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Biomedical subjects

V Strbák

Publications and source records attributed to V Strbák.

At least 73 records · Page 4Linked to original sources
PubMed1983

TRH transport to rat milk.

Neonatal rat possess several unique features in relation to TRH. Thus, the hypothalamus does not control pituitary TSH secretion, neonatal plasma does not degrade TRH and a significant quantity of this neurohormone is present in upper part of gastrointestinal tract, contractile response of duodenum to TRH being dependent on suckling. Therefore, a possible role of exogenous TRH from maternal milk was studied. Repeated or single injection of 50 micrograms TRH to lactating rats resulted in an increase of serum TSH and decrease of pituitary TSH content in sucklings. Repeated TRH administration to thyroidectomized lactating rats prevented a decrease of plasma T4 in their pups. After intravenous administration of 3H-TRH the total radioactivity of plasma and milk equalized at 25 min and increased continuously in milk during 2 h study. The presence of unaltered 3H-TRH in rat milk and gastric content of pups was confirmed by paper chromatography, electrophoresis and specific antibody precipitation. TRH degrading activity of rat milk, though qualitatively similar, represents one fifth of plasma activity in vitro. It is concluded that there is one way transport of TRH between plasma and milk and that this neurohormone is transferred to rat milk in a biologically active form.

Animals↗
PubMed1982

Postnatal development of the circadian adrenocortical rhythm in rats with different neonatal nutrition.

The development of diurnal rhythm of plasma and adrenal corticosterone levels was examined in rats overfed, standardfed and underfed during the suckling period (realised by adjustment of the number of suckling pups per litter to 4, 8, and 14). The first presence of circadian rhythm of plasma corticosterone was observed in 18-day-old overfed and standardfed rats, and slight delay in the manifestation of rhythm was noted in neonatally underfed animals (rhythm present in 21-day-old rats). The distinct circadian rhythm was present in 23- to 30-day-old rats. However in adult animals a significant diurnal rhythm of plasma and adrenal corticosterone content was noted in standardfed and underfed rats, whereas the variation of hormone levels was not significant in the neonatally overfed group. In young animals the peak of plasma corticosterone concentration occurred during the dark period while in adult animals it was shifted to the end of the light period. The values of amplitude of plasma corticosterone variation are increasing during the postnatal period. In weaned and adult rats the mesor values were found to be higher in neonatally underfed rats in comparison to the neonatally overfed group.

Adrenal Cortex↗
PubMed1981

Thyroliberin (TRH) induced growth hormone (GH) release: test of maturation of hypothalamo-pituitary axis in postnatal rat.

Small doses of TRH elicit GH release from rat pituitary provided the pituitary lacks CNS influences (e.g. in vitro or in ectopic pituitaries). We have found previously that hypothalamic regulation of TSH secretion matures between the 5th and 12th postnatal day. Therefore the possibility of TRH induced GH release was investigated in neonatal rats. GH concentration was measured by RIA at 10 min after s.c. TRH administration (4.1 pmol g-1 BW) into female Wistar rats at the age 3, 9, 12, 15, 21, 30 and 100 days. Control animals were injected the same volume (1 microliter g-1 BW) of saline. Serum GH in saline treated animals gradually decreased during postnatal ontogenesis. The TRH induced increase of serum GH level decreased during maturation: the most marked response was found at 3 days, it was somewhat lessened but still significant at 9 days and was absent in 12, 15, 30 days old and adult animals. Surprisingly, in 21 days old animals the increase of GH after TRH administration was again present. We conclude that the ability of TRH to elicit GH release in newborn rats may depend on the maturity of the hypothalamo-pituitary axis. The effect of hypothalamic somatostatin is likely to inhibit such a response at the pituitary level in older rats.

Animals↗
PubMed1980

Transport of 3H-TRH from plasma to rat milk: accumulation and slow degradation in milk and presence of unaltered hormone in gastric content of pups.

