and FSH were diminished by Danazol, but the pituitary contant of gonadotropin was not. Danazol injected once a day in the dose of 4 mg/rat for 3 days significantly ( P

Prolonged Release of LH and FSH and Depletion of Pituitary Gonadotropin Content after Administration of [d-LEU6, desGly-NH210]-LH-RH Ethylamide

Summary LH and FSH releasing activities of [D-Leu6, desGly-NH2 10]-LH-RH ethylamide were examined using immature male rats. The gonadotropin release induced by various doses of [D-Leu6, desGly-NH2 10]-LH-RH ethylamide followed a different pattern than when LH-RH was given, reaching a peak at 2 hr after injections, serum LH and FSH being still elevated at 4 hr. In contrast the LH and FSH release induced by LH-RH reached a peak in 15 min and declined at 1 hr. This provides further evidence that this analog is indeed long-acting. The LH-RH analog had a potency 20-60 times greater for LH release and 10-30 times higher for FSH release than LH-RH. [D-Leu6, desGly-NH2 10]-LH-RH ethylamide also caused a significant depletion of the pituitary gonadotropin content. The authors express their thanks to Mrs. J. Gau-thier and Mrs. D. Pierson for their technical help, and to Dr. G. Niswender, Dr. A. Ward and NIAMDD Rat Pituitary Program for the gift of the Material used for radioimmunoassays.

Effects of Danazol on gonadotropin secretion after ovariectomy in rats

The effects of Danazol on the elevated levels of serum gonadotropins and on the pituitary response to LH-RH in ovariectomized rats pretreated or not pretreated with estradiol and progesterone, were studied. Danazol depresses significantly the elevated serum levels of LH, but not those of FSH. The LH and FSH response to LH-RH in ovariectomized rats was increased by Danazol. This compound partially modified the inhibitory action of estradiol and progesterone on the serum levels of LH and nullified the depression of FSH. The results indicate that the effects of Danazol on the gonadotropic function of the pituitary depend on the functional state of the gland and/or the duration of the treatment.

Hypothalamic Hormones Regulating Pituitary (and Other) Functions: Their Physiology and Biochemistry as Well as Recent Studies with Their Synthetic Analogues

It is well established now that the hypothalamic releasing and inhibitory hormones produced in the neuronal cell bodies regulate the secretory activity of the anterior pituitary gland. The discovery of several of these hormones and their isolation, structural identification and synthesis furnished the evidence for the theory of neurohumoral control of the pituitary gland put forward by Harris (1) and others.

Biphasic fluctuation of pituitary responsiveness to LH-RH during the rat estrous cycle. Role of endogenous LH-RH and ovarian steroids in its modulation.

The role of the endogenous LH-RH and gonadal steroids on the fluctuation of the pituitary responsiveness to an analog of LH-RH in rats was studied. A specific sheep serum against LH-RH and a superactive analog of LH-RH [D-Ala6,desGly-NH2(10)]LH-RH ethylamide, which does not cross-react with the LH-RH antiserum, were used. In control animals, the pituitary response to 400 ng of LH-RH varied during the estrous cycle, the greatest responses being on the days of proestrus (P) and estrus (E) and the lowest on diestrus I (DI) and diestrus II (DII). A similar pattern was observed in the same animals when 10 ng of [D-Ala6,desGly-NH2(10)]LH-RH ethylamide were used. In animals treated with anti-LH-RH serum, the LH response to the analog was greater than that in control rats on day I (DI) and day 2 (DII) and was smaller on day 3 (P) and on day 4 (E). The magnitude of the pituitary responsiveness to the analog in animals treated or not with the anti-LH-RH serum depended to some extent on the serum progesterone/estradiol ratio. The antiserum against LH-RH lowered the high serum levels of estradiol which are normally seen on P and E but not of progesterone. This indicates that a possible extraovarian source of progesterone exists, possibly from the adrenals. In conclusion, the cycling fluctuation of the plasma progesterone/estrogen ratio in the female rat could act at the pituitary level to modify LH-RH action.

Effects of administration of a LH-RH inhibitory analogue on stages of the rat estrous cycle.

Summary [d-Phe2, Phe3, d-Phe6]-LH-RH, a potent antagonist of LH-RH, was injected during the different stages of the estrous cycle in rats at a dose of 1.5 mg/rat. When it was administered at noon or proestrus, a 100% blockade was observed. This decreased to 33% and 17% when the analogue was injected at 9 am on proestrus and diestrus 2, respectively. No blockade of ovulation was observed after the injection of the analogue on diestrus 1 or on the previous estrus. The sequential administration of the analogue twice daily on E, D1 and D2, brought about almost complete suppression of LH surge on proestrus and an 86% blockade of ovulation without altering the cyclic vaginal smear pattern. In this case, serum levels of estradiol were not modified but progesterone levels were significantly lower on proestrus and higher on diestrus 1 in the analogue treated group as compared to control rats. This higher level of progesterone on diestrus 1 might account in part for the inhibition of the LH-surge and blockade of ovulation by the inhibitory analogues of LH-RH. We thank. Mrs. J. Gauthier and Mrs. J. Wade for their valuable technical assistance; Dr. G. Niswender, Dr. Ward and NIAMDD-Rat-Pituitary Hormone Program for the gifts of materials used in radioimmunoassays.