Characteristics of the inhibitory effect of chronic treatment with an LHRH agonist on testicular steroidogenesis in the dog

Testicular toxicity induced in dogs by nefiracetam, a neutrotransmission enhancer

To investigate mechanisms of the testicular toxicity of nefiracetam and to find sensitive parameters to predict the toxicity, male beagle dogs were orally administered 180 or 300 mg/kg per day of the drug once and for 1 and 4 weeks. Time-course changes in serum and/or testicular hormone levels and semen parameters, and testicular morphology were examined. The testicular testosterone level was decreased 4 h after single administration of nefiracetam at 300 mg/kg per day, but the progesterone level showed no change at that time. The serum testosterone level was decreased after single, 1-week or 2-week treatment. In contrast, the serum estradiol level was increased from 1- to 4-week treatment. No changes in serum LH, FSH and inhibin B levels were observed throughout the experimental period. Decreased sperm motility and increased number of malformed sperms were first observed in semen after 4-week treatment. Histopathological examination of the testis revealed moderate and severe seminiferous atrophy with multinucleated giant cell formation at 180 and 300 mg/kg per day, respectively, after 4-week treatment, but not 1-week treatment. These results show that nefiracetam decreases testicular testosterone level in dogs following single oral administration of a high dose, and induces severe morphologic changes after 4-week treatment. This reduction is shown to be a sensitive parameter to detect the toxicity, and is suggested to be induced by the impaired conversion of progesterone to testosterone in Leydig cells.

Mechanism of action and pure antiandrogenic properties of flutamide

Although treatment of intact adult male rats with the pure antiandrogen flutamide or a luteinizing hormone-releasing hormone (LHRH) agonist alone leads to partial inhibition of ventral prostate weight, maximal inhibition is achieved by combination of the two drugs. Potentializing effects of the two compounds were observed even on prostatic ornithine decarboxylase activity. Because LHRH agonists are widely used to achieve medical castration in men treated for prostate cancer, it is of interest to observe that in the dog, known for being the best model for studies of the action of LHRH agonists, flutamide does not interfere with the potent desensitizing action of the LHRH agonist on pituitary LH secretion, thus supporting the combined use of flutamide with an LHRH agonist for maximal androgen blockade without loss of efficiency of the LHRH agonist. Because prostate cancer is known to show a high degree of heterogeneity of its sensitivity to androgens, we analyzed the effect of combined antiandrogen therapy on parameters more sensitive to androgens than ventral prostatic weight itself. In agreement with its pure antiandrogenic characteristics, flutamide alone has no stimulatory effect on the intraprostatic level of mRNA encoding the C1 or C3 component of prostatic binding protein (PBP), whereas cyproterone acetate (CPA), megestrol acetate (MEG), and, especially, medroxyprogesterone acetate (MPA) markedly stimulate PBP-C1 and PBP-C3 mRNA levels, an effect reversed by flutamide, thus further supporting the intrinsic androgenic activity of all these steroidal derivatives. Similar androgenic effects of the steroidal derivatives were observed on prostatic ornithine decarboxylase activity. Androgen-sensitive Shionogi tumor cells were then used to assess the antiandrogenic/androgenic properties of flutamide and the above-indicated steroidal derivatives. MPA, MEG, CPA as well as spironolactone-stimulated cell proliferation under both in vivo and in vitro conditions, thus illustrating the intrinsic androgenic activity of all these compounds. Flutamide was inactive by itself and reversed the stimulatory effect of all other compounds, thus indicating its pure antiandrogenic activity. Although castration reduces intraprostatic dihydrotestosterone (DHT) to undetectable levels in the rat and guinea pig, the concentration remains at about 50% of the value found in intact men after castration, thus indicating an important contribution of the adrenals to DHT in the human prostate, a finding that requires the addition of an antiandrogen to block the action of this important amount of DHT remaining after castration.