10 microCi 3H-TRH was administered intravenously to lactating rats 14 days after delivery. The total radioactivity of plasma and mild equalized about 25 min after injection and increased continually in milk during the 2-hour study. The percentage of activity bound to specific TRH antibody was the same in extracts of plasma and mild (about 60% of standard binding) throughout the experiment. Besides milk, the radioactivity was also accumulated in pituitary, thyroid, kidney and liver; the tissue:plasma ratio being 2:4 2 h after injection. The presence of 3H-TRH in milk extracts was also confirmed by paper chromatography (butanol-acetic acid-water-ethylacetate, 1:1:1:1) and electrophoresis (in pyridine acetate buffer, pH 5.8). TRH-degrading activity, representing about one fifth of that in plasma, was found in rat milk in vitro by means of paper chromatography and electrophoresis. The gastric contents of suckling pups after injection of 3H-TRH were also analyzed. The total radioactivity increased from 30 to 60 min after the injection. The percentage reacting with the specific TRH antibody in extracts of gastric contents was the same as that in plasma and milk and did not change throughout the 2 h of experiment. Our results show one-way transport of TRH from plasma to milk, low TRH-degrading activity of milk and passage of unaltered neurohormone from plasma to milk and stomach of suckling. The gastric content does not have a deteriorating effect on TRH. We suppose that the presence of accumulated TRH in maternal milk could be some biological significance in suckling, in which the plasma TRH-degrading system is lacking.

Animals↗
PubMed1980

Differences in growth and thyroid activity persisting in adult rats reared in nests of different sizes during suckling period.

The undernutrition or overnutrition during a suckling period achieved by adjusting the number of infants per lactating rat to 4 (overfed-0), 8 (control-C) or 14 (underfed-U) resulted in long lasting differences in body weight. The consumption of the diet in 260-day old males and females was similar in all experimental groups if expressed per unit of body weight, thus suggesting the differences in energy utilization. An increase of thyroid hormone secretion rate was found in U rats aged 30, 120 and 300 days as compared to 0 ones. Serum TSH level was also higher in U rats at the age of 30 days and 1 year. However, serum thyroxine level in U groups was either higher or similar as in controls. Paper chromatography of thyroglobulin hydrolyzate 24 h after 125I injection to 300 days old males showed a decrease of radioactivity in iodide area in U animals and an increase in triiodothyronine area in 0 animals. The analysis of thyroglobulin from 200 days old females on linear sucrose gradient did not reveal any rough change in its iodination. The results indicate an increase of thyroid activity in adult, previously moderately underfed male and female rats. Some changes in feedback sensitivity of hypothalamo-pituitary-thyroid axis may presumably also occur in these animals.

Animals↗
PubMed1979

Comparison of the effect of TRH on plasma TSH level in young and adult rats.

Since it is known that TRH degrading system in plasma is inactive during suckling period in the rat, it was of interest to see whether this might prolong the effect of TRH on plasma TSH. Time course of plasma TSH after s. c. administration of 2 ng TRH g-1 was studied in 7, 48 and 120 day-old rats. The highest basal TSH level (448 +/- 72 microU ml-1) was found in 48 day-old males, while it was the lowest (82 +/- 22.8 microU ml-1) in 7 day-old animals. Time course was essentially the same in all three age groups. If the increase of plasma TSH was compared to the level of saline treated controls at the same time, 8.2 and 10.1 fold increase was found 10 and 30 min after TRH injection, respectively, in 7 day-old pups. However, the increase was only 2.3 and 3.4 fold in older animals at the same time intervals. The highest absolute level obtained during TRH stimulation was found in 48 day-old animals (1055 +/- 121.6 microU ml-1). These results show that the effect of TRH on plasma TSH was not prolonged in neonatal rats thus suggesting that extravascular TRH degradation may be of some importance in TSH regulation.

Aging↗
PubMed1978

Changes of adrenal catecholamines and their synthesizing enzymes during ontogenesis and aging in rats.

Male Wistar specific-pathogen-free rats aged 2, 7, 17, 30, 60, 120, 200, 360 and 600 days, all killed in experiment on the same day, were examined. The body weight significantly increased until the 200th day, the weight of adrenals until the 120th day and the adrenal protein content until the 30th day of life. The adrenaline content of the adrenals increased continuously during the 600 days studied. Adrenal noradrenaline content increased rapidly over the first 17 days, remained at a stable level until the 120th day, and rose to a higher level after 200 days. The activity of adrenal catecholamine-synthesizing enzymes also increased with age: tyrosine hydroxylase gradually increased until the 360th day, dopamine-beta-hydroxylase and phenylethanolamine-N-methyl transferase until the 200th day. Our results demonstrate that, in the rat, during development there is a gradual increase of adrenal weight, adrenaline content, tyrosine hydroxylase and phenylethanolamine-N-methyl transferase activity until maturation (120th day), whereas the adrenal noradrenaline content reaches the adult values earlier, around the 17th day. During aging, adrenal catecholamines significantly increase when compared to young-adult rats (120-day-old), probably due to the elevated activity of the adrenal catecholamine-synthesizing enzymes. The increased adrenal catecholamine levels in old animals might be connected with a higher incidence of cardiovascular diseases in aged.

