Endocrine function and regulation of the fetal and neonatal testis

An interesting sex difference prevails in the early development of endocrine functions in the ovary and testis. The testis actively produces androgens already in utero whereas the physiologically important steroid hormone production of the ovary does not start until puberty. Likewise, the different components of the hypothalamic-pituitary-gonadal axis seem to mature earlier in the male. The hormonal regulation of the fetal testes differs in many respects from that of the adult, and these differences make it possible for the fetal testes to function in the intrauterine endocrine milieu. The purpose of this review is to summarize our findings on the development, special functional characteristics and physiological role of the fetal and neonatal pituitary-gonadal axis.     

Endocrine responses in relation to compensatory testicular growth after neonatal hemicastration in boars

Mass (TM) and relative mass (organ mass/body mass; RTM) of the right testis and epididymis (EM and REM, respectively) were determined every 14 days from 10 to 122 days of age for intact boars (I) and boars hemicastrated on Day 10 (HC) in two crossbred herds (Trial 1 and Trial 2). Plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, growth hormone (GH), and testosterone were determined in four blood samples from each pig, three collected 24 h prior to castration and one immediately prior to castration. Values for TM and RTM of HC boars were approximately double (p less than 0.0001) those of I boars by 38 days of age, and these differences were maintained through Day 122. Both EM and REM were greater (p less than 0.05) in HC than in I boars from Day 52 to Day 122. The TM, RTM, EM and REM were greater (p less than 0.05) in Trial 1 than in Trial 2 for both I and HC boars from Day 80 to Day 122, indicating an earlier onset of pubertal testicular growth in the Trial-1 boars. Plasma GH concentration was greater (p less than 0.05) in HC than in I boars from Day 16 to Day 38. A transient increase in plasma FSH (p less than 0.05) was observed from Day 24 to Day 38. After Day 38, there was no difference (p greater than 0.05) in FSH or GH between HC and I boars, or between trials. Plasma LH, prolactin, and testosterone concentrations were also similar in HC and I boars.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maternal, neonatal and community factors influencing neonatal mortality in Brazil

Child mortality (the mortality of children less than five years old) declined considerably in the developing world in the 1990s, but infant mortality declined less. The reductions in neonatal mortality were not impressive and, as a consequence, there is an increasing percentage of infant deaths in the neonatal period. Any further reduction in child mortality, therefore, requires an understanding of the determinants of neonatal mortality. 209,628 birth and 2581 neonatal death records for the 1998 birth cohort from the city of S?o Paulo, Brazil, were probabilistically matched. Data were from SINASC and SIM, Information Systems on Live Births and Deaths of Brazil. Logistic regression was used to find the association between neonatal mortality and the following risk factors: birth weight, gestational age, Apgar scores at 1 and 5 minutes, delivery mode, plurality, sex, maternal education, maternal age, number of prior losses, prenatal care, race, parity and community development. Infants of older mothers were less likely to die in the neonatal period. Caesarean delivery was not found to be associated with neonatal mortality. Low birth weight, pre-term birth and low Apgar scores were associated with neonatal death. Having a mother who lives in the highest developed community decreased the odds of neonatal death, suggesting that factors not measured in this study are behind such association. This result may also indicate that other factors over and above biological and more proximate factors could affect neonatal death.     

Endocrine cells and brush cells at the bronchiolo-alveolar junctions of neonatal syrian hamster lungs

Endocrine cells and brush cells at the bronchiolo-alveolar junctions of the lung of neonatal hamsters were studied by transmission electron microscopy. On both sides of the junctions (bronchiolar and alveolar), clusters of endocrine cells occur as neuroepithelial bodies (NEB). A few solitary endocrine cells are also present at the alveolar sides of the junctions. Some endocrine cells reach from the basement membrane to the air space but the area of apical cell membrane exposed to the airway is small as the cells are largely covered by Clara cells in the bronchioles and by thin attenuations of alveolar type 1 cells in the alveoli. Some Clara cells around NEB contain cytoplasmic lamellar bodies, similar to those characteristically associated with alveolar type 2 cells. A few brush cells are also seen at both sides of the junctions. Long wide microvilli with filamentous cores extend from the apices of the brush cells. Endoplasmic reticulum and Golgi apparatus are moderately developed. Well-developed bundles of intermediate filaments course throughout the cytoplasm of some of the brush cells. The functions of endocrine cells and brush cells are unknown. However, the presence of these cells at the bronchiolo-alveolar junctions of neonatal hamster lungs suggests a role in regulation of respiratory function.     

