Spyros N. Pavlou

Suppression of bioactive and immunoreactive follicle-stimulating hormone and luteinizing hormone levels by a potent gonadotropin-releasing hormone antagonist: pharmacodynamic studies *

Dose-dependent gonadotropin suppression by a potent gonadotropin-releasing hormone (GnRH) antagonist, Nal1 Glu6 [( Ac-D2Nal1,D4ClPhe2,D3Pal3,Arg5,DGlu(AA)6,- DAla10]GnRH), was determined in five postmenopausal women by frequent sampling for immunoreactive luteinizing hormone (I-LH) and immunoreactive follicle stimulating hormone (I-FSH) for 72 hours after single intramuscular (IM) injections of 10, 50, 150, and 300 micrograms/kg. Bioactive (B) LH and B-FSH also were measured after the IM administration of the 50-micrograms/kg dose. Serum levels of Nal1 Glu6 were determined by a radioreceptor assay for the first 24 hours after the 50-micrograms/kg IM dose and in three women after a 10-micrograms/kg intravenous (IV) dose. While the disappearance rate of serum Nal1 Glu6 after a 10-micrograms/kg IV injection was rapid, gonadotropin suppression persisted longer than detectable serum levels. In contrast, after a 50-micrograms/kg IM injection, the decline from peak circulating levels was slower, contributing to its longer duration of action (greater than 24 hours). All IM doses tested resulted in a similar 51% to 63% decrease in I-LH, which was maximal by 8 hours. The duration of action was dose-dependent, with decreased levels lasting up to 72 hours at the 300-micrograms/kg dose. While decline of I-FSH was smaller (14% to 33%), the duration of suppression was also dose-dependent, although the nadir occurs later (8 to 9 hours after administration) and suppression lasted longer (72 hours at the 150-micrograms/kg dose). The reduction of B-LH was greater than that of I-LH and the suppression of B-FSH also was greater than that of I-FSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Sperm motion parameters after suppression of spermatogenesis with a gonadotropin-releasing hormone antagonist plus testosterone supplementation * †

Objective To evaluate whether the chronic administration of a GnRH antagonist supplemented with T enanthate affects sperm motion parameters. Design Prospective study. Setting Academic medical research environment. Patients/Participants Six normospermic men of reproductive age. Intervention A 20-week treatment included the administration of 10mg of GnRH antagonist every day and 25mg of T enanthate once a week. Main Outcome Measure Computerized sperm motion analysis on each participant every 2weeks for a period of 11months. Results Sperm concentration decreased after 4weeks of the GnRH antagonist administration, accompanied by a reduction of sperm motility from an initial mean value of 56% to 34% on treatment week 4 and 21% on treatment week 6. In contrast, sperm velocity, linearity, amplitude of the lateral head displacement, and beat cross-frequency values did not significantly change in spite of reduced overall sperm concentration and motility. Azoospermia was reached within 6 to 12weeks of the GnRH administration, and it was sustained during the treatment period. During recovery of spermatogenesis, sperm movement parameters returned to initial values earlier than sperm concentration and normal morphology. All participants recovered initial semen parameters 20weeks after the end of treatment. Conclusion The administration of a GnRH antagonist supplemented with T enanthate successfully induced reversible suppression of spermatogenesis. The sperm motion characteristics appeared to be the last parameters to decline and the first to return to initial values after the treatment.

entaaification of Atrial Natriuretic Factor Receptor of Neuroblastoma N4TG1 Cells: Binding Characteristics and Photoaffinity Labeling

We have found specific receptors for atrial natriuretic factor (ANF) in cultured neuroblastoma cells (N4TG1) of peripheral ganglionic origin. Scatchard analysis of the displacement binding revealed noninteracting, singleclass binding sites with a KD of 1 ± 1010M and a density (Bmax) of 110,000–150,000 sites/cell. The cell‐bound 125I‐ANF was displaced by unlabeled ANF in a dose‐dependent manner. Hormones unrelated to ANF such as angiotensins, adrenocorticotropic hormone, or arginine vasopressin were ineffective in displacing the cell‐bound radioactivity. Using azidobenzoyl‐125I‐ANF as a photoaffinity ligand, an ANF receptor with an apparent Mr of 138,000 was identified by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and autoradiography. The addition of unlabeled ANF (1 μM) to the incubation medium completely abolished the labeling of this protein band, but atriopeptin I (1 μM) or angiotensins I, II, and III (each 1 μM) were not effective in inhibiting the affinity labeling. The treatment of the neuroblastoma cells with ANF stimulated intracellular cyclic GMP levels in a dose‐dependent manner with an EC50 of 5 nM. ANF(1 ± 107M) stimulated cyclic GMP accumulation in <5 min by 30‐fold as compared to the controls.