Effect of 2-week combination therapy with the luteinizing hormone-releasing hormone (LHRH) agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide and the antiandrogen flutamide on prostate structure and steroid levels in the dog

Treatment of adult dogs for 15 days with the luteinizing hormone-releasing hormone (LHRH) agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide (50 micrograms daily, s.c.) causes a 41.6% inhibition of prostatic weight while a 55% inhibition is achieved when the antiandrogen flutamide (250 mg, twice daily) is given in association with the LHRH agonist (p less than 0.01). At histology, the glandular acini in the prostate of animals treated with the combination therapy are more atrophied than with either treatment used alone. A 2-week treatment with the LHRH agonist is characterized by two distinct phases, namely a stimulation of testicular androgen secretion between days 0 and 8 followed by an inhibition between days 9 and 15. During the inhibitory phase, the concentration of all testicular steroids progressively decreased to castration levels, thus indicating that the differences observed at the prostatic level at 2 weeks are due to the inhibition of androgen action by the antiandrogen flutamide during the period which precedes complete chemical castration by the LHRH agonist. Flutamide administered alone had no effect on plasma or prostatic steroid levels measured after 2 weeks and it did not interfere with the potent and generalized inhibitory effect of the LHRH agonist on the serum and prostatic concentration of all steroids measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible inhibition of testicular androgen secretion by 3-, 5- and 6-month controlled-release microsphere formulations of the LH-RH agonist [D-Trp6, des-Gly-NH10(2)] LH-RH ethylamide in the dog

This study examines the effect of treatment with controlled-release poly(DL-lactide-coglycolide) microsphere formulations of the LH-RH agonist [D-Trp6, des-Gly-NH10(2)]-LH-RH ethylamide (LH-RH-A) designed to release about 100 or 200 micrograms of the peptide per day for 3, 5 or 6 months in male dogs. Plasma levels of testosterone and LH-RH-A were measured at 2-day intervals. After the first injection of the 100-micrograms/day formulation, plasma testosterone increased from 1.6 +/- 0.2 to 3.5 +/- 0.6 ng/ml for 5-7 days before decreasing and remaining at 0.05 +/- 0.008 ng/ml for approximately 150 days (5 months). After two months of recovery, microspheres designed to release 100 micrograms for 6 months of LH-RH agonist per day were then injected. Plasma testosterone levels showed an elevation from 1.5 +/- 0.5 to 4.7 +/- 2.0 ng/ml during the first few days before gradually decreasing to castration levels for 200 days (6 months). One month later, plasma testosterone had returned to normal levels. When microspheres designed to deliver an average of 200 micrograms per day of the peptide for 3 months were injected in another series of animals, castration levels of plasma testosterone were maintained for 95 days with a progressive increase to normal values at later time intervals. The animals of the first series of experiments were then sacrificed after 4 months of recovery following maintenance of plasma testosterone at castration levels for a total period of 11 months. The testes, prostate and pituitary gland were kept for histological examination which was completely normal in all tissues. The efficacy and excellent tolerance of the controlled-release form of LH-RH-A as inhibitor of the pituitary-gonadal axis strongly support the use of such long-term controlled-release formulations of LH-RH agonists for the treatment of sex steroid sensitive diseases.

Normal gonadal functions and fertility after 23 months of treatment of prepubertal male and female dogs with the GnRh agonist [D-Trp6, des-Gly-NH2(10)]GnRH ethylamide

The GnRH agonist [D-Trp6, des-Gly-NH2(10)]GnRH ethylamide was administered to prepubertal male and female dogs daily for 23 months by subcutaneous injection. During GnRH agonist treatment, plasma steroid levels, namely dehydroepiandrosterone, androst-5-ene-3 beta-17 beta-diol, androstenedione, testosterone, dihydrotestosterone, 5 alpha-androstane-3 alpha, 17 beta-diol, 5 alpha-androstane, 3 beta, 17 beta-diol were markedly inhibited in male animals, whereas in female animals, the plasma concentration of DHEA and delta 5-diol were decreased. Within 2 months following cessation of therapy, all steroids increased to normal adult levels. Morphological studies reveal that treatment of male animals with the GnRH agonist is accompanied by a small volume of seminiferous tubules, Leydig cells, and prostate gland, whereas in the ovaries of female animals, there is a large number of primordial follicles, a few primary follicles, but no secondary follicles. In the pituitary gland of animals of both sexes, LH-secreting cells have high levels of glycogen particles in their cytoplasm and tend to be either of normal appearance with dilated rough endoplasmic reticulum (RER) or strongly atrophied with a dark-stained cytoplasm, a contraction of RER, and a decrease in the number of secretory granules. Reticular cells of the connective tissue also show high levels of glycogen particles. After the 14 month recovery period, spermatogenesis has a normal adult appearance, the prostate gland shows a normal secretory epithelium, and secondary follicles are easily observed in the ovary. Gonadotrophs are free of glycogen accumulation, but reticular cells continue to show an accumulation of glycogen particles in their cytoplasm. Two male and two female animals were mated after the recovery period and produced normal offspring with normal fertility. The present results indicate that GnRH agonist treatment achieves a blockade of sexual maturation and that following cessation of treatment, normal pituitary-gonadal functions resume, with apparently normal fertility and normal offspring.

