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Biomedical subjects

W J Bremner

Publications and source records attributed to W J Bremner.

155 records · Page 9Linked to original sources
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Daily testosterone and gonadotropin levels are similar in azoospermic and nonazoospermic normal men administered weekly testosterone: implications for male contraceptive development.

Weekly intramuscular administration of testosterone esters such as testosterone enanthate (TE) suppresses gonadotropins and spermatogenesis and has been studied as a male contraceptive. For unknown reasons, however, some men fail to achieve azoospermia with such regimens. We hypothesized that either 1) daily circulating serum fluoroimmunoreactive gonadotropins were higher or testosterone levels were lower during the weekly injection interval, or 2) monthly circulating bioactive gonadotropin levels were higher in nonazoospermic men. We therefore analyzed daily testosterone and fluoroimmunoreactive gonadotropin levels as well as pooled monthly bioactive and fluoroimmunoreactive gonadotropin levels in normal men receiving chronic TE injections and correlated these levels with sperm production. After a 3-month control period, 51 normal men were randomly assigned to receive intramuscular TE at 25 mg (n = 10), 50 mg (n = 9), 100 mg (n = 10), 300 mg (n = 10), or placebo (n = 12) weekly for 6 months. After 5 months of testosterone administration, morning testosterone and fluoroimmunoreactive follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were measured daily for a 1-week period between TE injections. In addition, fluoroimmunoreactive and bioactive FSH and LH levels were measured in pooled monthly blood samples drawn just before the next TE injection. In the 100-mg and 300-mg TE groups, mean monthly fluoroimmunoreactive FSH and LH levels were suppressed by 86%-97%, bioactive FSH and LH levels by 62%-80%, and roughly half the subjects became azoospermic. In the 1-week period of month 6, daily testosterone levels between TE injections were within the normal range in men receiving placebo, or 25 or 50 mg of weekly TE, but were significantly elevated in men receiving 100 or 300 mg of weekly TE. At no point during treatment, however, were there significant differences in daily testosterone or fluoroimmunoreactive gonadotropin levels, or monthly bioactive gonadotropin levels between men achieving azoospermia and those with persistent spermatogenesis. This study, therefore, demonstrates that neither monthly nor daily differences in serum testosterone, or fluoroimmunoreactive or bioactive gonadotropins explain why some men fail to completely suppress their sperm counts to zero with weekly TE administration. Innate differences in the testicle's ability to maintain spermatogenesis in a low-gonadotropin environment may explain persistent spermatogenesis in some men treated with androgen-based contraceptive regimens.

Adult↗
PubMedDate not supplied

Oral testosterone-triglyceride conjugate in rabbits: single-dose pharmacokinetics and comparison with oral testosterone undecanoate.

Development of a safe and effective oral form of testosterone has been inhibited by the rapid hepatic metabolism of nonalkylated androgens. Since triglycerides are absorbed via lymphatics and bypass the liver, we hypothesized that a testosterone-triglyceride conjugate (TTC) might allow for safe and effective oral testosterone therapy. Therefore, we studied the single-dose pharmacokinetics of oral administration of TTC in rabbits. Female New Zealand rabbits were administered 2, 4, or 8 mg/kg of TTC in sesame oil by gastric lavage. Testosterone undecanoate (TU) by gastric lavage was used as a positive control. Blood was sampled from a catheter in the auricular artery at 0, 15, 30, 60, 90, 120, 180, 240, 360, 480, and 600 minutes after drug administration. Samples were assayed for testosterone by a fluoroimmunoassay. Mean serum testosterone, area under the curve (AUC), and terminal half-life were calculated. Oral TTC administration resulted in rapid and marked increases in serum testosterone. Oral TTC resulted in higher maximum serum testosterone concentrations than oral TU at 8 mg/kg (TTC: 28.6 +/- 7.9 nmol/L vs TU: 11.9 +/- 2.1 nmol/L; P <.001) and 4 mg/kg (TTC: 11.5 +/- 4.2 nmol/L vs TU: 3.6 +/- 1.0 nmol/L; P <.001). In addition, the AUC was 1.8 to 2.6 times greater for TTC than TU at both doses (P <.05). The terminal half-life for both TU and TTC was between 3 and 5 hours and was not significantly different. We conclude that oral TTC is rapidly absorbed from the rabbit intestine and results in elevated concentrations of serum testosterone. The absorption of TTC appears to be superior to that of TU; however, the in vivo persistence of the 2 compounds is similar. TTC may offer an alternative to the use of TU for oral testosterone therapy. Further testing of this compound is warranted.

