Jesus A. Vilchez-Martinez

Synthesis and biological properties of (D-Ala-6, des-Gly-NH2-10)-LH-RH ethylamide, a peptide with greatly enhanced LH- and FSH- releasing activity.

Abstract A nonapeptide analog of luteinizing hormone-releasing hormone (LH-RH), [D-Ala 6 , des-Gly-NH 2 10 ]-LH-RH ethylamide, was prepared by solid-phase methodology. The peptide was assayed against LH-RH in two in vivo systems and was found to be many times more potent than the naturally occurring hormone. In one of the tests, based on elevation of LH and FSH levels after infusion into immature male rats, the analog showed LH-releasing activity of 1600% and FSH-releasing activity of 1200% compared to LH-RH.

Synthesis and biological properties of [Leu-6]-LH-RH and [D-leu-6,desGly-NH210]-LH-RH ethylamide

Abstract [Leu 6 ,desGly-NH 2 10 ]-LH-RH ethylamide and [Leu 6 ]-LH-RH, two analogs of LH-RH, were prepared by the solid phase method. LH- and FSH-releasing activity of these peptides was assayed against LH-RH by subcutaneous administration in immature male rats. When the integrated levels of LH and FSH over a 6 hr period after the injection were used as parameter of the LH- and FSH-releasing activities, the [Leu 6 ]-LH-RH showed LH-releasing activity of 9 times and FSH-releasing activity of 5 times greater than that of LH-RH. [Leu 6 ,desGly-NH 2 10 ]-LH-RH ethylamide showed LH- and FSH-releasing activities of 53.6 and 14.5 times greater, respectively, than that of LH-RH.

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.

Gonadotropin-releasing activity of two highly active and long-acting analogs of luteinizing hormone-releasing hormone after subcutaneous, intravaginal, and oral administration.

The gonadotropin-releasing activities of two synthetic analogs of luteinizing hormone-releasing hormone (LH-RH), D-Ala6-des-Gly10-LH-RH ethylamide and D-Leu6-des-Gly10-LH-RH ethylamide were evaluated in immature female rats after subcutaneous, intravaginal, and oral administration. Maximal peaks of serum LH and follicle-stimulating hormone (FSH) levels after administration of both analogs by any of the three routes were obtained at 2 hours. Therefore, serum gonadotropin levels declined slowly, so that at 6 hours LH levels had returned to base line values, whereas FSH levels remained elevated for up to 10 hours. The integrated serum gaondotropin levels after LH-RH and both analogs over a 10-hour period indicated that D-Leu6-des-Gly10-LH-RH EA and D-Ala6-des-Gly10-LH-RH EA released more LH and FSH than did the LH-RH decapeptide. The intense and long-acting properties of these analogs in releasing LH and FSH suggest the possibility that they may be more useful therapeutically than LH-RH.

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

The Effect of Oral and Vaginal Administration of Synthetic LH-RH and [D-ALA6, DES GLY10-NH2]-LH-RH Ethylamide on Serum LH Levels in Ovariectomized, Steroid Blocked Rats

Summary Effects of oral and vaginal administration of LH-RH and [D-Ala6, DesGly10-NH2]-LH-RH ethylamide (D-Ala6-LH-RH-EA) on serum LH levels in ovariec-tomized, estrogen, progesterone treated rats were investigated. Oral administration of synthetic LH-RH induced a quick rise of serum LH levels with the greatest elevation at 15 min at any dose levels tested. On the other hand, oral administration of D-Ala6-LH-RH-EA resulted in a slow but progressive rise of LH during 120 min of observation. The total amount of LH released by 10 μg of the analog was much greater than the total released by 1000 μg of LH-RH. Vaginal administration of 100 μg of LH-RH mixed with Carbowax induced a progressive rise of LH which was indistinguishable from that following 10 μg of the analogue, suggesting that the potency of the analogue is 10 times greater than that of LH-RH for vaginal administration. Ten μg of LH-RH given through the vagina induced a rapid rise of LH with the peak at 15 min, whereas 1 μg of the analog induced a slow but progressive rise. Greater resistance of D-Ala6-LH-RH-EA than LH-RH against in vivo breakdown is postulated as one of the causes of greater and prolonged LH release by the former.

Comparison of the Anti-LH/FSH-RH and Anti-Ovulatory Activities of [p-Phe2, D-Leu6]-LH-RH and [O-Phe2, D-Ala6]-LH-RH

The anti-LH/FSH-RH and antiovulatory activities of [D-Phe2, D-Leu6]-LH-RH and [D-Phe2, D-Ala6]-LH-RH were compared in rats. Both peptides inhibited the LH and FSH release induced by LH-RH in immature male rats, but, 4 hr after the injection, [D-Phe2, D-Leu6]-LH-RH still suppressed the LH and FSH release whereas the [D-Phe2, D-Ala6]-LH-RH did not. When the peptides were administered in equal doses on the afternoon of the day of proestrus in 4-day cycling rats, [D-Phe2, D-Leu6]-LH-RH more completely inhibited the ovulation occurring on the following morning than [D-Phe2, D-Ala6]-LH-RH. Thus, the incorporation of D-Leucine into position six of the decapeptide chain gives a more potent inhibitor than that resulting from the insertion of D-Alanine.

Anti-Luteinizing Hormone (LH)-Releasing Activity of Several Analogues of LH-Releasing Hormone *

The anti-LH-releasing activity of several analogues of LH-RH was tested by 2-hour infusion in ovariectomized, estrogen-progesterone-pretreated rats and in immature male rats. [Leu3]LH-RH, [Leu3, desGly10]-LH-RH ethylamide, [desHis2, Leu3,desGly10]-LH-RH ethylamide, [Gly2, Leu3,desGly10]-LH-RH ethylamide, [Leu1, desGly10]-LH-RH ethylamides, [desHis2,D-Ala6,desGly10]-LH-RH ethylamide, [desHis2,Leu3,D-Ala6, desGly10]-LH-RH ethylamide, and [D-pGlu1,desGly10]-LH-RH ethylamide, and and [D-pGlu1,desHis2,desGly10]-LH-RH ethylamide showed some anti-LH-releasing activity, but never completely inhibited the increase in serum LH in response to LH-RH. No significant differences were found among the analogues tested and [desHis2,desGly10]-LH-RH ethylamide, and inhibitory potency was not improved with those peptides containing D-alanine in position 6 of the chain. None of the analogues tested, including [desHis2,desGly10]-LH-RH ethylamide, was able to block the LH-RH-induced FSH release in these systems.