L. Debeljuk

Isolation and properties of the FSH and LH-releasing hormone☆

Abstract LH-releasing hormone (LH-RH) was obtained in apparently a homogeneous state from extracts of pig hypothalami. The LH-RH preparation isolated has FSH-releasing hormone (FSH-RH) activity, which appears to be intrinsic to LH-RH. The amino acid composition of LH-RH/FSH-RH as determined on acid hydrolysates is: His 1, Arg 1, Ser 1, Glu 1, Pro 1, Gly 2, Leu 1 and Tyr 1. The hormone isolated stimulates the release of FSH and LH in vivo and in vitro in doses of a few nanograms. This polypeptide appears to represent the hypothalamic hormone which controls the secretion of both LH and FSH from the pituitary.

Effect of estradiol and progesterone on the LH release induced by LH-releasing hormone (LH-RH) in intact diestrous rats and anestrous ewes.

Summary The effect of pretreatment with estradiol, progesterone, or a combination of both steroids on the response of serum LH levels to a large dose of LH-RH was investigated. In groups of intact diestrous rats, it was demonstrated that estradiol augmented LH release induced by LH-RH. Progesterone did not block the LH release induced by 1 μg of LH-RH, but suppressed that induced by 0.05 μg LH-RH. In these rats, as well as in intact anestrous ewes, the combination of estradiol and progesterone clearly suppressed the pituitary LH response to LH-RH. The authors express their gratitude to Dr. W. Locke for his editorial advice, to Dr. G. D. Niswender for the gift of ovine LH antisera, and to Dr. H. Papkoff for the gift of purified ovine LH. The excellent technical assistance of Mrs. Nancy Machen, Mrs. Joan Gauthier, and Mrs. Meredith Nickel is also acknowledged.

LH Release by LH-Releasing Hormone in Golden Hamsters at Various Stages of Estrous Cycle

Summary Stimulation of LH release by administration of natural or synthetic luteinizing hormone-releasing hormone (LH-RH) was studied at different stages of the estrous cycle in the golden hamster. The animals were pretreated with phenobarbital to prevent a spontaneous preovulatory surge of LH. In these animals serum LH levels after saline injection remained low throughout the estrous cycle. Intravenous injection of 0.1 or 0.4 μg LH-RH significantly increased serum LH levels compared to appropriate controls. The greatest response to LH-RH was observed during proestrus. The smallest response was observed on the day 1 of diestrus, and in most of the animals, at estrus. The pituitary response to LH-RH on day 2 of diestrus was smaller than during proestrus, and greater than that observed during day 1 of diestrus and estrus. The results indicate that pituitary responsiveness to LH-RH varies at different stages of estrus cycle in the golden hamster. The authors are indebted to Drs. G. D. Niswender and H. Papkoff and to NIH, Endocrinology Study Section for the gift of antiserum and ovine LH for iodination and standard preparation respectively. The technical help of Mrs. N. Machen, Mrs. J. Gauthier and Mrs. M. Esslinger and the editorial advice of Dr. E. B. Ferguson, Jr., are also gratefully acknowledged.

Antiserum to LH-RH blocks haloperidol-induced hyperprolactinemia in female rats.

We investigated the effect of blocking endogenous LH-RH, by injection of anti-LH-RH sera, on serum prolactin levels previously elevated by treatment with haloperidol for 5 days. An acute intravenous injection of rabbit anti-LH-RH serum significantly reduced serum LH levels and blocked the hyperprolactinemia induced by haloperidol. In another group of rats, sheep anti-LH-RH serum induced a significant decrease of serum LH and also lowered serum prolactin levels previously elevated by haloperidol. In ovariectomized rats, sheep anti-LH-RH serum markedly reduced serum LH levels and also decreased serum prolactin elevated by the pretreatment with haloperidol. It is concluded that the blocking of endogenous LH-RH action results in a decreased release of prolactin in response to stimuli like haloperidol. These results support the possible existence of a paracrine interaction between the pituitary gonadotrophs and lactotrophs.