LHRH Antagonists in Normal Men

During the last few years contraceptive research has focused on LHRH agonistic analogues because of their ability to inhibit gonadal function through a complex mechanism of pituitary desensitization [1–4]. However, in spite of our initial optimism, LHRH agonists do not completely and reliably suppress spermatogenesis [5–9]. Attention has therefore shifted to the investigation of potent antagonistic analogues of the hormone. Antagonistic analogues would be of considerable theoretic advantage in that not even transient stimulation of pituitary gonadotropin secretion would occur when such agents are used. Animal studies with LHRH antagonists have already shown that these analogues are more effective in inhibiting gonadal function and spermatogenesis than are agonists [10–16]. Until now such antagonists have been of relatively low potency. However, new LHRH antagonists have recently been synthesized that are potent enough to be evaluated in humans [12–14].

The effect of haloperidol on aldosterone secretion

Haloperidol (0.02 mg/kg, intravenous) did not stimulate aldosterone secretion in six normal controls or in six schizophrenic subjects. This is contrary to our hypothesis, which was based on the finding that peripheral D2 receptor antagonists stimulate aldosterone secretion, including haloperidol in rats and chlorpromazine in man. We speculated that a different dose of haloperidol would stimulate aldosterone in man. As expected, prolactin release was markedly stimulated in both groups of subjects, but no difference was found between groups.

Clinical Pharmacology of LHRH Antagonists

Hypothalamic LHRH controls the pituitary synthesis and secretion of the gonadotropins that are essential for the regulation of gonadal function. Since the molecular structure of LHRH has been known, several synthetic chemical derivatives of LHRH have become available for basic and clinical studies. These analogs constitute two groups [1]. One group, LHRH agonists, are analogs up to 230 times more potent than LHRH in stimulating LH and FSH release. The other group, LHRH antagonists, are analogs that compete with endogenous LHRH at the hypophysial receptor level and directly inhibit the secretion of gonadotropins. Both groups of LHRH analogs, however, suppress pituitary and gonadal function because even LHRH agonists, when given repeatedly, lead to pituitary desensitization. This ability of LHRH analogs to selectively inhibit gonadal steroid secretion and therefore, induce a reversible medical gonadectomy has several clinical applications. These include hormone-dependent tumors, precocious puberty, cryptorchidism, in vitro fertilization, endometriosis, male and female contraception and several others. The mechanism of action of LHRH agonists and antagonists, however, is completely different.

Combined Administration of a Gonadotropin-Releasing Hormone Antagonist and Testosterone in Men Induces Reversible Azoospermia Without Loss of Libido

GnRH antagonists suppress pituitary and gonadal function by competing with endogenous GnRH for binding to receptors on pituitary gonadotrophs. We studied the effects of GnRH antagonist administration to men in a protocol simulating a likely male contraceptive regimen combined with a low dose of testosterone. The GnRH antagonist Nal-Glu was given daily (10 mg, sc) for 20 weeks to eight normal men, and a low dose of testosterone enanthate (25 mg, sc) was given every week. Sperm counts started declining during week 4, and complete azoospermia was reached within 6-12 weeks in six of the eight subjects. Subjects 7 and 8, whose sperm counts and serum gonadotropin levels were not suppressed after 10 weeks, were given 20 mg Nal-Glu starting at week 10. One became azoospermic at week 16, while the others total sperm counts continued declining and reached a nadir of 1.4 million by week 20. Sperm motility and viability in this subject were completely suppressed after week 14. Sperm counts returned to baseline levels 12-14 weeks after the end of Nal-Glu administration. The mean serum LH level of the first six subjects decreased from 3 +/- 03. U/L at baseline to less than 0.1 U/L until week 20, and then levels returned to baseline. FSH levels similarly decreased from a combined mean of 3.6 +/- 0.9 U/L at baseline to below 0.3 U/L after 4 weeks of Nal-Glu administration. Serum mean testosterone levels between weekly injections of testosterone enanthate ranged from 27.4 +/- 5.9 to 4.8 +/- 1.4 nmol/L, but remained in the hypogonadal range (less than 10 nmol/L) for 4 of the 7 days. None of the subjects, however, complained of decreased libido or potency, as assessed by a questionnaire. No systemic or significant local side-effects were observed, other than a minimal reaction at the injection site. These data suggest that complete sustained azoospermia can be achieved in man, without loss of libido, by chronic administration of a GnRH antagonist plus testosterone.