Administration, Oral↗
PubMedDate not supplied

The gonadotropin secretion pattern in normal women of advanced reproductive age in relation to the monotropic FSH rise.

OBJECTIVE: Women of advanced reproductive age are known to demonstrate subtle FSH elevations (monotropic FSH rise) while still retaining ovulatory function. The purpose of this study was to investigate the hypothesis that the physiologic basis for the monotropic FSH rise is an alteration in the secretion pattern of the GnRH pulse generator. METHODS: The subjects were 11 normal women age 40-45 years who underwent 24 hours of frequent blood sampling in the follicular (EF) and/or midluteal (ML) phases of spontaneous menstrual cycles. The controls were 11 normal women age 20-25 years. The respective gonadotropin secretion patterns were analyzed for LH pulse frequency, mean LH and FSH levels, and LH pulse amplitude. RESULTS: There were no differences between the groups for estradiol (E2) and progesterone when the respective cycle phases were compared. The 24-hour mean FSH level was significantly increased in the older women in both the EF and ML phases. There were no differences between the groups in either cycle phase for LH pulse frequency, LH pulse amplitude, and mean LH levels. CONCLUSION: The results lend no support to the hypothesis that a slowing or other alteration of the GnRH pulse generator is the basis for the monotropic FSH rise in older ovulatory women. Other possibilities include the dynamics of E2 secretion or changes in FSH-modulating peptides (i.e., inhibin) in these women.

Adult↗
PubMedDate not supplied

Androgen and progestagen effects on plasma lipids.

Androgens are 19-carbon steroid rings. Progestagens include both 19-carbon and 21-carbon steroid rings; the 19-carbon progestagens are generally more androgenic than are the 21-carbon compounds. Both androgens and progestagens are physiological regulators of plasma lipids, particularly high-density lipoprotein (HDL) cholesterol. The structure of a particular hormonal preparation, as well as its route of administration, modulates its regulatory effects. Both endogenous and exogenous androgens have a suppressive effect on HDL cholesterol in males, with little effect on other plasma lipoproteins. Oral and nonaromatizable androgens have a greater suppressive effect on HDL cholesterol, particularly on HDL2, than do aromatizable androgens. Cross-sectional studies in males generally show a positive relationship between serum T and plasma HDL levels; data in females suggest an inverse relationship between androgens and HDL cholesterol. Medroxy-progesterone acetate and related progestagens have a mild suppressive effect on plasma HDL levels. The C-19 compounds have a greater suppressive effect on HDL cholesterol and the HDL2 density subfraction.

Aging↗
PubMedDate not supplied

A lower dosage levonorgestrel and testosterone combination effectively suppresses spermatogenesis and circulating gonadotropin levels with fewer metabolic effects than higher dosage combinations.

