Influence of thyroid hormones on collagen content in tissues of guinea pigs.

Collagen fractions content and level of collagen catabolites in body fluids were determined in normal, hypo- and hyperthyroid guinea pigs. An increase of urinary excretion of hydroxyproline and hydroxylysine as well as concentration of these amino acids in blood serum was found in hyperthyroidism, and a decrease was shown in hyperthyroid guinea pigs. Hyperthyroidism stimulated an increase of neutral-salt-soluble and acid-soluble collagen in skin and liver, and a decrease of insoluble collagen in skin as well as increase of all collagen fractions in bone samples. Hypothyroidism induced a decrease of all collagen fractions in skin and liver, and an increase of acid-soluble and insoluble collagen in bone samples.     

Morphofunctional status of the thymus in guinea pigs exposed to thymus and bone marrow preparations

Study of the effect of the polypeptide thymic factor (thymalin) and the polypeptide bone marrow factor (hemalin) on the morphofunctional status of the thymus in guinea-pigs has shown that injection of thymalin into animals increases the count of small lymphocytes whereas injection of hemalin the count of medium-sized lymphocytes and lymphoblasts. Injection of thymalin magnifies the size of the nuclei of the reticuloendothelial cells.     

Lymphatic vessels and Kurloff cells in the thymus of estradiol-treated guinea pigs

Summary Male guinea pigs were given a single subcutaneous injection of estradiol, which induces formation of Kurloff cells, and serial sections of thymus were examined after 10, 12, 15 and 21 days. Kurloff cells were found in large numbers in lymphatic vessels, both outside the thymus, in the interlobular tissue, at the cortical surface and inside the cortex, suggesting migration via such structures. Large extrathymic or interlobular lymphatics communicated with a previously undescribed thymic structure-the lymphatic centre-surrounded by a marginal sinus. The orientation of lymphatic valves, and the concentration of Kurloff cells within this lymphatic centre at an early time after the administration of estradiol, indicate the existence of an afferent migratory pathway. The different morphology at different times after estradiol suggest that the treatment caused a dynamic remodeling of thymic lymphatic structures.     

Autonomic and behavioral thermoregulation in guinea pigs during postnatal maturation

Fewell, James E., Maria Kang, and Heather L. Eliason.Autonomic and behavioral thermoregulation in guinea pigs during postnatal maturation. J. Appl.Physiol. 83(3): 830-836, 1997.Serial experimentswere carried out on seven chronically instrumented Hartley-strainguinea pigs at 1, 3, and 5 wk of age to define their autonomic andbehavioral thermoregulatory profiles and to test the hypothesis thatthey have the mechanisms in place shortly after birth that allow themto optimize their energy expenditure for thermoregulation by selectinga thermal environment that requires the lowest metabolic oxygenrequirements. Each animal was studied in both a thermocline todetermine selected ambient temperature and in a metabolic chamberto determine the thermoregulatory response to forced changes in ambienttemperature. In the thermocline, the guinea pigs at all postnatal agesselected an ambient temperature that placed core temperature, oxygenconsumption, thermal conductance, heart rate, and respiratory rate atlevels comparable to those observed at ambient temperatures in whichminimal oxygen consumption occurred in the metabolic chamber. Thus ourexperiments provide evidence that guinea pigs have theneurophysiological mechanisms in place shortly after birth that allowthem to optimize their energy expenditure for thermoregulation byselecting a thermal environment that corresponds to the lowestmetabolic oxygen requirements.

     

Pre- and postnatal toxicity induced in guinea pigs by N-nitrosomethylurea.

Oral administration of N-nitrosomethylurea at maximally tolerated doses to guinea pigs on alternate days from days 34-58 of pregnancy induced prenatal toxicity, as evidenced by a high frequency of stillbirths and intrauterine growth retardation, and postnatal toxicity, as evidenced by stunting and progressive mortality. Similar administration of N-nitrosomethylurethane at maximally tolerated doses did not induce such toxic effects.     

Early postnatal development of peptide hydrolysis in chicks and guinea pigs.

1. To characterize the development of peptide hydrolysis the activities of pancreatic carboxypeptidase A (CPA) and intestinal glycylleucine dipeptidase (GLDP) were registered in 1-45 days old chicks, as well as GLDP activities in newborn and adult guinea pigs. 2. The highest values of CPA and GLDP relative activities were found immediately after hatching, maximal decrease of activities took place during the first week. 3. GLDP activities gradient on the surface of the small intestine of chicks has two maximums: one in the upper jejunum, the other one--in the lower ileum. The development of proximo-distal gradient began at the age of 7 days and finished at the end of the first month. 4. Total CPA and GLDP activities decreased during the first week; up to the 15-20 day they reached the initial level and later exceeded it. 5. Relative GLDP activity in guinea pigs declined with aging, while the total activity increased, as it was demonstrated for chicks. 6. GLDP activity was distributed equally along the surface of the small intestine in newborn guinea pigs as well as in mature animals.     

Development of different types of muscle fiber in the postnatal ontogeny of guinea pigs

As demonstrates estimation of myosin ATPase and SDG activity, the guinea pig is already born with differentiated muscle fibers (MF), and the first histochemical differences between them take place in the uterine 10 days before birth. Tonic oxidative fibers of the first type, arranging hexagonally, develop especially quickly at early stages of postnatal ontogenesis. Their relative contents up to the end of the observations (185 days) do not change, and area of their transversal section increases but slightly in comparison to the phasic fibers. The main age changes of the muscle tissue are connected with formation and rearrangement of the phasic fibers. The most intensive reconstructions of the phasic fibers coincide with the period of game activity and sex maturation. In mixed muscles the part of the glycolytic fibers increase during the postnatal ontogenesis. In the process of ontogenesis the soleus muscle fully consists of oxidative fibers. The definitive level of the MF development is established after the guinea pigs have reached their sex maturation. Comparing the results of the given investigation with the previous data on development of MF in rats, it is possible to conclude that term and premature animals have various rates in development of the muscle system, however, main stages of myogenesis coincide, though they are connected with various phases of ontogenesis.