Endocrine mechanisms of seasonal adaptation in small mammals: from early results to present understanding

Seasonal adaptation is widespread among mammals of temperate and polar latitudes. The changes in physiology, morphology and behaviour are controlled by the photoneuroendocrine system that, as a first step, translates day lengths into a hormonal signal (melatonin). Decoding of the humoral melatonin signal, i.e. responses on the cellular level to slight alterations in signal duration, represents the prerequisite for appropriate timing of winter acclimatization in photoperiodic animals. Corresponding to the diversity of affected traits, several hormone systems are involved in the regulation downstream of the neural integration of photoperiodic time measurement. Results from recent studies provide new insights into seasonal control of reproduction and energy balance. Most intriguingly, the availability of thyroid hormone within hypothalamic key regions, which is a crucial determinant of seasonal transitions, appears to be regulated by hormone secretion from the pars tuberalis of the pituitary gland. This proposed neuroendocrine pathway contradicts the common view of the pituitary as a gland that acts downstream of the hypothalamus. In the present overview of (neuro)endocrine mechanisms underlying seasonal acclimatization, we are focusing on the dwarf hamster Phodopus sungorus (long-day breeder) that is known for large amplitudes in seasonal changes. However, important findings in other mammalian species such as Syrian hamsters and sheep (short-day breeder) are considered as well.     

Endocrine control of cytosolic factors stimulating adenylate cyclase in rat lung

Endocrine control of cytoplasmic factors modulating adenylate cyclase activity in rat lung membranes was investigated. Hypophysectomy, adrenalectomy and thyroidectomy showed an adverse effect on the body and organ weights. Lung protein, glycogen and DNA contents were decreased in the endocrine ablated animals which were restored to the normal values on hormone treatment. Phosphodiesterase and phosphorylase activities were increased and decreased in adrenalectomized and thyroidectomized animals, respectively. The activities of these enzymes were restored to normal values on hormone treatment. Adrenalectomy and thyroidectomy affected ATPases differently. Basal adenylate cyclase activity in rat lung membranes was not affected by adrenalectomy and hormone treatment. However, the total enzyme activity was increased by both dexamethasone (DEX) and thyroxine (T4) treatments. The activation of the particulate adenylate cyclase by the cytoplasmic factors was markedly decreased in the lung from hypophysectomized, adrenalectomized and thyroidectomized rats. This decrease in the cytoplasmic activation of adenylate cyclase was restored to or above the control values on hormone treatment. Alteration in the activation of enzyme by cytoplasmic factors did not appear to be due to the change in the responsiveness of the enzyme. Glucocorticoids appeared to have a specific effect on the cytoplasmic factors modulating the enzyme.     

Cross-action of extracellular stress adaptation factors in microorganisms]

The capacity of microorganisms from different taxa to adapt to stress conditions with the help of extracellular factors exhibiting similar mechanisms of action was demonstrated. The action of adaptation factors synthesized by the enteric bacterium Escherichia coli, the soil bacterium Bacillus subtilis, and the yeast Candida utilis was characterized in biological tests. It was demonstrated that the factor of accelerated adaptation to new media (FAANM) and the growth-rate-reducing factor (factor X(II)), which decreases the rate of exponential culture growth, were synthesized by all microorganisms tested. Antilysin (factor X(I)), which accelerates cell adaptation to N-ethylmaleimide, was not produced by C. utilis.     

Endocrine and metabolic factors involved in the effect of nutrition on the production of colostrum in female sheep

We investigated the physiological relationship between diet during pregnancy and colostrum production in ewes to test the hypothesis that for ewes that are in low body condition, with low fat reserves, the food supply will be the main source of energy for colostrum synthesis. To this end, we measured the amount of colostrum accumulated by ewes under two levels of nutrition. We also measured the circulating concentrations of metabolites and hormones associated with lactogenesis (beta-hydroxybutyrate, glucose, progesterone, prolactin, cortisol, growth hormone, leptin, insulin and insulin-like growth factor-I) Ewes were either under-fed at 70 (n = 15) or well-fed at 110% (n = 10) of their daily metabolisable energy requirement during the last two months of pregnancy. Colostrum accumulation up to parturition was 168 +/-48 g for under-fed ewes and 451 +/-103 g for well-fed ewes. After birth, under-fed ewes produced less colostrum than well-fed ewes but the difference was no longer significant. The level of nutrition also influenced the plasma concentrations of hormones and metabolites related to lactogenesis. Progesterone concentrations decreased before lambing in all animals but in under-fed ewes the fall appeared to be too small to initiate the onset of colostrum production. Beta-hydroxybutyrate concentrations were higher in under-fed than in well-fed ewes, suggesting that the under-fed ewes were mobilising more adipose tissue but they still did not meet their ME requirements for colostrum production. We concluded that, in underfed ewes, there are insufficient nutrients for adequate lactation and the hormone regime is inappropriate for good udder development and colostrum synthesis.