Studies using exogenous high-dosage testosterone (T) or a combination regimen of physiologic T plus high-dosage levonorgestrel (LNG) administration in normal men have shown that oligoazoospermia (<3 million/mL) or azoospermia can be achieved in the majority of the men. However, these hormonal regimens have been associated with significant weight gain and suppression of serum high-density lipoprotein (HDL) cholesterol levels. We hypothesized that a combination of physiologic exogenous testosterone and lower dosage LNG would result in uniform severe oligoazoospermia or azoospermia in normal men but would cause fewer adverse metabolic side effects. We conducted a randomized, placebo-controlled, single-blind trial comparing 6 months of T enanthate (100 mg IM, weekly) plus LNG, 125 microg by mouth, daily (LNG 125; n = 18) or LNG, 250 microg by mouth, daily (LNG 250; n = 18) and compared these regimens with our previous study of the same dosage of T enanthate combined with placebo LNG (LNG 0; n = 18) or with 500 mg of LNG (LNG= 500; n = 18). All three combination regimens of T enanthate and LNG suppressed spermatogenesis more rapidly and resulted in significantly more uniform severe oligoazoospermia (<1 million/mL) than the T-alone regimen. Severe oligoazoospermia was achieved in 89% of the LNG 125, 89% of the LNG 250, and 78% of the LNG 500 groups, respectively, versus 56% of the men in LNG 0 (P < 0.05 for the combination groups vs. LNG 0), but there were no significant differences between the combination regimens (P = NS). All four groups gained significant weight compared with their baselines, although the gain tended to be greater as the dosage of LNG increased (2.0+/-0.9, 2.9+/-1.1, 3.6+/-1.0, and 5.4+/-1.0 kg gained, compared with baseline in the LNG 0, 125, 250, and 500 groups respectively; P < 0.05 compared with baseline). Serum levels of HDL cholesterol decreased in all of the groups, but the effect was larger as the dosage of LNG increased (4+/-4% vs. 13+/-4%, 20+/-3%, and 22+/-4% decrease in HDL levels from baseline in the LNG 0, LNG 125, LNG 250, and LNG 500 groups respectively; P = 0.06 for LNG 125 compared with LNG 0, and P < 0.05 for LNG 250 and LNG 500 compared with LNG 0). We conclude that 1) the combination of physiologic exogenous T enanthate and LNG suppresses spermatogenesis more effectively than T enanthate alone and that 2) the combination regimen of T enanthate plus lower dosage LNG suppresses sperm production comparably to T enanthate plus higher dosage LNG, while causing less weight gain and HDL cholesterol suppression. A combination regimen of physiologic testosterone plus a low dosage of levonorgestrel offers great promise as a safe and effective male contraceptive regimen.

Acne Vulgaris↗
PubMedDate not supplied

The effects of normal aging on the response of the pituitary-gonadal axis to chronic clomiphene administration in men.

Serum androgens decline with age in normal men, despite normal or elevated bioactive serum gonadotropins, suggesting that primary testicular dysfunction occurs with aging. The authors further assessed the question of age-related testicular dysfunction by evaluating whether raising serum gonadotropins above the normal serum range for an extended time in healthy elderly men might result in bringing their gonadal function to a level similar to that found in young adult men. Five elderly (65 to 85 years old) and five young adult men (26 to 33 years old) were given 50 mg of clomiphene citrate (CC) twice a day for 8 weeks to stimulate gonadotropin production. During that time, testosterone (T), non-sex hormone-binding globulin bound T, and estradiol increased significantly in both age groups, while serum inhibin increased significantly only in the young adult men. The increases in serum androgens with CC administration were significantly greater in the young adult men than in the elderly men. These hormone changes occurred in the setting of serum gonadotropins that increased significantly in both age groups, although there was a tendency for the elderly men to have a smaller increase in luteinizing hormone. Despite 8 weeks of stimulation of the pituitary-gonadal axis by CC administration, the elderly men demonstrated significantly diminished testicular responses compared with the young adult men. Sertoli cell function, as determined by inhibin production, was more diminished in the elderly men than was Leydig cell function. These data strengthen the hypothesis that normal aging in men is accompanied by a decline in testicular function.

Adult↗
PubMedDate not supplied

Effects of castration and recombinant human inhibin administration on circulating levels of inhibin and gonadotropins in adult male monkeys.

