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M Ching

Publications and source records attributed to M Ching.

31 records · Page 2Linked to original sources
PubMed1982

Correlative surges of LHRH, LH and FSH in pituitary stalk plasma and systemic plasma of rat during proestrus. Effect of anesthetics.

An effective recovery procedure has been utilized for determining luteinizing hormone-releasing hormone (LHRH) concentrations in rat pituitary stalk plasma. With this new recovery protocol it was revealed that stalk plasma immunoreactive LHRH concentrations increased 5-fold to 206 pg/ml during proestrus(p less than 0.001) and decreased to diestrous levels during estrus. In contrast, the LHRH concentration in systemic plasma extracts remained unchanged throughout the estrous cycle and did not exceed 4 pg/ml. The stalk plasma: systemic plasma ratio increased from 12:1 at diestrus to 76:1 at proestrus; it then decreased to 22:1 at estrus (p less than 0.001). Correlative luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surges of statistically significant magnitudes were observed in the systemic plasma of nonanesthetized cardiac-catheterized rats during proestrus. When administered before the onset of the critical period, Althesin and other anesthetic agents suppressed but did not completely inhibit the peripheral LH surge in cardiac-catheterized rats. The FSH surge was suppressed also but to a lesser degree. These results indicate that the brain triggers the preovulatory surge of LH and FSH via massive secretion of LHRH into the pituitary portal circulation. They also reveal that, aside from any dosage considerations, the type of anesthetic used and the time of administration in relation to the critical period, can significantly affect the magnitude of pituitary LH and FSH secretion.

Anesthetics↗
PubMed1981

Does-related effect of growth hormone on thyroidal radioiodine uptake.

Even though growth hormone was reported to play a role in mammalian calorigenesis, few studies have examined its effect on thyroid function. Consequently, the modulatory effect of bovine growth hormone (BGH) on thyroid incorporation of 131I was studied in hypophysectomized (H) rats. Not surprisingly, H recipients fed a low iodine diet consistently displayed greater thyroidal uptakes of radioactive iodine than recipients given regular diets. Furthermore, thyroid radioactive counts increased predictably in direct proportion to the quantity of bovine thyrotropin administered. Larger doses of BGH suppressed the thyroidal uptake of 131I whereas smaller doses either had no effect or enhanced thyroidal activity. Thus, these results affirm that radiolabelled and non-radiolabelled iodine compete in thyroid metabolic processes and furthermore demonstrate that high doses of BGH inhibit thyroid activity.

Animals↗
PubMed1977

A re-assessment of the effect of thyrotrophin (TSH) on the tibial plate bioassay for growth hormone (GH).

The claim has been made that thyrotrophin (TSH) can augment the action of growth hormone (GH) to stimulate growth of the epiphysial cartilage plate of the hypophysectomized rat's tibia. The TSH induces its effect via secretion of thyroid hormones which in turn enhance the stimulatory action of GH. If this is true then the employment of the tibia test, whose endpoint is the increase in thickness of the epiphysial cartilage plate in response to GH present either in crude pituitary extracts or relatively purified preparations, which also are likely to contain modest or appreciable quantities of TSH, requires further examination. The present study utilized various fractions of crude pituitary extracts from intact and thyroidectomized rats that respectively contained appreciable quantities of GH or essentially no GH. Fractional aliquots of pituitary extracts from thyroidectomized rats were administered concomitantly with graded doses of exogenous GH to hypophysectomized rats to determine the point at which TSH in the extracts was sufficiently able to stimulate significant tibial plate growth when compared to recipients given GH alone. Purified GH and TSH were also administered in various doses to hypophysectomized recipients in a further attempt to delineate the dose range at which TSH augments the action of GH to promote significant chondrogenesis of the epiphysial plate. The results indicate that the enhancement of the GH effect on the cartilage plate by TSH was evident only when quantities above 100 microng bovine GH were co-administered with 100 mU bovine TSH. As little as 40 mU TSH augmented the growth effect of 400 microng GH on the cartilage plate, demonstrating that smaller quantities of TSH could potentiate larger quantities of GH. These data, therefore, suggest that extracts equivalent to not more than one-half of a normal adult rat's anterior pituitary gland should be administered to hypophysectomized rats for bioassay of GH. Fractions of glands greater than this may contain sufficient amounts of TSH to augment the appreciable quantities of GH already present.

Animals↗
PubMed1976

Inconsistency of the tibia test for estimating growth hormone in crude pituitary extracts.

