LH-releasing activity of hypothalamic extracts not attributable to GnRH.

LH secretion is under hypothalamic control, mostly through GnRH. Hypothalamic extracts stimulate LH release in vitro, an action usually attributed to the presence of GnRH. However, the presence of other LH-releasing factors cannot be ruled out since there are other neuromediators endowed with the capacity to influence LH release. We analyzed the presence of an LH-releasing activity in bovine median eminence extracts (ME extracts) different from GnRH using cultured rat pituitary cells. Both, GnRH and ME extracts caused a dose-dependent stimulation of LH release. The maximum response obtained with ME extracts (up to 10-fold the respective baseline) was significantly greater than the maximum response obtained with GnRH (up to 5-fold the respective baseline). Monoclonal or polyclonal GnRH antibodies in the solid phase completely eliminated the LH-releasing activity of 10(-7) M GnRH; in contrast, they only partially removed the activity present in ME extracts. The GnRH receptor blocker, Nal-Glu, 10(-7) M, which completely blocked the effect of GnRH could not totally suppress the LH-releasing activity of ME extracts. These findings indicate that ME extracts contain, in addition to GnRH, an LH-releasing activity not attributable to GnRH because it differs in its immunoreactivity and in its ability to stimulate LH release when GnRH receptors are blocked.

Enzyme-linked immunosorbent assay for rat and human luteinizing hormone.

A sensitive and specific enzyme-linked immunosorbent assay (ELISA) suitable for measuring rat and human luteinizing hormone (LH) is described. The LH-ELISA used anti-bLH beta subunit monoclonal antibody-coated plates, an antiserum against rLH or hLH and an antibody against rabbit IgG labelled with peroxidase. Using rLH-RP-3 or hLH WHO IRP 68/40 as standard diluted in assay buffer, the LH-ELISA had a sensitivity of 50 pg/ml and 0.78 mIU/ml, respectively. The LH-ELISA allowed accurate determination of LH in buffer, cell culture media, anterior pituitary extracts and sera and was highly specific for rat and human LH. The use of this ELISA offers improvements in convenience, economy, sensitivity and safety over comparable radioimmunoassay procedures.

[Hypothalamic inhibiting factor of luteinizing hormone secretion: relation to the fragment 1-5 of the LH releasing hormone]. / Factor hipotalámico inhibidor de la secreción de hormona luteinizante: relación con fragmento 1-5 de hormona liberadora de LH.

In this paper we review the mechanisms underlying the control of gonadotrophin (Gn) release and present evidences of the existence of a luteinizing hormone release-inhibitory factor. We have extracted and partially characterized this factor from rat hypothalamus and bovine median eminence. Our data indicate that the factor is a peptide that has a common antigenic determinant with GnRH, but is of smaller molecular weight than GnRH (750 daltons approximately). These facts strongly suggest that it may be a fragment of the GnRH molecule. The synthetic fragment GnRH (1-5) has similar biologic effects and molecular weight to those of the inhibitory factor obtained from the median eminence and hypothalamus. GnRH (1-5) has been shown to be produced in vitro by cleavage of GnRH by an hypothalamic endopeptidase. Based on this evidences, we suggest that the inhibitory peptide found by us is formed in vivo by degradation of GnRH. Moreover, we suggest that this factor may play a role on the regulation of LH release induced by GnRH.

Gonadotropin-releasing hormone (GnRH) inhibits ovulation induced with luteinizing hormone (LH) in proestrous hypophysectomized rats.

In this paper we present evidence that a single low dose of the natural synthetic gonadotropin-releasing hormone (GnRH), inhibits ovulation induced by LH in proestrous-hypophysectomized rats. Rats hypophysectomized by the parapharyngeal route in the morning of proestrus received an intravenous injection of 100 or 300 ng GnRH at 1400 h immediately followed by 1.0 microgram LH per 100 g bw. In control groups, either one or both hormones were replaced with 0.9% NaCl. Ovulation was assessed the following morning by counting the ova present in oviductal flushings. All the rats treated with LH alone ovulated, and the addition of GnRH reduced significantly the number of ovulating rats and the number of ova per ovulating rat. In other groups of rats hypophysectomized in the morning of proestrus and treated in the same way, ovarian or adrenal secretory rates of estradiol and/or progesterone were measured after cannulation of the corresponding vein, in the afternoon of proestrus. In these animals, GnRH failed to inhibit either the ovarian progesterone surge observed 2 h after LH administration, or the adrenal progesterone secretion. All hypophysectomized rats showed lower ovarian secretory rate of estradiol than intact rats; this rate was not affected by treatment with LH or LH plus GnRH. The systemic estradiol levels in plasma of hypophysectomized rats were distributed within a range of 20 pg/ml to 50 pg/ml. The number of rats whose levels were above 21 pg/ml on estrus day was significantly higher in rats receiving 300 ng GnRH as compared to those receiving 100 ng GnRH, reaching values that surpassed the concentration found in intact, untreated animals at the same time of estrus. This effect did not depend on LH administration.

Gonadotropin-inhibitory contaminants in partially purified pharmaceutical preparations of human chorionic gonadotropin.

Various commercial preparations of partially purified human chorionic gonadotropin, inactivated by heating, inhibited the uterine growth induced in immature mice with the same active gonadotropins as well as spontaneous uterine growth. The more purified preparations of chorionic gonadotropin failed to produce these effects after inactivation by boiling, suggesting that the inhibitory activity is not generated from gonadotropin by the procedure but may be related to some contaminant similar to the gonadotropin-inhibitory substance previously found in human urine.

Luteinizing hormone content of the pituitary gland in pregnant and non-pregnant women.

PIP: Pituitary glands were obtained from autopsies of women who had died suddenly during normal pregnancy (8), a few days after a septic abortion (17), or from traumatic injuries while nonpregnant (19). The adenohypophyseal content of immunoreactive luteinizing hormone (LH) was measured by means of solid phase radioimmunoassay. The LH content was significantly (p .0001) lower in pregnant women than in nonpregnant women; the same was true (p .0005) for post-abortion women versus nonpregnant women. The level of LH declined progressively with age of gestation in pregnant women; the correlation was .99.^ieng

Subcellular hypothalamic fractions active on ovulation and luteinizing hormone release in the rat.

Nuclear, microsomal and cytosol fractions were obtained from hypothalamic cells by differential centrifugation in sucrose solutions of different molarities. The nuclear fraction (NF) from immature female rats had an inhibitory effect on ovulation induced with pregnant mare's serum (PMS) in immature rats and with luteinizing hormone (LH) in chlorpromazine (CPZ)-treated proestrous rats. The microsomal fraction from the same rats increased both types of ovulation. Nuclear and microsomal fractions obtained from immature male rats were inactive on ovulation. Cytosol fractions were inactive. NFs active to inhibit ovulation significantly reduced the release of LH induced with synthetic LH-RH in immature male rats and in chronically castrated male rats primed with testosterone (T).