Inhibin has been suggested to play a role in gonadal feedback regulation of follicle-stimulating hormone (FSH) secretion; however, neither the half-life nor the time course of action of recombinant inhibin has been reported in any primate species. We sought to determine the disappearance half-life of circulating endogenous inhibin following castration in adult male monkeys, Macaca fascicularis, and to determine the half-life of administered recombinant human inhibin A and its effect on bioactive FSH and luteinizing hormone (LH) levels in castrate monkeys. Endogenous inhibin fell from 8,122 +/- 2,077 U/L (mean +/- SEM, n = 5) prior to castration to 383 +/- 84 U/L at 24 hours and 269 +/- 44 U/L at day 21 (P < 0.05 at 24 hours vs. day 21) (detection limit of assay 234 U/L). The early phase half-life of endogenous inhibin was 34 minutes (between 8 and 60 minutes) and a later phase half-life of 75 minutes was observed between 1 and 4 hours following castration. Recombinant inhibin exhibited a 14-minute early phase half-life between 8 and 60 minutes following the 5 micrograms intravenous (i.v.) recombinant inhibin dose, and a later phase half-life of 70 minutes between 1 and 4 hours in castrate monkeys (n = 3). Serum inhibin levels were maintained within or above the precastration range for 15 minutes. Single dose recombinant inhibin, 100 micrograms subcutaneous (SC) or intramuscular (IM) administered to castrate monkeys (n = 3), achieved and maintained normal serum inhibin levels for 6 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

The direct pituitary effect of testosterone to inhibit gonadotropin secretion in men is partially mediated by aromatization to estradiol.

In men, administration of exogenous testosterone (T) exerts direct negative feedback effects at the pituitary as well as at the hypothalamic level. This study was undertaken to determine whether T itself causes the inhibitory effects on the pituitary, or whether conversion to estradiol (E2) or dihydrotestosterone (DHT) is required. We assessed the biological activity of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH), as well as immunoactivity. Blood samples were drawn before, during, and after a continuous, 72-hour i.v. infusion of T (15 mg/day), E2 (90 micrograms/day), or DHT (500 micrograms/day). Each of these doses is twice the daily production rate of the steroid. Each man received each of the three steroid infusions. We studied four men, ages 23-35, with idiopathic hypothalamic hypogonadism (IHH), who were treated with pulsatile gonadotropin releasing hormone (GnRH) until their gonadotropins reached the normal range. Serum levels of T, E2, DHT, and levels of immunologically active and biologically active LH and FSH were measured. We found that administration of each steroid increased serum levels of the infused steroid to the upper physiologic range. Administration of T or E2 resulted in decreased mean levels of biologically and immunologically active LH and FSH; administration of DHT did not alter gonadotropin secretion. These data suggest that some of the direct effect of T at the pituitary level in men is mediated by E2, whereas peripherally formed DHT may not play an important role in this process.

Adult↗
PubMedDate not supplied

Quantitative (stereological) study of the normal spermatogenesis in the adult monkey (Macaca fascicularis).

