Effect of oestrogen and ascorbic acid on the serum ceruloplasmin level in rats.

The administration of long-acting oestrogen (1 mg twice a week for 3 weeks) is followed, in rats, by an increase in the serum ceruloplasmin concentration to about 150% of the control value. The simultaneous administration of ascorbic acid in a dose of 10, 20 or 50 mg/rat/day in food raises the ceruloplasmin concentration to 180-200% of the control value (no significant difference was observed in the effect of the various doses of ascorbic acid). The increase produced by combining ascorbic acid with the oestrogen amounts to 20-30% of the value recorded in animals treated only with oestrogen. The mechanism by which ascorbic acid potentiates the effect of oestrogens on the ceruloplasmin level is not known.     

Regulation of thyroid hormones on the production of testosterone in rats

The effects of a thyroidectomy and thyroxine (T4) replacement on the spontaneous and human chorionic gonadotropin (hCG)-stimulated secretion of testosterone and the production of adenosine 3',5'-cyclic monophosphate (cAMP) in rat testes were studied. Thyroidectomy decreased the basal levels of plasma luteinizing hormone (LH) and testosterone, which delayed the maximal response of testosterone to gonadotropin-releasing hormone (GnRH) and hCG in male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored the concentrations of plasma LH and testosterone to euthyroid levels. Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH, and testicular testosterone as well as the LH response to GnRH and testosterone response to hCG in vitro. T4 replacement in Tx rats restored the in vitro release of GnRH, GnRH-stimulated LH release as well as hCG-stimulated testosterone release. Administration of T4 in vitro restored the release of testosterone by rat testicular interstitial cells (TICs). The increase of testosterone release in response to forskolin and androstenedione was less in TICs from Tx rats than in that from sham Tx rats. Administration of nifedipine in vitro resulted in a decrease of testosterone release by TICs from sham Tx but not from Tx rats. The basal level of cAMP in TICs was decreased by thyroidectomy. The increased accumulation of cAMP in TICs following administration of forskolin was eliminated in Tx rats. T4 replacement in Tx restored the testosterone response to forskolin. But the testosterone response to androstenedione and the cAMP response to forskolin in TICs was not restored by T4 in Tx rats. These results suggest that the inhibitory effect of a thyroidectomy on the production of testosterone in rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH and its response to GnRH; 2) the decreased response of TICs to gonadotropin; and 3) the diminished production of cAMP, influx of calcium, and activity of 17beta-HSD. T4 may enhance testosterone production by acting directly at the testicular interstitial cells of Tx rats.     

Circadian oscillations of thyroid hormones and insulin in the serum of fasting rats

Adult male Wistar rats adapted to a 12:12 h light:dark regimen, fed or after a 24- or 48-h fast, were decapitated at 3-h intervals during a single day. They were deprived of food at day-time intervals ensuring that on decapitation they had fasted for the same length of time, i.e. 24 or 48 h. Thyroid hormones, insulin and glucose concentrations were determined in their serum. Fasting did not significantly affect circadian thyroxine, triiodothyronine and reverse triiodothyronine rhythms compared with the findings in fed animals; 24, but not 48 hours' fasting led to a shift in the acrophase of circadian insulin and glucose oscillations compared with fed rats. The maintenance of original circadian thyroid hormones and insulin rhythm in rats which fasted for short lengths of time testifies to a dependence of the stimulus on the time of day.     

Effect of 3,3',5' triiodo-L-Thyronine (rT3) on the serum concentration of thyroid hormones in rats

50, 100 or 150 micrograms/100 g body weight/day of very pure 3,3',5' triiodo-L-thyronine (rT3), obtained from a new synthetic method, was intraperitoneally administered in male Wistar rats for 5 weeks. Serum total thyroxine (T4), free thyroxine (FT4) and total 3,5,3' triiodo-L-thyronine (T3) concentrations were increased with all the doses of rT3. Free T3 (FT3) was also but non-significantly elevated. Different assumptions are put forward in order to explain this rT3 effect.     

Developmental patterns of thyroid hormones and testosterone in ferrets

Plasma levels of thyroxine (T4) and triiodothyronine (T3) were measured in male and female ferrets at regular intervals between postnatal day 20 and 150 as well as in adult animals. In addition, testosterone level in male ferrets was measured. All hormones showed characteristic developmental patterns. There is a T4 maximum prior to a T3 maximum in subadult animals which in both cases surpasses adult levels. Testosterone level shows a different developmental pattern. There is an outstanding peak in subadult males around day 60-80, which, however, is surpassed by adult levels during the mating season.     

Ipriflavone对雄性大鼠生长及血液睾酮水平的影响

目的：观察伊普异黄酮（IP）对雄性动物生长、骨骼肌肉发育以及相关内分泌的影响。方法：24只1月龄雄性大鼠分为IP组和对照组,IP组于基础日粮中添加伊普异黄酮3mg·kg^-1,实验持续30d。结果：与对照组相比,IP组大鼠日增重和采食量分别提高12．4％（P〈0．01）和17．8（P〈0．01）;胴体重增高10．70％（P〈0．05）,骨骼肌重有所增加,而腰胁部脂肪重则显著降低;股骨重和骨密度均有增加;血液睾酮含量IP组大鼠超过对照组约42％,而雌二醇含量略有降低。结论：伊普异黄酮能促进雄性大鼠生长,内源睾酮在参与这一生理过程中起重要作用。     

Effect of sex and age on serum aldosterone and thyroid hormones in the laboratory rat

Serum levels of aldosterone, tri-iodo thyronine (T3) and thyroxine (T4) were measured in male and female rats aged 3 months, 12 months, and 18 months. Female rats were found to have higher aldosterone and T3 levels, and lower T4 level than the male. No age-related change was observed in serum aldosterone in either sex. In contrast, serum T4 were found to decrease with age in both sexes while serum T3 showed an age-associated diminution in the male only. Serum testosterone was also measured in the male rats and was found to decline with age.     

