Influence of gonadal steroids on rat pituitary growth hormone secretion

Opposite effects of dihydrotestosterone and estradiol on apoptosis in the anterior pituitary gland from male rats

Hormones locally synthesized in the anterior pituitary gland are involved in regulation of pituitary cell renewal. In the pituitary, testosterone (T) may exert its actions per se or by conversion to dihydrotestosterone (DHT) or 17β-estradiol (E2) by 5α-reductase and aromatase activity, which are expressed in this gland. Previous reports from our laboratory showed that estrogens modulate apoptosis of lactotropes and somatotropes from female rats. Now, we examined the in vitro and in vivo effects of gonadal steroids on apoptosis of anterior pituitary cells from adult male rats. T in vitro did not modify apoptosis in anterior pituitary cells from gonadectomized (GNX) male rats. DHT, a non-aromatizable androgen, exerted direct antiapoptotic action on total anterior pituitary cells and folliculo-stellate cells, but not on lactotropes, somatotropes, or gonadotropes. On the contrary, E2 exerted a rapid apoptotic effect on total cells as well as on lactotropes and somatotropes. Incubation of anterior pituitary cells with T in presence of Finasteride, an inhibitor of 5α-reductase, increased the percentage of TUNEL-positive cells. In vivo administration of DHT to GNX rats reduced apoptosis in the anterior pituitary whereas E2 exerted proapoptotic action and reduced cells in G2/M-phase of the cell cycle. In summary, our results indicate that DHT and E2 have opposite effects on apoptosis in the anterior pituitary gland suggesting that local metabolization of T to these steroids could be involved in pituitary cell turnover in males. Changes in expression and/or activity of 5α-reductase and aromatase may play a role in the development of anterior pituitary tumors.

Serum concentrations of insulin-like growth factor 1 and cholesterol in relation to protein and fat deposition in growing pigs

The nutrient partitioning of growing pigs was altered through nutrition and castration in order to investigate the relationship between serum insulin-like growth factor 1 (IGFl) and protein deposition and serum cholesterol and fat deposition. In a 2 × 2 factorial experiment 18 entire and 18 castrated male pigs, of 20 kg initial live weight, were given either 2·25 (low) or 3·4 (high) times maintenance energy requirements to a scale based on live weight. Nitrogen and energy balances were measured over 7-day periods when the pigs reached about 30, 60 and 90 kg. Fasting blood samples were taken at each weight and serum was analysed for IGFl and insulin and total- and high density lipoprotein (HDL)-cholesterol. Protein and fat deposition, IGFl and cholesterol concentrations were higher for pigs given the high, as opposed to the low, feeding level. Protein deposition and IGFl concentrations were higher for entire males, as opposed to castrated males, whereas fat deposition and cholesterol concentrations were higher in castrated than in entire males. IGFl and protein deposition increased with age for entire but not for castrated males. Conversely, fat deposition increased with age in castrated but not in entire males. There was no effect of age on serum cholesterol. Serum IGFl was correlated with protein deposition at 30, 60 and 90 kg (r = 0·40, r = 0·63 and r = 0·67; P < 0·05, P < 0·002 and P < 0001 respectively, no. = 36). Serum total cholesterol and low density lipoprotein (LDL)-cholesterol were correlated with fat deposition at 60 and 90 kg (r = 0·65 and r = 0·54; both P < 0·001 for total cholesterol; r = 0·66 and r = 0·50; both P < 0·001 for LDL-cholesterol). Insulin levels were similar for pigs in all treatment groups. It is concluded that serum IGFl and cholesterol may give a useful indication of protein and fat deposition in pigs of between 60 and 90 kg live weight.

Delayed ovulation and pregnancy outcome: effect of environmental toxicants on the neuroendocrine control of the ovary(1)

In the female rat, we have shown that a burst exposure to environmental toxicants known to alter noradrenergic function will block the ovulatory surge of LH when administered during a sensitive period on the day of vaginal proestrus. Such treatments will delay ovulation by 24 h and affect embryo survival. These results demonstrate clearly that brief, appropriately timed, toxicant exposure can initiate a cascade of changes that can alter reproductive outcome. However, we also found that continued exposure to the same compound is without an apparent influence on the reproductive capacity of the female, indicating that the female can become tolerant to such adverse reproductive effects. These observations raise a number of questions concerning the approaches currently used to examine potential reproductive toxicants. In this review, we describe the consequences of appropriately timed exposures to chlordimeform and dithiocarbamates on the timing of ovulation and subsequent alterations in pregnancy outcome. We also review the available literature on phenobarbital delays in ovulation and oocyte function in the rodent and the relevance to ovulatory delays in the human.

Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid function in the male rat. A focus on the EDSTAC recommendations. Endocrine Disrupter Screening and Testing Advisory Committee

Puberty in mammalian species is a period of rapid interactive endocrine and morphological changes. Therefore, it is not surprising that exposure to a variety of pharmaceutical and environmental compounds has been shown to dramatically alter pubertal development. This concern was recognized by the Endocrine Disrupter Screening and Testing Advisory Committee (EDSTAC) that acknowledged the need for the development and standardization of a protocol for the assessment of the impact of endocrine-disrupting compounds (EDC) in the pubertal male and recommended inclusion of an assay of this type as an alternative test in the EDSTAC tier one screen (EPA, 98). The pubertal male protocol was designed to detect alterations of pubertal development, thyroid function, and hypothalamic-pituitary-gonadal (HPG) system peripubertal maturation. In this protocol, intact 23-day-old weanling male rats are exposed to the test substance for 30 days during which pubertal indices are measured. After necropsy, reproductive and thyroid tissues are weighed and evaluated histologically and serum taken for hormone analysis. The purpose of this review was to examine the available literature on pubertal development in the male rat and evaluate the efficacy of the proposed protocol for identifying endocrine-disrupting chemicals. The existing data indicate that this assessment of puberty in the male rat is a simple and effective method to detect the EDC activity of pesticides and toxic substances.

Anthropometric-hormonal correlation patterns in fertile and post-menopausal women from Austria

Correlations between sex-hormone levels and body dimensions were investigated in a group of women from Vienna. Since sex-hormone concentrations in women are subject to dramatic changes with increasing age, both 124 fertile and 142 postmenopausal women were examined. Twenty-nine anthropometric traits were correlated with oestradiol, the gonadotrophins luteinizing hormone (LH) and follicle-stimulating hormone (FSH), the gestagens progesterone, 17-hydroxyprogesterone and prolactin, and the androgens testosterone, androstenedione and DHEA-S, as well as with the transport protein, sex-hormone binding globulin. It was also found that oestradiol concentration was related to levels of gonadotrophins, prolactin, progesterone and androgens and was equally correlated with metric traits. Statistically significant correlations could be observed between all sex-hormone concentrations and the 29 anthropometric traits. The most striking result is the change in direction of correlations between metric traits and oestrogen, gonadotrophin, prolactin and gestagen levels between both proband groups, which is probably due to changes in sex-hormone concentrations in women after menopause. The direction of correlations with androgens remained the same. In post-menopausal women the great impact of fat tissue for sufficient synthesis of oestrogen is shown by a positive correlation between oestradiol and circumference measures.

Anthropometric-hormonal correlation patterns in San and Kavango males from Namibia

Correlations between sex hormone levels and body dimensions--so far investigated only in Caucasian populations--were analysed using data from 114 !Kung San hunter-gatherers and 137 urban and rural Kavango men from Namibia. The androgens testosterone (Tser) and 5 alpha-dihydrotestosterone (DHT) in the serum and free testosterone in the saliva (Tsal) as well as oestradiol (E2) in the serum were determined by the radioimmunoassay method. The body dimensions were described by 50 anthropometric features which were additionally subjected to factor analysis yielding seven factors. Most of the individual measurements as well as the resulting factor scores correlated significantly with the sex hormone variables and the hormone ratios Tser/DHT, Tsal/Tser, and Tser/E2 in the !Kung San and the two Kavango samples. For an extended comparison pertinent data from a German sample were included in the analysis. This made it possible to test the stability of metric hormonal correlations in different populations living under various ecological and economical conditions. While the breadth measurements in all samples show relatively consistent correlations to both absolute hormones and hormone ratios, the correlations to the other body measurements and individual factor scores turn out to be less stable. Here, the effect of sex hormones on physical growth, which is experimentally well documented, is obviously differentially covered by genetic and environmental factors specific for the groups in question.