Germ cell and Sertoli cell numbers were estimated in six normal adult monkeys (Macaca fascicularis) using a contemporary unbiased and efficient stereological method--the optical disector. The data was used to assess the efficiency of spermatogenesis from type B spermatogonia to elongated spermatids. Animals underwent orchidectomy, and the right testis (volume 17.5 +/- 1.7 cm3 [mean +/- SEM], range 13.2-25.1 cm3) was fixed in Bouin's fluid. Blocks were embedded in methacrylate resin and germ cells were counted in thick (25 microm) sections using the optical disector in conjunction with a systematic uniform random-sampling protocol. The total numbers of Sertoli cells and all germ cells per testis were 566 +/- 43 (419-683) million and 12.8 +/- 1.6 (9.0-20.2) billion, respectively. On average, one Sertoli cell supported 12.4 +/- 1.9 (range 8.2-18.4) step 1-12 spermatids, 3.1 +/- 0.4 (2.3-4.5) pachytene spermatocytes, and 23.7 +/- 4.1 (15.0-39.0) total germ cells. Sertoli cell number correlated poorly with both testicular size (correlation coefficient r = -0.12) and germ cell numbers (r = -0.35 with total germ cell number). However, testicular size had a consistent and significant correlation with germ cell numbers (r = 0.97 with total germ cell number). The conversion ratio of pachytene spermatocytes to step 1-12 spermatids was 3.94 +/- 0.19, which is close to the theoretical maximum of 4. Similarly, the conversion between other cell types was consistently close to the maximum theoretical value. We conclude that the efficiency of spermatogenesis in the adult monkey is high, with stepwise conversion being consistently close to the maximal values. The capacity of Sertoli cells to support a cohort of germ cells varies widely between monkeys. Although absolute number of cells per testis is always the preferred parameter, it cannot always be obtained in an experimental situation where cost and ethical constraints mean that biopsies, rather than whole testes, are collected. Thus, if absolute data on germ cell numbers are not available, experimental outcomes impacting on cells beyond preleptonene spermatocytes may be best expressed in terms of changes in germ cell conversion rather than the traditional germ cell: Sertoli cell ratio.

Animals↗
PubMedDate not supplied

A pharmacokinetic study of injectable testosterone undecanoate in hypogonadal men.

Testosterone undecanoate (TU) provides testosterone (T) replacement for hypogonadal men when administered orally but requires multiple doses per day and produces widely variable serum T levels. We investigated the pharmacokinetics of a newly available TU preparation administered by intramuscular injection to hypogonadal men. Eight patients with Klinefelter's syndrome received either 500 mg or 1,000 mg of TU by intramuscular injection; 3 months later, the other dose was given to each man (except to one, who did not receive the 1,000-mg dose). Serum levels of reproductive hormones were measured at regular intervals before and after the injections. Mean serum T levels increased significantly at the end of the first week, from less than 10 nmol/L to 47.8+/-10.1 and 54.2+/-4.8 nmol/ L for the lower and higher doses, respectively. Thereafter, serum T levels decreased progressively and reached the lower-normal limit for adult men by day 50 to 60. Pharmacokinetic analysis showed a terminal elimination half-life of 18.3+/-2.3 and 23.7+/-2.7 days and showed a mean residence time of 21.7+/-1.1 and 23.0+/-0.8 days for the lower and higher doses, respectively. The area under the serum T concentration-time curve and the T-distribution value related to serum T concentration were significantly higher following the 1,000-mg dose than following the 500-mg dose. The 500-mg dose, when given as the second injection, yielded optimal pharmacokinetics (defined as mean peak T values not exceeding the normal range and persistence of normal levels for at least 7 weeks), suggesting that repeated injections of 500 mg at 6-8-week intervals may provide optimal T replacement. The mean serum levels of estradiol were normalized following the injections, and prolactin levels were normal throughout the study. Significant decrease of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels was observed, with the decrease in LH levels being more pronounced. There were no significant differences in serum LH and FSH levels between the two doses. Sex hormone-binding globulin (SHBG) levels before any T therapy were near the upper limit of normal for adult men and were reduced by approximately 50% just prior to the second dose of TU. The decreased SHBG levels produced by the first TU injection could have led to lower peak total T levels and to a more rapid clearance of T following the second TU injection. We conclude that single-dose injections of TU to hypogonadal men can maintain serum T concentration within the normal range for at least 7 weeks without immediately apparent side effects. It is likely that this form of T would require injections only at 6-8-week or longer intervals, not at the 2-week intervals necessary with currently used T esters (enanthate and cypionate). This injectable TU preparation may provide improved substitution therapy for male hypogonadism and, in addition, may be developed as an androgen component of male contraceptives.

Adolescent↗