Adrenal Glands↗
PubMed1978

Thyroid activity in early weaned and suckling infants and their lactating mothers.

The activity of thyroid gland was estimated in a group of lactating mothers and their suckling infants as well as in a group of early weaned infants. In both groups of infants the same level of thyroxine and triiodothyronine was found, but it was higher than that in mothers. The binding properties of specific plasma proteins and free thyroxine index were the same in both groups of infants. The level of TSH in serum of suckling infants (4.7 +/- 0.5 microunits ml-1) was significantly higher (P less than 0.01) than that in weaned infants (3.0 +/- 0.3 microunits ml-1). The level in mothers (4.0 +/- 0.3 microunits ml-1) did not differ significantly from that in both groups of infants. A positive correlation was found between the level of TSH in lactating mothers and their suckling infants (r = +0.494, P less than 0.05). The data suggest that the regulation of thyroid activity in infants may be affected by suckling.

Female↗
PubMed1978

The effect of lactation on thyroid activity of women.

The study comprised 12 lactating (L) women, 26 women who interruped the lactating during study (IL) and 6 women failing to lactate (NL). All women gave birth to normal fullterm infants after uneventfull pregnancy and vaginal delivery. Sampling was done during the 2nd day and 10th week after parturition. Lactating women showed more pronounced decrease of thyroxine, decreased thyroxine: triiodothyronine ratio and increased TSH level during the 10th week after parturition in comparison to IL group. The women on NL group showed similar changes as L women, but without increased level of TSH in comparison to IL ones. Results suggest the effect of lactation on the thyroid activity. This effect could be due to the loss of iodine and thyroid hormones to the milk.

Adolescent↗
PubMed1977

Increase of serum thyrotropin (TSH) os suckling rats after thyroliberin (TRH) injection to lactating mothers.

Injection of 50 microgram TRH to lactating rats 15 days after parturition was followed 4 h after treatment by an increase of serum TSH and a decrease of absolute and relative pituitary TSH content in suckling pups when compared to sucklings of saline-treated mothers. The weight of the pituitary and thyroid also decreased. Results indicate that TRH administered to lactating rats induces release of TSH from the pituitary of suckling pups. An increase of the variability of serum TSH and a decrease of pituitary TSH content at noon in pups of saline-treated mothers suggest the presence of diurnal variation of TSH secretion in 15-day-old rats.

Animals↗
PubMed1976

Effect of gamma irradiation on biological activity of thyrotropin.

The biological activity of thyrotropin (TSH) was tested after sterilization by 0.5 and 12.5 Mrad of gamma irradiation. It was found that the biological activity (McKenzie's assay) of TSH irradiated in dry state was not affected during the first month after sterilization by doses of 0.5 and 2.5 Mrad. However, substantial decrease of TSH biological activity was observed 3--5 months after the irradiation, the lower activity being after the former dose. The irradiation of TSH by 12.5 Mrad in dry state and by 0.5 and 2.5 Mrad in solution resulted in a decrease of biological activity already during first month. The structural changes in the molecule of TSH were apparently not very extensive, since a decrease of disulfide bonds from 0.96 to 0.77 M per 1M of TSH was found immediately after the irradiation, while UV absorbancy and electrophoretic mobility on polyacrylamide gel electrophoresis were unaffected. These changes were followed by the decrease of TSH stability during storage in dry state. It is hypothesized that TSH molecule may be affected in beta subunit or in its connection with alpha.

Disulfides↗
PubMed1976

Thyroxine (by competitive protein binding analysis) in human and cow milk and in infant formulas.

In 45 mothers of full term infants the level of thyroxine (T4) in serum (45 samples) and unskimmed milk (92 samples) was estimated with the aid of competitive protein binding analysis. On the 3rd day after delivery the T4 level in serum was found to be 11.1 +/- 0.4 mug/100 ml, while that in milk was 1.3 +/- 0.3 mug/100 ml. During following days of lactation the T4 concentration in sera decreased. In contrast, however, a gradual increase of the T4 content in milk was observed. The serum and milk levels equalized during the third week post partum (7.3 +/- 1.3 and 7.6 +/- 1.4 mu6/100 ml, respectively). After the 25th day the T4 level in milk was found to be higher than in sera from the same women (paired test: P less than 0.005). Values of 12.9 +/- 1.3 in milk and 8.1 +/- 0.7 mug/100 ml in sera were found in the second month of lactation. A negative correlation between serum and milk T4 level was found during the early lactation (3-20 days), while after 20th day this correlation was positive. Very low and almost undetectable levels of T4 were found in cow's milk and infant formulas derived from it.

Animals↗