The rise in testicular androgens during the first days of treatment with an LHRH agonist in the dog can be blocked by aminoglutethimide or ketoconazole

Up to day 6 of treatment of adult dogs, daily subcutaneous administration of 50 micrograms of the LHRH agonist [D-Trp6, des-Gly-NH2-10]LHRH ethylamide causes up to a 3-fold increase in serum testosterone (T) concentration which is followed by a progressive decrease to castration levels (less than or equal to 0.2 ng/ml) at later time intervals (up to 21 days, the last time interval studied). Both aminoglutethimide and ketoconazole, two inhibitors of steroid biosynthesis, cause a 30-40% rise in serum T when administered alone. However, either drug administered in combination with the LHRH agonist completely blocks the transient rise in serum T observed when the LHRH agonist is administered alone. On the other hand, the LHRH agonist prevents the secondary rise in steroid secretion observed when either of the two inhibitors of steroid secretion is used alone. Administration of the pure antiandrogen Flutamide alone or in combination with LHRH-A and an inhibitor of steroid biosynthesis does not influence serum T levels. When the serum levels of pregnenolone, 17-OH-pregnenolone, progesterone, 17-OH-progesterone, dehydroepiandrosterone (DHEA), androstenedione (delta 4-dione), androst-5-ene-3 beta, 17 beta-diol (delta 5-diol), T, dihydrotestosterone (DHT), androstane-3 alpha, 17 beta-diol, androstane-3 beta. 17 beta-diol and 17 beta-estradiol (E2) are analyzed in detail, it can be seen that both aminoglutethimide and ketoconazole not only prevent the rise in serum steroids observed during the first 8 days of treatment with the LHRH agonist but that both compounds enhance the inhibitory effect of the LHRH agonist at later time intervals. A predominant inhibitory effect of ketoconazole is exerted on 17,20-desmolase activity. Aminoglutethimide has little influence on the loss of serum LH bioactivity induced by the LHRH agonist while ketoconazole stimulates the concentration of serum bioactive LH in the absence or presence of simultaneous treatment with the LHRH agonist. The present data clearly demonstrate that aminoglutethimide or ketoconazole can prevent the rise in serum androgens accompanying the first days of treatment with an LHRH agonist in the dog. Moreover, after 3 weeks of treatment, the inhibitory effect of the LHRH agonist on serum androgen levels is enhanced by addition of aminoglutethimide or ketoconazole. Moreover, Flutamide does not interfere with the inhibitory action of the LHRH agonist, aminoglutethimide or ketoconazole, thus suggesting that maximal inhibition of androgen action is likely to be achieved by a combination of these drugs.

Reversible effects of long-term treatment with D-Trp6-LH-RH-microcapsules on pituitary-gonadal axis, spermatogenesis and prostate morphology in adolescent and adult dogs

The effect of long term treatment with D-Trp6-LH-RH in microcapsules (GnRH-A) on pituitary gonadal axis was studied in a adolescent and adult Fox-terrier dogs. They received intramuscularly 50 micrograms/GnRH-A/kg, on day 1 and 21 and every 4 weeks thereafter. Three adult dogs received 4 injections. cLH, cFSH and T levels were undetectable on day 7. Detectable then normal levels occurred 60 and 90 days respectively after the last injection on day 77. Testis thickness was respectively 22.1 +/- 0.8 mm and 16.3 +/- 0.8 mm on days 0 and 77; initial values were observed 90 days later. Spermatozoa disappeared from the ejaculate on day 21 in 2 dogs; reappearance and complete recovery were observed on days 161-175 and 252 respectively. Histological findings showed on day 91 atrophic lesions of testis and prostate and spermatogonia were present in all seminiferous tubules. After recovery a normal histological appearance was noticed. Three adolescent 29 weeks old dogs received 14 injections, the last one on day 357. cLH, cFSH and T levels were undetectable only from day 105. Testis thickness were respectively 15.8 +/- 0.7 mm, 18.1 +/- 0.7 mm, 12.5 +/- 0.3 mm and 21.4 +/- 0.7 mm on day 0, 21, 357 and 490. Initially, no spermatozoa were present in the ejaculates, they appeared in 2 dogs after 2 months for 20 to 40 days then disappeared until day 449. Normal semen characteristics were observed in all three dogs on day 581. Histological findings on day 371 were comparable to those observed in the adult dogs. This study demonstrates that longterm treatment with D-Trp6-LH-RH in microcapsules leads to a reversible inhibition of spermatogenesis in dogs. The delayed response in adolescent dogs might be due to a transient resistance to therapy related to.