Synthesis and biological evaluation of 4-alanine-luteinizing hormone-releasing hormone ([Ala4] LH-RH)

Abstract Synthesis of [Ala 4 ] LH-RH as well as its chemical, physical and biological properties are described. This analogue exhibits only 5% of the activity of LH-RH decapeptide. This demonstrates that the hydroxyl group of serine 4 is not absolutely essential for LH-RH activity. Although serine may be one of the groups necessary for a strong combined functional effect, it is more likely that its role is concerned with binding to the receptors.

Development of a Method to Test Anti-LH-RH Activity in Rats

A method for testing anti-LH-RH activity wasdevised. The substance to be investigated was infused for 2 h i.e. in ovariectomized, estrogen- and progesterone-pretreated rats, followed by an acute injec

Release of Luteinizing Hormone by Synthetic LH-Releasing Hormone in the Ewe and Ram

Summary Large or small doses of synthetic LH-RH were injected into the carotid artery or intramuscularly in three anestrous ewes and one vasectomized ram. Intracarotid injection of 5 pg of synthetic LH-RH elicited monophasic responses in LH-release; the highest levels of serum LH were reached within 5-10 min after injection of LH-RH, followed by a gradual decrease. Injection of 250 pg of LH-RH resulted in a rise of serum LH within 5-10 min which was indistinguishable in magnitude from that after 5 pg of LH-RH. These levels remained steady or kept rising very gradually for 25 rnin or longer, then again started rising sharply. The peak levels were observed at 1.5 hr after injection, followed by a gradual decrease. Four hours after injection of LH-RH, serum LH levels were still higher than during the preinjection levels. Intramuscular injection of a large dose of LH-RH elicited patterns similar to those observed following intracarotid injection of LH-RH. The magnitude of response after intramuscular injection was the same or greater than that induced by the intracarotid injection of the same dose of LH-RH. The authors are indebted to Mrs. N. Machen, Mrs. J. Gauthier, and Mrs. M. Nickel for their excellent technical assistance. They also wish to thank Dr. H. Papkoff and NIH, Endocrinology Study Section, for the gift of purified ovine LH and NIH-LH-S-17, respectively, and to Dr. E. Ferguson for his editorial advice.

Effect of TRH and triiodothyronine on prolactin release in sheep.

Summary The intracarotid injection of TRH, sufficient to increase serum TSH, brought about a considerable rise in serum prolactin levels in three female anestrous ewes and one vasectomized male ram. The peak in serum prolactin was seen 5 and 10 min after injection of TRH; then the levels declined, but they were still elevated 60 min later. Pretreatment of the sheep with T3 inhibited the rise in serum prolactin as well as serum TSH after injection of TRH.

Effect of Estradiol on the Response to LH-RH in Male Rats at Different Times After Castration

Summary The effects of pretreatment with estradiol benzoate on the pituitary release of LH and FSH in response to LH-RH were investigated in male rats at various time intervals after castration. In oil-treated control rats, LH-RH brought about a significant increase in serum LH at all the periods after castration. One day after castration, pretreatment with estradiol significantly inhibited the response to LH-RH, as observed in normal male rats. One week after castration estradiol induced a greater response to LH-RH than observed in oil-treated control rats, although the difference was not significant. One and two months after castration, estradiol significantly increased the response to LH-RH. The authors express their gratitude to Dr. G. D. Niswender, Dr. H. Papkoff and to NIAMD, Rat Pituitary Program, for the gift of materials used in radioimmunoassays. Thanks are also given to Mr. L. Garcia, Mrs. M. Esslinger, and Mrs. J. Gauthier for technical assistance.

Stimulation of Release of FSH and LH by Infusion of LH-RH and Some of its Analogues

Previous studies showed that LH-releasing hormone(LH-RH) can stimulate a considerable release of FSH as well as LH in vivo if given by prolonged intravenous infusion. The effect of