The effect of acute treatment with two goitrogens on plasma thyroid hormones, testosterone and testicular morphology in adult male rats

1. Hypothyroidism was induced in adult male rats by treatment with either iopanoic acid (IOP) or propylthiouracil (PTU). The hypothyroid animals were maintained for a period of 4 weeks. 2. The IOP and PTU treatments produced drastically different thyroid hormone profiles during the treatment period. 3. Serum testosterone levels were not significantly different from controls in either of the goitrogen-treated groups. 4. Testes weights and germ cell populations were not significantly different from controls in either of goitrogen treated groups. 5. Seminiferous tubule morphology showed no significant variation in lumen size or basal lamina structure in either of the treatment groups when compared to the controls.     

Effect of nonylphenol on serum testosterone levels and testicular steroidogenic enzyme activity in neonatal, pubertal, and adult rats.

Previous dose range-finding studies with nonylphenol (NP) administered to rats in a soy- and alfalfa-free diet showed apparent feminization of several endpoints in male rats at doses of 25 ppm and above. One possible mechanism contributing to these effects is a reduction of testosterone at critical developmental periods. The present study was conducted as an adjunct to a multigeneration study and was designed to examine the effect of NP on testosterone production. Male rats in the F1 and F2 generations were exposed through their dams or directly to various dietary doses of NP (0, 25, 200 and 750 ppm) throughout gestation and until sacrifice at either postnatal day 2 (PND2), PND50, or PND140. Male pups in the F3 generation were examined only on PND2. At PND2, serum testosterone levels were significantly decreased in all groups exposed to NP in the F1 generation, but not in the F2 or F3 generations. The activity of 17alpha-hydroxylase/C17, 20 lyase (P450c17) in PND2 testicular homogenates was not affected by NP treatment. In F1 and F2 PND50 and PND140 rats, NP treatment did not affect serum testosterone levels. The absolute dorsolateral prostate weight was increased in the 200 and 750 ppm dose groups only in the F1 PND50 rats, however, no significant effects were observed in other male reproductive organs. NP treatment did not affect P450c17 activity in microsomes prepared from testes of F1 PND50 or PND140 rats. However, P450c17 activity was significantly decreased in testicular microsomes of F(2) PND50 (200 and 750 ppm dose groups) and PND140 (25, 200, and 750 ppm dose groups) rats. A decrease in testicular beta-nicotinamide adenine dinucleotide phosphate (NADPH) P450 reductase was also observed in all PND50 and PND140 NP-exposed rats of the F1 and F2 generations. The ability of NP to directly inhibit P450c17 activity in vitro at concentrations of 1-100 microM was also demonstrated. These results indicate that NP can inhibit the activity of enzymes involved in testosterone synthesis, but suggest minimal effects on testosterone or testosterone-dependent endpoints via this mechanism.     

Effect of progesterone, estradiol & stilbestrol on serum ceruloplasmin in rabbits

To test whether progesterone also influences the serum ceruloplasmin activity (CSA) like estrogen (in the form of ethinyl estradiol and stilbestrol) and oral contraceptives containing both estrogenic and progestogen components, and if so to find out the relative influence of estrogen and progesterone, rabbits were treated with progesterone, estradiol dipropionate, a combination of these two and diethyl stilbestrol, and the SCA was estimated. Progesterone caused 194 and 262% increase in two and three weeks respectively. (p less than .001) Estradiol dipropionate failed to increase SCA, while diethyl stilbesterol caused an increase similar to that of progesterone.     

Structure of the thyroid gland, serum thyroid hormones, and the reproductive cycle of the Atlantic stingray, Dasyatis sabina.

This study examines the role of the thyroid gland in the control of reproduction in the viviparous Atlantic stingray, Dasyatis sabina. Thyroid activity in individuals in different reproductive stages was assessed both by microscopic examination of the gland, and by analysis of circulating levels of thyroid hormones from the same individuals. The thyroid gland is a cylindric organ, embedded in a connective tissue capsule, and composed of follicles, i.e., monolayer spheres of thyroid epithelial cells. Stingray follicular cells possess several characteristic features, namely apical cilia and a well-developed endoplasmic reticulum. Cells vary in size and shape, according to the activity of the gland. No structural differences were observed between the thyroid glands of the two sexes. Both thyroid hormones, triiodothyronine, [T(3)], and thyroxine, [T(4)], were detected in the serum of all animals examined. Levels ranged from 1.3-2.6 microg/100 ml for total T(4), and from 1.2-2.6 ng/ml for total T(3). The T(4) levels did not vary significantly in any group. Immature individuals and females undergoing oogenesis had the lowest levels of circulating T(3) and mature females from ovulation throughout gestation had high thyroid gland activity and high levels of circulating T(3). J. Exp. Zool. 284:505-516, 1999.