A pure antiandrogen does not interfere with the LHRH agonist-induced blockade of testicular androgen secretion in the dog

Daily subcutaneous administration of 50 micrograms of the luteinizing hormone-releasing hormone (LHRH) agonist [D-Trp6]LHRH ethylamide in adult dogs causes a transient increase in the serum testosterone (T) concentration which reaches a maximum at 200% above control on days 2-4 of treatment and progressively decreases to 7% of the pretreatment value on day 21, the last time interval studied. After a transient increase, the concentration of serum bioactive luteinizing hormone (LH) was progressively decreased on days 11 and 19, thus suggesting that in analogy with human findings, the loss of LH bioactivity is responsible for the inhibition of testicular steroidogenesis induced in the dog by LHRH agonists. Of major significance is the finding that the changes in serum T levels observed during the first 3 weeks of treatment, as well as the complete inhibition of the intratesticular concentration of sex steroids observed at the end of this period of treatment with the LHRH agonist were not affected by simultaneous administration of flutamide (125 mg per os every 8 h). Such findings indicate that at the dose used, the LHRH agonist is in full control of gonadotropin secretion, thus completely overcoming feedback influences. Since the administration of the antiandrogen flutamide does not decrease the efficacy of the LHRH agonist as blocker of testicular androgen biosynthesis, the present data support the use of a pure antiandrogen in order to neutralize the effect of the transient rise in testicular androgen secretion which always accompanies the first days of treatment with LHRH agonists in patients with advanced prostate cancer.

Radioimmunoassay in blood plasma of arginine esterase: the major secretory product of dog prostate

We have developed a radioimmunoassay to determine serum levels of arginine esterase, the major secretory product of the canine prostate. Although the antibodies recognized other related proteins in immunoblotting conditions, particularly in the pancreas, the radioimmunoassay appeared specific for arginine esterase of prostatic origin and reacted only slightly or not at all with cytosolic proteins from salivary glands, liver, skeletal muscles, and kidney. In serum samples, the sensitivity limit of the assay was about 2.5 ng per ml. The interassay and intraassay variations for serum samples that contained concentrations of arginine esterase ranging from 6 to 21 ng per ml were, respectively, 14% and 24%. Sera from 30 adult males and 14 adult females contained, respectively, 71 +/- 9 and 5.3 +/- 0.4 ng per ml. In a group of 12 dogs treated daily for 36-39 days with 50 micrograms of D-Trp6-luteinizing hormone-releasing hormone ethylamide, the concentrations of arginine esterase in the serum decreased progressively and became identical with those observed in the females. These results constitute the first evidence for the presence of a serum marker of the normal prostate in an experimental model. It should be particularly useful to test the effects of various agents on the prostate.

Reversible inhibition of gonadal functions by a potent gonadotropin-releasing hormone agonist in adult dog

This study examines the recovery of spermatogenesis, testicular and plasma steroidogenesis and prostatic steroid content 26 weeks following cessation of daily treatment for 16 weeks with [D-Tryp6]LHRH ethylamide (LHRH-A) in the adult dog. While administration of LHRH agonist resulted in testicular and prostatic weight reductions of 40-60%, a complete recovery is observed 26 weeks after cessation of treatment. The number of sperm in LHRH-A-treated dogs declined rapidly in the first 4 weeks, after which no ejaculation or erection is observed in these animals. Spermatogenesis completely recovered four months following cessation of treatment. While testicular steroidogenesis is completely inhibited during the treatment with the agonist peptide, normal levels of testicular steroids are observed with the exception of 17-hydroxypregnenolone, dehydroepiandrosterone and androst-5-ene-3 beta,17 beta-diol which are elevated above control levels and, furthermore, an accumulation of these delta 5-steroids is also observed in the prostate after the end of treatment. Our data strongly suggest that chronic administration of an LHRH agonist may induce, after cessation of treatment, an overproduction of testicular steroids.