The complement fixation immunoassay (CFIA) was used for quantitating growth hormone (GH) in crude anterior pituitary extracts from rats subjected to thyroidectomy with or without cortisol and exogenous GH administration. The results obtained from this study were compared with pertinent bioassay (tibia test) results or correlated with the pituitary acidophil cell counts. Whereas it has been reported that pituitary GH levels are normal by the tibia test at 2 weeks after thyroidectomy, the highly specific CFIA method showed an actual 87% decrement which correlated well with the reduction in acidophilis. In addition, the apparently normal content of GH after cortisol administration to thyroidectomized rats, as measured by the tibia test, was contradictory to the very low acidophil population and to the marked reduction in pituitary GH content as measured by the CFIA. Furthermore, theoretical tibia responses illustrate the inconsistency of the bioassay in different experimental conditions. If, as previously suggested, the content of thyrotrophin (TSH) in the crude pituitary extracts renders the bioassay of GH a dubious procedure, then the superiority of immunoassay is obvious.

Animals↗
PubMed1976

TRH-degrading enzyme activity in peripheral and pituitary-portal plasma of the rat.

The enzymatic degradation of TRH was measured in peripheral and pituitary-portal plasma. Enzyme activity in peripheral plasma was 3.20 pg/min/mug plasma protein; in pituitary-portal plasma the rate of degradation was only 0.83 pg/min/mug protein. After dialysis, which removed virtually all endogenous TRH and LHRH, enzyme activity in peripheral and portal plasma was 2.24 and 0.60 pg/min/mug respectively. These data suggest that portal plasma contains large concentrations of unidentified substances which are competitive inhibitors or substrates for the enzyme or that portal plasma contains less TRH-degrading enzyme.

Animals↗
PubMedDate not supplied

Effect of barbital on the pituitary-thyroid axis.

Barbital (diethylbarbituric acid), administered via the drinking water (0.1% solution), elicited mild goitrogenic responses in rats (p less than 0.05), accompanied by a slight depression in serum T4 titers (p less than 0.02). The goitrogenic responses appeared to be the result of slight elevations in the serum TSH levels and in the case of neonate rats, whose mothers were fed barbital during pregnancy and lactation, the elevations of TSH in the circulation were pronounced (p less than 0.01). However, continuation of barbital treatment beyond puberty resulted in mean serum TSH titers declining to twice the mean control values so that only the variances between the data were different(p less than 0.05). This group of young adults showed endocrine profiles which resembled those of more mature rats. The latter group included the mothers of these young adults and of the neonates. In contrast to the action of barbital, feeding rats 0.05% propylthiouracil (PTU) in the drinking water caused substantial increases in mean serum levels of TSH (p less than 0.001) and goiter size (p less than 0.001). Moreover, the precipitous declines in serum T4 elicited by PTU were of far greater magnitude than that caused by barbital (p less than 0.001).

Animals↗
PubMedDate not supplied

Norepinephrine stimulates LH-RH secretion into the hypophysial portal blood of the rat.

The present study was designed to investigate the effect of intracerebroventricular infusion of norepinephrine (NE) on the secretion of luteinizing hormone-releasing hormone (LH-RH) into the hypophysial portal blood of steroid-primed ovariectomized rats. Saline infusion into the third ventricle caused no significant change in LH-RH levels. NE infusion (20 micrograms) resulted in a significant release of LH-RH (p less than 0.05) into the portal blood 10-30 min later. This endogenous LH-RH was similar to synthetic LH-RH when characterized by thin-layer chromatography. LH secretion in similarly treated rats but with intact portal vessels, also was significantly elevated (p less than 0.05) at 20 and 40 min after the start of NE infusion. These results show that NE stimulated the secretion of LH-RH into the hypophysial portal blood and this correlated with an enhanced release of LH.

Animals↗
PubMedDate not supplied

Ethanol acutely reduces LH and prolactin secretion: possible involvement by dopamine.

Ethanol (ETOH) administered acutely to castrate male rats caused a decline in pituitary luteinizing hormone (LH) and prolactin (PRL) secretion. This was associated with an elevation in hypothalamic and median eminence stores of dopamine (DA) that was related to the dose of alcohol given. Pituitary stalk transection (PST) resulted in a significant rise in plasma PRL levels compared to sham control animals, which suggests that DA in the hypophysial portal blood exerted an inhibitory influence on pituitary PRL secretion. The DA agonist bromocriptine failed to alter mean plasma LH levels in stalk-transected rats. The ETOH-treated castrated rats showed a significant rise in circulating PRL after injection of the DA receptor antagonist haloperidol metabolite II (HAL), but the administration of the DA receptor agonist R(-)-apomorphine HCL (APO) caused plasma PRL to decline to near undetectable levels. Plasma LH levels remained unchanged in the HAL- and APO-treated rats and were similar to those of sham controls. These results suggest that lactotroph DA receptors were still functional. Thus our previous finding of ETOH-induced reduction on LH secretion may be attributable to an inhibitory effect by DA on the luteinizing hormone-releasing hormone (LHRH) peptidergic neurons rather than a direct inhibition by DA on the pituitary gonadotroph.

Animals↗
PubMedDate not supplied

The use of touch in nursing practice.

This paper examines the types of touch used in nursing practice and the effects of touch on the body and mind. The effects of two types of touch, therapeutic touch and massage, are evaluated by reviewing research studies conducted by nurses.

Humans↗